Glaucoma
What Is Glaucoma?
Glaucoma is the term for a diverse group of eye diseases, all of which involve progressive damage to the optic nerve. Glaucoma is usually, but not always, accompanied by high intraocular (internal) fluid pressure. Optic nerve damage produces certain characteristic visual field defects in the individual's peripheral (side), as well as central, vision.
What Are the Different Types of Glaucoma?
There are three basic types: primary, secondary and congenital.
Primary glaucoma is the most common type and can be divided into open angle and closed angle glaucoma.
Open angle glaucoma is the type seen most frequently in the United States. It is usually detected in its early stages during routine eye examinations. According to the Glaucoma Research Foundation (GRF), it occurs when the eye's drainage canals become clogged over time. This increases inner eye pressure since enough fluid cannot drain out of the eye.
Closed angle glaucoma, also called acute glaucoma, has a sudden onset in people with anatomically narrow angles. It is characterized by severe eye pain and blurred vision. According to the GRF, eye pressure increases very quickly because "the drainage canals get blocked or covered over" with closed angle glaucoma. "The iris and cornea are not as wide and open as they should be. The outer edge of the iris bunches over the drainage canals when the pupil enlarges too much or too quickly."
Secondary glaucoma occurs as a complication of a variety of other conditions, such as injury, inflammation, vascular disease and diabetes.
Congenital glaucoma is elevated eye pressure present at birth due to a developmental defect in the eye's drainage mechanism.
Symptoms
Subtle loss of contrast
Difficulty driving at night
Loss of peripheral vision (late-stage glaucoma)
Loss of central vision in terminal cases
Early on, glaucoma causes a subtle loss of contrast between objects and their backgrounds -- for example, not being able to distinguish the curb from the sidewalk or missing a step in a staircase. Many people are uncomfortable or afraid to drive at night because of contrast loss. When glaucoma progresses, the resultant optic nerve damage causes an irreversible loss of peripheral vision.
Diagnosis
Early detection of open angle glaucoma is extremely important, because there are no early symptoms. Routine eye exams, common after age 45, are a major factor in early detection. People with a family history of glaucoma should be checked at intervals even in their 30s to establish a baseline. Initially, detection is based on intraocular pressure readings, but also includes observation of the optic nerve as well as evaluation of optic nerve function using visual field and other scanning tests, such as the Heidelberg Retinal Tomograph (HRT).
Risk Factors
Age
Family History
Being African- or Hispanic-American
Diabetes
Myopia
The latest findings are that those with high myopia may have abnormally thin corneas so that the intraocular pressure test is inaccurate - i.e. the results of the test read normal in an eye that actually has higher pressure than normal.
What You Can Do to Reduce Risk
The most helpful advice concerning glaucoma is to keep in mind the importance of early detection through routine eye examination, faithful use of prescribed medications, and close monitoring by an eye doctor of the optic nerve, visual fields and pressures.
Treatment
Treatment options for glaucoma are always evolving -- another reason to visit your eye doctor regularly to screen for the condition. Be sure to ask for a contrast test, which can help identify subtle changes in contrast sensitivity due to the loss of retinal cells. Also, ask for the HRT and pachymetry -- a test to measure corneal thickness.
As a rule, elevated eye pressure can be managed with eye drops, medication, laser treatment or surgery. If detected early, eye drops most likely will be prescribed to control the pressure and prevent peripheral vision loss from advancing glaucoma.
Response to treatment is as varied as the patients themselves. Regardless of which treatment a doctor chooses (based on the patient's medical history and eye findings), the patient must understand that it is vital to follow the medical prescription regimen and to have regular follow-up eye exams. Eye drops are most commonly prescribed, although oral medications may also be used.
Eye Drops and Their Side Effects
Pilocarpine is the oldest drug used to treat glaucoma and has been in use for over a century. It has some unpleasant ocular side effects. Since it usually contracts the pupil, vision is darkened due to a reduced amount of light entering the eye. Use of low-strength drops or a gel at bedtime may reduce this side effect.
Propine, in the adrenalin epinephrine family, is also helpful and is often prescribed with pilocarpine or other drugs. Propine and other drugs in this family may cause red, teary eyes.
Timolol is a commonly prescribed "Betablocker." Side effects may include reduced pulse rate and bronchial asthma. If you are taking a Betablocker for glaucoma, be sure to tell your general physician.
Xalatan (latanaprost) is a groundbreaking addition to the treatment of glaucoma. It is an antiprostaglandin drug that is administered at night either as the sole medication or with a morning dose of a Betablocker.
Since Xalatan, other drugs have been developed to facilitate the treatment of glaucoma. Lumigan, Travatan, and Cosopt are also used to treat increased eye pressure caused by open-angle glaucoma in adult patients.
Oral Medication and Laser Surgery
If eye drops do not control the pressure, doctors can prescribe a pill that reduces production of eye fluid (aqueous). However, this may cause side effects, such as tingling of the extremities, nausea and weight loss. Another alternative is laser surgery, which does not require hospitalization and may be a safe means to regulate eye pressure for a year or more and to enhance the effectiveness of eye drops.
Surgery
When medication and laser surgery fail to control progression of glaucoma, a surgical procedure known as a filtering operation is recommended to create an artificial outlet for fluid from the eye, thus lowering intraocular pressure. Requiring use of an operating microscope and a local anesthetic, this procedure is performed in the hospital. If such a procedure is not feasible or has failed, production of aqueous fluid may be reduced by freezing (cryoprobe) or laser energy directly applied to the eyeball over the area where the fluid is produced.