Retina Disorders (Retinitis Pigmentosa, Retinopathy)

The retina, the thin membrane that lines the back of the eyeball, receives the images formed by the lens and transmits them to the optic nerve, an extension of the brain. Anything that interferes with the retina's ability to receive or transmit visual images can impair eyesight. A problem may originate in the membrane itself; examples are detached retina and macular degeneration. It may also result from occlusion of blood flow to the retina due to glaucoma. The retinal disorders described below are either hereditary or are caused by other diseases.

Diabetic retinopathy. About half of the approximately 14 million Americans with diabetes have some degree of retinal impairment, with about 700,000 of them threatened by blindness. Diabetic retinopathy has two major manifestations: Macular edema, the most prevalent of the two, develops when the small retinal blood vessels leak fluid into the macula, the part of the retina responsible for clear vision. As the fluid accumulates, the macula swells and vision becomes blurred.

More serious, but much less common, is proliferative retinopathy, in which abnormal new blood vessels multiply on the surface of the retina. These vessels frequently rupture, forming scar tissue that blocks vision.

Retinitis pigmentosa. This inherited disorder leads to progressive destruction of the retinas rods and cones, the cells that send signals about light perception to the brain. The earliest symptom is a loss of normal nighttime vision. There is also a gradual loss of peripheral, or side, vision. Typically, the person has only tunnel vision by the age of 40 and may become blind within the following 20 years. Nearly 100,000 Americans and 1.5 million people worldwide have this disorder.

Diagnostic Studies and Procedures

Retinal disorders are usually diagnosed by examining the eye with a lighted magnifying device, such as an ophthalmoscope. A doctor will first apply medicated eye drops to widen, or dilate, the pupil. By training the magnifying instrument through the enlarged pupil, he can inspect the retina and other eye structures for diabetes-related retinal changes, even before symptoms occur.

A doctor may also order fluorescein angiography, special X-rays of the eyes blood vessels taken after injecting dye into a vein to make them more visible.

Retinitis pigmentosa is often diagnosed early in life when a child complains of not being able to see clearly at night. Special tests are used to measure the eyes adaptation to the dark as well as any loss of the peripheral vision.

If a retinal problem is caused by a systemic disease, such as diabetes or high blood pressure, the patient will be referred to an internist or other primary-care physician for a complete physical examination that includes blood and urine studies. X-rays and a CT scan or MRI may also be ordered, especially if the patient recently suffered a head injury, a stroke, or a mini-stroke.

Medical Treatments

Treatment varies according to the specific retinal disorder and its cause, achieving good control of diabetes, high blood pressure, and other diseases that affect the eyes is essential.

Diabetic retinopathy can now be treated with laser surgery. Powerful light beams are directed into the eye to seal off leaking blood vessels, a procedure called photocoagulation. Laser photocoagulation also is used to stop proliferative retinopathy by destroying the diseased retinal tissue.

There is no specific treatment for retinitis pigmentosa, although nutrition therapy may slow its progress.

Alternative Therapies

Nutrition Therapy. A study published in 1993 in the Archives of Ophthalmology reported that a daily dose of 15,000 international units of vitamin A can slow the progress of retinitis pigmentosa. Because this dosage is four or five times the normal dietary intake, this treatment should not be undertaken without a doctor's supervision. A buildup of vitamin A in the body can cause liver disease and, if taken during pregnancy, can result in severe birth defects or even fetal death.

Self-Treatment

Self-care for retinal disorders centers on controlling any underlying disease, such as diabetes or high blood pressure. If diminished vision cannot be avoided, there are numerous optical devices that maximize partial sight, or low vision. Practical aids to daily living include large-print newspapers, magazines and books; special calculators and typewriters; television screen magnifiers; and voice-activated computers, clocks, and other devices.

Patients with retinitis pigmentosa are advised to plan for progressive vision s loss by learning to read braille and use other aids for the visually impaired.

Other Causes of Retinal Damage

In addition to the disorders cited above, the retina may be damaged by sickle cell anemia, kidney disease, leukemia, syphilis, and toxicity from quinine drugs.