Should I add a quarter cyl diopter to every quarter sph diopter reduction?

to see 20/20 without directional blur in normalized I use L -4.0 -0.25cyl R -4.25 -0.5cyl. if I only want to reduce the sph to 20/40 or 20/30 without getting directional blur, do I have to add 0.25 cyl to the normalized because the sph is reduced? in order to get sph blur without cyl blur

Ex: -4.0 -0.25cyl L :arrow_right: -3.75 -0.5cyl L
-4.25 -0.5cyl L :arrow_right: -4.0 -0.75cyl R

Only you can answer that, it’s rather quite case specific.

Do you know how to calculate shpereical equivalent power? If you see 20/20 with no directional blur why would you add cylinder?

That’s not how it works.

A “spherical reduction” is exactly that. A drop of usually 0.25 D, in sphere only. A “cylinder reduction” is a 0.25 D drop in the cylinder. In both of these, nothing else changes.

A sphere for cylinder exchange is designed to change the focal plane in your correction in an attempt to reduce cylinder without excessive blur challenge. It also has the effect of maintaining spherical equivalent. There are a number of reasons you might want to do this. I’ll leave those as an exercise for the reader.

Finally, as someone who is struggling to reduce astigmatism, I can’t think of one reason ever to increase my cylinder.

On another note, I think you’re asking a generic question, but it sounded awfully close to diopter specific advice. Please be mindful of group rules and forum policies in future.


I’d say, drop your cylinder at all, it even does not reach 1.

I would not use spherical equivalent, as it would be overcorrection and can lead to further axial elongation (and more lens astigmatism).