Baffling eyeglass problem
January 15, 2022 12:47 PM Subscribe
Do you have an especially thorough understanding of optics? My new progressive lenses supposedly have the same distance prescription as my old ones. The optician insists they're the same. They are not the same.
In early October I got new lenses, with supposedly identical options as last time, from the same place I've been going for years. The add for close-up changed somewhat, but not dramatically. The sphere went from +5 in both eyes to +5 in one and +5.25 in the other. The frames got slightly smaller and the lenses lost a few mm in height, but the opticians said there was plenty of room for my prescription.
With the new glasses my closeup vision was great, but I immediately noticed that something was off with the distance portion, making anything more than 10-15 feet away slightly blurry.
I waited 2 weeks before going back in to address it, in case I needed to acclimate to the slight changes. There was no improvement. The doctor wasn't in at the time, but one of the technicians assumed the problem must've been due to the +0.25 change to the sphere on one side, and ordered new lenses with the same sphere as my old glasses, i.e. +5 in both eyes.
Reverting to my old distance 'scrip didn't fix the problem. Everything is fine at typical indoor distances, but road signs on the freeway and the sign that says CANNED VEGETABLES at the far end of a long supermarket aisle are problematically blurry. The worst are bright LED billboards, which are uncomfortable to even have in my field of vision. At Christmas on the turnpike, the graphically simple "EASY PASS" signs at toll booths (LEDs, heavy purple block lettering on a black field) made it obvious that I'm seeing two overlapping images: instead of just purple characters, it was a set of purple characters partially overlapping a set of pale pink characters. In all of these cases, if I switch to my old glasses with their beat-to-hell lenses, everything is immediately crisp and clear. The difference is not subtle.
My due to craziness at work (late-semester academia) and it was almost 2 months before I found time to go in again. The technicians read and measured my old and new glasses six ways from Sunday, and insisted that the distance portions were exactly the same. They also double-checked the PD and position of the lens centers on the new glasses, and declared it all just right. They were polite and understanding anyhow, and promised they would talk to the doctor and get back to me. That was three weeks ago, and I've heard nothing. I feel like they're blowing me off. Whether I'm able to get them to take this seriously, or have to take my problem and business elsewhere, I'd like to have some idea of what could cause this sort of issue. If by some miracle what I'm describing rings a bell, I'd really appreciate hearing what you have to say.
In early October I got new lenses, with supposedly identical options as last time, from the same place I've been going for years. The add for close-up changed somewhat, but not dramatically. The sphere went from +5 in both eyes to +5 in one and +5.25 in the other. The frames got slightly smaller and the lenses lost a few mm in height, but the opticians said there was plenty of room for my prescription.
With the new glasses my closeup vision was great, but I immediately noticed that something was off with the distance portion, making anything more than 10-15 feet away slightly blurry.
I waited 2 weeks before going back in to address it, in case I needed to acclimate to the slight changes. There was no improvement. The doctor wasn't in at the time, but one of the technicians assumed the problem must've been due to the +0.25 change to the sphere on one side, and ordered new lenses with the same sphere as my old glasses, i.e. +5 in both eyes.
Reverting to my old distance 'scrip didn't fix the problem. Everything is fine at typical indoor distances, but road signs on the freeway and the sign that says CANNED VEGETABLES at the far end of a long supermarket aisle are problematically blurry. The worst are bright LED billboards, which are uncomfortable to even have in my field of vision. At Christmas on the turnpike, the graphically simple "EASY PASS" signs at toll booths (LEDs, heavy purple block lettering on a black field) made it obvious that I'm seeing two overlapping images: instead of just purple characters, it was a set of purple characters partially overlapping a set of pale pink characters. In all of these cases, if I switch to my old glasses with their beat-to-hell lenses, everything is immediately crisp and clear. The difference is not subtle.
My due to craziness at work (late-semester academia) and it was almost 2 months before I found time to go in again. The technicians read and measured my old and new glasses six ways from Sunday, and insisted that the distance portions were exactly the same. They also double-checked the PD and position of the lens centers on the new glasses, and declared it all just right. They were polite and understanding anyhow, and promised they would talk to the doctor and get back to me. That was three weeks ago, and I've heard nothing. I feel like they're blowing me off. Whether I'm able to get them to take this seriously, or have to take my problem and business elsewhere, I'd like to have some idea of what could cause this sort of issue. If by some miracle what I'm describing rings a bell, I'd really appreciate hearing what you have to say.
There are two possible explanations which come to mind. 1. The lenses are mis-aligned or 2. power error
Those are really quite strong lenses, with a + 5 diopter correction, and this requires a significant curvature in the lens. Each lens is oriented along a line, the focal axis, which runs from the focus of the lens at the fovea through the center of the lens and out to some distant point. If the lenses are not aligned, The focal axes point in slightly different directions (which diverge with distance) and the images on the retina will not be the same. Consider the case of a pair of binoculars where the two sides aim at different points. This is the reverse of prismatic correction which is used for patients with amblyopia (where the eyes do not point in the same direction so the lens is shaped to focus the image at different points in each eye).
Power error is the result of each eye looking through a part of the lens with different effective magnification, so that the 2 images are not misaligned but do not superimpose because they are of different sizes. This can also be related to mis-position of the lens so the optical axis/center of the lens is not directly in front of the pupil and one eye is looking through a thicker lens area providing more magnification.
It’s difficult to get good distance vision with such high levels of correction.
posted by sudogeek at 1:25 PM on January 15, 2022 [3 favorites]
Those are really quite strong lenses, with a + 5 diopter correction, and this requires a significant curvature in the lens. Each lens is oriented along a line, the focal axis, which runs from the focus of the lens at the fovea through the center of the lens and out to some distant point. If the lenses are not aligned, The focal axes point in slightly different directions (which diverge with distance) and the images on the retina will not be the same. Consider the case of a pair of binoculars where the two sides aim at different points. This is the reverse of prismatic correction which is used for patients with amblyopia (where the eyes do not point in the same direction so the lens is shaped to focus the image at different points in each eye).
Power error is the result of each eye looking through a part of the lens with different effective magnification, so that the 2 images are not misaligned but do not superimpose because they are of different sizes. This can also be related to mis-position of the lens so the optical axis/center of the lens is not directly in front of the pupil and one eye is looking through a thicker lens area providing more magnification.
It’s difficult to get good distance vision with such high levels of correction.
posted by sudogeek at 1:25 PM on January 15, 2022 [3 favorites]
In other words, the tests your providers are swearing up and down reveal no differences are probably testing the lenses, not so much the way the new frames are making the new lenses sit on your face compared to the old frames.
posted by flabdablet at 1:31 PM on January 15, 2022 [10 favorites]
posted by flabdablet at 1:31 PM on January 15, 2022 [10 favorites]
It's possible your new frames aren't tall enough, or the tech has chosen a poor progressive to fit them. Different models of progressive have different lengths of "corridor", which is how far apart the full far and full near prescriptions are on the lens. In between is an intermediate prescription, for intermediate distances.
Perhaps your full distance prescription is so near the top of the lens that you aren't looking through it very much, it may be much smaller than you expect, or it may even be cut off if the lenses are edged particularly badly. Or you are just wearing the frames higher than they measured in the shop.
The lenses come with markings that show where the full distance and full near areas are on the lens. These are now cleaned off, but can be reproduced for you to see (and try to adjust your habits accordingly.)
These lenses may also be made out of a high index (extra thin) material, when your previous ones weren't, and you're seeing chromatic aberration. Do high contrast edges break up into different colors? Do you see rainbows? Because of how progressives work, there is NO spot on the lens that you can look through to get your full distance prescription with no chromatic abberation, because the optical center of the lens is in the intermediate area. If this is what's bugging you, and it absolutely may be, the only fix is to remake them in low index material or switch to traditional multifocals (bifocal or trifocal) that give you a large distance area that includes the optical center. 1.499 index CR-39 is the only material that works for me because of chromatic aberration (my prescription is a bit stronger than yours.)
As you know, your lenses are quite strong, and that makes everything more finicky. I wear regular bifocals because I didn't like the tradeoffs in progressives. Please keep going back to get it sorted out. Be aware you might have to try different people to help you, because some of them simply don't understand what it means to wear strong lenses, and they don't understand the tradeoffs. Their most expensive (high index) lens is NOT going to give you the best vision, a super cheap low index plastic lens will. Everything is a tradeoff.
posted by fritley at 1:39 PM on January 15, 2022 [9 favorites]
Perhaps your full distance prescription is so near the top of the lens that you aren't looking through it very much, it may be much smaller than you expect, or it may even be cut off if the lenses are edged particularly badly. Or you are just wearing the frames higher than they measured in the shop.
The lenses come with markings that show where the full distance and full near areas are on the lens. These are now cleaned off, but can be reproduced for you to see (and try to adjust your habits accordingly.)
These lenses may also be made out of a high index (extra thin) material, when your previous ones weren't, and you're seeing chromatic aberration. Do high contrast edges break up into different colors? Do you see rainbows? Because of how progressives work, there is NO spot on the lens that you can look through to get your full distance prescription with no chromatic abberation, because the optical center of the lens is in the intermediate area. If this is what's bugging you, and it absolutely may be, the only fix is to remake them in low index material or switch to traditional multifocals (bifocal or trifocal) that give you a large distance area that includes the optical center. 1.499 index CR-39 is the only material that works for me because of chromatic aberration (my prescription is a bit stronger than yours.)
As you know, your lenses are quite strong, and that makes everything more finicky. I wear regular bifocals because I didn't like the tradeoffs in progressives. Please keep going back to get it sorted out. Be aware you might have to try different people to help you, because some of them simply don't understand what it means to wear strong lenses, and they don't understand the tradeoffs. Their most expensive (high index) lens is NOT going to give you the best vision, a super cheap low index plastic lens will. Everything is a tradeoff.
posted by fritley at 1:39 PM on January 15, 2022 [9 favorites]
To keep me from going online for eyeglasses, the places where I get my prescription will not measure pupil-to-pupil or pupillary distance (PD) until I buy a pair of glasses from the same shop that houses the optometrist. This distance is needed for making accurate lenses. It is legal extortion, I guess.
One problem I have had with the last four or so pairs is that whichever shop I go to does not measure that distance correctly, so the glasses are unusable. I have to have a re-measurement done and then wait another two weeks for new lenses. It has gotten worse as my astigmatism has worsened.
My guess is that your shop is also holding out on the same info and only collects this data when you buy a pair. And then they bungle that measurement, which makes for a dud pair of lenses. Reverting to your old prescription wouldn't change anything, if they are still using the same wrong PD measure.
One way to see if this is true for you is to move the glasses further down your nose, or to turn your head in various angles and look straight ahead. This changes what corrected light gets to your eyes. If your sight improves, the PD was taken incorrectly and your lenses would need to be remade.
posted by They sucked his brains out! at 1:46 PM on January 15, 2022 [3 favorites]
One problem I have had with the last four or so pairs is that whichever shop I go to does not measure that distance correctly, so the glasses are unusable. I have to have a re-measurement done and then wait another two weeks for new lenses. It has gotten worse as my astigmatism has worsened.
My guess is that your shop is also holding out on the same info and only collects this data when you buy a pair. And then they bungle that measurement, which makes for a dud pair of lenses. Reverting to your old prescription wouldn't change anything, if they are still using the same wrong PD measure.
One way to see if this is true for you is to move the glasses further down your nose, or to turn your head in various angles and look straight ahead. This changes what corrected light gets to your eyes. If your sight improves, the PD was taken incorrectly and your lenses would need to be remade.
posted by They sucked his brains out! at 1:46 PM on January 15, 2022 [3 favorites]
(LEDs, heavy purple block lettering on a black field) made it obvious that I'm seeing two overlapping images: instead of just purple characters, it was a set of purple characters partially overlapping a set of pale pink characters
How did I miss this the first time? Purple/magenta is the worst because there's red and blue both, the farthest-apart colors. These will get split up the most badly.
This is ABSOLUTELY chromatic aberration and the problem is surely that you have high index (extra thin) lenses, and your old lenses were not. If they were foolish enough to sell you polycarbonate lenses, which have the worst ABBE (measure of this aberration), this effect can be VERY bad at your prescription, not subtle, as you say.
I strongly suspect if you had them remade in CR-39 (1.499 index) material, the problem would be solved, and you should get some of your cost refunded too. The lenses will be a little thicker.
At some shops it can be hard to even learn what materials they are using, because they hide that information behind names like "feather light" and "thin-o-matic" or whatever. You really might have to go through several people in the shop before you get the help you need.
Please report back!
posted by fritley at 2:10 PM on January 15, 2022 [14 favorites]
How did I miss this the first time? Purple/magenta is the worst because there's red and blue both, the farthest-apart colors. These will get split up the most badly.
This is ABSOLUTELY chromatic aberration and the problem is surely that you have high index (extra thin) lenses, and your old lenses were not. If they were foolish enough to sell you polycarbonate lenses, which have the worst ABBE (measure of this aberration), this effect can be VERY bad at your prescription, not subtle, as you say.
I strongly suspect if you had them remade in CR-39 (1.499 index) material, the problem would be solved, and you should get some of your cost refunded too. The lenses will be a little thicker.
At some shops it can be hard to even learn what materials they are using, because they hide that information behind names like "feather light" and "thin-o-matic" or whatever. You really might have to go through several people in the shop before you get the help you need.
Please report back!
posted by fritley at 2:10 PM on January 15, 2022 [14 favorites]
Seconding what fritley said about purple LEDs. My prescription's twice as bad as the OP but an interesting side effect with lenses so thick (even when I get the high-index Zeiss my ophthomologist recommends) is prismatic effects at the edges, which not only makes spectra in sunlight, but also separate the light of purple LEDs into their component blues and reds.
the places where I get my prescription will not measure pupil-to-pupil or pupillary distance (PD) until I buy a pair of glasses from the same shop that houses the optometrist. This distance is needed for making accurate lenses. It is legal extortion
Sounds like a great idea to me. With lenses as strong as mine, the placement of the center is SO important -- yet the way the optician does it is to sloowly bring their hand in, and touch each flat lens in the new frame with a Sharpie (while telling me to focus over their shoulder, sorry -- my eyes don't obey). This slow movement makes my eyes cross, and I've had to return glasses through which I couldn't see right, and I'm sure this very casual (but so crucial!) measurement is the cause. Why isn't there some fancy machine to find and mark this center, with precision?
posted by Rash at 2:46 PM on January 15, 2022 [4 favorites]
the places where I get my prescription will not measure pupil-to-pupil or pupillary distance (PD) until I buy a pair of glasses from the same shop that houses the optometrist. This distance is needed for making accurate lenses. It is legal extortion
Sounds like a great idea to me. With lenses as strong as mine, the placement of the center is SO important -- yet the way the optician does it is to sloowly bring their hand in, and touch each flat lens in the new frame with a Sharpie (while telling me to focus over their shoulder, sorry -- my eyes don't obey). This slow movement makes my eyes cross, and I've had to return glasses through which I couldn't see right, and I'm sure this very casual (but so crucial!) measurement is the cause. Why isn't there some fancy machine to find and mark this center, with precision?
posted by Rash at 2:46 PM on January 15, 2022 [4 favorites]
I tend to "cope" with blurriness by lowering my eyelids, which changes the focus of my eyeballs, and actually changes my prescription. My eyes focus differently when I have them wide open, vs. "slightly droopy". So this is a bit of a measuring problem at the optician's office, and forcing yourself to NOT cope-focus your eyes.
And I have some suggestions about your PD. There are many ways to measure PD without visiting an optician. You can buy a gauge on amazon that you basically wear it like glasses and go stand in front of a mirror and fiddle with it until you think you got it centered, and read it off. I think there's also a way to check it with an app and a custom set of frame only. Basically, wear the frame, run the app, take a selfie, highlight the pupil in the photo, and voila, you get your PD.
posted by kschang at 3:15 PM on January 15, 2022 [1 favorite]
And I have some suggestions about your PD. There are many ways to measure PD without visiting an optician. You can buy a gauge on amazon that you basically wear it like glasses and go stand in front of a mirror and fiddle with it until you think you got it centered, and read it off. I think there's also a way to check it with an app and a custom set of frame only. Basically, wear the frame, run the app, take a selfie, highlight the pupil in the photo, and voila, you get your PD.
posted by kschang at 3:15 PM on January 15, 2022 [1 favorite]
I don't think OP's problem or question is about PD, but I want to point out that once you're fully grown, your PD will never change, so this is a thing you can have measured once and write down and then this obstacle to ordering glasses online is solved forever.
If you wear multifocals, ideally you'll have monocular PD measurements (one for each eye) instead of the single number. This can account for your nose being off center.
posted by fritley at 4:33 PM on January 15, 2022
If you wear multifocals, ideally you'll have monocular PD measurements (one for each eye) instead of the single number. This can account for your nose being off center.
posted by fritley at 4:33 PM on January 15, 2022
Response by poster: Please report back!
I mistimed this ask, posting it an hour before the arrival of my first houseguest since 2019, so I haven’t been able to keep up with the replies. I’ll read through everything again tomorrow (too tired to digest it now). I wanted to confirm that these are indeed a higher index material, BUT so were the last pair which don’t share the same problems.
I really appreciate all the answers, and look forward to having the brain power to parse them.
posted by jon1270 at 8:37 PM on January 15, 2022
I mistimed this ask, posting it an hour before the arrival of my first houseguest since 2019, so I haven’t been able to keep up with the replies. I’ll read through everything again tomorrow (too tired to digest it now). I wanted to confirm that these are indeed a higher index material, BUT so were the last pair which don’t share the same problems.
I really appreciate all the answers, and look forward to having the brain power to parse them.
posted by jon1270 at 8:37 PM on January 15, 2022
PD being sufficiently off (your brain corrects to an extent) seems to get you side side by side double vision - check to see if it's on any of your documents and if it's the same as before. I've had mine vary by 3mm (same optician, different years) and, while my brain will deal with any of those measurements, if I swap to an old pair of glasses I get a bit of double vision until I get used to it. Note that the two-colour thing you describe is likely chromatic aberration as described above, though - double vision would get you the same image twice in the same colours.
They check the pupil height when measuring up the glasses for varifocals, and if they get it wrong it can lead to looking through the wrong part of the lens for this distance you're trying to see. My peculiar nose and ears meant they didn't do a good job there, and my first pair of varifocals did work, but only if I had them part way down my nose all the time because the distance vision was too high up in the lens. (You might just try that technique yourself, actually.)
Note that neither of these is going to come up as
'The lens is wrong' - the lens is exactly what they asked for, but they asked for the wrong thing because the measurements are wrong. These measurements are typically done by the glasses salesperson, not the optometrist.
posted by How much is that froggie in the window at 9:31 PM on January 15, 2022 [1 favorite]
They check the pupil height when measuring up the glasses for varifocals, and if they get it wrong it can lead to looking through the wrong part of the lens for this distance you're trying to see. My peculiar nose and ears meant they didn't do a good job there, and my first pair of varifocals did work, but only if I had them part way down my nose all the time because the distance vision was too high up in the lens. (You might just try that technique yourself, actually.)
Note that neither of these is going to come up as
'The lens is wrong' - the lens is exactly what they asked for, but they asked for the wrong thing because the measurements are wrong. These measurements are typically done by the glasses salesperson, not the optometrist.
posted by How much is that froggie in the window at 9:31 PM on January 15, 2022 [1 favorite]
I wanted to confirm that these are indeed a higher index material, BUT so were the last pair
There are lots of materials that are sold as "high index", which only means "higher than standard plastic". Your old lenses may be Trivex which have an ABBE of around 44, while the new ones might be polycarbonate with an ABBE of 30. For comparison, CR-39 plastic and optical glass both have an ABBE around 59. You can google ABBE but the tldr is that the higher the ABBE number, the better the lens keeps different colors together at a certain power. Glass and CR-39 ("standard plastic") are the best you can find, both at about 59. Polycarbonate is the worst common material, at 30. I suspect your new lenses are polycarbonate, which opticians really push because it's both thin and cheap.
If you want a high index progressive lens with better ABBE, Trivex is probably a good choice today. Spectralite is really good, but I think it's less common than it was years ago. Here is a table I found showing index and ABBE of a lot of materials. Higher index means thinner lens. Higher ABBE means better vision. (Your optician can probably only get a few of these.)
posted by fritley at 10:24 AM on January 16, 2022 [1 favorite]
There are lots of materials that are sold as "high index", which only means "higher than standard plastic". Your old lenses may be Trivex which have an ABBE of around 44, while the new ones might be polycarbonate with an ABBE of 30. For comparison, CR-39 plastic and optical glass both have an ABBE around 59. You can google ABBE but the tldr is that the higher the ABBE number, the better the lens keeps different colors together at a certain power. Glass and CR-39 ("standard plastic") are the best you can find, both at about 59. Polycarbonate is the worst common material, at 30. I suspect your new lenses are polycarbonate, which opticians really push because it's both thin and cheap.
If you want a high index progressive lens with better ABBE, Trivex is probably a good choice today. Spectralite is really good, but I think it's less common than it was years ago. Here is a table I found showing index and ABBE of a lot of materials. Higher index means thinner lens. Higher ABBE means better vision. (Your optician can probably only get a few of these.)
posted by fritley at 10:24 AM on January 16, 2022 [1 favorite]
Response by poster: There are lots of materials that are sold as "high index"
Thanks — I understand that part. The shop I use has a number of high-index offerings, but the new lenses are supposedly the exact same stuff as the old ones. I don’t have an order sheet with the specific details enumerated, but I was in a desperate hurry when I ordered the glasses, and to save time the technician just asked, “do you want everything the same as last time?” I said yes, and that was that.
posted by jon1270 at 12:19 PM on January 16, 2022
Thanks — I understand that part. The shop I use has a number of high-index offerings, but the new lenses are supposedly the exact same stuff as the old ones. I don’t have an order sheet with the specific details enumerated, but I was in a desperate hurry when I ordered the glasses, and to save time the technician just asked, “do you want everything the same as last time?” I said yes, and that was that.
posted by jon1270 at 12:19 PM on January 16, 2022
« Older Help me get someone else to help me with my life | Muscle pain after hip arthroscopy - can you relate... Newer »
This thread is closed to new comments.
posted by infinitewindow at 1:14 PM on January 15, 2022 [2 favorites]