How does glaucoma cause vision loss?

Glaucoma is a group of eye diseases that can lead to irreversible vision loss through damage to the optic nerve (a collection of specialized nerve fibers that transmit visual impulses to the brain). When damage to the optic nerve fibers occur, blind spots develop. These blind spots usually go undetected until the optic nerve is significantly damaged. If the entire nerve is destroyed, blindness results.

Early detection and treatment by your ophthalmologist are the keys to preventing optic nerve damage and blindness from glaucoma. Glaucoma is a leading cause of vision loss in the United States, especially for older people. However, loss of sight can often be prevented with early treatment.

Glaucoma is caused by a problem with the circulation of fluid in the eye. Normally, a clear liquid called aqueous humor circulates inside the front portion of the eye. To maintain a healthy level of pressure within the eye, a small amount of this fluid is constantly produced while an equal amount flows out of the eye through a sieve-like system called the trabecular meshwork.

In glaucoma, this drainage system becomes less efficient, slowing or blocking the outflow of fluid. The fluid then backs up in the eye, much like water in a clogged sink, and internal pressure rises. This, in turn, puts stress on the optic nerve, which provides the eye's wiring to the brain. If the pressure continues unabated, nerve fibers that carry the optical messages begin to die off, and vision starts to fade. Loss of vision may also result from the obstruction of tiny blood vessels that feed the retina and optic nerve. Nerve fibers on the outer edge are typically affected first, so vision loss begins with peripheral vision and gradually closes in until the cells supplying central vision are lost. The damage that occurs in glaucoma is irreversible but can often be prevented if detected early.