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Comment by raihansaputra | Hacker News Reader

I don't have a lot of myopia (max -1.5 on both eyes) but I also have astigmatism (around 1.75 for both). I find I can work fine on my computer distance-focus wise but the astigmatism means text are slightly blurry. Do any of you have this problem too? Do you have another set of glasses that are just correcting the astigmatism?

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you can substitute spherical correction for astigmatism correction. the spherical equivalent is the normal spherical value plus 50% of the cylinder. so for -3.00 sphere -1.00 cylinder 100 axis, the spherical equivalent would be -3.50 sphere (blank cylinder, blank axis).

Do you happen to have a resource on the math behind it. I am also in this situation. Even my near vision is affected by it...

yes, it's in the PDF linked in the article, from 2014.

Why would you ever do that?

It makes your vision worse (because the astigmatism is really not corrected) and might trigger a myopia progression (because the glasses are too strong)

It's the normal thing to do if only spherical lenses are available. E.g. cheaper off the shelf contact lenses. Contacts with cylinder correction are relatively novel and have downsides. The lenses are not "too strong", astigmatism causes two focal points, and the spherical equivalent puts you in the middle of these two.

no, it doesn't, because astigmatism is caused by wearing the glasses in the first place. read the PDF linked in the article.

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