Glaucoma is a condition caused by excessive fluid pressure in the eyes that can damage the optic nerve and lead to blindness if left untreated. The two most common types are open-angle glaucoma, where fluid fails to drain properly from the eye over time, and angle-closure glaucoma, where the drainage angle is blocked. Symptoms often do not appear until permanent damage has occurred. While there is no cure, treatments exist to lower pressure and prevent further vision loss.