On my way to 20/20: From -3.75 SPH and -3.50 CYL

I’m not sure if you understood my point so I’m going to repeat it just in case but with different words.
If there are only two different types of basepoints of blur you can use as a point of reference to see improvement: 1) Until text was almost impossible to read 2) Noticable blur but still legible.

Then using 1) as a reference point is less reliable than 2) . This is because if your point of reference is 1) there is a wider range of myopic blur and astigmatic blur combinations that recreate the same almost impossible to read reference point. For example, if there is no change in distance to 1), it could be A) no change in visual level B) Myopia improved but astigmatism worsened C) Astigmatism improved but myopia worsened. Albeit, A, B and C look different, in practice it is difficult to notice the difference. If instead your base point of reference is 2).then it will be easier to note improvements in myopic blur without the noise of astigmatic blur messing up with the visual signal, because as your reference of point approaches clear text the signal caused by myopic blur begins reducing, and when the myopic blur signal is 0 the signal caused by astigmatic blur begins reducing.

In addition to reducing the signal to noise ratio, an additional benefit of moving your point of reference closer to clear text is that your ability to detect differences in blur is greatly improved due to the 1/x mathematical nature of changes in clarity… (That is, your ability to notice whether your vision has changed each time you measure is improved.)

That said, in theory using 3) which is maximizing clarity of text but still having noticeable blur is the best point of reference. In practice. There is no meaning difference between 2) and 3).

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Thanks for the clarification!

I guess in my case it makes more sense to measure noticeable blur and not until text was impossible to read. I basically ignored the fact that the blur caused by my astigmatism would affect these measurements. I’m really jealous that people with low astigmatism don’t have to deal with much astigmatic blur. Even measuring with stenopaeic slit is difficult (it’s hard to tell when blur starts). I’ll have to research more DIY tools and methods for measuring SPH with high CYL. If it weren’t for your explanation, I probably would not have found any importance in measuring distance to noticeable blur for SPH.

Thanks again!

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Have you looked into spherical equivalent of cylinder? Dropping 3 Cyl, averaged across all axes is like dropping 1.5 Sphere. If you dropped a bunch of cylinder AND sphere, that would be way too underpowered. You might still be over prescribed for cylinder. The bad news is that the brain adapts to overcorrection for cylinder, so even if you’re over prescribed, it might be difficult to step back. Give any new cylinder adjustment at least two hours for vertigo and distortion to start to settle out, but it can take 6 months to fully adapt. (And that study was done on patients changing from uncorrected to the “correct” prescription, not stepping back down.)

If you have any side effects besides blur when reducing, back it up and take it slower. Part of why we don’t change normalized and diffs at once is to give the visual cortex some rest time wearing the other glasses while dealing with difficult changes.


Well, when choosing my diffs, I first considered:

  1. standard SPH drop of 1.50 and drop ALL CYL
  2. standard SPH drop of 1.50 ONLY
    Later I actually did consider:
  3. spherical equivalent

After doing a bit of reading on SE on the forum, I found that many people were not successful with it. I’m kind of bummed I didn’t try it just because of what I heard from other people’s experiences.

Yeah, I can see now that it was really under corrected.

I’m certain I am over corrected for CYL; my recent CYL reduction had no noticeable, visual side effect (no blur, no double vision, etc.), just vertigo.

I think SE is actually a good approach for my diffs. I was worried about the SPH to CYL ratio and I think if SE is successful, I won’t have to worry about that anymore. Say if I were to use spherical equivalent for my diffs, would I also need to use spherical equivalent for my norms? To me it seems like SE would only be tolerable in close up.

Cylinder dependency is very individual. I have very low cylinder and took it all off at once with doctor approval, but if I was trying to reduce, I’d not drop more than 0.5 Cyl at at time, same as we drop 0.25 Sph at a time.


An update:

I figured out why I was confused with the wheel measuring method. I was confused why the second measurement was measuring our SPH correction because as compared to my prescription, that would only be tolerable in close up. My first measurement was always closer to my SPH correction for distance vision. This might not be the case for others, I think this method just doesn’t work for me right now since my SPH to CYL ratio is so high (basically 1:1).

What I did find out is that I was confusing the instruction with the instructions for measuring with stenopaeic slit. It makes more sense for me to use stenopaeic slit to measure SPH because it basically cancels out the astigmatism. With this method, there isn’t a “second” or “first” measurement. Your SPH is determined by whichever measurement has more cm (less power). I guess the same applies for the wheel method–you choose the cm measurement that gives less power–it just doesn’t work for me.

In my case, stenopaeic slit is more accurate for measuring SPH–as it is difficult to measure with bare eyes. Though both methods provide similar results for measuring CYL, I feel stenopaeic slit is much more accurate.

A few sample measurements:
OD: -2.00, -2.25, -2.5
OS: -2.00, -2.25
OD: -1.00, -1.50, -1.25
OS: -1.00, -2.00, -1.75

Stenopaeic slit
OD: -3.25, -3.75
OS: -3.00, -3.25, -3.75
OD: -1.25, -1.00
OS: -1.75, -1.5, -2.50

Once again, emphasizing that stenopaeic slit is definitely more accurate for measuring SPH; I know my eyes and a drop of 1 diopter SPH in norms would be too much blur challenge. CYL however, is still difficult to measure with both methods, but perhaps my eyes are overcorrected in CYL–it’s hard to tell since I’ve got so much correction.

Looking further into the future:
I’ve got two weeks of spring break starting next friday. I’m looking forward to going outside more during that time (it’s been difficult to get outside for the past few weeks since I’ve been swamped with schoolwork). I really want to make sure I can see the 20/20 line on my snellen clearly before making another reduction.

Currently, my right eye is lagging behind (it’s actually been like this since my first pair of differentials). For my norms, I didn’t fix this because I wanted to deal with CYL first so for my next reduction I definitely need to fix it. at that point my subscription for norms would be:

OD: -3.25 | -3.00 | 165
OS: -3.25 | -3.25 | 175

If my right eye were to still be behind, I would reduce CYL in my left eye to -3.00. And if my right eye was still behind, I could go back up or patch.

Once I find the right subscription that gives both my eyes equal blur challenge, I plan to make reductions as follows:

  • binocular SPH reduction of 0.25 diopters
  • binocular CYL reduction of 0.50 diopters (since it’s equal to 0.25 diopters SPH but if my eyes can’t handle that I’ll just stick to 0.25 CYL diopter reductions)
  • pattern continues



Your visual cortex and accomodation can compensate for astigmatism. The ciliary twitches around between the focal length where one axis is clear and the other (assui the whole range is within your accomodation range.) And the visual cortex forms a composite image from those different blurs.

The stenopeic slit doesn’t let your muscles/brain cheat the test, it measures refraction only.

I can imagine this is the case for anyone who has 1:1 or higher ratio of sph cyl. Well done for searching on and finding a method suiting your needs. It makes sense that limiting the vision to a slit gives more accuracy for high cyl. The wheel is more useful for lower cyl especially as even optos are often unsure about the axis and the strength needed when cyl is under 1D.

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Can you rephrase this? I don’t think I completely understand.

When you focus on something close or near, you’re actively changing your focal range, that’s called accommodation. When your focus is tuned one way, the angle that you have the shorter distance to blur with the stenopaeic slit is clear, and when your focus is tuned the other way, the 90 degree angle is clear. And your eye adjusts through all the steps between too. The multiple images can then be combined to get more visual information than either image has alone.


People having much astigmatism sometimes could have (anterior and/or posterior) crossbite. You might want to also look into this (and fix if it’s present) while reducing cylinder to possibly boost your experience. By seeking a professional you would want to find one also dealing and taking into account cranial biomechanics. Simple braces could only harm.



That’s actually quite interesting. I think I might have some sort of crossbite probably caused by 2+ years of braces use. Sadly, I’ve got no way to tell when my astigmatism started to increase–or if braces use increased it–since every single opto I ever went to never gave me my prescriptions. I’ll have to get in touch with a professional to see if I do have a crossbite. In the meantime I’ll do a bit more research on the topic.

Thanks for bringing this up!

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Braces without cranial correction mess all the things to the third power…

My advice as far as bite is concerned is to seek who near you is trained in craniodontics. And redo everything there, incuding braces after cranial correction. Elimination of crossbite usually also eliminates scoliosis (if there’s any).

You might want to read this: The consequences of getting braces: what no one warned you about - tooth-for-a-tooth.com

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Some optometrists won’t give you this unless you clearly ask them to do it. There is a big enough possibility the law is on your side :slight_smile:

When I was younger, my parents never asked for my prescription. I guess they didn’t have any reason to. It wasn’t until the past couple of visits that I began asking for my prescription but it was only to order glasses online. I heard you can go to your previous optos and ask for your previous prescriptions but I’m not sure if they would still have prescriptions from nearly a decade ago.

So it’s been around 6 and a half weeks since my last reduction. Today
April 26, 2021 I received my:
OD | -3.25 | -3.00 | 165
OS | -3.25 | -3.25 | 175

OD | -1.75 | -3.00 | 165
OS | -1.75 | -3.25 | 175

A 0.25 monocular reduction of SPH in the left eye. I did my zero diopter reset as usual but what surprised me was when I got home after my usual walk I was able to see the 20/15 line on my snellen–which I was previously able to see with my N1s–though not crystal clear.

Kind of bad news: my left eye still has no blur challenge. It’s really overcorrected and my right eye is still lagging behind. Last week I started patching for two 5 minute sessions but now I just do one 10 minute session. This reduction has been the second time I’ve reduced my norms and diffs at the same time and It seems like I’ll need to do one more–hopefully that one will be the last. I’m not in a rush but I do hope my right eye can improve in the next couple months or so.

This is starting to get a bit lengthy. One good thing to take from this:

  • I started at SE -5.5
  • this reduction put me at SE -4.875

So I’m officially down to the -4 diopter range :grin:


This is a very interesting journey. Well done so far :blush:
So how do the new pairs of glasses feel?
I know it is early days, but do you have an idea for the next reduction - weeks later of course, once N2 and D3 feel OK?

Ah ha! I see what you mean. When I read this a few days ago it didn’t have the same meaning as now that I also see 20/15 with new norms.

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For this reduction I felt almost no change. Previously, I reduced 0.25 CYL in my norms and diffs and that made me feel kind of woozy. This reduction had no side effects at all and I think it’s because it was a SPH reduction.

My N2s feel the same as my N1s but I can’t see the 20/15 as sharply with them. My D3s were noticeably less corrected than my D2s so I had to scoot closer to my computer—this usually happens with all my diffs. Since my previous diffs had my left eye way over corrected and my right eye under corrected, it was really difficult to find the edge of blur. As @gemilymez described in one of her videos, everything seems clear but there is some blur that feels “messy.” My new diffs have made it easier to find the edge of blur so now I think my right eye will be able to catch up.

I actually do. I’m planning on reducing CYL in my left eye—my left eye is still overcorrected—by 0.25 in my diffs and norms. By then my lenses will be fully equalized so that will hopefully be the last time I have to reduce my norms and diffs at the same time.

In the meantime, I’ll be patching my left eye so my right can catch up. It’s only been a couple days since I’ve started patching but I can tell my right eye is improving in close up.


This morning, I was able to see the 20/20 line with my right eye and it was crystal clear! When I first reduced to my current subscription, my right eye could only see 20/40 and I was worried I would be stuck with this subscription for longer than usual. I’ve been patching almost everyday now because I noticed that whenever I don’t, my right eye gets worse again. I’ve also been doing a lot of astigmatism exercises with the astigmatism app. I definitely spend more time patching though. It’s only been three weeks since I got this subscription but now I’m way more confident that this will work out. I’ll give it another week or two before I reduce to my next set. I’ll get those in the beginning of June so I’m looking forward to some summer gains.