system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do glasses correct astigmatism?

I can understand how glasses fix myopia and hypermetropia, but I can't get around the fact that glasses can correct imperfections in the cornea and lens. 

From what I could understand, astigmatism happens when there are multiple focus point on your retina, but how can glasses fix this issue without having to be uniquely crafted for each imperfections?

Thank you!
gpt
Ideally cornea and eye lens have perfectly round curvature. Astigmatism happens when either cornea or eye lens have elliptical (egg-shaped) curvature instead, producing two overlapping images on the retina. The precise shape of that curvature can be measured with the various instruments that ophthalmologists and optometrists have. Glasses can be made to compensate for the curvature imperfection.