Glaucoma is a group of eye conditions that damage the optic nerve and can cause blindness. The most common type is open-angle glaucoma, which develops slowly over time due to increased pressure in the eye from blocked drainage canals. Angle-closure glaucoma develops quickly from a sudden rise in pressure caused by a closed angle between the iris and cornea. Treatment involves medications, laser therapy, or surgery to lower pressure and slow further damage to the optic nerve.