What is Glaucoma?

Glaucoma is a disease that causes deterioration of the optic nerve. Vision loss from glaucoma is permanent but can usually be prevented with early detection and treatment. Because the symptoms of early glaucoma are so slight, the disease often goes unnoticed until significant, permanent vision loss has occurred.

Glaucoma is a disease caused by increased intraocular pressure (IOP) resulting either from a malformation or malfunction of the eye’s drainage structures. Left untreated, an elevated IOP causes irreversible damage to the optic nerve and retinal fibers resulting in a progressive, permanent loss of vision. When glaucoma damages your optic nerve, transmission of visual information from the eye to the brain is limited which causes visual impairment. Glaucoma typically causes you to begin to lose patches of vision, usually side (peripheral) vision initially. Over time, glaucoma may also damage straight ahead (central) vision. You may not notice a loss of peripheral vision until you have lost a great deal of your sight.

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 produced constantly while an equal amount flows out of the eye through a microscopic drainage system. This liquid is not part of the tears on the outer surface of the eye.

Glaucoma causes damage to the nerve fibers of retinal ganglion cells and is manifest clinically by alterations in the appearance of the optic disc. There is a rather typical sequence of change that occurs to the optic disc in uncontrolled glaucoma.

Optic Nerve Head Cupping a. – d., left to right; C/D = Cup-to-Disc Ratio)

a. Normal optic nerve head with small central physiologic cup, C/D ratio ~ 0.2
b. Concentric enlargement of the central cup, C/D ratio ~ 0.5
c. Irregular enlargement of the cup, especially inferiorly due to loss of inferior neural rim tissue, C/D ratio ~ 0.7
d. Marked glaucoma cupping with high degree of central atrophy and loss of inferior rim, C/D ratio ~ 0.9

What Causes Glaucoma?

In most cases, glaucomatous optic nerve damage occurs from high eye pressure. For some people, fluid can’t drain properly because of a faulty drainage system. Drainage that once worked well may gradually slow down as you get older. Similar to a sink that becomes clogged and backs up with water, when the aqueous humor in the eye is unable to drain adequately and there is no place for the excess fluid to go, pressure inside the eye builds up.
Other factors besides intraocular pressure appear to contribute to glaucoma. Some people with normal pressure may experience vision loss from glaucoma, and many people with high IOP (ocular hypertension) do not develop glaucoma. However, the higher the IOP, the more likely optic nerve damage will occur. Some normal tension glaucoma may be related to problems with blood flow in the eye. Doctors continue to study eye pressure and other possible causes of glaucoma.

Nerve damage can usually be slowed down or stopped by lowering the eye pressure. The goal of glaucoma treatment is to lower the eye pressure with medicines, lasers, or surgery. Although vision loss from glaucoma cannot be restored, treatment can typically slow down or prevent further vision loss.

What is Eye Pressure?