Glaucoma is a nerve disorder of the eye, damaging the optic nerve and causing a loss of vision. Increased pressure in the eyeball is often associated with glaucoma.
Both the anterior and posterior chambers of the eye are filled with a thin fluid called the aqueous humor. The fluid is produced in the posterior chamber, passes through the pupil into the anterior chamber, and then drains from the eye through the outflow channels. If the flow of fluid is interrupted, usually by an obstruction that prevents the fluid from flowing out of the anterior chamber, pressure increases.
Usually, glaucoma has no known cause, but can be brought on by some medications (cortisone) and diseases (diabetes mellitus). The risk also increases with age (40+) and genetics (family history of glaucoma). If the outflow channels are open, the disorder is called open-angle glaucoma. If the channels are blocked by the iris, the disorder is called closed-angle glaucoma.
An ophthalmologist or optometrist can measure the pressure in the anterior chamber by using a simple, painless procedure called tonometry. In general, measurements greater than 20 to 22 millimeters of mercury indicate increased pressure. Occasionally, glaucoma occurs when pressures are normal. Sometimes a series of measurements must be taken over time to determine that the problem is glaucoma. An examination with an ophthalmoscope (an instrument used to view the inside of the eye) may reveal visible changes in the optic nerve caused by glaucoma. Sometimes, the examiner uses a special lens to observe the outflow channels; this procedure is known as gonioscopy.
Glaucoma produces a loss of peripheral vision or blind spots in the visual field. To find out if such blind spots exist, an examiner asks the person to look straight ahead at a central point and indicate when light can be seen. The test may be done either using a screen and pointer or an automated device that uses spots of light.
The most prevalent form of glaucoma, open-angle glaucoma is common after age 40 but occasionally occurs in children. The condition tends to run in families and is most common in people with diabetes or nearsightedness (myopia).
Symptoms and Diagnosis
Initially, increased pressure in the eyes produces no symptoms. Later symptoms may include narrowing peripheral vision, mild headaches, and vague visual disturbances, such as seeing halos around electric lights or having difficulty adapting to darkness. Eventually, tunnel vision (an extreme narrowing of the visual fields that makes it difficult to see anything on either side when looking straight ahead) may develop.
Open-angle glaucoma may not cause any symptoms until irreversible damage has developed. Usually, the diagnosis is made by checking intraocular pressure. Therefore, every routine eye examination should include a test of intraocular pressure.
Treatment is more likely to be successful if started early. Once vision is greatly impaired, treatment may prevent further deterioration, but it usually can’t restore vision completely.
Medicated eyedrops can usually control open-angle glaucoma. Typically, the first eyedrop medication prescribed is a beta-blocker which probably decreases the production of fluid in the eye. Other useful medications work either by improving outflow or decreasing fluid production.
If medication can’t control eye pressure or if side effects are intolerable, an eye surgeon can increase drainage from the anterior chamber by using laser therapy to create a hole in the iris or using surgery to cut out part of the iris.