Glaucoma is a group of eye disorders that lead to progressive damage to the optic nerve. People with glaucoma can lose nerve tissue, resulting in vision loss.
The optic nerve is a bundle of about 1 million individual nerve fibers that transmits the visual signals from the eye to the brain. In the most common form of glaucoma, primary open-angle glaucoma, the fluid pressure inside the eye increases. This increase in pressure may cause progressive damage to the optic nerve and loss of nerve fibers. Vision loss may result. Advanced glaucoma may even cause blindness.
Not everyone with high eye pressure will develop glaucoma, and some people with normal eye pressure will develop glaucoma. When the pressure inside a person's eye is too high for a particular optic nerve, whatever that pressure measurement may be, glaucoma will develop.
Glaucoma is the second-leading cause of blindness in the U.S. It most often occurs in people over age 40, although an infant (congenital) form of glaucoma exists. People with a family history of glaucoma, African Americans over the age of 40 and Hispanics over the age of 60 have an increased risk of developing glaucoma. Other risk factors include thinner corneas, chronic eye inflammation and taking medications that increase the pressure in the eyes.
The most common form of glaucoma, primary open-angle glaucoma, develops slowly and usually without any symptoms. Many people are not aware they have the condition until they have significant vision loss. Initially, glaucoma affects peripheral or side vision, but it can advance to central vision loss. If left untreated, glaucoma can lead to significant vision loss in both eyes, and may even lead to blindness.
A less common type of glaucoma, acute angle-closure glaucoma, usually occurs abruptly due to a rapid increase of pressure in the eye. Its symptoms may include severe eye pain, nausea, redness in the eye, seeing halos or colored rings around lights and blurred vision. This is an emergency condition in which severe vision loss can occur quickly; see your optometrist immediately.
Glaucoma cannot currently be prevented. But if it is diagnosed and treated early, it can usually be controlled. Medication or surgery can slow or prevent further vision loss.
However, vision already lost to glaucoma cannot be restored. That is why the American Optometric Association recommends an annual dilated eye examination for people at risk for glaucoma. Depending on your specific condition, your doctor may recommend more frequent examinations.
What causes glaucoma?
There are many theories about the causes of glaucoma, but the exact cause is unknown. Although the disease is usually associated with an increase in the fluid pressure inside the eye, other theories include lack of adequate blood supply to the nerve. Following are the different types of glaucoma and their potential causes.
Primary open-angle glaucoma. This is the most common form of glaucoma. Damage to the optic nerve is slow and painless. Those affected can lose a large portion of vision before they notice any vision problems.
One theory about its development is that the eye's drainage system becomes inefficient over time. This leads to an increased amount of fluid and a gradual buildup of pressure within the eye. Another theory about the cause of this type of glaucoma is that there is poor blood flow (perfusion) to the optic nerve. Other theories also exist.
Angle-closure glaucoma. This type of glaucoma, also called closed-angle glaucoma or narrow-angle glaucoma, is a less common form of the disease. It is a medical emergency that can cause vision loss within a day of its onset.
It occurs when the drainage angle in the eye (formed by the cornea and the iris) closes or becomes blocked. Many people who develop this type of glaucoma have a very narrow drainage angle. With age, the lens in the eye becomes larger, pushing the iris forward and narrowing the space between the iris and the cornea. As this angle narrows, the fluid in the eye is blocked from the drainage system. Therefore the fluid builds up and eye pressure increases.
Angle-closure glaucoma can be chronic (progressing gradually) or acute (appearing suddenly). The acute form occurs when the iris completely blocks fluid drainage. When people with a narrow drainage angle have their pupils dilated, the angle may close and cause a sudden increase in eye pressure. Although an acute attack often affects only one eye, the other eye may be at risk of an attack as well.
Secondary glaucoma. This type of glaucoma results from an injury or other eye disease. It may be caused by a variety of medical conditions, medications, physical injuries and eye abnormalities. Infrequently, eye surgery can lead to secondary glaucoma.
Normal-tension or low-tension glaucoma. In this form of glaucoma, eye pressure remains within the "normal" range, but the optic nerve is damaged nevertheless. It is not known why this happens.
Possibly, people with low-tension glaucoma have an abnormally sensitive optic nerve. Or they may have a reduced blood supply to the optic nerve caused by a condition such as atherosclerosis, a hardening of the arteries. Under these circumstances even normal pressure on the optic nerve can cause damage.
How is glaucoma diagnosed?
Glaucoma is diagnosed through a comprehensive eye examination. Because glaucoma is a progressive disease, meaning it worsens over time, a change in the appearance of the optic nerve, a loss of nerve tissue, and a corresponding loss of vision confirm the diagnosis. Some optic nerves may resemble nerves with glaucoma, but the patients may have no other risk factors or signs of glaucoma. These patients should have routine comprehensive exams to monitor any changes. Glaucoma testing includes:
Patient history to determine any symptoms the patient is experiencing and if there are any general health problems and family history that may be contributing to the problem.
Visual acuity measurements to determine if vision is being affected.
Tonometry to measure the pressure inside the eye to detect increased risk factors for glaucoma.
Pachymetry to measure corneal thickness. People with thinner corneas are at an increased risk of developing glaucoma.
Visual field testing, also called perimetry, to check if the field of vision has been affected by glaucoma. This test measures your side (peripheral) vision and central vision by either determining the dimmest amount of light that can be detected in various locations of vision, or by determining sensitivity to targets other than light.
Evaluation of the retina of the eye, which may include photographs or scans of the optic nerve, to monitor any changes over time.
Supplemental testing, which may include gonioscopy. This procedure offers a view of the angle anatomy, which is where eye fluid drainage occurs. Serial tonometry is another possible test. This procedure acquires several pressure measurements over time, looking for changes in the eye pressure throughout the day. In addition, devices can be used to measure nerve fiber thickness and to look for tissue loss on specific areas of the nerve fiber layer .
There is no cure for glaucoma. Patients with glaucoma need to continue treatment for the rest of their lives. Because the disease can progress or change without warning, compliance with eye medications and undergoing eye examinations are essential; treatment may need to be adjusted periodically.
Keeping eye pressure under control can slow or stop damage to the optic nerve and continued loss of vision. Your optometrist may focus on lowering the eye pressure to a level that is least likely to cause further optic nerve damage. This level is often referred to as the target pressure and is likely a range rather than a single number. Target pressure differs for each person, depending on the extent of the damage and other factors. Target pressure may change over time. New medications to help fight glaucoma are always being developed.
Early detection, prompt treatment and regular monitoring can help to control glaucoma and reduce the chances for vision loss.