Understanding Glaucoma - Basic Information

What Is It?

More than 2 million adult Americans suffer from glaucoma, making it one of the leading causes of blindness. The most common form, chronic open angle glaucoma, generally appears in middle age and seems to have a genetic component: one out of five sufferers has a close relative with the condition.

It is a common misconception that the eyeball is a closed tank of fluid. On the contrary, the inside of the eye continuously produces and drains away a fluid called aqueous humor. As fresh aqueous is produced by cells inside the eye, an equal amount must  drain out through a drainage passageway called the trabecular meshwork. If the inflow does not match the outflow, pressure will increase inside the eye. Persistent high pressure on delicate retinal nerve fibers and the optic nerve results in permanent vision loss.

Glaucoma has long been called "the thief of sight" because there can be significant damage to the eye before the problem is identified. Glaucoma damage is irreversible. At first, usually the outer areas of the visual field (peripheral vision) are lost, but if untreated, glaucoma may eventually lead to blindness in central vision as well.

Types of Glaucoma

Glaucoma is a collection of diseases, all of which share a common outcome: irreversible damage to delicate retinal nerve fibers and the optic nerve. The most common type of glaucoma is called chronic open-angle glaucoma, accounting for about 75%-90% of cases. There are multiple causes of this type of glaucoma. In chronic open-angle glaucoma, vision loss occurs very gradually and may not be noticed until it has advanced significantly into the center. Both eyes may be affected at the same time, but one eye is often worse than the other.

Narrow or closed-angle glaucoma is less common and occurs suddenly with blurred vision, pain, and redness, usually in one eye first. In closed-angle glaucoma, the flow of aqueous is blocked from entering the drainage system (trabecular meshwork), causing a sudden rise in the intraocular pressure. Just like in open-angle glaucoma, the high pressure permanently damages the retinal nerve fibers and optic nerve. Acute closed-angle glaucoma is a medical emergency and needs immediate medical care to restore normal aqueous outflow, reduce pressure, and prevent permanent damage to the eye.

Congenital glaucoma is rare. It is present in some infants at birth or within the first few years of life. Infants with glaucoma usually have cloudy eyes that are sensitive to light and have excessive tearing. Severe vision loss and even blindness may occur if the problem is not diagnosed and treated early. When a similar type of glaucoma occurs between age 3 and adulthood, it is called juvenile glaucoma.

Secondary glaucoma is a broad category of glaucoma problems usually associated with another eye disease or disorder, such as a very mature cataract, uveitis (inflammation inside the eye), bleeding, eye tumor, or an eye injury. People with diabetes can develop abnormal blood vessels inside the eye, making them susceptible to neovascular glaucoma, a particularly severe form of the disease.