Illinois Society for the Prevention of Blindness

In an eye with open-angle glaucoma, the aqueous humor drains too slowly through the channel system, creating a chronic rise in fluid pressure inside the eye. This elevated pressure may gradually interrupt the metabolic processes of cells in the optic nerve, leading to a progressive destruction of nerve fibers that are essential for vision.

In a normal eye, aqueous humor--a clear, nutrient-rich fluid--passes continuously through the pupil and into a small space at the front of the eye, called the anterior chamber. As it leaves this area, the aqueous humor flows to the periphery of the chamber, or angle, where it exits through a complex channel system and drains into blood vessels in and near the sclera, the white outer coat of the eye.

Open-angle glaucoma is so called because the angle of the anterior chamber is open to aqueous humor outflow. It is the slow drainage of aqueous humor through the drainage system that increases fluid pressure. Conversely, in angle-closure glaucoma, part of the iris suddenly obstructs the angle and blocks the aqueous humor from reaching the drainage system. This causes a very painful rise in intraocular pressure and requires emergency medical attention.