Normally, fluid is continually secreted into the front of the eye by a structure called the ciliary body to nourish the tissues and maintain the shape of the eye. Any excess fluid drains away through a gap called the drainage angle.
In glaucoma, the flow of fluid is blocked and the fluid builds up, raising pressure in the eye and leading to impaired vision or even blindness.
Acute glaucoma develops quickly, causing pain and sudden loss of vision. It requires emergency treatment with drugs or surgery. Chronic glaucoma develops more slowly, is painless, and may go unnoticed for years until it eventually causes significant deterioration of vision.
Both types of glaucoma are treated with medication or surgery. Treatment usually prevents further visual loss but does not restore any vision already lost.