How do I know I've made too big a CYL correction?

Hello all!

I’m a relative newcomer, still trying to figure out my first set of steps. It’s tricky with such prescription complexity! (high astigmatism, medium myopia) So I’ve been trying stuff out … slowly.

Here’s my question for the day: How do I know if I’ve made too big a CYL correction for my normalized glasses? And what would indicate that I might need CYL correction in my diffs?

Here are some things I’m noticing:

  1. I can see very clearly out of the sides of my glasses (when I’m looking somewhat sideways there is no blur) but looking at something straight on creates a lot of blur.

  2. The directional blur horizon for my normalized glasses starts pretty close, within ten feet.

  3. Sometimes when I look at bright things at night (the moon, stoplights), I see very clear double vision! I haven’t been able to fully clear that yet.

  4. The directional blur overall is slight but quite noticeable-- I can still see road signs pretty well and would feel quite comfortable driving, but things can feel a little distorted.

  5. I’ve been measuring my astigmatism and haven’t noticed particular changes yet… but I’m not sure how long that might take to be measurable in that way.

  6. I think I’ve been able to practice active focus with this – sometimes I blink and something gets clearer for a second – or gets clear double vision (if that makes sense). And sometimes I will stare at something for a while with no change.

  7. For my diffs, I can see and clear blur… but it’s unclear to me at such close distances whether it is directional or just distance that is causing the blur.

So, again: How do I figure out if I’ve made too big a jump on my CYL correction?

Thanks so much.

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Is this your first normalized / differential glasses? If yes, then you should had not do any CYL correction, only for SPH. CYL is always tricky and you should only tackle it after some successful SPH reduction.

Depending on the power and cut of your lens, the side can end up being a different power than the optical center. That clear vision to the side could just be because the lens is stronger there. There will also be more optical distortion there, so don’t get in the habit.

Thanks for the reminder – this is my first set of normalized/differential glasses and I got some without CYL as a test since I’m still trying to figure out how much of my original prescription is accurate. I guess as the first step any amount of directional blur is too much!

Seems like instead I should focus on getting my differentials right, then follow the instructions outlined in the “Reducing Prescription Complexity” post. AKA, get diffs, develop good habits, make a couple of SPH reductions, etc.

How do I know if my diffs need CYL correction? I remember reading that most diffs don’t need CYL, except for limited cases of high myopia and astigmatism – which is not me. That being said, I *think I’m getting some directional blur when I wear my diffs at a computer. Is that normal?

Thanks again for the reminder!


Thanks! That is good to know. I wondered if it had something to do with astigmatism … and appreciate the caution not to get into the habit of looking at things from the side!

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Astigmatism on Diffs usually not needed because the closer the focal plane, the less visible the astigmatism (in)correction. Most people don’t have high astigmatism, so it’s usually not visible. But what you’ve written would be more precise like this:

except for limited cases of high myopia and / or high astigmatism

If you see directional blur in close up, you should have astigmatism correction in your diffs. Unfortunately what I cannot tell if it’s fine to have lower astigmatism correction for diffs, I have not much experience with that (I’ve had really minimal astigmatism to start with).

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In theory you’d want to drop cylinder as a constant percentage of sphere, but in reality you can only order in .25 increments, so hard to do that unless you are dealing with larger drops than the eye can really handle.

I just realized. 0.25 cylinder provides a distorted 0.125 sphere. How many docs end up introducing cylinder when what is really needed is more resolution on the sphere measurement?

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You dont want to make it too complicated. Start at the ciliary spasm. If you need glasses to see close up and you are working with a prescription just drop that 1 or 1.5 and dont change anything else. You want you eyes to relax a bit not have to deal with too much changes.
When you get going on the process you will want to have read a bunch on the endmyopia site or other le meow experience so you can make your own plan.
For example I didnt reduce cyl out of my glasses but I never had it in my contacts. Later on I realized I could have just increased sph to correct for cyl. But I dont think that would have been the best thing for me anyways. I still had a distortion in my vision due to cyl. So I’m glad I am reducing it instead of ignore it and add sph.
But you’ll just need to get the hang of the process. And depending on what you do for work, if you can see 40 cm from your face you can go without glasses. Lots of people work at computers here so may not be possible. But I dont use computers often so I just didnt use diffs much and to be honest I never bothered to get a proper set. I used a -1 -1 and that was a big drop for one eye and too close for the other.
So we all make a bit of change and then either deal with it or change. I :wink: