Main Page / Login Option Forums General Myopia & Astigmatism Discussion How Important Is It to Know the Diopters for Current Pair of Glasses?

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    nrmalo2020
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    Post count: 60

    Hey all,

    I am in an interesting situation. I have my centimeter measurements and Snellen chart results logged (several weeks’ worth actually)…but I don’t know for sure my current glasses’ prescription. I believe I have the prescription, because it’s my most recent one written by my ophthalmologist, but it’s from two years ago. The place where I bought my frames that would have the prescription used for them was hit by a tornado six months ago (I live in Texas) and was completely destroyed. Thankfully, the owners are OK and no one was hurt, but I have no way of contacting them and I’m sure my prescription was demolished along with the building anyway.

    I have tried calling my ophthalmologist’s office and other optometrist offices to just see if I can come in to have the lenses scanned really quickly, but due to the Corona virus pandemic, offices are closed except for urgent cases until further notice. [which I completely understand; but the timing isn’t ideal]. So, given the circumstances, could I either figure out the differential diopters I need from the measurements I have without the glasses presc. or can I use the last prescription I have from my doctor and make the educated guess that it is in fact the correct prescription? Or do I need to hold off for a little while until I can get the lenses checked?

    Help please! 🙁

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    • Jake S.
      Keymaster
      Post count: 8757

      Yes in this case it’ll be a bit more of a guess based on available diopter numbers and your centimeters / eye chart.

      It’ll be fine, especially if there isn’t much astigmatism / cylinder to guess.

    • nrmalo2020
      Participant
      Post count: 60

      Thank you! Yeah, it says on my prescription that my left eye is -3.50 with +0.50 cylinder correction at 66 degrees and my right eye is -4.50 sph. So the astigmatism in the left is low enough to not factor in for the differentials, right? And is it OK to have a full diopter difference between eyes?

    • Jake S.
      Keymaster
      Post count: 8757

      In many cases a half diopter of cylinder can be ignored for differentials – no guarantees, but likely fine.

      The diopter ratio is what it is for a start. Compare to your centimeter results to make sure it looks about right. We’ll eventually get on to reducing the ratio over time. 🙂

    • nrmalo2020
      Participant
      Post count: 60

      Awesome, thank you 🙂
      One more question: I have a ton of centimeter measurements (14 days’ worth, haha). I tend to go overboard on these things… Should I take the average of all the measurements for each eye and then use those averages to calculate the diopters from there? I noticed that when I did that, it was only about a 0.5 diopter difference between the right and left eye (instead of the full diopter difference in my current glasses).

      Sorry for so many questions!

      Natalie

    • Jake S.
      Keymaster
      Post count: 8757

      Questions are fine!

      Yes, averages tend to be best. 50% less diopter ratio is a curious thing. One possibility is measurement error – though if it isn’t then adjusting the diopters may take a bit of getting used to. 🙂

    • nrmalo2020
      Participant
      Post count: 60

      Thank you 🙂

      It’s totally possible that I’m measuring incorrectly, haha! However, my centimeter measurements don’t really change a whole lot (they stay within a consistent range, at least on my right eye which ranges from 27-30; my left eye measurements span a larger range from 28-37, which doesn’t seem right). I sometimes wonder if I’m being consistent with finding the edge of blur. Do you have any suggestions for improving accuracy?

    • Jake S.
      Keymaster
      Post count: 8757

      Check out this app (if you run Windows): https://community.endmyopia.org/t/vision-log-tool-for-windows-test-version-current-0-1-3/5945/141

      The red / green boundaries for measuring are helpful for some. 🙂

    • nrmalo2020
      Participant
      Post count: 60

      Thank you! I have downloaded the zip drive and will check it out. 🙂 I will see if the measurements change using this technique.

      Could the 0.5 ratio difference be explained by the astigmatism correction? And when I end up ordering my first pair of differentials, would it be better to use the centimeter measurements and subtract 1.5 to determine the diopters or the current prescription I’m wearing?

      Thank you for your help.

      Natalie

    • Jake S.
      Keymaster
      Post count: 8757

      Yes indeed possible. Though whether changing that will work will require trying it out. 🙂

    • nrmalo2020
      Participant
      Post count: 60

      Ok. So if my glasses diopters seem to be -4.50 (right) and -3.50 (left; with +0.50 Cyl), but my centimeter measurements give me -3.50 (right) and -3.0 (left), would you recommend going off the centimeter measurements and subtracting 1.50 on each eye to get the differentials, and then just try it out and see? I could always order two pairs of glasses and try them each out for size.

      Also, due to the lock down, I ended up buying reading glasses from the grocery store so I have a 1.50+ and a 1.75+ to try on over my glasses. We’ll see how this goes! 😉

    • Jake S.
      Keymaster
      Post count: 8757

      Also, due to the lock down, I ended up buying reading glasses from the grocery store so I have a 1.50+ and a 1.75+ to try on over my glasses. We’ll see how this goes! 😉

      Temporarily fine, but realize it’s not a great ongoing solutions. Optical centers don’t line up, net refraction won’t be exact, etc.

      As far as the above guess, yes indeed. First differentials regardless of how much data we have, always end up being a bit of an experiment regardless (how eyes respond in any case is something to be explored).

    • nrmalo2020
      Participant
      Post count: 60

      Ok, great. Thank you!

    • nrmalo2020
      Participant
      Post count: 60

      So just to be clear, trying out a 1.5 reduction from the the centimeter measurements I got would be OK? (meaning going down from -3.5 and -3.0 to -2.0 and -1.5), even though that ratio is different from my current normalized glasses? I remember reading in one of the sessions that it’s important to keep the same ratio in the eyes and make the same reduction for each eye to not throw off the visual cortex. Or is it better to try a 1.5 reduction from the normalized? (from -4.50 and -3.50 to -3.0 and -2.0). Sorry for going round in circles with these questions! I’m just being thrown off by the 0.5 difference in ratio from my data and getting confused.

    • Jake S.
      Keymaster
      Post count: 8757

      Depends which you think is right. You can easily check your normalized and see if that diopter ratio is no longer accurate there – if so then address on differential then normalized.

    • nrmalo2020
      Participant
      Post count: 60

      Ok, perfect. Thank you!

    • Jake S.
      Keymaster
      Post count: 8757

      Keep me posted! 😉

    • nrmalo2020
      Participant
      Post count: 60

      Will do! I’m going to try to get into an optometrist’s office to see if they’ll check the lenses for me. If not, I may just go ahead and go off my centimeter measurements, because I get the feeling I’m over-corrected in my current normalized anyway (just based off my Snellen chart results and trying the reading glasses experiment).

    • Jake S.
      Keymaster
      Post count: 8757

      Sounds good. Stay safe.

    • nrmalo2020
      Participant
      Post count: 60

      Hello again. 🙂 I was able to have my lenses scanned at an optometrist’s office (yay!), and it’s true that I’m wearing the old prescription that I thought I was. I am at -4.50 sph (right) and -3.50 +0.5 cyl (left). I’m now wondering if actually the astigmatism correction makes the ratio match up to my centimeter measurements after all. My centimeters are -3.50 (almost -3.25) right and -3.0 left. I think I’m over-corrected in my lenses by a factor of 1.0 diopter. So now I’m going to order differentials (woohoo!) 😀 and I honestly don’t know whether I should go based off the glasses prescription or the centimeter measurements. I think I will try the centimeter measurements, but what do you think?

      Thanks, Jake!

    • Jake S.
      Keymaster
      Post count: 8757

      Yes if you prefer centimeter measurements as basis, that should be fine. 🙂

    • nrmalo2020
      Participant
      Post count: 60

      Awesome 🙂 Thank you! I just ordered the differentials from Zenni’s. (woo!) Do you know if they require a doctor’s prescription in order to send the glasses? Or will they send them regardless?