Glaucoma results from damage to the optic nerve fibers, often due to elevated eye pressure. Primary open-angle glaucoma (POAG) is the most common type and is painless — vision loss typically occurs gradually over many years.

Acute closed-angle glaucoma is a medical emergency causing sudden severe eye pain, headache, nausea, and blurred vision. Vision loss from glaucoma is irreversible, making early diagnosis and treatment critical.