Spherical equivalence - Eye physiology changes?

There are many suggestions on the forum and the EM website to replace the cylinder correction through half its value of spherical correction.

Can someone explain how that will change the corneal shape?

My logic is the following:

When there is astigmatism, the light gets refracted before the retina on the specific axis. This wrong refraction is due to a badly shaped cornea.

So for me the thing to do would be to ONLY reduce gradually cylinder correction, so that the cornea can reshape.

If one does replace CYL trough SPH, it would lead to the eyeball elongating in order to cope with the unnecessary correction that shifts the focus beyond the retina for its parts that are not on the previous astigmatic axis.

What do you think about it?

I’ll try to answer what I can. If you take it out your glasses, your eyes become more like a baseball and not like a football for example. To me, if you don’t have a ton of CYL like -3 for example, it isn’t really enough to justify putting it on there. Honestly, even then, I would probably convert it to SPH if I happened to have that much.

We don’t really know yet how cyl is reduced successfully over time. What we do know is that in many cases, astigmatism reduces slowly when cyl is reduced. In some cases, it happens years after the cyl is reduced, but the vision may improve faster than the physiology.

This question reminds me of when I was in flight training. We had scores of graphs showing things like takeoff roll required given different temperatures and humidity levels, that sort of thing, for a particular airframe.

I can just visualize such a chart for varying levels of sphere and cylinder correction required, with suggested paths for reducing either or both back to 0.0.

I think getting a grasp on the topology of the astigmatic eyeball is one of the most difficult things I’ve had to do since starting #endmyopia. The only reason I think I need it is for decision making about the next set of reductions. As my experience has shown, I have been casting about for solutions. I think I’m finally in a place where I can gradually step it down in both sphere and cylinder, letting the eyeball reshape itself to a normal, emmetropic condition.

I’d be interested to hear what you have done/tried and your results since this thread was originally posted.


The problem is that my norms have a lot of spherical power and they feel very strong. I have to think of how to reduce power from norms/diffs so that the other focal plane is not in the way of the other (to keep the gap the same).

Someone on the forum said that it’s not necessary to reduce only +0.25 cyl at a time and nothing else. Although that would be a sureshot strategy, it would take some time. If I’d have 20/20 or 20/15 vision, then I’d reduce 0.50 cyl when it’s time as a necessary step and easier for the brain to manage. I mean, the diffs are already pulling the eyes downward in diopters. But will the cornea reshape itself to take in enough light nobody knows.

Someones opto reduced 0.25 sph and 0.50 cyl at the same time when he/she complained about glasses being too strong. That must be near maximum the brain can tolerate with ease and comfort.