# Real glass eyeglasses for worse than 20/200 vision? **URL:** \ **Category:** Factual Questions\ **Created:** [March 22, 2023, 12:58am UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466 "2023-03-22T00:58:25Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![alphaboi867](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alphaboi867/32/3898_2.png) [@alphaboi867](https://boards.straightdope.com/u/alphaboi867)\ **Post date:** [March 22, 2023, 12:58am UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/1 "2023-03-22T00:58:25Z")
How thick would bifocal eyeglasses made of actual glass need to be for a patient who’s both nearsighted and farsighted with vision between 20/200 and 20/220? ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [March 22, 2023, 1:54am UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/2 "2023-03-22T01:54:44Z")
Hmm, I’ll have to look up my prescription, but i might be able to answer that. I have a fairly string prescription, progressive lenses, in glass, on my nose right now. New opticians are always surprised that it’s not super thick. ---
**Author:** ![Didi44](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@Didi44](https://boards.straightdope.com/u/Didi44)\ **Post date:** [March 24, 2023, 5:38pm UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/3 "2023-03-24T17:38:32Z")
I don’t think bifocals/trifocals with a line(s) a thing anymore. It’s progressive lenses without lines. Much easier to get used to. My prescription is ~20/250-260 each eye and my high index plastic progressive lenses are ~3/16" thick. My non-high index pair are ~5/16" thick. More important than thickness is weight. I used to have glass lenses and they would constantly work down my nose. They were also in a heavier frame. My current pair is heavier in the earpieces than the front. and well balanced. I wouldn’t go with glass unless absolutely necessary. Say if I was working around things that my hit my glasses. But if I were in that type of workplace, I’d also have on safety goggles. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [March 24, 2023, 6:03pm UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/4 "2023-03-24T18:03:23Z")
My prescription is -6.25 diopters, with +2.5 for the near vision part. Maybe someone can translate that into 20/??? At the very widest point, they are 6mm thick. Most of the lense is thinner than that. They are made of glass. I’ve gotten glass because when i tried other stuff, i was annoyed by distortions and weird color interactions. So i went back to glass. Perhaps there are plastics with better optical properties today. My lenses in “ordinary” plastic would be a lot thicker, and they’d be a little thinner in high index plastic. They weigh more than plastic, but it generally doesn’t bother me. I’ve been wearing them for years, and I’m used to it. They do have a higher specific heat than plastic lenses, which means they are more likely to fog up when i walk into a hot muggy place from a cooler place ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [March 24, 2023, 6:08pm UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/5 "2023-03-24T18:08:22Z")
> **[20/20 Vision: How to convert 20/20 based measure to Diopters | Happy Eyesight](https://www.happyeyesight.com/get-20-20-vision/)** > > Just about everyone with defective \[…\] This says that 20/400 is about -4 diopters, and my eyes are significantly worse than that. Also, 6mm is just a little less than a quarter inch. ---
**Author:** ![Didi44](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@Didi44](https://boards.straightdope.com/u/Didi44)\ **Post date:** [March 25, 2023, 4:01am UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/6 "2023-03-25T04:01:14Z")
I can’t find a cite, but as I recall, glass used to be required above a certain level until plastic technology improved. I’ve been wearing glasses for over 50 years and remember a time when glass was recommended over plastic as my eyes worsened. ---
**Author:** ![Didi44](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@Didi44](https://boards.straightdope.com/u/Didi44)\ **Post date:** [March 25, 2023, 5:55pm UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/7 "2023-03-25T17:55:48Z")
Sounds like you may have had polycarbonate lenses: And they’re probably what I’m remembering as having a limitation as to how high power they could go. _#### Lower Abbe value_ _Abbe value measures the dispersion of light for different eyeglass lens materials._ _Polycarbonate rates are lower, meaning they have the potential to cause slight chromatic aberrations (visual distortions) in your peripheral vision. However, many people do not notice this._ _#### Not Suitable for All Prescriptions_ _Polycarbonate lenses are a popular choice, but they’re not for everyone. People with eyeglass prescriptions stronger than +/- 4.0 may need [high-index lenses](https://www.visioncenter.org/eyeglasses/high-index/)._ > **[Complete Guide to Polycarbonate Lenses](https://www.visioncenter.org/eyeglasses/polycarbonate/)** > > Regarding eyeglasses, polycarbonate lenses are the gold standard for many people. This type of lens is lightweight yet strong and resilient. They're made of ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [March 25, 2023, 6:19pm UTC](https://boards.straightdope.com/t/real-glass-eyeglasses-for-worse-than-20-200-vision/981466/8 "2023-03-25T18:19:25Z")
It wasn’t a slight chromatic aberration, it was striking and drove me nuts. But i also think i get better acuity with glass. I think i started with polycarbonate, and then tried high index plastic and then went back to glass. I’m much fussier about my vision than most people. I’m shocked at how many people go through the day with dirty glasses, or with coatings that are wearing off, and don’t even notice.