Will I be exempted from the military service for have astigmatism?

I doubt it. Many people have astigmatism, So do I. You might not be able to go in the Air Force, though. About 80% of those who wear glasses have astigmatism...so that would eliminate an awful lot of relatives.

Having astigmatism isn't a disability.
If you can see lightning and hear thunder you will be accepted. I don't think so. Military needs ancestors.