The optical center of your eyeglass lenses is the part that gives you the truest vision, and it should be directly in front of your pupils. To determine how to place the lenses in your frames so the optical center is customized for your eyes, the eyeglasses lab needs to know the distance between your pupils, or PD.
It can be tricky to measure your own PD, somewhat akin to trying to cut your own hair. Dispensers need lots of practice to be able to measure PDs correctly, and even experienced opticians have difficulty taking their own in a mirror.
Most online optical providers present you with several ways to go about this important task. Some suggest the simplest method, which is to have your prescribing eye doctor or an optician take the measurement for you. Alternatively, they offer step-by-step explanations of how to take your own PD in the mirror, or how to have a friend take it for you.There is only one reason you would your want your own PD measurement: your want to buy glasses online, without the expense of an optician's expertise. Ok, fine. I'm a professional optician and I have reasons to hate that people do this. But I just love opticianry. What irritates me more than the erosion of respect for and practice of professional opticianry are the endlessly reused wrong methods of obtaining an accurate PD perpetuated all over the anything-for-a-dollar online glasses websites. So I'm going to tell you why their instructions are wrong, and then I'm going to tell you simply how to do it right.
There are two systems proliferated online to obtain your own PD: manually measure yourself, or via software manipulate an uploaded photo of yourself to produce the data.
To measure yourself the common instructions are (courtesy of random online glasses site justeyewear.com)
Have ready: a straight ruler*, a pencil, and a mirror
If you have a willing assistant, you can simplify the process even further by having your friend measure your PD using a ruler. (Your job will be to stand still.)
- Facing the mirror, place the ruler on the bridge of your nose, bringing the start of the ruler directly below the center of one eye’s pupil.
- Looking straight into the mirror, hold the ruler (keeping it steady and parallel to the floor!) and mark the location on the ruler of the other eye’s pupil.
- Measure the distance in millimeters between the two marks. This is your PD.
- Repeat this process a couple of times to ensure you have an accurate measurement.
Whether measuring with someone or alone, be sure to hold the ruler steady and parallel to the floor!
 |
| Does this inspire you with confidence or what? |
You may get close to your actual PD using this method, but prescription eyewear is neither horseshoes nor hand grenades, so maybe a more precision method is called for.
The second method is to upload a photograph of yourself with some sort of size reference device in the photo. This was initially developed as the iPhone app Pupil Meter using a credit card as the size-reference device. Since most credit cards are fixed size, once you know the size of the card one can calculate the distance between the pupils in the image.
The idea is sound. It's a simple ratio equation. But the app is notoriously flawed and inaccurate. Witness it's awesome 1 star rating and the many uncomplimentary comments.
The system caught on, though, and websites developed their own more sophisticated versions of the same measuring system. I've tried a dozen and the best-designed one I found is this PD Self-Test. This uses you own current glasses as the reference device. You just measure the size of the glasses and highlight your pupils in the image using their slick interface and it does the calculation.
The whole point of getting a PD measurement is to have the optical center of the lens centered in front of the eye. If it is decentered, that induces prism: "A lens with prism correction displaces the image, which is used to treat muscular imbalance or other conditions that cause errors in eye orientation." Double vision and focusing difficulties can be caused because your eyes don't work together perfectly, and prism can be prescribed by doctors to correct that and force your eyes to focus together properly. However, prism that is not prescribed and unnecessary will do the opposite: it will create double vision and focusing problems.
So unnecessary prism is bad. But nothing can be measured perfectly, even the most accurate eyewear has some margin of error. How much is too much? Well let's figure out what a pair of glasses I would order myself using the above PD Self Test measurements would be like. If my PD ended up being decentered by the test's 4mm error how much prism would I get?
The Prentice Rule is a simple optician's equation to calculate exactly that. The formula is:
- P is the amount of prism in diopters D
- c is decentration in centimeters
- f is lens power in diopters D
We are looking for the prism P. I know the decentration is 4mm, which is 0.4cm. My Rx lens power is a moderate 2.5D (-2.50, but signs don't matter for this calculation). P = 0.4*2.5 = 1.0D. To put this in perspective 0.25D is typically the smallest increment prescribed by doctors, generally because it is the smallest amount that will have noticeable impact on vision in most people. 1.0D is four times that. That is literally suffering four times the prescribed dosage. The ANSI standards for prism deviation in a spectacle lens is no more than 0.67D, or at slightly higher power ±2.5mm. The lenses made off that PD calculation at 4mm decentration and 1.0D fail both standards and are worthy only of the garbage bin.
Here's a kicker. My actual PD, measured many times by every method from a ruler held to the face to the Visioffice digital measuring system, is 69mm. The online calc didn't even come close. If I had used it's average result of 63mm, that would not possibly, but exactly cause my resulting glasses to be decentered 6mm, inducing a whopping 0.6*2.5=1.5D unnecessary prism, more than double ANSI standards. Those glasses would certainly cause double vision, strain, and focusing failure.
How can the system be that off? Well, because you have two PDs. When you focus on objects within 20 feet, your eyes converge and the distance between your pupils decreases. How far away is the cameraphone or webcam you're using to take the image for the online systems? 2 feet? 4 feet? Those systems are measuring your near PD, not the 20+ foot distance PD you want in your glasses. They don't even get the near PD right either.
There is no accuracy to online PD systems. It is improbable that glasses made from theses PDs even accidentally end up being correct.
So you've hung out through my lecture and you want to know how to do it right. It's ridiculously simple. I don't know why no online opticals recommend this. I'm sure people simply assume a slick looking digital system like the one above is more accurate than any manual system, and are inspired with confidence in their cut-rate online supplier. But manual is simply the best for doing this on your own. Here it is:
- Wear your glasses. (Or any glasses if you don't have your own. Even just try on demo glasses at the mall if you are that bold.)
- Have a felt-tip maker handy.
- Focus on a single object in the far distance (anything farther than 20 feet works, but farther is better).
- Raise the marker to your right lens and precisely put a dot on it directly over the distant object.
- Repeat for your left eye. If done correctly, with both eyes open the two dots should overlap into a single dot over the distant object. If not repeat making the markings until they do form a single dot.
- Measure the distance between the two dots on your lenses with a millimeter ruler.
- That's your distance PD.
- If you need a near PD for reading or computer glasses, just do the same procedure but focus instead on the object you will be looking at, either reading material or computer monitor.
I don't mind educating about this because despite the online opticals' claims, PD is not the only barrier between you and high quality eyewear. There are 30 other ways the online guys can and will ruin your glasses. Only a knowledgeable and skilled optician can make great eyewear. For excellent vision, a perfect comfortable fit, and beautiful eyewear that will last at least a year, you just gotta see an optigeek like me.
But if you want to bring me your own PD measured by my method, I'll take it. But you wouldn't mind if I just double-checked that PD myself first though, right?
I'd really like to thank you for this post. I've had growing problems with prescriptions and glasses over the past few years as I've more recently been getting them from the VA and WalMart. Although I can't say that either one is the cause, I can't seem to be able to wear any one pair of glasses for very long and I've returned many pairs after either complaining that my eyes aren't adjusting to them, or after complaining and then learning things like the lenses are in crocked or my PD is wrong.
ReplyDeleteI looked at a lot of online videos and considered the iPhone app but then saw this and decided it makes sense. My eye's won't lie. I took out 3 pairs of glasses, all that fit differently and did this over and over with all of them. I cam up with a PD between 61 and 65 but was able to be comfortable with the decision that my PD is 63. Not because it was right in the middle though but because it was most common amongst all my glasses. I even took off the glasses and manually changed a mark to try 62 and 64 to assure they did not line up. The system here worked very well.
Thanks again.
Working as an opticians is not so easy and reason behind this is the experience need to perform the job sharply otherwise this might be harmful to the eyes visibility.
ReplyDeleteJeffD I'm glad you liked the info and I hope it helps you on your next pair.
ReplyDeleteIt's true this is no replacement for a skilled optician, but it can be a beneficial replacement for a poor optician, or none at all.
I modified the method a bit: I used 8mm stick on dots and a pair of safety glasses. using a circle on the computer monitor, I placed the dots and then moved them with my fingernail until they had no discernible overlap while looking at the circle. Then I measured them with vernier calipers. Next used a streetlamp outside. For the near vision I got 61 and for distance I got 64. The website you said was the best was quite a bit out, just as you found (58/60). The distance reading was same as Zenni's ruler method and 1mm off what my spouse got using the calipers while I stared at the smoke detector. So the lesson I took away from this is I may have been OK with the distance prescription using the online directions and the printout ruler, but the PD for the readers would have been out by 3mm. One other thing you may want to mention to your readers, if you mark your lenses with a marker, make sure it's not a permanent marker !
ReplyDeleteGlad you got some good measurements Tom.
ReplyDeleteOne of the best features of my technique is verifiability. As long as you are looking directly through the dots on your lenses, and you measure the dots correctly, you know you have an accurate PD.
Even permanent marker comes off with alcohol. Better yet invest in good quality anti-reflective lenses which are so slick and easy to clean that even permanent marker wipes off with a dry microfiber cleaning cloth.
Great information...
ReplyDeleteIt s really very interesting to determine my PD. The way you have explained it has made it a game rather than a serious study.
Thanks...
Interesting but the thing I don't get is once I have had my eye test I don't see an optician again. i.e. a salesperson sells me some glasses and when I pick them up the sales person check they feel ok but I don't see an optician again, so why shouldn't I use an online shop to get glasses from?
ReplyDeleteAlso instead of charging us stupid amounts for the glasses they should charge us the time for the optician and sensible prices for glases.
HLR, the optician is the one aiding you in selecting eyewear and then fitting them. If you shop the malls and chain stores, yes they seem more like simple salespeople than opticians.
ReplyDeleteA true optician not only helps you select frames, but also educates you on the best frame choices, and more importantly designs the best lens for your frame, Rx, and vision needs. Eye doctors do not do this, frame salespeople do not do this, online glasses vendors do not do this.
Therefore, even with a good Rx, correct PD, and a frame you selected yourself, your vision may be poor or uncomfortable, and will DEFINITELY not be as good as it could be if your eyewear was made start to finish by a skilled optician.
Buying online or in the discount chain opticals may be cheaper (though often not), but you sacrifice the comfort and quality of your vision and eyewear fit. These business just cannot provide what and optician does.
Ok,so I'm not sure what's up with my glasses and the PD is the only ting I didn't have when I ordered. The description of prismatic effects doesn't really seem to be what is happening to me, but I could (easily) be wrong.
ReplyDeleteI don't have poor vision and these glasses were intended to be used for looking at a board in the classroom without squinting. I do have astigmatism and there were corrections for it. I ordered two pairs and both of them do this. When I look at things that should be rectangular, both the top and bottom edges converge to the right. I asked a friend to put them on (yes his rx is different) just to see if he saw the same effect and he did. Is it just poorly made (both pairs) or is it something amiss on my rx? Thanks!
Chelsea, that is a hallmark effect of astigmatism correction in glasses. Poorly made lenses can make this effect worse, but if they are made well and your Rx is good, the distortion will disappear with wear as your visual system accommodates to the different perspective.
ReplyDeleteThank you so much for the answer! I got the cheaper pairs just because they weren't going to be used all the time and I have so much trouble finding a pair I like to wear :-) I'll be back into my eye doctors' office Monday to see if I can find a set of frames and get their optician to make me better lenses!
ReplyDeleteThanks for explaining the importance of using an optician. I don't think most people realize how important seeing an optician is, if you want glasses that are comfortable to wear and allow you to see as well as you are supposed to with the glasses on.
ReplyDeleteI think sometimes people think that once they have the correct prescription, that's all that's necessary. As you have explained here, other factors are in play.
I appreciate the compliment, thanks!
ReplyDeleteDaniel
ReplyDeleteI recently ordered new frames and lenses after an eye exam through the local Army base optical shop. I thought the sales person was helpful. When the glasses came and I wore them for a few days, I developed dizziness and severe headaches. I took the glasses back. This time I was helped by the manager who had 16 years experience (Optician??) PD was 5mm off the original measurement! Next time I will find the certified optician. What do I look for? License? Certificate?
If the PD was off from the measurement, the fault lies with whomever made the glasses and whomever failed to inspect and reject them, not necessarily the optician that helped you in the first place. The manager likely didn't do anything except correct the fabrication error, which he as manager is responsible for seeing to it those errors never happen in the first place.
ReplyDeleteAn optician with ABO Certification, or in those that require it state licensing, is always desirable, and often more than experience. To ensure the best quality you have to find an optician you trust can do the job right. Good eyewear is not a commodity, it's a service, and you need to select your optician like you would a minor contractor. There's always someone doing it cheaper, but to do so they have to cut corners and you usually only find out the problems after the fact. A good optician will make the eyewear themselves and take pride in the finished product, and would never let a pure laziness error like 5mms off get through to you.
Hi Daniel, this post is the most helpful pupillary distance article on the internet--full stop!
ReplyDeleteI have a silly question: do all trained, licensed opticians measure pupillary distance with the method you described here? Mine seemed to just use a very fancy caliper/ruler--after reading your article I got quite suspicious of him!
Thank you!
ReplyDeleteOpticians don't use this method at all. This is a way to subjectively self-assess a generic PD good enough for simple single vision glasses. Modern technology enables opticians to design extraordinarily precise and custom fitted lenses beyond anything one can get online with superior visual quality and comfort. To do so we employ sophisticated measuring equipment that discerns PDs unique to each frame (which they are) as well as several other fit factors that impact visual quality, none of which is captured by this or any generic PD measurement method.
This method works as well as any simple PD measurement technique, but good opticians have already advanced well beyond such basic vision correction and provide superior measuring accuracy, personalized lens design, and visual clarity.
Thanks for the info. I decided to risk buying online. I walked into a glasses store and paid them $20 to measure my PD.
ReplyDeleteThe savings I'm looking at is $400 and in my opinion worth the risk. Maybe I'll get bad glasses, maybe I won't but $400 is too much to pay for the service. I would have gladly paid extra, but not 4 times as much.
Amen to that! I have bought several pairs of glasses online and have never had a problem with them. (The reason for buying several pair is because I love having lots of different frames to choose from. I could never do that at $200 a pop!)
DeleteWal-Mart Vision center had measured me at 62 pd a few years ago and I recently just re-ordered glasses at a higher end store and they measured me at 64 pd - if the 62 was right and I get new glasses at 64 would that be terrible? Would I notice a huge difference do you think?
ReplyDeleteThat depends on your Rx. 2mm isn't huge but for higher powers and anything other than single vision lenses it will cause problems. Regardless always accept the PDs measured by your lens maker, because at least if they are at fault they will fix it.
ReplyDeleteok, not everybody who wants to buy frames online is some cheapskate with a disdain for skilled opticians. i actually really like my optician and wish he would take my PD measurement … but he won't! this is all because i looked at every pair of glasses he has (a couple hundred) and didn't like any of them. on the other hand, there is an online store that has very stylish (not cheap) frames that i'd love to use. i understand that making glasses is part of his business, and i would love to give him that business if i could, but i really just can't stand the frames he has (they're all outdated by about 3 years, none of them matches the shape of frames i've traditionally used, etc.) so, i've resorted to the cc-verifying method in the past because i didn't have any other option. that said, this year i'll be happy to use the felt marker method. thanks for the post.
ReplyDeleteYou don't need your PD to buy frames online. If you truly like and trust your optician, buy whatever frames you like and take them to him to have proper Rx lenses put into them.
ReplyDeleteI understand in my shop even the 1,000+ frames I feature don't cater to everyone, so I gladly accept the opportunity to fit lenses to whatever frame my customers want to bring me.
The optician's primary responsibility is comfortable vision. I would love to supply complete frames and lenses for all my customers, but if that's not possible I'll gladly acquiesce the frames for the more important Rx lenses. I believe $200 lens technology in a $20 frame is superior eyewear compared to $20 lenses in a $200 frame.
If your optician doesn't have what you want, then get the frames with which you will be happy. Barring egregious fit errors on your part, a good optician will provide you the best vision possible regardless of you frame choice.
I would believe the argument that opticians/RDOs care about people's vision IF they gladly provided the PD when requested by a patient.
ReplyDeleteAs I see it, and some opticians freely admit online, they are attempting to protect their income stream.
The hypocrisy of "I'm not giving you the PD" (when I've already paid for that as part of my exam) "because I care about your vision" just doesn't jive when the PD is not provided upon request. If your "care" about my vision was truly your concern, provide the PD when asked. Otherwise, you appear greedy to me. And now you've lost more than your income stream -- you've lost my trust. And you can be guaranteed that I won't be coming back.
I would like to add to the comment immediately above: this is not addressed to anyone in particular (Daniel Livingston), it is a general comment.
ReplyDeleteThere are several reasons opticians may not give out PDs for use elsewhere, and some do advocate "protecting" the profession, but as my advice here should make clear I am not such an advocate.
ReplyDeleteOpticians care about your vision in the same way as your lawyer cares about your legal rights and your accountant cares about your financial health. When you enlist our services, we do care to ensure you get the best vision we can provide. If you do not enlist our services, you have chosen not to be cared for.
PDs are not accurately measured during your exam, only an approximation is made to fit the lenses in front of your eyes, satisfactorily only for a fixed straight ahead gaze and just the few minutes of time you spend looking at the chart. I guarantee you do not want those numbers being made into eyewear.
I do not provide PDs for eyewear I do not make, for two reasons. The most obvious is that my skill as an optician will provide excellent accuracy perfect for any Rx, and if that's what you want it’s a paid professional service like any other. If that skill isn't valuable to you, then just use my method and do it yourself.
The most important reason I don't give out PDs, even for a fee, is because obtaining good measurements for lenses is the responsibility of the eyewear maker. If I'm not making the eyewear myself, I want no part in the process. There's dozens of ways someone else can screw up eyewear even with accurate PDs, and I won't contribute to the eyewear when I can't guarantee quality.
Accurate PDs denote where you look through the lenses of a particular frame for a particular use, not the mere distance between your pupils. They therefore depend on your frame, adjustment, and your lens design as much as on your eyes. There is no single biometric PD value that produces accurate eyewear. I measure and use unique PDs for every pair of eyewear I make for my customers, and the variance from pair to pair is significant. If you want measurements perfectly accurate for your frame, fit, and lens design, I do care about your vision and will ensure you receive such accuracy in eyewear I make for you. Find a good optician and they will care about your vision the same way.
http://pd.warbyparker.com/ provides pretty accurate PD's - do you agree ?
ReplyDeleteClearly didn't read the article and are just posting ad-spam, because obviously I don't agree because I tested the credit card method and it sucks. All the online methods are horrendously flawed. My DIY is easily superior.
ReplyDeleteThank you for this very informative post. I wish I had read it last week before ordering my glasses online. They arrived yesterday and are unusable. I get the prism effect and am sure it has to do with the PD measurement. For me, it was more of the convenience factor in ordering online but clearly this is an area where personal attention is needed. Fortunately this was not a very expensive lesson but my great deal just ended up in the trash bin. See a real optician people!
ReplyDeleteThanks for sharing your story!
ReplyDeleteOver the years I've ordered a dozen pairs from various online stores as they appear to check out the quality and inspect materials. They've all been filed in the round bin too.
Very interesting article. Thank you for posting it
ReplyDeleteI have a question. My nose is crooked from being broken. How is that going to affect my PD? Will a single number be sufficient, or do I need a left and a right measurement? My nose is curved to the left. With my current glasses, the left pupil is closer to the inner edge of the frames. My prescription is single vision, -150 in each eye.
Thanks again.
Monocular PD, i.e. separate values for each eye, is almost always more accurate. If you have reason to believe your eyewear might fit less evenly than usual, such increased accuracy will be valuable to you.
ReplyDeleteOne can obtain monocular PD values via my method. However doing so introduces greater inaccuracy and relies heavily on your own measuring skills.
If you have any reason to believe you require less than routine eyewear design, online eyewear is not for you. Seek an optician to get proper eyewear for your needs.
I understand Opticians' frustrations with people asking for the PD, but seriously....it's medical information. We should have a right to know our pupil distance. Also, sometimes there are options online that are easier to get,especially with RX sunglasses. G-15/Green lenses for way less than the $300 Lenscrafters wants. Real glass lenses instead of Trivex or polycarb. And of course...many times opticians don't take a particular insurance plan. So why should I drive all around town wasting gas looking for one that takes my insurance for a discount on the glasses (or call, which I've done too), when I can buy them online for the same discounted price or cheaper?
ReplyDeleteI've been getting glasses at Optometrists for 20 years and I still go to them for adjustments. But for sunglasses...online is a better option. It just is. If you already have your frame and you know it fits and looks good, and all you want is a simple, cheaper options for the lenses, it just makes more sense.
Yup that's the Walmart argument I make myself: when you don't care about quality, Walmart's fine. If they don't fit too well, you don't see clearly or comfortably, or they break with 3 months of wear, but you don't care, then why spend any more than you have to? But don't make the mistake of thinking your getting the same thing for less. You only get Walmart quality at Walmart prices.
ReplyDeleteBut what if you do care about your glasses or sunglasses? Would you like them to last 2 or more years? Would you like to enjoy the clearest most comfortable vision possible for that whole period? Would you enjoy a comfortable proper fit every time you put them on? That's not going to happen online or at cheap opticals.
As far as PDs, they are medical information only if taken by a state licensed professional, and only if your state legislates them. States that don't regulate PDs (every one AFAIK) don't care, and states that don't enforce license on their opticians (lots) can't regulate it because an unlicensed professional can't create protected medical information, therefore the PDs they take us not legal medical information.
Well, to be honest what I've done with my last two pairs of glasses and last two pairs of sunglasses, since probably 2004, is buy the frames on Ebay (where prices are usually lower...almost $100 lower for my last pair of Burberry frames than what Lenscrafters was asking) and get the lenses fitted by Optician (since my last optician retired and my eye doctor's glasses shop doesn't take my insurance, Lenscrafters has been where I go).
ReplyDeleteThanks to Youtube, I have learned how to adjust the temples and nose-pieces for a proper fit; the only thing I still have trouble with is if the bridge gets twisted. I've also replaced screws, nose-pieces etc. myself.
So the problem of course is the lenses. My last pair of Serengetis lasted 6 years, so I recently got two pairs of Ray Ban and Randolph Aviators. The Ray Bans have green lenses; Lenscrafters quoted me almost $300 for the green polarized lenses alone, but cheaper if I bought a new frame too. Well, I already bought the frame; I didn't need a new one....
Bottom line is, it's getting ridiculous. Some online places like Zenni look sketchy, but then there are places like Hidalgo's which claim to have sold Rx eyewear since 1969, so I'm sure they have some experienced opticians on hand. Can't get them done without the PD though...so I'm either going to try what you suggest here or track down one of those little PD-specific rulers that sits on the bridge of your nose. Do those work well? I'm sure it won't let me know my PD accurate to 2 decimal places but it can't be that far off right?
In any case, my next eye appointment is in November. I will ask them to measure my PD before they dilate my pupils.
Daniel,
ReplyDeleteThanks for taking the time to post this blog and keep up with it. Last week I got new glasses at a well-known chain optical shop, They are progressive lens. I think the only change from 4 years ago was the add power for reading. I have had headaches and eyestrain since i got the glasses. When I look at objects at a distance or even computer distance, to see clearly out of the right lens, i need to turn my head right slightly. and turn left with the left lens. they are not both in focus at once. does this sound like they measured the PD to short? or is it a script problem?
the store used a "camera" which took a snapshot of my eyes and did the measurement. It was 61. using your method, I came up with 63 for distance. How can the camera/computer test my distance PD,when I am not focusing on a distant object?
Thanks Paul
Hi Paul, and thank you!
ReplyDeleteI know the chain you mean. The digital measuring devices can be great (I use a sophisticated model myself), but they can also be poor. They are accurate but do not compensate for user error. If the operator is not well-versed with the machine they can generate poor results. Newer salespeople in the chains are trained only on these devices and may not understand exactly what is even being measured, and cannot troubleshoot the results or even recognize erroneous ones. As with all computers, they happily spit out garbage results when they get garbage user input.
Also good catch about measuring distance PD while you focus on a near object. From the fixed near distance, and the near PD captured, the software extrapolates the far PD.
As to your specific problem, it sounds like a PD issue but it could be any number of factors. PD is easy for an optician to verify, so go back to the store and have them mark the PDs on the lenses and see how they line up with you gaze. If they do, then the real optician troubleshooting begins. If they don't, we'll that's an obvious starting place.
Hi Daniel.
ReplyDeleteThanks for your post. I've been agonizing about buying online, because I'm thinking "How bad can it be?". I've worn glasses all my life (I'm 39) I have high myopia-high astygmatism (OD Sph. -6.00 Cyl. -2.75 and OS Sph. -2.00 Cyl -4.00). The last 2 pairs of glasses I've bought over a period of 4 years (Ray-ban frames, Zeiss Lantal 1.9 Super ET lenses) have not worked for me. I've spent USD 1.600,00 in 2 pairs of glasses I can't wear, bought from reputed opticians, who supposedly tried everything they could to get them right, but never did...
Online, I can get organic lenses, 1.74 Ref + titanium frames for just over 100 bucks.
Can they be that bad? Can they be dangerous to my eyesight or simply not work? Why do some sites use 63mm as an "universal" PD?
Thanks!
Sandro, Portugal
Wrong glasses won't damage your eyes, but will certainly provide poorer vision and may cause eye strain, double vision, headaches, etc.
DeleteYour Rx is complex and I would not recommend shopping online for you, but if the opticians' solutions didn't work for you the online couldn't be any worse than useless. If the gamble is worth the $100+ to you, take the gamble. Worst that happens is they are useless and you lost your bet.
If the opticians did everything right, there is nothing the online guys can do to improve upon that. But if you are 100% confident in the accuracy of the Rx, the only risk is the money on buying something that works no better.
As for the generic 63 PD, it's the same as a generic XL shirt or 9 shoe size: NOT right, but close enough that it will work for many. Definitely would cause you problems, unless you serendipitously happen to be a perfect 63 PD!
Yes, this is a great series of posts, thank you!
ReplyDeleteI've been dealing with a PD problem and noticed (suspected) that as my Rx has gotten stronger it seems to need to be more precise. My question is probably related to the distance vs. the reading PD dual measurements, though my hunch is there is likely a further complication in that I have one eye which was slightly crossed at birth, and while it resolved itself I think it still turns in a bit when I look down (I wear progressives). Do I need a special measurement, and/or to get the Optician to double check with the felt-tip pen trick? Is it possible to have one eye which requires a rotated channel (not straight down)? Other advice/insight would be appreciated!
Yes it is indeed possible that one eye may not focus along normal channels, typical if one has a history of amblyopia ("lazy eye"). This is not something an optician alone would correct. For such a scenario an optometrist might prescribe prism in the Rx, which a good optician will have no difficulty including in progressive lenses.
DeleteIf you have any special visual concerns for your eyewear, always see an optometrist and optician that work together to satisfy your visual needs. Otherwise the likelihood of successful eyewear is greatly diminished.
Daniel,
ReplyDeleteI have a question for you. What if you have bought glasses from two different opticians in the last couple weeks (my eyes change, at times I need prisms, and at times I don't). So I bought one with prisms, and one without. I go between those pairs, depending on how bad the double vision is on any particular pair. However my question pertains to PD measurements they both did. One measured a PD of 34/35.5 and two days later the other measure 32.5/34. I tried your measuring system and I got 34/35, which was pretty close. I actually went back to the second retailer and had them measure it again. They still came back to 32.5/34. I'm blown away two different opticians get two different measurements. Any ideas?
Daniel,
ReplyDeleteThat was supposed to be I go between the different glasses (one with prism and one without) depending on what the double vision is doing on that day. I have a vertical diplopia that is neurological, and comes and goes. What stunned me, is why the two measurements were so different. That is roughly 1.5mm per eye. They where both "distance" measurements. Any guidance you could provide would be helpful.
Chris
The dissenting measurement may be due to a miscalibrated pupilometer (PD measuring device), assuming these PDs were not taken manually.
DeleteEvery pair of eyewear made by different opticians will differ, even if the Rx is the same. Measuring skill and accuracy, equipment calibration, lens brand and design, fabricating machine design, lens and frame assembly, final fitting… every one f these factors will impact the final eyewear quality regardless of the Rx.
I recommend find someone who does is right and stick with them.
How about this PD measuring technique? Look through a pair of binoculars. Adjust the distance between the eyepieces until the two circles of view seen by the eyes merge exactly into a single circle. Remove the binoculars from the eyes and measure the distance between the centers of the eyepiece lenses. Given the nature of binoculars, this should work for distance PD but probably not reading PD.
ReplyDeleteThank you for the description of your method. I'll try it to see how closely it conforms to my ophthalmologist's measurements for both near and distance prescriptions. Thus far I have ordered 4 pairs of eyeglasses on line and each has been very good. Twice I've asked the tech. in my ophthalmologist's office to measure the lenses to see how closely they conformed to the Rx. Each time she said they were perfect. The most I've paid was $12.85.
ReplyDeleteBy the way, "it's" is a contraction not a possessive.
There is a lot of criticism here about buying eyeglasses online, but what else can us myopes with narrow faces really do? Most opticians and all chain stores cater exclusively to people with an average to wide PD. The adult frames they carry generally have a lens width no smaller than 48mm, which is still way too wide for someone like me. That leaves only the children's section, and those frames are either not much narrower or else not suitable for adults.
ReplyDeleteOn the other hand, some of the online stores sell frames with a lens size of 42mm or even smaller. This is a blessing for those of us with a PD under 60, and in fact, the first pair of eyeglasses that ever fit my face well was a pair that I bought online. It seems ridiculous to me, given all the opticians there are in the U.S., that I had to go online just to find a pair of good fitting eyeglasses. While I can perfectly understand small local businesses not wanting to carry expensive designer brands, I don't see why they refuse to carry smaller frames. Shouldn't the fit of eyeglasses also be considered part of optometry?
Of course the lack of selection I've experienced at opticians and chain stores has often been accompanied by a poor attitude as well. Some of the doctors and workers at these places will definitely make you feel bad if you have a narrow PD. They will make snide comments about your face - I had this happen to me just the other day! - and they can get even nastier when you refuse to buy a pair of their ill-fitting frames. Despite all this, I would still prefer to purchase eyeglasses from an optician or even a chain store, as the service is personal and there are more risks to buying online. If only they would improve the attitude and the selection, I would definitely go back, irrespective of the higher prices. Sadly, I don't see it happening, as there is a definite bias in the eyecare industry against people with small faces.
Mike I'm sorry to hear you've had such negative experiences with opticians, for no reason at all. Certainly the chain stores are going to be less able to cater to your needs, and many optometrists' offices as well because they are often very small with narrow selection. What you need is an independent optician or better optometrist office that has the selection and access to a wide variety of frames that will work for you. I have plenty of customers with very narrow and very wide faces and I have quite a few good fit options for them, but I can also research and find many additional frames I don't carry in my optical. Chains can't do that, and if your current opticians won't do that, find better opticians.
DeleteEven if you can't find the selection you need, go ahead and buy a frame online. If its decent quality and you like the fit there is nothing wrong with that. Take that frame to an optician and have them professionally design and fit lenses for your frames. Now you have the frame you want and the lens expertise you want. Any optician that objects to using frames you bring them (assuming they are quality of course) is one to avoid. I have refused a few people over the years that brought me terrible frames because I knew there was no way to make a decent final pair of eyewear with the frames, but I have accepted many dozens more that bought fine frames online but wanted my lenses, and that's fine by me.
Bit late to the game but I had to leave my 2 cents. I've been buying glasses online for years now and have to say that there are good and bad online shops (Coastal- good, EyeBuy- bad) but saying that only an Optician can sell glasses is hilarious. Sure if we all lived in a magic world where frames and lenses were under a hundred and Opticians sold and fitted glasses I could see the argument to buy from them. We don't though.
ReplyDeleteAfter getting my new prescription I asked how much it would be to just change out my lenses... $125!! I could buy a great new pair of glasses for below that online. I love my optometrist but the prices are outrageous. Luckily he is understanding and checks my online bought glasses and guess what? They have always been correct.
allylti I've never said only opticians can, or even should, sell glasses. In fact I provide advice here for buying glasses online. If your needs are simple and your expectations moderate, online glasses may serve you fine. But many questions here have been about problem situations, and online purchases will not address these issues. For that you need professional advice, and online retailers have little interest or ability to provide that.
ReplyDeleteSimple uncomplicated commodity products are safe to buy online or at simple retailers like Walmart . If your eyewear needs fit this description, give it a shot. If you are more critical of your vision than you are of your toiletries, iPods, and housewares, then you might want professional expertise.
David, can your PD be off 1/2 mm - 1 mm and still be okay? I've had three different measurements by opticians, 35-34...35-34.5...35-35. I wear progressive lenses. I already have two pair that are 35-34 and they seem fine but I want to buy a new pair. Should I make sure they are 35-34? The opticians said that my eyes would adjust and not to worry about it because the measurement is so close. Is this true?
ReplyDeleteThanks!
Thanks so much Daniel!
ReplyDeleteQuick question as I want to reduce the margin of error...
When you say measure the distance between the dots, do you mean measure from the center of each dot, or from the inside of the dot?
Thanks for clarifying!
Saas3814, measure center to center. Use a sharp tip marker and make you dots as small and precise as you can.
DeleteGeorge, those PDs are pretty close and one will "get used to it", but one will get used to off sized clothes or a poorly ergonomic chair too. Just because its "ok" doesn't mean it's right. If you are getting standard progressives from a retail store, "ok" is as good as it gets. If you are getting premium digital technology progressives from and independent optician or optometrist's office they should be able to offer more reliable accuracy than that. If they can't, find an optician that can.
Thanks Daniel, That's the info that I needed to hear. Much appreciated.
ReplyDeleteDaniel,
ReplyDeleteHi. I recently went to my optometrist for a routine eye examination. An assistant administered the first part of the exam. One of the first things she did was check my vision with an autorefractor machine, the Marco ARK-700A. I asked if she could tell me my PD. She gave me a slip of paper with the results from the autorefractor. It listed a PD of 64. Do you think this is a reliable measurement for my distance PD?
From what you've written I have a hard time believing it is since you stressed the object be 20 feet or greater in distance.
I tried your method but am unclear on one thing. Am I to cover the opposite eye when I mark the lens? It's extremely difficult, if not impossible, for me to mark the lens unless I have the opposite eye covered up.
Mike,
ReplyDeleteDo not use the auto refractor PD, they are routinely up to 5mm off. This is the same reason not to use any PD eye doctors provide, because they are just forwarding the auto results. No eye doctor I know actually measures PDs. They don't need to because for the 5 or less minutes you are actually looking through their refracting device (phoropter) the double vision, headache, fatigue and eye strain of improper PD will not set in. Putting that PD into full time wear spectacles is no better than just guessing.
If you need to cover one eye at a time while measuring, you may. Once both lenses are marked just confirm that while looking with both eyes your marks overlap into a single dot over the distant point. If you see two separate dots you haven't got it accurate enough.
I just ordered new glasses online. My prescription is -6 and -7. I didn't know my pd and I thought it wasn't a big deal. Oops. If I wear these new glasses with the wrong pd, will my vision get worse? I should be going to the eye doctor in the next few months. I see a lot sharper with these new glasses than old glasses. How would I know if my pd is off? Would I know immediately?
ReplyDeleteThe maximum acceptable prism due to PD error is 0.67 diopters, abd with your strong Rx this maximum is reached with only 1mm of error. Any more than 1mm and the glasses would be unacceptable to any decent optician.
DeletePrism from a bad PD will not damage your eyes, but because your eyes must constantly struggle against the error it will cause eye strain, fatigue, headaches, and double vision once your eyes get tired of fighting.
It's like having a terrible wheel alignment in you car. You can still drive ok, but you're constantly pulling the wheel to keep going straight, and after a while it gets stressful and fatiguing to fight it all the time. Once you get the alignment fixed, all of a sudden driving seems effortless and easy again.
You may seem to see fine with the wrong PD, but the stress will make seeing unpleasant, instead of crisp and effortless as it should be.
Thank you for responding. I feel that the lenses could be too strong. When I close each eye, I see fine, but together it's strong and when I look to the side, I don't see clearly. If I go to the eye doctor to straighten them (they keep siding down my nose), can I ask about the pd? I asked where I bought my glasses and they wouldn't provide me the information. I tried doing the measurements that you suggested and I couldn't see the dots. I have an astigmatism (sp) but my eyes ignore it. Thank you for your advice and help.
ReplyDeleteThat you see fine with each eye individually, but poorly together, is a strong indicator of bad PD. The blur out of the edge of the lenses is due to poor material and bad lens design. A professional optician can solve both those issues for you.
DeleteDaniel,
ReplyDeleteDoes a pupilometer provide a reliable measurement for distance PD?
If so, how can a device that close to my face provide an accurate distance PD?
Yes a pupilometer is the standard method of obtaining an accurate PD. The device forces your eyes to focus individually instead of binocularly, negating the convergence that would produce a near PD.
DeleteDaniel,
ReplyDeleteI had my PD measured with a pupilometer and I was very surprised with the results. It was only 62.
I've measured my PD at home several times by myself in a mirror and I get around 66 over and over. I make sure to cover the opposing eyes as I read the ruler.
Thus, I thought with the pupilometer my PD would be 66 at a minimum.
I told this to the person operating it and she said she had just calibrated it so she was confident in the results. She measured my PD a second time just to appease me and got 62 once again.
Should I be confident with this result?
That's a huge discrepancy. I recommend you use my method, not the mirror, and see what you get. If you're still at odds with the optician's measurement, then you have a dilemma.
DeleteYou can either trust the professional optician or your own measurement, which you have more confidence in is up to you. The benefit is, if you trust the optician and it's wrong they will fix it. If they accept your measurement instead, you're on the hook for it.
I would trust the optician.
Hey Daniel,
ReplyDeleteIf I was examined by a skilled optician,and he found no special problems (like cylinder), All I need is a regular lens.
I have a precise measurement of the PD, and I order online a very precise lens.
What do you think is the main threat for an excellent visibility when ordering online, provided All that I stated here is correct.
Thanks for all the info
Jav
Even if the PD and Rx are are accurate and made perfectly, other factors can negatively affect vision.
DeleteLens material, coating, curvature, optical center height, sphericity/asphericity, and for stronger rx's frame angle, wrap curvature, and distance the lens is held from the eye will all affect the quality of vision. Online vendors are unlikely to take any of these into account, and are not required to do so to produce legally compliant glasses.
A fun way to illustrated the problems possible with even correct PD and Rx: flip your glasses upside down and look through the front of the lenses (make sure your right and left eyes are still looking through the right and left lenses, respectively). The Rx and PDs are still correct, what's changed is the curvature, tilt, and wrap angles relative to your eyes. The glasses are technically satisfactory according to Rx and PD, but I'm sure you wouldn't be happy with that vision!
There is no way to guarantee a proper custom made product through online shopping, there are just too many variables that are not taken into account with a point and click shopping basket purchase. All you can do is buy and gamble, then go through the returns process if it fails.
A good optician will take all these factors into account when designing your eyewear and ensure none of these problems occur.
Hi Daniel thx for the info. i got a rx for progressive lenses but the optician did not give me pd. they said they can do that for an additional $25 if i want to then order frames with progressive lenses online. however they also said i do not need the actual frames i'd be buying online, even for progressives, since the measurements are only taken of my eyes/face. this is incorrect isn't it??
ReplyDeleteYes that is incorrect. Good progressive measurements are entirely frame-dependent. Any attempt to make progressive lenses without measuring the frame on the wearer will be a mere guess, and guaranteed to provided poor results.
DeleteI recommend against ever buying progressive lenses without an accurate measurement of your pupil location in the frames you will be wearing. Without that the lenses will never be fit well enough to be worth the expense. Single vision lenses can be fudged a bit and still function well, progressive lenses cannot.
Can I get your professional opinion on which of these are best? I have 3 different options from 2 different opticians. All are for polycarbonate progressive lenses with anti-glare.
ReplyDelete1 - ultima hd lenses (which I can't find any info on) for $389.
2 - standard no name lenses for $200.
3 - Varilux Comfort for about $300.
My rx is R: -1.50 add on +1.50.L:-1.75 -0.25 x180 add on +1.50.
Thank you so much for your advice!
Hi Daniel, thanks for emailing!
DeleteGo with the Comfort. Generic progressive are fine if your needs are extremely simple and generic. Full time glasses like yours are not simple or generic. The Ultima are kind of generic too, they are a "house" brand, and the same lens design is sold under many different names. The "HD" moniker is used to indicate they are likely a free from/digital technology that increases precision. However, an extremely precise generic may not be as good as a conventionally fabricated excellent design, like the Comfort.
If you want the best if both worlds, ask for the Comfort Enhanced. It combines the most successful progressive design in history with the precision of modern digital lens making technology. Far superior to your other options.
It measured me from a 61mm to 65mm PD. So call it accurate within ±4mm.
ReplyDeleteUh, no... This is ±2mm (around a center value of 63)
Oh yes that's true, I meant to explain it is inaccurate by up to 4mm.
DeleteDear Daniel,
ReplyDeletethis is a very interesting post.
The refusal of opticians to give out PDs is very annoying.
I live in Canada. PDs are not part of the prescription. I just bought regular glasses for $500. Two weeks later the frame of my prescription Oakley sunglasses snapped. I went to at least 5 opticians trying to find decent RXable sports sunglasses. The problem is that there is no choice. Pretty much the only brand they carry in Canada (with few exceptions) is Oakley, which I don't want to buy again.
I tried really hard to buy RXable sunglasses from opticians in my city. (I visited at least 5 stores.) But they just have no choice for sports frames other than Oakley.
One option I considered was a non-name brand for the frames with RXable lenses for a total of roughly $660. Using framesdirect.com, I can get designer frames with the same prescription, same lense options (e.g. polycarbonate, AR and polarized) for $300.
Essentially Canadian opticians leave me no choice other than buying it online.
I went to the optician from whom I bought my regular glasses just 2 weeks ago and asked for my PD. They wouldn't give it to me (store policy).
There's something really broken in Canada. Prices are just not competitive and the customers suffer. That's why people buy from online shops. I'd be happy to pay a reasonable amount more if I could get a real optician's service. But what they do here is a rip-off.
It's too bad you are having so much trouble. Such issues of service and selection are not the norm in the optical industry, at least in my experience.
DeleteIf you truly want opticians' service but are simply dissatisfied with the selection, you can always buy a frame of your choice from wherever you like and take it to an optician to have proper lenses made. You'll get the selection you want and the expertise and quality only a good optician can provide.
Oakley is massively popular, one of the few brands people ask for anymore, and too many opticians play it safe by banking on that popularity. I personally don't carry Oakley, but when people ask for it I advise them to just buy online directly from Oakley and bring it to me to be Rx'd right.
Thanks a lot for this post! Recently come out from under NHS entitlement and the price of getting even a basic pair of glasses skyrocketed. Having managed to get a free eye check at the opticians, I figured giving that to an online glasses website would be enough. Finding out about PD was new.
ReplyDeleteThough could you answer? Does a person's PD change?
An adult PD does not change, though truly precise measurements are frame dependent and should be measured independently per pair of frames.
DeleteThanks very much, Daniel, for your willingness at least to talk about a problem from inside the optical profession that to us outside the profession looks like simple greed. I believe everything you say about your own practice and your own motivations. I wish you were local.
ReplyDeleteI cannot believe, however, that the extremely hostile and abusive optician I encountered at the optometrist's office two weeks ago shares your values. Nor do I believe most do. I believe YOU add real value in return for high fees; if the others did, why would they be so extraordinarily hateful when we even think about buying our glasses online? If it's really US who are the potential losers, getting poor quality eyeglasses online, why do they ALL act like it's THEM who are being threatened?
They could keep the customers who are willing and able to pay for their services without mistreating and alienating those of us who can't afford it. I'd rather waste a few hundred dollars buying dozens of pairs of throwaway glasses online until I finally luck out and find the right combination of variables than pay that slimy, hateful jerk the $50 he demanded for a PD measurement, acting like I was a child abuser for even asking. It was the most unpleasant experience I've had anywhere in many, many years.
When a customer's insurance company pays an optometrist over $200 for an exam and prescription, it's not unreasonable for the customer to expect to receive everything required to have a pair of glasses made. To be hit up for another $50 out of pocket for the magic key they withhold (which is how it seems to the customer) is outrageous.
Thanks also for your suggested method of measuring PD at home. Like an earlier commenter whose comment you didn't respond to, I couldn't see the marks on my glasses when looking at the distant object. I kept making the marks bigger and bigger, and finally, when they were about 1/4" in diameter, I could see them well enough to tell whether they were overlapping.
Maybe you and others for whom "Use a sharp tip marker and make your dots as small and precise as you can" works have vastly different prescriptions from mine, but the dots had to be monsters before I could even see them. The very rough measurement I came up with was around the same 72 mm I had arrived at over several days of trying online tools, rulers, photographs, and my own variations on the above, so it's confirmation, at least.
For the monocular PDs I'll need in order to get progressive lenses, I'll take an educated guess and see what happens. There seems to be no more than 1 or maybe 2 mm difference between my two eyes, and I don't read with glasses anyway, so it may not matter much. I only need the progressive lenses so I can take an occasional glance down at the speedometer while I'm driving; I always take my glasses off for reading. Anyway, I don't need the best possible glasses money can buy; good enough is fine with me.
Thanks for demonstrating that there is at least one decent human being in the optical profession. I just wish there were more like you.
The almost universal hostility to the internet among optical professionals is rapidly eroding what goodwill they had and sabotaging their own futures. For their own sakes, they should follow your example and consider their customers' welfare instead of punishing and abusing the people who pay their bills. They can't stop the tide flowing inexorably toward online sourcing of eyeglasses, any more than Woolworth's could stop Walmart or GM could stop Toyota.
continued below...
As I said, Daniel, I believe you when you say that you supply valuable services that aren't available online. Now. But if you think everything you do will NEVER be available online, you'd better give it another think. The optical pros had better quick find a way to ride the internet tide before they're left behind with the other garbage on the beach.
ReplyDeleteI'm talking now mainly about the combined optometrist/optician practice that is the norm in most places I've lived. I think you said you're independent, which is good. It's that combination that now seems abusive and unworkable.
When I pay a doctor for something, like a prescription for eyeglasses, I expect it to be something I can use. I do NOT expect to have to pay somebody else in the same office (the optician) a second, exorbitant fee for the tiny piece that they've colluded between them to withhold, in order to coerce me into buying my glasses from them.
It seems to me that the internet is going to force those two professions to decouple if either is going to survive. A setup in which a doctor's (optometrist's) services are covertly subsidized by a separate business, the selling of eyeglasses, is a serious conflict of interests that does not benefit the patient anywhere near as much as it benefits the "doctor".
I'm using quotes because I'm starting to see optometrists not as medical professionals but as opportunistic businessmen and women whose first priority is their profit margin, not the patient's welfare. Maybe it'll be a good thing if they all go under and we get our eye exams online as well as our eyeglasses. I say, Good riddance.
Jim, sorry you had such a bad experience. It's true some opticians (and doctors) are mistakenly trying to "defend their profession" by being difficult on the PD issue. It's a knee-jerk response the relatively recent challenge of online opticals, and unfortunately does some harm and zero good.
DeleteI do firmly believe accurate optical measurements, PDs among them, are the responsibility of the spectacle maker. Not some other optician, and certainly not a doctor who has no training in taking accurate spectacle measurements. I would not lightly make spectacles with someone else's PD measurement without confirming it myself. It just invites error.
But i
f one just needs "good enough" glasses, then taking your own measurements will be just as good as those of an uncaring optician or unskilled doctor. Sloppy results from poor opticals (online or not) render precisely accurate optical measurements irrelevant anyway, so don't fret too much about a millimeter here or there. Cheap glasses, like cheap anything, are only perfect for when performance doesn't matter much. If you're Rx or visual tolerance is such that a little imprecision bothers you, you need to be looking for quality first, which only comes from a good professional.
In other posts I explain we professionals have no exclusive access to any lens or frame technologies anymore. Every *product* is available online. But the raw material is only a small piece of good spectacles. If you have anything but the most basic needs, it's the professional consultation, design, measurement, fabrication, and fitting that makes or breaks your spectacles.
The best opticians do use extraordinary quality materials, but its not their product that separates them from competition, it's their professional service. I think there will always be demand for that, and while the Internet may shutter a few poor opticals' doors, the good ones will continue to do well.
This makes me sad. Angry, but sad too.
ReplyDeleteI've been wearing glasses for almost 60 years, and every pair I've ever had I got in person from an optician. I've never even gotten glasses from a chain like Lenscrafters, always from an optician either in an independent optical shop or affiliated with an optometrist or ophthalmologist. But what's happening in the field now has so deeply offended and alarmed me that I will never buy glasses from an optician again.
If I happened to live where you are, I might consider you, but I'm now so thoroughly convinced that all optometrists are crooks, and by association that all the opticians who work for them are crooks too, that I cannot bring myself to trust them, even though right now I wish I could.
I'm on my second pair of online glasses, and I'm already discouraged. I see now how important the work you do is, but the hateful, selfish, greedy attitude of the optometrist-optician syndicate has burned me too badly to turn to them now.
So I'll keep trying online and either finally get glasses that I'm comfortable with (maybe "good enough" isn't really good enough for me after all) or die trying. The only thing I'm sure of is that I will never again set foot in an optometrist's office.
They're the real villains; I see the opticians who are stuck in dependent, symbiotic relationships with them as their victims too, although the opticians are still responsible for their own actions as individuals. But in practically all of those situations it's the optician who works for the optometrist, not the other way around, and the policies of the practice are set by the optometrists.
In the past I never was particular as to whether I saw an optometrist or an ophthalmologist for eye care, but that's changed now and won't change back.
Any relationship between a patient and a medical practitioner is based on trust. When the trust has been bludgeoned to death by the practitioner, as optometrists have bludgeoned my trust in them and in the opticians who work for them, it can't be resurrected. The possibility that there may be honest optometrists somewhere doesn't help, because the bad apples I got have ruined the whole bunch for me.
Jim, I think you could assuage some of that distaste by separating your optometrist (or ophthalmologist, as you prefer) and optician. Get your Rx from whoever you like and leave with it (and don't worry about PD). Find an optician of your choice to fill it. Even opticians working for optometrists will accept Rxs from other doctors. Alternatively, they are harder to find, but there are independent opticals that have no doctors and exist solely to fill other docs Rxs.
DeleteIf you can't find an optometrist/optician partnership that you trust, seek them each independently. That way the collusion that upsets you won't be an issue. The optician will have no influence from a doc to do anything other than fill your Rx as you request.
Daniel,
ReplyDeleteI have been considering buying glasses for my son online because they are SO much cheaper, and he's 6, so let's face it, I will probably be replacing them more than once due to breakage.
We went to an eye center on our local military base, and they gave me a prescription of OD sphere+1.00 cylinder -.075 axis 0303, OS +.075 -.50 150. But, alas, no PD. I called and asked them for the information, but they would not give it to me. How do I measure my son's PD? He is highly wiggly, and just will not sit still or focus long enough for me to even try to measure. The "ruler method" gives me somewhere between 49-55. Is the PD really that important for glasses at his age?? The Dr said he is only to wear them for reading/watching tv/video gaming.
Any help you can provide is greatly appreciated!
Stefanie,
DeleteWith your son's Rx there is an acceptable ±2.0mm tolerance, so if the 49-55 range you measured is at all accurate using the middle value of 52 should be within the standards.
PD is important to comfortable vision regardless of age. Children may not complain of visual stress due to poor PD, but that does not mean there is no problem. Also, there is no easy way for you to verify the PD you get from an online vendor. You could ask for 52 and get 62 and would not know otherwise unless you son complains, which is unlikely.
His Rx is mild, but he is also in his neurological developmental years. It would be worth ensuring he has proper eyewear to maximize the future of his vision. I recommend consulting with his eye doctor first to find if there may be any developmental concerns the eyewear addresses, in which case precision is of greater importance.
Thanks, Daniel. I've snapped back from my temporary discouragement and am okay again with doing it online. It will take a while, but breaking free of the optometrist/optician racket is worth it to me. I'm realizing that it's the optician, not the optometrist, who is withholding the PD, so the sooner I'm free of both of them the better. Once I have the correct PDs, I won't have to repeat this part of the ordeal in the future.
ReplyDeleteI've found an online supplier called Visio-Rx that is far above the others in trying to get it right. They have extraordinarily responsive, helpful, personal and knowledgeable customer support (and marvelously patient with a fretful OCDer like me), and they clearly understand and are trying hard to provide the custom fitting services an optician provides.
I send them a specific series of photographs of my current glasses on and off my face and they use measurements from those photos to customize the lenses in the new frame and adjust the frame to my head. They may not have the process perfected yet (although they may - I just don't know yet), but I'm pretty confident they'll get there before long. I'd much rather invest my time and money with them than in wandering around town trying to find an optician I trust but not knowing whether they're trustworthy until they've already got my $500.
Returning to an issue you seem to be avoiding (although it may not be intentional), how can anybody focus on a tiny dot less than an inch from his eye (on the outside of the lens) and on a distant object at the same time? I don't see how your PD self-measurement technique can work for anybody, not just me. Can you explain how such vision is even possible? How a person can tell whether the dots line up while looking at a distant object? It seems impossible. It definitely is impossible for me, and my vision isn't unusually bad.
Thanks.
I haven't had any problem with my method. I and others have found it helpful and accurate. Perhaps it doesn't work for everyone, but then again what does?
DeletePerhaps your internet guys will trump me and solve your problems. Good luck!
Daniel, I've got a situation that I'm sure will make you cringe. If nothing else, let it serve as a cautionary tale to others, but I hope you can also give me some advice on what to do.
ReplyDeleteLet me just say first that I know I've been irresponsible about my eyesight. I'm trying to be better! Anyway, here's my story: I have 3 pairs of glasses that I wear interchangeably, but lately I mostly stick to two that I got off Coastal.com. The other one I got from a rather shady optometrist, and I wear them only once in awhile. When I ordered my glasses off Coastal a couple years ago, my optometrist would not provide me with my PD, so I had a friend measure me. I didn't do any research into PD at the time - what's normal, what can happen if it's wrong, etc. Long story short, I ordered my glasses with a PD that is almost 10 mm larger than it should be. Fast forward 2 years, and I'm looking online for a new pair of glasses. I find a pair I like, so I go back to my Coastal account and look up my prescription they have on file. The PD I entered two years ago was 74. Now bear in mind, I know NOW that that's an insanely high number, but at the time, I didn't think anything of it. It's only when I go to order my new frames, and see that the PD option doesn't even go as high as 74 for the pair I'm trying to order, that I begin to suspect that something's wrong. Because I really don't have an abnormally wide face...I start to question why there are so few glasses on this site that will accommodate this PD! So I start researching, and FINALLY realize, to my horror, that I've been walking around wearing glasses with a PD that's way, WAY off for the last two years. I remeasured myself with a ruler first, then found this page and measured myself with your method, and sure enough - both confirmed my measurement was off by a LOT. Yes, I am prone to headaches, and no, stupidly, I never traced the cause of them back to my glasses until now. I do notice a change, a feeling of distortion, when I switch to my pair of old glasses, but I always kind of thought THEY were the pair that was a little off, because they came from one of those bargain places. I never see the telltale prism effect caused by incorrect PD that I keep reading about....maybe that's because my prescription is not that strong? (-2.75 in both eyes)
My question now is - is it possible I've done damage to my eyes? And if I order a pair of glasses now with the correct PD, will my eyes have trouble making the adjustment? Is it harmful (aside from headaches) to switch from one PD to another? Must I really throw my old glasses out? (I guess I know the answer to that - but I just really like them!)
Hallie,
DeleteGet rid of those specs. They are cheap enough where you are buying them that you should not suffer the bad PD.
Your Rx is actually moderately strong, and with a 10mm error you are suffering 2.75 diopters of prism, more than three times the maximum acceptable variance of 0.66 diopters.
Though you are not doing permanent damage to your eyes, that amount of unnecessary prism is certainly causing headaches and serious eye strain and fatigue. It will take some adjustment to correct glasses because you have spent years neurologically adapting to the high prism, but once you do it will be a massive relief. Switching glasses with very different PDs just subjects your visual system to constant change and forces sustained adaptation. Your eyes never get to relax. Every pair should have equivalent PDs and Rx to eliminate variance, and therefore the stress of adaptation.
Well-made eyewear with a good Rx should cause zero strain or fatigue, and should provide comfortable and effortlessly clear vision. If your eyewear does not do so, get better eyewear.
And if you really love your frames, take them to a good optician to get proper lenses in them. Keep the style you love, get the vision you need!
Thanks for your response, Daniel. Glad to hear I've not inflicted my poor eyes with any permanent damage. I've ordered my new pair and I'm looking forward to finally fixing this horrible problem I've caused for myself! :)
ReplyDeleteI also just want to say that, while I respect your decision as an optometrist not to hand out PDs to your patients willy-nilly, I also REALLY appreciate the fact that you acknowledge that there are cheap-skates like me out here who would do anything to save a couple bucks, and you're willing to at least steer us in the right direction by putting this information out there, not for profit, but out of the kindness of your heart. I think that makes you the best kind of doctor. Thanks again!
Thanks for this post! Unfortunately, I find that I can't precisely place the mark on my glasses while simultaneously gazing at a far-away object. The pen/sticker/etc looks entirely too blurry to me.
ReplyDeleteIs the following method sound? Take a zoomed-in picture of yourself from a distance (use self-timer or have a friend take it) while focusing your gaze on the camera lens or something adjacent to it (if the flash is hurting your eyes!). Hold an object of known length (I used a T-square) near your eyes. Finally, use image manipulation software (e.g. GIMP) to measure both your pd and the object of known length in pixels - then a simple ratio calculation gives you your pd in mm, much like the credit card app.
Using the popular internet methods that you decry, I usually got about 63 mm for myself. Using the method I describe above with 4 different pictures, I got a range of 6.43 to 6.49 mm - this is with a middling point-and-click camera, which got a bit blurry at that distance, so you could do better with better gear, I'm sure. I'm assuming the greater pd with the camera method is because I was looking at a distant object rather than a nearby one, as you explained.
Does this seem like a decent do-it-yourself-at-home method? Thanks!
Jaime, thanks for sharing. Seems like a lot of steps and possibilities for error, but I'm glad you got good results with your method! It's similar to the existing online methods. I never got a decent result from them, but perhaps that's just me. I have never replicated my generic PD more accurately than with my method, so that's why I shared it. YMMV.
DeleteI understand where you are coming from in advocating the use of an optician over cheap online providers, but I am frustrated because some people, like myself, have to make a choice between quality and price. I simply cannot afford to pay $400 for glasses. It's not that I'm cheap or don't want to pay, it's simply an impossibility.
ReplyDeletePeople that turn to online glasses are just trying to get vision, a medical necessity, at a price they can afford. I respect your profession, but I think it is wrong that quality eyeglasses are only available to those with vision insurance or deep pockets.
Balancing cost and quality is necessary with any non-trivial purchase, but turning to unseen online sellers for $20 glasses is the nuclear option. By sidestepping the optician altogether you completely abandon the issue of quality and are shopping on price only. Online is almost zero cost for zero quality assurance. The best opticians are high expense for guaranteed best quality. But there is a huge middle ground of moderate priced opticals providing satisfactory quality eyewear.
DeleteIf $400 is a fiscal impossibility for your vision needs, there are plenty of opticals and opticians that can make you decent glasses for less than that and still offer service and peace of mind you will never get online. Any moderately populated area will have dozens of optical retailers, and probably almost as many optometrist/optician offices. Every one of them will have the ability to make you better eyewear than you get online, with customer service, advice, and follow up care, for less than $400. You will never get $400 eyewear for $100 online, you will only get $100 glasses and without any service or quality guarantee. But $200 glasses from a retail optical or optician will be quite serviceable, and at least you'll have someone to advise you about your eyewear, and talk to in the event you have a problem.
Daniel, if my optician had been as forthright and honest as you seem to be I would have no problem paying for your services. Unfortunately I have to second the above post as being treated like a piece of scum for even asking for my PD and it makes me never want to set foot in my optometrist's office ever again. I chose visio-rx which rents out digital pupilometers for you to take the most accurate measurements yourself. I would prefer to deal with a real person but I've tried a couple different places and been treated so awful it makes me feel like finding someone like you is nigh impossible in my city. I'm very happy with my online glasses but I'll keep my mind open to going back to a real optician thanks to you and posts like these. Treat your patients/customers like human beings and you might just nip this online thing in the bud. My GP Doctor would never give me a hassle if I wanted to take his prescription online to save some money, in fact my insurance company saves me money by shipping my blood pressure medicine to me in a 3 month supply. Why are eye docs so mad that people might want to do the same for glasses?
ReplyDeleteJames I'm glad you got a satisfactory result from your online experience, and it's a shame you experience with optical professionals drove your there. There is no excuse for treating customers poorly.
ReplyDeleteThere should be no problem taking your Rx to be filled elsewhere, as you are legally entitled to your Rx at the conclusion of your examination. However, PD and other biometrics necessary to design eyewear are not included in a vision Rx. Asking for your PD information is asking for professional service without giving them the eyewear business. That can cause anyone to bristle, though a professional should take it in stride.
I mentioned to another commenter that had the same poor experience: defuse the whole issue and separate your eye doctor and optician. All you need from the doctor is the raw Rx data; the optician from whom you buy eyewear with take care of all the biometrics. The optician you go to see is doing business directly with you, unattached from your doctor, and has no reason not to provide you with the utmost service.
Daniel, thanks for the response, you seem like an honest guy who genuinely cares about the people you help. If I lived in your city you'd have my regular business for sure. You are of course correct, the optometrist shouldn't provide the PD and the optician isn't compelled to work for free. That said, the attitude of some of your peers really rubs people the wrong way. I've been fitted for suits and asked for and been given my custom measurements without the slightest hesitation. I paid a fee for a service when I bought that suit, the measurements that made it shouldn't be held hostage from me...but with glasses, I've been denied my PD even after offering to purchase a pair. How is a customer supposed to feel? I know glasses are medical devices, but I can order a CPAP machine over the internet, in fact, I'm required to by my insurance for them to pay for it. People are willing to pay for services, if they wanted to charge me extra I would pay it for my PD, when I had it done, it took all of 5 seconds. Do you really think that 5 seconds of time with that pupilometer that visio-rx sells for $100 is hurting you? I could buy my own for less than the cost of glasses at retail rates. I acknowledge your time and education and its value and worth, if you're so convinced I'll get a substandard experience online, why deny me the right to an education of my own on the subject by letting me try? I'm sure my glasses bought online are inferior to a pair you'd fit me with, but can you honestly say the same for every optician out there? If so, opticianry would be an odd field to have no useless people at the bottom of the curve who don't know what they're doing.
ReplyDeleteUnfortunately, there's another good reason for measuring your own PD, which is to determine whether your optician has totally blown it, which appears to be my situation. I just had a pair of glasses made at LensCrafters, and the person who made the measurement, with some sort of camera rig mounted on a monitor, seemed to be having serious troubles with it. After four or five shots, she declared that it was good enough. Fast forward to today, got my glasses, which are progressives, and my vision is surprisingly fuzzy. After a little experimentation, I'm seeing that one serious problem with them is that the best-focused spot (at four feet) is off to my right with my right eye, and off to my left with my left eye. So when I look at something with both eyes, at least one is seeing serious blur. I'm guess this is due to PD being completely wrong. Or could it be something else? Is there a good way to get their "best" quality when I ask for the remake?
ReplyDeleteAlso, my bill for these has three line items for the lenses: (1) Plastic Hi-Index 1.67 Prem AR 6301 at $155, (2) Progressive HD 0389 at $265, and (3) Premium AR S43 at $135. It seems odd that AR is listed twice, as there can hardly be two AR coatings. Does this look right, or was I overbilled?
Thanks for any advice.
Mike,
DeletePD could certainly contribute to your issues, but the reading area alignment and the straightness if the lens mounted in the frame could be an issue as well. You are right about checking your own PD, because even if you bring your complaint to them and they check and say the eyewear is right you have a hard time doing anything other than accepting their word.
You can ask them to mark the progressive fitting height on the lenses. If everything is placed properly you should end up looking straight out through the marks exactly as if you had measured your own PD by my method. You can also ask them to fill in the progressive markings etched in the lenses. If the lenses are situated level the four marks (two per lens) should all align perfectly on a single line. If they don't the lenses are crooked.
I can't offer any advice about the pricing, that's unique to each company. Ask the personnel there to explain your bill.
Thanks Daniel--that's very helpful. The four marks you mention are definitely not on a single line. Both slant downwards to the right, with the right circle on each lens being maybe 2mm lower than the left (relative to the line connecting the outer two circles).
ReplyDeleteI'm wondering whether I shouldn't revert to single vision. My add is only 1.25 at this point, and I can actually read fine with no glasses at all. I'd want a second pair for computer work (which I do all day), but that wouldn't be difficult.
Am I right in thinking that single-vision lens are more fool-proof? That is, less likely to be made/fitted incorrectly?
Yes single vision is much simpler to make properly.
DeleteHaving separate single vision pairs for distance and computer, and simply removing your eyewear to read is a perfectly good solution. Putting all the different viewing areas together in one progressive lens is purely for the convenience of not taking glasses on and off all the time. If the compromise to your vision isn't worth the convenience, ditch the progressive.
Hi Daniel, thanks so much for all the information you’ve given.
ReplyDeleteI’ve been wearing glasses since I was 2 (I am 29 now) and have a very severe prescription of -10.25 (both eyes)
Recently I’ve been looking into buying online due to the massive difference in price. I generally spend around $600+ for my specs and can get a pair online for around $150 so you can obviously see why it’s tempting to me.
Whenever I have had my PD read, they’ve always just used a ruler up to my face to measure it. No fancy machines or anything. Unfortunately, the optical place I use (Hakim Optical in Canada, just bought a pair of glasses from them at “half-off” at $598.00 lol) absolutely refuses to give out my PD which is fine and I was going to use your method as described above but I would assume given my prescription that any deviation whatsoever in my correct PD would cause issues so I am a bit concerned.
I would just like to make clear the types of problems I could have if I get the PD off. They are not visual issues but other physical issues like headaches and eye strain?
Yes Amanda, headaches, eye strain, severe fatigue, double vision, and of course lack of clarity are symptoms of prism produced by poor PDs. As you said with your Rx even a single millimeter of inaccuracy produces unacceptable prism.
ReplyDeleteThe prices of online glasses are tempting, but I recommend seeking a lower priced optician or retail chain instead. It won't be $150 or $600, but in between, and at least you'll have the assurance of customer service if you need troubleshooting.
Thank you! I have a question... I recently had a pair of lenses fitted for my frames at Costco. They gave me double vision. I know about an adjusment period, but I have never had this. Eventually, I could tell tha the clear zone (center) was not centered over my right eye. They never measured my PD and now I think I know how to get it corrected (or at least have the discussion with the optician). That would be horizontal positioning. My question is about the vertical positioning. How can I go about making sure the center of the lens is vertically positioned properly and not to high or too low? Thank you. It is a wonderful thing you do.
ReplyDeleteHi John,
DeletePD is the horizontal distance between pupils, ocular center (OC) height is the vertical location of pupils in the frame. The best made eyewear measures the true ocular center of the eyes in a frame, vertical and horizontal.
OC height typically has less impact on eyewear, which is why some opticals don't measure it. However incorrect OCs can cause all the same prism problems as incorrect PDs.
My method does in fact isolate true ocular center in a frame. You can have an optician mark the OC of the lenses and if they are correct they should generally sit right in front of your eyes, or at least be vertically located at the same height in the frame (unless your eyes are very unequal and the optician intentionally accommodated for this with dissimilar heights). Note if they are not directly in front of your eyes that may not be wrong, frame fit factors such as tilt affect the vertical OC placement.
Quizz your optician about these fit factors, if they know what they're doing they will have answers.
This comment has been removed by a blog administrator.
ReplyDeleteThis comment has been removed by a blog administrator.
ReplyDeleteHi Daniel,
ReplyDeleteWhen measuring my distance PD using your method I had difficulty accurately marking my lenses and getting consistent readings and so I tried a variation of it and wanted to know if you thought it would be as accurate a method as yours.
Using my Digital Calliper, I measured and pierced a series of 2 pin holes in strips of dark pieces of paper at distances I thought would bracket what I thought was my PD. I then hold up the papers in turn up to my glasses and look through each pair of holes, one eye open at a time, until I find a pair which enables me to focus on the same spot(a tree) about 30 feet away.
Thanks for sharing your insight and answering our questions.
Ian, you that gets at the same result. Others commenters mentioned a similar system and as long as you can keep the paper and holes aligned accurately and still measure it precisely, it should duplicate the results.
ReplyDeleteI have alternating strabismus and it was really tricky to take a PD measurement. My eye doctor would not perform the measurement (which seemed very odd), and the chain optical store that I used in the past would not just take the PD dimension - they insisted on a full-blown exam for upwards of $75 dollars. I did it myself using several methods (including the one that Daniel describes here), and after repeating the process about 20 times I finally came up with what appeared to be the correct value. Ordered online glasses and have had no problems.
ReplyDeleteI appreciate you sharing this information. I normally go to an optician and prefer the service as you described, but I recently moved abroad and do not speak the local language yet. I tried to see an optician but there were some major language barrier issues. We just couldn't work through all the choices for the lenses and what not :( Also none of the frames were a very good fit anyway...with my big round European face here in Asia...So I feel ordering online is my only choice :(
ReplyDeleteAnyway...thank you...I hope you will not judge me. Haha. I will see an optician next time I am stateside!
It should be noted somewhere in this post that the PD is necessary are proper binocular function of the eyes. A person with alternating strabismus would rarely have and issue with an inaccurate but acceptably correct PD. Also, vision problems such as blur or eyestrain that exist while closing on eye are rarely PD related.
ReplyDeleteI live in Ontario and optometrists in this jurisdiction will not furnish PD on a progressive prescription. I so want to deal with an online supplier and I already sent my first progressive pair back - I strongly suspect PD was the problem. I'm an architect so I "get" the convergence issue. The online supplier furnished an out-of-scale tape measure ( I fixed that) and offered no explanation of near vs. far PD.
ReplyDeleteThat's pretty typical Architrove. Progressive lenses are supremely sensitive to proper fit, so even slight PD error makes a huge difference. Also, there are literally over a thousand progressive lens models on the market, all suitable for different purposes and needs. Even with perfect measurement you might have been provided a less than optimal design.
DeleteOnline stores just provide dry goods at lower cost by cutting something out. Obviously the expense of a brick and mortar location, but also service and expertise. All you get is the physical product, without proper explanation of its suitability for your needs, or how it should be designed or used.
You can read up on all the info online, but you still can't be sure it's being done right. One could memorize the entirely of WebMD and one still wouldn't be able to make the prudent decisions a medical professional would.
You do not get the same for less online. You just get less for less.
You mentioned several times that PD can change based the frame. Is this because the PD is the horizontal measurement from pupil to pupil and the your pupils may vary depending on where the frame sits on your nose?
ReplyDeleteRegarding online vs B&M stores, ive received good and bad service from both. What gets me the most though is how high the B&M stores markup the glasses and lens. My last (2) pairs of glasses have come from online stores and they cost 1/4 of what the B&M stores charge.
Hi ZakM,
DeleteOnline stores are certainly cheaper, that's even the case with true generic commodities like TVs and shoes. However, as opposed to TVs and shoes you almost certainly aren't getting the same thing offered by a good optician.
There are very few sites that offer the same quality branded materials you get from a good optician. It's easy to comparison shop commodities, because you can compare specs and model numbers, the seller doesn't affect that. Even a crappy seller can get you a good tv as long as the model is correct. However eyewear is not a simple commodity, consumers cannot easily compare quality between different eyewear, and online vendors (and low end B&M chain stores) prey on that.
They claim their product is the "same" for less, but it's false. There are a dozen lens materials, in varying quality from another dozen manufacturers, in another dozen curvatures, available in a handful of designs, in literally *thousands* of progressive designs, and with several dozen anti-reflective and scratch coating options. Even if you simply order a single vision plastic with anti reflective, there are *hundreds* of lenses that can fulfill that, ranging the spectrum from excellent to par to the cheapest crap manufacturable. Name brands protect the consumer by providing a standard if quality. Most online vendors don't use branded lenses because they are expensive and eliminate their ability to price compete. If you believe they get you the "same" product as your optician for less, you are mistaken. They give your a lesser product for less. If you cannot get less for less from your optician, I wager it has nothing to do with greed and everything to do with their desire to provide only quality product. Independent opticians can source very low cost product, most dot because they, like me, know it's crap.
As far as the frame dependent PD, yes it's due to variance of frame fit. Every frame fits differently on the bridge, often unevenly, so any PD measurement that does not account for frame fit is merely close, it cannot be correct. Note, if you use my method with the actual frame to be used, it will get you and accurate frame dependent PD.
Thanks Daniel for the quick reply. I am still confused about how the PD works based on the frame. The last couple of glasses I purchased through a B&M store, the "fitter" just took my PD with a machine and didnt do anything with the frame. It would seem like a measure from my pupil to the top edge of the frame would be needed. No? When you take a patients PD, do you take another measurement from the top edge of the frame?
ReplyDeletePD is the mere basest information necessary to make eyewear. PD alone still isn't enough for any but the mildest Rxs. Additional info would be the vertical ocular center height, like you refer to, as well as the vertical and horizontal tilt of the frame, as well as the distance the lens is held from your eye. The best measurement takes an A (PD), B (OC height), X (pantosoptic tilt), Y (wrap angle), and Z (vertex distance). PD is merely the A alone. Solves one problem, leaves at least four more uncorrected.
ReplyDeleteDaniel, that makes sense, but Ive never seen anyone take these kinds of measurements. Ive been wearing glasses over 30 years and Ive never had my eye distance from lens or any of those values you listed measured. Can you list some reputable B&M eyeglass providers that do these measurements?
ReplyDeleteZakM, for the best information about such detailed measurements check out my article about digital lens technology http://www.daniellivingston.com/2013/07/digital-lens-technology.html
ReplyDeleteTraditionally, horizontal (PD) and vertical (OC) measurements have always been taken by good opticians. Additional X, Y, and Z measurements were taken when Rxs or frame fits were extreme. However, that was professional private opticians. The last few decades have seen an explosive growth of chain retail optical stores, and with them an explosive growth of hastily and inadequately trained salespeople. For the sake of brevity and simplicity in training and sales time, all proper quantification of eyewear fit was abandoned save the PD.
To obtain a true and correct spectacle fitting, only a good professional optician will do. Others simply don't have the tools or skill to do it right. Almost certainly any retail optical chain you have heard of will *not* be of the caliber required. Use the brand locators below to find some practices near you. If they are listed with these premier lens makers, they ought to be able to deliver the expertise necessary for the best eyewear possible.
http://www.essilorusa.com/EN/AboutVision/Pages/StoreLocator.aspx
http://www.shamirlens.com/index.php?option=com_k2&view=itemlist&layout=category&task=category&id=88&Itemid=269&lang=en
http://www.zeiss.com/85256A2C00462B09/DealerLocator?OpenForm
Hi Daniel
ReplyDeleteAfter having trouble finding a correct measurement for PD with the ruler method I decided to pay the fee to get it measured with the device. They gave me two different measurement, one for each eye, but the place i am ordering from (coastal.com) asks for one number for the PD. Am I to just add each eye together?
Yup that's it. Hopefully your values aren't much different otherwise the lenses will be off.
DeleteOD is 28 and OS is 30.5. Think that will be ok?
ReplyDeleteAs long as your rx is 5.00 or less, and the glasses makers get the PDs *perfect*, it shouldn't cause trouble. However reality is they will accept a small error in the final PDs they make, so that error coupled with the rounding error they begin with means I would call only an Rx of total power 2.00 or less safe. Anything higher has only a 50% chance of being within acceptable tolerances.
ReplyDeleteok my prescription is OD: +4.50, -3.25, 180 and OS: +4.50, -2.50, 170. Unfortunately getting glasses at my eye doctor office is not an option for me because it will cost 400 -600 whereas online will only be 80.
ReplyDeleteThank you for this info. I took your advice and saw an optician. I ordered a nice pair of glasses through them (Coach!) but I would like to order a cheaper backup pair online. Problem is, I don't understand the PD she gave me. It was 66/63. I live in Japan, but I want to order from a US website. Do you know how to convert this?
ReplyDeleteAs an aside, since you love your job, you might be interested to hear about my glasses shopping experience as an American here in Japan. I had a remarkably difficult time finding glasses that work on my face here! I could practically see under the bottom rim of nearly every pair of glasses I tried on. The Japanese opticians I spoke to were quite amused, saying they are not used to helping customers with such "prominent" European noses, lol. They actually suggested I order from an American website...but none would help with the PD. I was happy to finally find a pair that worked, and to order with somebody who could measure my PD accurately. But I could really use some help on that question - I can't afford to pairs of Coach glasses! Thanks!
Audrey the 66/63 is your distance/near PD. Use the 66 for everything except reading glasses or lined bifocals.
DeleteYour fitting story is amusing, thank you! It's less so, but the reverse is true here: Asian patients often have difficulty finding frames to accommodate their flatter bridges. There is a large enough Asian population in the U.S. that many frame makers have "Asian fit" models, and of course a good optician working with adjustable nose pads can accommodate nearly any bridge fit, but it can take some effort to get the right fit.
so daniel this is in response to this post by you. my comment is at the end..........Daniel Livingston said...
ReplyDeleteThere are several reasons opticians may not give out PDs for use elsewhere, and some do advocate "protecting" the profession, but as my advice here should make clear I am not such an advocate.
Opticians care about your vision in the same way as your lawyer cares about your legal rights and your accountant cares about your financial health. When you enlist our services, we do care to ensure you get the best vision we can provide. If you do not enlist our services, you have chosen not to be cared for.
PDs are not accurately measured during your exam, only an approximation is made to fit the lenses in front of your eyes, satisfactorily only for a fixed straight ahead gaze and just the few minutes of time you spend looking at the chart. I guarantee you do not want those numbers being made into eyewear.
I do not provide PDs for eyewear I do not make, for two reasons. The most obvious is that my skill as an optician will provide excellent accuracy perfect for any Rx, and if that's what you want it’s a paid professional service like any other. If that skill isn't valuable to you, then just use my method and do it yourself.
The most important reason I don't give out PDs, even for a fee, is because obtaining good measurements for lenses is the responsibility of the eyewear maker. If I'm not making the eyewear myself, I want no part in the process. There's dozens of ways someone else can screw up eyewear even with accurate PDs, and I won't contribute to the eyewear when I can't guarantee quality.
Accurate PDs denote where you look through the lenses of a particular frame for a particular use, not the mere distance between your pupils. They therefore depend on your frame, adjustment, and your lens design as much as on your eyes. There is no single biometric PD value that produces accurate eyewear. I measure and use unique PDs for every pair of eyewear I make for my customers, and the variance from pair to pair is significant. If you want measurements perfectly accurate for your frame, fit, and lens design, I do care about your vision and will ensure you receive such accuracy in eyewear I make for you. Find a good optician and they will care about your vision the same way.
April 27, 2013 at 9:16 AM
so you are saying no pd because you will not be a part of getting wrong glasses so why give out the prescription in the first place because their can be error in the prescription in the first place.
Thanks for discussing rja rja!
DeletePrescribers are legally obligated to provide vision Rxs independently from whether or how they are filled. Vision Rx information is valid and diagnostically useful apart from any device which fills the Rx. They may or may not provide PDs as well.
PDs are not diagnostically valuable apart from eyewear. They are an integral of the eyewear making process, and ought to be taken by the eyewear maker. I am not a prescriber, I am an optician and my business is making eyewear. If the maker won't or can't get proper measurements (e.g. because they choose to run an internet business) I am not interested in filling the gap. I am interested in making excellent eyewear for customers that value my expertise.
If you try enough you will find optical workers who will supply PD either for free or a small fee. I am just committed to doing it all myself, perfectly, or not at all.
Wow, this is the most helpful article I've come across after quite some time spent googling. My ophthalmologist told me that my PD is 57. But the glasses I ordered online (before visiting him) used quite a different PD (measured at home, apparently inaccurately), and I see just fine. Could I be harming my vision by wearing them? If I order glasses online again (I'm a student living abroad), what happens if I order glasses for a PD of 58 or 60? (sites don't seem to have a large selection of frames that accommodate my PS? My prescription is moderate, I think-- -5.50 and -4.75. Thank you so much for this article--it was so helpful! (And it made me miss my optician from the US.)
ReplyDeleteMegan,
ReplyDeleteI'm glad my article was useful to you, and thanks for the praise!
You won't *harm* your eyes by having PDs a bit off, and you may see ok, but you are certainly suffering unnecessary eye strain. For your Rx even a 2mm deviation from your correct PD induces an unacceptable amount of prism. Use my method to double check your PD value yourself. Even with a correct PD entered when you order online, there's no guarantee the glasses match up. Best would be to have them verified by an optician, if possible.
Wow, thank you so much for your prompt and helpful response! The glasses I've been wearing for 3 years now were made for a PD of 61, but when the ophthalmologist measured me (by holding a ruler up to my eyes), he got a 57. Should I be worried that his measurement is incorrect, if I've been wearing a significantly different one for years without any headaches, etc? Should I go ahead and trust him? (I guess the obvious solution would be to go back to him/someone else, but I'd have a tough time finding a provider here.)
ReplyDeleteThank you so much, again, for this article and for your assistance.
I wouldn't use the doctor's measurement. Ophthalmologists are petty far removed from the whole process of making quality eyewear; a manual measurement with a ruler from a non-expert is not reliable.
DeleteUse my method in the article to measure for yourself. If done correctly the accuracy will be very good. Getting someone (especially onliners) to make it that accurately is unfortunately another issue.
Wow, thank you so much! I'm off to try your method...or maybe even to brave finding an optician in this country--you've convinced me! Thanks again for this article and for all the advice you've given me.
ReplyDeleteDaniel,
ReplyDeleteThank you so much for this extremely useful information. I hate to admit it now, but I was looking for a better way to measure my PD from home in order to get glasses online again when I stumbled across your site. You are right on all counts when it comes to the inaccuracy of the measurement systems available, I think I took my picture ten times and still maintained an error range of 3mm.
Having said that I have a question. I am a woodworker, and my glasses perform a visual as well as a safety function at work. As a result of flying debris and solvent exposure due to finishing processes, I can blow through a pair of glasses in no time flat. So when I found out how cheap a pair of glasses could be online I thought I had hit the jackpot with a semi-disposable solution to keeping my nice glasses nice and my work glasses working. In order to keep them as cheap as possible I got lenses that had a lower refractive index than the ones I use for daily wear and I have gotta say, they took some getting used to. I switch in and out of these both when I get to work and leave for home and now it is no problem. But is it possible I am screwing with my eyes by doing this? Just wondering...
Thanks.
Wes, thanks for the compliments!
ReplyDeleteYou won't harm your eyes switching between different glasses. The strains that you feel are your eyes and brain getting used to the different fields of vision produced by different lens materials, curvatures, and designs, all of which can vary even though the Rx is the same. Good opticians always design multiple pairs to be compatible, but getting different pairs from different places negates that kind of service. You will probably always feel the strain when switching pairs or different design and there is little that can be done other than get every pair made the same from the same place.
So I took your advice and got 2 specialists to measure my PD (as I am having significant difficulties with my eyes) and both of them have given me 2 different numbers. Now what?
ReplyDeleteKarine, now you have the responsibility and luxury of choosing between competing professional opinions.
DeleteGo with the optician in whom you have more confidence. You will also then have a professional committed to getting your eyewear done right, and fixing any issues you may have down the road.
"Karine, now you have the responsibility and luxury of choosing between competing professional opinions.
ReplyDeleteGo with the optician in whom you have more confidence. You will also then have a professional committed to getting your eyewear done right, and fixing any issues you may have down the road."
You see here in lies the problem. You do not pay store mark-up and the additional professional PD measurement fees to have to be subjected to constantly bringing back your glasses to redo the lenses, and the hassle with dealing with "professionals" who think they were right all along. Her experience is why people say "well I'll roll the dice with doing it myself and buying online". A lot of trained "professionals" either just use the auto refrac, or just measure near PD and add 2 to 4mm for the far. And to be honest with you, the reason they can do this is because the effects are so small, it's negligible to most people.
Now I agree with your idea that being "ok" isn't perfect, and even though your brain will get used to it being slightly off, it's not perfect, and why should I settle for less than perfect when it comes to my vision? See that is what makes your profession one of sales and less of science.
I am positive that you have fitted someone incorrectly with a pair of glasses. I am sure you incorrectly measured a persons PD. I know for a fact that your patients don't even know it, they trust you and even though you sell them the "don't settle for ok" mantra at a very high mark-up they are settling for it. When it comes down to it, your technique and the manufacturing process isn't perfect. Tolerances exist and are sometimes exceeded for certain individuals. However, if they can't detect it, which most won't, you just got away with charging a premium price for a sub-premium service. That is the reality for most practices these days. I'll stick with the best price/performance service, which sadly are no longer brick and mortars. Keep up the good work though, selling that premium product to folks who wouldn't be able to tell the difference.
I'm glad you have such success with online eyewear. Given your poor experiences with "professionals" it is unsurprising your understanding of what I do is skewed. If you see no value, then don't pay more.
DeleteSo I am having a bit of a problem with my PD. I am in the market for new glasses, and want to have accurate measurements but can't afford to spend the 600 dollars that Pearle Vision would charge for high quality lenses and frames. Given the fact that they have given me different PD's I can't even see why I should pay 600 dollars for new glasses. After getting an eye exam, I had my PD measured at a glasses showroom and was measured at R33.5/L34.5 I later had this checked again at Pearle Vision and the person checking my PD gave me R34.0/L32.5. I decided to get another opinion and had the optical technician at Target measure me and he gave me R32.5/L34.0, the exact opposite of the results from Pearle. Since I received so many different answers from people measuring me with the same device, I called Pearle and asked them for the PD they used the last time I got glasses, and they gave me 33.5/33.5. It seems to me that there is at least a 1mm margin of error in these tests, contingent even on how the person is holding the device and how it is calibrated, so how can I be sure that I'm ever getting good glasses and that the person measuring my eyes knows how to get accurate measurements? Even if I were to measure myself using your method, wouldn't the slightest angling of my head alter the results? most markers are thicker than 1mm and most glasses surfaces are curved which would alter the self measurements as well. Does the 1mm difference even mater that much if I used the 33.5/33.5? My prescription is different in each eye but is at most a -4 combined sphere (-275) and cylinder (-125) in my left eye. My right eye is a -300 sphere with a -75 cylinder. I am very interested in your opinion on this matter as I am quite frustrated.
ReplyDeletePD measurements will vary due to the precision limitations of equipment and personnel. Your spread is small so any will do if ordering online. Online outfits and basic labs use conventional lens technology that produce lenses only within 1-2mm of specification. Don't sweat 1mm because they are unlikely to make it within 1mm accuracy.
DeleteIf you are concerned about accuracy do not order online. Get your eyewear from someone who can confirm and demonstrate the accuracy of the final eyewear.
Very informative post, thank you!
ReplyDeleteCan your PD be worked out accurately from your old glasses? An online retailer (who also have a retail outlet) stated they can work out my PD by this method. My PD is apparently 60.5, I've found some old prescriptions with 60 (and no other figures next to it) written on them, so assuming that there's a 0.5mm tolerance?
Yes the PD can be read off an existing pair of glasses. Note this is the PD of the glasses, not the wearer. Presumably it is close, but problems can occur. There are tolerances in eyeglass making and measuring, and they depend on the Rx. Duplicating and existing PD copies errors in the original glasses, and possibly compounds them with more errors.
DeleteE.g. say your PD is 60. An optician measures you at 60.5, then makes glasses which end up being 61.5, which may well be within tolerance. To duplicate that PD one reads the glasses, but there is room for error in ability to read the PD too. Say they read 62, then make glasses that again come out in tolerance of that value at 63.
Every step was within acceptable tolerance, but the net result of compounded error could end up well out of tolerance. If your Rx is significant even a 2mm error will cause problems. With my method there is only one step of measurement and one of fabrication, so the potential for compound error is minimized.
This comment has been removed by a blog administrator.
ReplyDeleteMy optician has competed my prescription with two PDs. 29 and 30?
ReplyDeleteHow is that possible?
That's your right and left eyes measured separately. Add the two for your total PD.
DeleteThanks, Daniel, for a very informative blog! In case it is helpful to others, let me pass along here a slight modification to your method that I found worked even better for me.
ReplyDeleteI tried the marker method for getting a PD and found I could never hold the fine-tip marker steady enough to get a really sharp line. Something about a pointed object heading straight into my field of vision kept me from getting it just right. By the time I did one lens and got to the other, I found my head had shifted slightly, throwing it off more than once when I went back to check with both eyes open. I thought about this and came up with a modified approach.
Here's what I did: I took a Post-It note and cut small sharp triangles such that the tip of the triangle was at the adhesive edge of the Post-It paper. These were about twice as tall as they were wide at the base. I made each of them about 3/4" from base to tip as this gave me sufficient paper (below the sharp tip at the top) to hold the triangles for position and then just touch the adhesive tip at the top to the lens for attachment. They stay in position but can easily be re-positioned as needed.
At first I tried them both pointing up, and then both pointing down, as I looked at a distant object for convergence. That worked pretty well but produced some overlap in my field of vision that made exact placement challenging.
Then I realized if I oriented them with one pointing up (from below the center of the lens) and the other pointing down (from above the center of the lens), with the tip of each triangle at the same vertical height on the lens, quality of convergence would be improved. Using this approach, I could open one eye, then the other and in each case see a sharp point at the same place on my distant reference target, or adjust one or the other closer together or further apart as needed to get that result with both eyes open.
Once the positions of the triangles were dialed in, I just measured the distance between the two pointed tips. This also allowed me to very precisely (with a millimeter ruler) place the triangles so as to try 65mm spacing, then 66mm, then 67mm. I found my PD was right between 66mm and 67mm and if ordering single-vision glasses online will probably specify 66mm since much of my viewing will be at shorter distances than the outdoor target I was viewing.
Thanks Leigh! There are many variations that get you to the same result. I like the simplest method possible, but if you find a way that works better for you great!
DeleteThanks for posting this Blog Daniel. It has made me more comfortable in choosing an Optician to make my new pair of glasses.
ReplyDeleteHere in Canada my new pair ranges from $899 - $1100 depending on who I decide to use.
It all depends on who instills in me the confidence that they are putting my vision and clarity over and above the almighty $.
David HL
Thank you David, I'm glad you got something beyond just the info I provide. As in everything there are good and bad opticians, but it is not a sleazy business as many peoples' poor experiences have led them to believe. Opticianry is not a business to get into for money, there are too many easier and better paying careers. One sticks with it because it is challenging and interesting, and allows one to provide valuable health service to people who really do need it. You may need to search a bit to find a good optician, but you will.
ReplyDeleteHello Mr. Livingston,
ReplyDeleteI have issues that bar me from actually going to the Opt. Disability. my prescription is OD -.50 -.75 OS +.50 -1.25. i DID get an exam recently because everything aligned just so, but couldn't get to the retailer to get the glasses ordered. My fiance had to go, but my exam, as has been pointed out, did not include the PD. So my question is, after all the bantering, with my prescription, should i be really worried about my order since i measured my eye with a ruler designed specifically for PD? I would have used you method, but i only just found this today. Thanks for the info as well.
Measuring your own PD with a ruler and a mirror is woefully inaccurate. There is nothing special about rulers made for PD measuring that enhances accuracy. Parallax and near focus convergence guarantee your results will not be correct even if you can read the fine millimeter ruler hashes accurately.
DeleteMy method eliminates almost all judgment and reduces the measuring process to a simple point to point on an object, which anyone can measure will good accuracy. Even if you have glasses, try my method anyway and see how much the result differs from what you ordered. If it's more than 2mm you are probably experiencing vision issues even if you don't realize it. If it's less than 2mm, you lucked out!
This comment has been removed by the author.
ReplyDeleteThis post was extremely helpful, Daniel. It's the best post on PD measurements and advocacy I've come across. Thank you for the information.
ReplyDeleteThanks for the great information. I spent $1000 (that's right, a grand) on my last pair of glasses. I need a backup pair and just can't afford to spend that kind of money again. My question: I am blind in my left eye. Will the method work for me?
ReplyDeleteYes my method will work fine. The major vision issues associated with PD arise from stereo vision. With a single eye there is much less likelihood of difficulties.
DeleteFirst of all, thank you for a thoughtful, well-written description of PD. I was particularly interested in your response that stated, "Accurate PDs denote where you look through the lenses of a particular frame for a particular use, not the mere distance between your pupils. They therefore depend on your frame, adjustment, and your lens design as much as on your eyes. There is no single biometric PD value that produces accurate eyewear."
ReplyDeleteI recently bought reading glasses from one of the national chains that operate in malls. They measured PD using the frames I bought and a computer camera about 4ft away from me. I wondered why they did not hold a device up to my eyes to take the measurement, but your explanation above made it clear that PD is specific to the frame.
I'll be buying sports/tactical sunglasses with the same Rxn added to them. I'm using a reputable optician who happens to be in another state. They asked for my PD. Based on what I've read here, my PD from my recently bought reading glasses might not be "correct" since these are not the same frames as the sunglasses. Am I understanding this correctly?
If so, I'm wondering how this works: how do you get proper sports/tactical lenses made remotely when your local shops do not carry the brands you want or aren't interested in fabricating lenses for frames they don't sell.
Thank you for the compliment!
ReplyDeleteYou have drilled right to the heart of the issue: "how do you get proper sports/tactical lenses made remotely when your local shops do not carry the brands you want or aren't interested in fabricating lenses for frames they don't sell".
The simple answer is you can't. A tailor can't custom design a suit without hand-ons evaluation, an optician can't custom design lenses without the same in-person access. Remote fabrication will necessarily sacrifice accuracy. The best precision can only be obtained from a good optician providing all services, including frame selection, tailored measurement, and lens design. Fragmenting your care and taking some steps out of the hands of your optician limits his ability to provide a quality final product.
If you *must* get it done remotely, I suggest you find a local optometrist or optician office that provides customs fit freeform/digital lenses. The most committed to custom digital technology will have either Visioffice or i.Terminal machines. They will have to communicate with your optician and be willing to provide custom measuring services, and if they are then they can obtain the information and provide it to your optician.
Your experience sound very much like LensCrafters to me. Though I am not intimately familiar with any technology improvements they may have made in the last year, last I knew their "custom" lenses did not account for individualized frame fit. Obscure to consumers is the fact that there are several levels of freeform/digital lens sophistication. Retail stores offer only the simplest level of the current technology, and will seriously fail in the high performance sports wrap sunglass category. Only a fully equipped private optical can deliver peak custom precision and technology necessary for the best sport performance eyewear.
Thank you for this good information! Please tell me what you think about my situation. I had the same glasses for 6 years. I finally had an eye exam and ordered my glasses online; I am a college student with no income, so this was my only choice.
ReplyDeleteI have had the glasses for about 4 weeks, and they seem perfect. The only problem I have is that once every few days I am sitting in a chair and suddenly feel like I am falling over, although I have not moved. It's like my vision quickly rotates to one side, just as if I were falling over, and then a few seconds later I feel normal again. I have never had this happen before I got these glasses, so I am assuming it is the glasses. It just doesn't make sense for the glasses to cause it because it only happens once every few days. Do you think the glasses could cause this? I also get mild headaches sometimes, but this is not abnormal for me so it is harder to blame on the glasses.
I brought my new and old glasses to the store that did my exam. They said the new glasses are made exactly to the prescription. I asked them to also check my old glasses, and the PD is 62. My new glasses have a PD of 65, which is what the store wrote on my prescription. They used a small machine to recheck my PD, and got 62.5. So they wrote my PD wrong on the prescription, and now my glasses are made to the wrong PD. This is the same store that made my glasses 6 years ago; they had my old prescription on file when they did the exam, compared both, and told me it did not change much. If they had 2 different PDs on file, they should have noticed it then. I was 22 years old when I got the last glasses and am now 28, so it would not have changed.
The store denied writing the PD, and said it wasn't their handwriting. I saw them write it on the paper after my exam! They said this as they wrote over the 65 on my copy of the prescription, making it 62.5, then crossed it out because you could still read 65, and wrote 62.5 next to it. They said the PD was not off enough to cause any problems so maybe I have a medical problem, but I don't trust them now. Do you think the PD is the cause of my symptoms, or does this seem like some weird medical problem? My prescription is OD -6.50 -0.75 007, OS -7.00 -0.50 021.
Also I got 2 pairs of new glasses because I was worried they were too cheap and would break; it was only $50 total. One has slightly wider frames and lenses and is 1.57 mid index; I wear these at home. The other pair has the exact frame & lens dimensions as my old glasses and has 1.61 high index lenses; I wear them when I go anywhere. So I switch glasses in the morning and then switch back at night, but when I feel like I am falling it is in the middle of the day. Could switching glasses like this cause my problem?
Sorry this is so long; it is just very frustrating. Thank you for your help!
There are too many variables in your situation to make a diagnosis of any connection between your vertigo problems and the glasses. You need a professional to take responsibility for the glasses. Unfortunately that's the sacrifice of online buying.
ReplyDeleteIrrespective of your problems, the glasses are wrong. Your Rx is strong and with a 2.5mm difference between your PD and the glasses, you are wearing 1.6 diopters of prism, more than double the maximum acceptable tolerance in the U.S. Additionally, those lenses are not optical grade material, they are something made up by foreign manufacturers and of unknown performance. Despite onliners' claims that they provide great quality at a fraction of the price, it's just a lie. They provide the cheapest goods possible and prey on consumers looking for a deal who believe all glasses are the same. They have no need to make the glasses well because they still turn a profit on their 50% refund.
Your budget for glasses should be proportional to your need and desire for excellent vision. With your Rx your need is extreme, and clearly you are not satisfied with uncomfortable vision. If you want any improvement you just need to make your vision a priority and get it done right by a good optician.
Thanks for posting this! I've never been confident about pupillary distance and I think your method will help me get a better idea of it. Eight years after lasik, as of today I have a very tiny prescription (-.5 in one eye, +.25 in the other) and I rarely wear my glasses and am picky about frames, so online glasses seems like the best option for me.
ReplyDeleteThere is one thing I'm wondering - would wearing very-out-of-date glasses to mark up to measure PD distort the PD? Or doesn't it matter? I don't have any glasses with anything like an accurate prescription. I guess I could try it with non-prescription sunglasses.
Grenacia, no the Rx in your old glasses won't affect your pd measurement.
ReplyDeleteHi Daniel,
ReplyDeleteI have got my PD from an old prescription my Optician had on file which they measured at 29 and 29 for right and left. this was measured a few years ago is this likely to have changed significantly or at all? Personally I would have thought not but if you could confirm or otherwise that would be most helpful.
Thanks
No adult PDs rarely change
DeleteThanks for this article. I'm just having some glasses made up by an online optician and the PD they read from my old pair exactly matches the measurement I took with this felt pen method (68mm).
ReplyDeleteA question I had, can we assume that the measurement from the bridge to each pupil is the same (i.e. the face is symmetrical)? If not, shouldn't the PD really be two measurements (distance from the bridge for each pupil)?
Interesting comments about need for proper optician fittings. Here in the UK our consumer watchdog rated a third of opticians "poor":
http://www.which.co.uk/news/2011/08/opticians-fail-the-which-eye-test-263296/
My own experience seems to bear this out. As an experiment, I had two eye tests done at two opticians on the same day. These were the results:
Optican 1
Left: -5.50, -0.50, 5.0
Right: -4.75, -1.50, 7.0
Optician 2
Left: -5.00, -0.50, 3.0
Right: -4.50, -1.50, 10.0
Didn't exactly fill me with confidence, so I ended up sending my favourite pair off to an online optician to have another made up with the same specification.
David, thanks for the comments!
DeleteYes, a more accurate PD will be monocular, separate measurements from pupil to center bridge. This is more difficult to measure accurately, and is more frame dependent as different frames sit differently on the bridge and will split the total PD slightly differently. However, my method does take all this into account and you can measure the PD monocularly once you have marked your lenses.
A vision Rx is not an objective value, it is a subjective finding that combines your responses to the examiner, as well as the examiner's skill and medical philosophy (some aim primarily for sharpness of vision, others more for comfort, as the two are often at odds). It's not surprising you would get the variance you did between examiners.
In the U.S. examiners and opticians are separate; they figure the Rx, we make the eyewear.
Hi!
ReplyDeleteThank you for the informative article. I'm going to order glasses online anyway because of my specific situation: I currently have no glasses and I need a pair for only a two month period. So in my case, cheap glasses would be a worthwhile compromise.
Hi Daniel!
ReplyDeleteQuestion on how to accurately measure a PD on a child? My 4 year old needed his 1st pair of glasses & the optician measured PD in 2 seconds with a ruler having him look at her nose???
He won't wear the glasses for longer than 10 min & keeps complaining his head hurts- I fear they weren't accurately made to his correct PD. I've taken them back and gotten the "it's his 1st pair... give it time" but his slightly older bro, myself, & my hubby all wear glasses & he was estatic to get them so it's not that he doesn't want them.
(he's farsighted. OD:+2.5 / -.5 / 53
OS: +2.75 / -.75 / 161)
I also ordered 2 pair (1 sunglasses) there & can't wear the sunglasses-I'll be doing this test on mine for sure!
They send the frame away to get the lenses made/cut/installed. Am I paying for an optician but getting "online quality". Are they even an optician at all? It's a large chain that our new optometrist recommended because of kid's frames.
Thank you, Daniel, for such a great, informative blog. I am a first year student in the Opticianry program at Hillsborough Community College in Tampa, Florida. Accurate measurement of PDs was covered thoroughly in class and caught my interest enough to do some research on my own for a paper I will have to write. This blog has certainly given me enough to write about, with your permission if you are inclined to give it. Thank you in advance for considering my request regardless of your answer.
ReplyDeleteGalen McCarty
... BTW, Loved your comment "It can be tricky to measure your own PD, somewhat akin to trying to cut your own hair." I am a late comer to Opticianry, after a 30 year career as a cosmetologist. I will never forget the customer who came in with a terrible haircut and was thrilled with the cut and style I provided. She called me a couple of days later to gush about her new look but had a question. She wanted to know why I charged almost twice as much as her previous hairstylist. I asked her, "Isn't the perfect cut worth more than a bad one? Anyone can cut hair, even a 5 year old who finds Mom's scissors. Knowing what to leave attached is key."
ReplyDeleteGalen
That's a pretty significant Rx for first time glasses, it's not surprising your son is disinclined to wear them. If you are concerned the glasses are not made properly, and are not confident in the opticians that measured them, I recommend taking them to a different optician and paying for their service to check the glasses Rx and PD. It's the only way to verify with confidence.
ReplyDeleteIt is common for opticals to send the work of making the glasses out to a large lab. That is not necessarily any sacrifice in quality, as that depends wholly on the quality of the lab to which they choose to send the work. If you trust the optician's skill and knowledge, trust his choice of lab. If you don't trust the optician, well then there is no reason to trust any other decisions he makes.
You are still getting something more than online opticals because the eyewear is being designed and measured by an optician, and then verified and fit by opticians when complete. Online opticals give you no design expertise, verification, or fitting.
It's all about trusting your optician. The chain stores are a crap shoot, you have no idea if the person helping you knows what they are doing or not. If you don't feel confident in your optician's skill, service, or attention to your needs, find another place. If you've tried several and none are satisfactory, try a private optical or optometry practice. I think you will surprised by the difference in quality.
Galen, thanks for the praise!
ReplyDeletePlease use whatever information you can. Proper citation is all that I ask.
Thanks Daniel, really informative answers, much appreciated, I wish I could find such a great optician here in the UK!
ReplyDeleteThanks Daniel, and of course I will cite you and your blog!
ReplyDeleteGalen
Interesting method of measuring your PD and interesting discussion about PD and troubles getting it. In the UK, opticians are obliged to give you a copy of your prescription but that doesn't include the PD so you can be bit stuck. I've just spent £450 onto two pairs of glasses from my opticians and want to get a pair of reading glasses but just can't afford the £130 they want to fit lenses into the frames I've provided. I'll measure my own PD and take my chances.
ReplyDeleteAt least you have good distance vision pairs. Ask for the PD they put in the glasses. That, after all, you have paid for and they should have little excuse to deny you that. If I want to know what brand and size nails my contractor used to build my house, I expect him to tell me correctly. That's very different form asking what brand and size nails he would use if he made my house, and then giving that information to a competitor instead.
ReplyDeleteThat will be your distance PD. To get your reading PD, if the distance is 60mm or less subtract 3mm, if more than 60mm subtract 4mm. That pretty accurately accounts for the PD change of near vision convergence.
Am I to understand then that a PD of 61 measured by an optometrist for distance should be downscaled by -3 for a reading glasses PD of 58, or is that dependant upon the chosen frames? Thanks for your expertise and unflagging comments,
ReplyDeleteBernieK.
Bernie, I would even reduce that 61mm PD by 4mm to 57mm. It depends on frames as much as distance PD depends on frames. If you are particularly concerned about precision you'll need an optician to measure you in the frames. If you're less interested, or because buying remotely, then it matters little and will be adequate for the basic purpose.
ReplyDeleteHi Daniel, Very informative article and comment section, thank you! I have measured using your method, the far pd is 65, close pd is 61. When you go get eyeglasses, a lot of times it's one pair for everything for the most part. But it does seem that the spread is too much to always be looking 2 mm off (if the pd is averaged) depending if you are looking with more distance or at your computer/reading. But isn't this the way it's usually done? Like for driving, one needs both distance and near, so is it an average of the near and far pd? or is it always best to have two separate pair of glasses with the correct pd for that usage? Kind regards, Gracie
ReplyDeleteGracie, it is true for single vision distance glasses only the distance PD is used, and that does compromise near vision focusing some. The majority of our visual tasks are at 10 feet and further distance so if we are forced to choose the distance measurement is primary. A compromise middling value would distribute the stress, but the result could be mild discomfort both at distance and near with no comfortable vision. Better to make distance comfortable and sacrifice the near.
ReplyDeleteLuckily, most people with single vision needs only still have enough flexibility and adaptive power to their vision that they can easily overcome the near vision compromise. That capability deteriorates as we age pushing us into reading glasses, bifocals, or progressives, but all those solutions take near PDs into account.
Yes, for best possible vision everyone should have dedicated pairs for distance, computer, and near (I do. I even have a fourth: dedicated higher power iPad glasses for up close Netflix in bed!). All those glasses can be inconvenient, so bifocals and progressives are more popular as a multi-use solution. But they do compromise vision more than dedicated pairs for every visual task.
Very informative reading. Thanks.
ReplyDeleteWhat do you think of this variation on your method for measuring PD.
Take two strips of paper. Fold the top and bottom of one and cut the other so that it slides inside the first. Poke a small hole in each piece of paper. Hold the paper on the right lens while looking straight ahead and focus, through the hole on a distant object. Slide the paper over the left lens until the distant object appears through the hole in the left eye. When the holes appear to become one, Remove the paper and measure the distance between the hole centers to get your PD.
Does this sound like an accurate way to determine your PD.
Any method that determines the actual points through which one looks will get a good PD, so this method can work. The more complicated the technique, the more opportunity for error, but if you can verify your results as accurate then great!
ReplyDeleteThanks for this helpful post. I agree that it is surely the case that me + some website will not provide as high quality eye care as a professional optometrist. However, I think that "hating" people who try to DIY their vision needs is a bit extreme. When it becomes possible for most people to have health insurance that covers optical, then you can scratch your head about those who'd rather order through Zenni and measure their PD with a ruler taped to their head. But I suspect that for a lot of people, including myself, dropping $300 at the optometrist is not an appealing option. I'd rather squint. And I even have health insurance through my school. It's strange that SEEING isn't considered an important enough bodily function to make it on the list of covered care procedures.
ReplyDeleteAlso strange is that many people don't consider SEEING important enough to pay for. Sight is our most important sense. Spending $300 for a device that perfects your vision, will continue to improve it indefinitely regardless of vision changes, and can enhance you experience of the world every waking moment, is nothing.
DeleteGood vision care seems expensive only because there are ridiculously cheap competitors that make it out to be so. In any market, the fact that cheap alternatives exist does not mean that higher price options are not worth the expense. Be prudent in your research and you will get exactly what you pay for. No one charges you a lot for a little, and no one charges you a little for a lot.
During the past year and a half, I've had my PD measured at 30/33, 29/32, and 29/33 by three different opticians. If I had a pair of glasses made with each PD, what differences would I see, if any?
ReplyDeleteCurrently I have a pair of sunglasses with a prescription of -1.50 in each eye with the 30/32 PD, and a pair of progressives with -1.25 and 2.00 in each eye made at 29/33 PD. I can't really compare them to each other.
Thank you for this very helpful post
John, the variance of up to 3mm is going to be minimal in your sv sunglasses with your very moderate Rx, but could be impactful in progressives. Progressive lenses require precision to work optimally and even a millimeter displacement can cause suboptimal near vision.
DeleteI didn't mention - my nose is crooked, so my PDs will be different for each eye. The measurements are within one millimeter of each other.
ReplyDeleteCould this be a slight difference in the placement of the pupilometer on my nose when the measurements were taken? The bridge of my nose is closer to the right eye than the left. Will I notice a difference between each PD?
Could be skill of the optician, calibration of the pupilometer, or other factors. Should have no impact on sv but progressives should be at or less than 1mm accuracy.
ReplyDeleteI'm diving into buying glasses online for the first time, and I went in to three different opticians and asked them to measure my PD (I offered to pay for the measurement, but all declined--very kind of them).
ReplyDeleteThe problem is that each one came up with a different set of numbers.
1. OD: 27.5, OS: 29.5
2. OD: 29.0, OS: 27.5
3. OD: 28.0, OS: 28.5
My prescription is -4.25 in both eyes (and one has an astigmatism), so I want to get hi-index lenses.
Unlike JohnRL above, I don't have a crooked nose, so I have no idea how to explain the differences. Should I go with an average? Would taking the measurement myself using your method give me better results? Very confused.
Crystal, all of those values fall within a 1.5mm tolerance considered acceptable for your prescription. Average them if you like, or use my method at least to confirm their findings, but any of those values are acceptable.
DeleteI got a prescription yesterday and only a year after my then, year old glasses frames broke. (Walmart) I went months with broken glasses, brokenat the nose piece, first repaired, then held together by E6000. I chickened out of ordering online due to lack of confidence, but a few weeks ago, decided I couldn't live with this. My last pair were on insurance and cost $275. This time,we had to DROP vision to be able to pay for our horrible 'upgraded' insurance. So no, I don't have money for glasses that are a necessity right now. Nobody would give me my PD, even though we'd bought thousands of dollars in glasses over the years and likely would continue to do so when things changed. Well, if they had GIVEN me my PD they would. I got a huge variety of readings until I did the glasses method. I also used a clear film sheet - got the same number REPEATEDLY. I also photographed myself with a ruler and adjusted it on a grid over my photo pupils and got within one mil of my number. Personally, I am now burned on physical eyeglass places entirely. You're NOT getting me to buy glasses from you when I have insurance by treating me that way while I'm in a bad financial situation that is temporary. I intend to send something similar to the rude eye tech when I get my glasses. I just want her to know that I have a file so she can't sneer and imagine I was never a paying customer. I could have done what was suggested,waste their time, pretend to want to buy glasses, act dumb about the pd, then decline the glasses after I got it.
ReplyDeleteThis has been fabulously helpful, Daniel! Thanks so much for talking about this subject and for responding to scathing commentary on your profession in such a measured way.
ReplyDeleteI asked an optician to measure my PD and he (matter of factly) gave me 4 numbers, which I have deduced must related to the fact that I wear progressives.
The mystery is that those numbers don't seem to make sense in light of what I've been reading here and elsewhere. Here is what he gave me:
OD Distance = 33 Near = 30.5
OS Distance = 32.5 Near = 30.4
Now, I have a fairly large head, and a broad-ish face. So, I'm expecting something in the 60's or more, right? Do I add the distance figures together? Do I add the near figures together?
Thanks so much for any advice you can offer!
Yes just add the distance values together for a single PD.
ReplyDeleteThank you for your commentary! Yes your optician can measure the specific near PD. A 9mm convergence is extraordinary, but your optician should be able to double check with methods similar to mine. I have used my own method on my patients, dotting the lenses and seeking a single-dot convergence when they view reading materials or computer screens. Your IOL should not have any impact on PD as that relies on your pupil and cornea, which lie ahead of and are unaffected by the IOL.
ReplyDeleteThis is a very good post. Thank you very much
ReplyDeleteThank you for this awesome post
ReplyDeleteHello, I am Ryan. I love your post btw. I cant seem get a strait information on this from anywhere or anyone but you seem to truly know what you are talking about. I have recently been told I need glasses for my job. So at 22 I have already gotten my first pair of glasses from them and they seem to work fine. I wouldn’t know figuring this is my first pair, but nothing seems too wrong. But from reading your posts, being properly taken care of is a much more personal experience. When I went in, they took my P.D. with the machine they put in front of my face and said to go find a frame that I liked, and see if its comfortable. So I did that and choose the Oakley double tap 51, (side note, I have a smaller head I guess because most glasses there are massive and looked miserable). So they took my prescription, put in the order, sent it out to what I assume is Oakley to be made, and 3 weeks later they come in. I pick them up, put them on, they ask if they seem ok, I say ok and then they are like alright, thanks for buying from yes. So my experience from them didn’t seem very comprehensive and personal for the amount more it cost compared to going to lens crafters which literally did all of the same things when they sized and fit me for glasses. I am ok for paying for more for a good service, but that doesn’t seem to be the case from what ive experienced unless they did a bunch of fancy stuff behind the scenes I have no idea about. Anyways, moving on.
ReplyDeleteNow I am looking into getting prescription sunglasses. Ive used my insurance on my last pair, so im getting no financial cushion with this pair. I already know the frame that I want, the Oakley flak jacket XLJs (my current pair of non-prescription sunglasses that I love the size, look, and comfort of). I also have access to great deals from Oakley and can get this pair frame and all for 240$ directly from them. As im sure you are aware, Oakley has strict pricing policies that doesn’t allow for discounts in stores. So if I want to get these from lens crafters or my other “optical associates” where I got my first pair, it will cost around 570-600$ with all of the options black iridium polarized lens with back AR. So you understand why I would want to order them online.
So my prescription is plano -1.00 90 axis, plano -1.25 75 axis. One of my eyes has a slight asthegism.. umm.. football shaped eye.. I have found out that the P.D. number they used for my first pair was 56, I somehow found out over the phone even though at their physical location they refuse to tell me. I have since gone to lens crafters and their measurement for my P.D. was 59. They used the same machine as the place I got my first pair. It wasn’t the new digital way of doing it. (They left the computer screen visible to me so I was able to see what they input for P.D.) So I have contradicting information there. Using an online app (pd.warbyparker.com) and that seemed to confirm a 58-60 range. Like your article, I am skeptical of how accurate an online program can be for something like this. So I did a lot of tests to see what difference they make on the program to get that range. I have now also done the test as you described and that is giving me a just around 59-60 range. (ive used a pair of tight shop glasses similar to my sunglasses. My focus point was around 200 ft away as well.) So most evidence seems to point towards a 59 even though the “professionals” are the outlier at 56. Note I am 5ft 8 athletic build. (trying to give you some perspective, ive heard 56 is a really small P.D. for an adult my size) But my glasses I got from the “professionals” seem to work fine to me. So at this point I don’t know who or what to believe. If I try a new place, who is to say they are right or wrong. So any guidance from you would be greatly appreciated. From your commitment to this page and comments over several years I would say you have a passion for helping people and great knowledge in the field so any help here would be appreciated, Thanks!
That price sounds to good to be true. Do be sure it really is Oakley making your glasses and not a third-party vendor, they could be cheating you on the lenses.
DeleteWith your Rx and error of up to 6mm (!) is tolerable and within standards, so you have little to worry about among the numbers you have gotten, they are all acceptable. If your Rx were more significant there would be a lot of other factors to consider, especially in sunglasses. But any reasonable optician using a decent lens should be able to give you satisfactory vision.
Awesome thank you so much for your insight! I just want to make sure I will do this right before I go dropping that much money on sunglasses. And yeah, Oakley has a special site for military and government employees where they offer great deals on a lot of different gear including eyewear, so I would be hard pressed not to take advantage of it :P
ReplyDeleteThanks again!
Ryan
I tried the online site you mentioned, and then I also did the manual exercise you described (I did it 6 times), and both of them actually came out almost identical. Time to order some glasses.
ReplyDeleteI was considering ordering online to get new frames due to financial issues this year. so glad I read your article before considering online. I do hate that I have to get frames online, as I'd much rather just get them from my optician but I really can't afford it right now, thought about using the glasses I have now for a few months until I can save enough money to purchase them from my optician, but I can't read the blackboard. I can't even afford to change the lenses, i had no idea it was $100 + for that (checked almost everywhere, can't find a cheap rate for getting your lenses changed). Most opticians said they needed cash up front and if the plastic frames were to crack it wouldn't be their fault... Not a good deal.. so now i'm considering just getting contacts.
ReplyDeleteMy prescription is -3.25 so i've been told that's mild, i found a pair online for 68$ with free shipping, but my only concern was the PD. If it's maybe 2-3 mm off will this affect me badly?
I used the Self-Test PD that you posted and I got values ranging from 59-61 so I think i'm going with 60.5.
I wonder if walmart would measure it for me, i don't mind paying a little to get this info. Nice article, will share it with friends if they decide to order glasses online.