What causes very rapid decline in vision to the point of needing glasses for astigmatism and farsightedness?

See an eye doctor. : Well, lots of things cause vision loss but the fact it seems correctable is good. You should see a eye doctor to really see for sure but, given your age, the two most likely culprits are cataracts and presbyopia. Usually cataracts give people better near vision initially but not always. Presbyopia, or aging of the lens, is most likely and necessitates reading glasses and sometimes distance glasses.

Presbyopia: Astigmatism and farsightedness do not cause rapid decline in vision. Any such symptoms needs evaluation by an ophthalmologist.