Glaucoma is a group of eye conditions characterized by progressive damage to the optic nerve, often associated with increased pressure inside the eye (intraocular pressure). Over time, this nerve damage can lead to gradual and irreversible vision loss, typically beginning with peripheral (side) vision and potentially advancing to central vision if untreated. The most common form, open-angle glaucoma, develops slowly and may produce no noticeable symptoms in its early stages, while angle-closure glaucoma can occur suddenly with eye pain, redness, blurred vision, halos around lights, and nausea. Risk factors include aging, family history, elevated eye pressure, diabetes, and certain anatomical features of the eye. Because early stages are often symptomless, regular eye examinations are important for early detection and preservation of vision.