Does glaucoma affect nearsightedness or farsightedness?

No. Nearsighted and farsighted people may have different incidences of the various types of glaucoma, but the need for glasses is not causative nor is the need changed by having glaucoma.
No. However farsighted people can have a higher chance of narrow angle configuration with or without glaucoma, and high myopes have a higher chance of open angle glaucoma from large population based studies. Having glaucoma surgery can affect your refraction.
Cause of blindness. I am not an opthalmologist, but glaucoma is second leading cause of blindness in the world after cataracts. Blindness from cataracts is reversible(surgery), but blindness from glaucoma is not. Glaucoma is treatable and thus regular follow-up with eye doc is important. So, glaucoma affects vision--near or far..It can lead to blindness if untreated. Consult your eye doc... Good luck.