How Glaucoma Occurs

Normally, fluid that nourishes the front part of the eye is produced behind the iris, passes into the anterior chamber, and drains into drainage canals (the "angle") in the front of the eye. Balance between fluid production and drainage—like that between an open faucet and a properly draining sink—keeps fluid flowing freely and prevents pressure in the eye from building up.

The drainage canals become partially or completely blocked in some people. Fluid cannot drain normally, and new fluid keeps being produced. In other words, the sink "backs up," while the faucet continues to run. Because the fluid has nowhere else to go, pressure in the eye increases. Glaucoma results when the pressure becomes higher than the optic nerve can tolerate. Sometimes eye pressure rises to levels that are unhealthy for the optic nerve, even though the pressure remains at or below a level that is considered normal for most people (low-tension glaucoma).

In open-angle glaucoma, the optic nerve damage occurs gradually over years. In closed-angle glaucoma, the drainage canals in the eyes become blocked or covered suddenly. Pressure in the eye rises rapidly, often to a much higher level than in open-angle glaucoma, because of the sudden blockage, while fluid production continues. Permanent damage to vision occurs within hours or days.

Back to Glaucoma.