Vision Disorders

(Astigmatism; Color Blindness; Near- and Farsightedness; Presbyopia)

Vision is a complex and delicate process that can be affected by injuries, aging, and various diseases. Vision problems are due mainly to errors of refraction -- the way in which the lens of the eye focuses light on the retina at the rear of the eye. The most familiar are:

Astigmatism, in which the cornea, the transparent membrane at the front of the eye, is misshapen. Light rays fail to focus on a single point of the retina, resulting in distorted images.

Farsightedness, or hyperopia, in which light rays focus at a point just beyond the retina, blurring near objects.

Nearsightedness, or myopia, in which light rays focus just before the retina, making far objects difficult to see.

Presbyopia, a condition that develops with age, in which the lens loses some elasticity, resulting in farsightedness.

Color blindness, in which the cone cells of the retina are unable to distinguish the full spectrum of colors. Most color blindness is hereditary, affecting men 10 times more often than women. Other forms may develop with age or be secondary to diabetes, glaucoma, medications, or accidental poisoning.

Diagnostic Studies and Procedures

Most vision problems are readily diagnosed by an ophthalmologist or optometrist. These eye specialists test visual acuity with a Snellen test, a chart with rows of letters or numbers in different sizes. (Special picture charts are used to test young children.) Typically, the patient reads the chart, first using the naked eye and then with special lenses or instruments. Peripheral vision may be tested by a device that blinks lights on and off while the person looks into it.

If a color vision problem is suspected, the patient will be shown patterns of colored dots and asked to identify objects traced in different colors. Eye drops may be given to dilate the pupils, in order to inspect the inside of the eye.

Medical Treatments

Vision problems involving refraction errors are usually treated successfully with corrective glasses or contact lenses that refocus the light rays on the retina. Because vision changes over time, a prescription for corrective lenses must also be changed periodically. With advancing age, more than one lens strength may be needed, which can be combined into bifocal glasses.

Color vision abnormalities are sometimes treated with colored contact lenses, but these reduce visual acuity, distort three-dimensional perception, and offer little help with light shades, generally the major problem area.

Nearsightedness can be corrected with radial keratotomy. This outpatient surgical technique, developed in Russia, involves making a series of tiny radial incisions in the cornea. Each eye is done separately, with several days between operations. An eye patch or dark glasses are worn for several days. The full effects may not be felt for several months.

In one long-term follow-up study, more than half of the patients reported fully corrected vision, and another one-fourth said their eyesight was improved. Anyone contemplating radial keratotomy should make sure that the surgeon has a high success rate.

Alternative Therapies

Exercises. In the Bates method, exercises are used to improve poor or weak eyesight. Ophthalmologists discount their value, but others contend that the exercises balance the optic muscles, nerve, and other eye structures.

Nutrition Therapy. High doses of vitamin A are reputed to improve faulty color vision, but this has not been proven. However, vitamin A is essential for night vision; good sources include yellow and dark green vegetables.

Self-Treatment

To test yourself for a possible refractive error, make a pinhole in a piece of paper and look through the hole at a well-lit object. If the object is clearer this way, you probably need corrective lenses. If not, your blurred vision may be due to another disorder. In either case, seek professional care.

Other Causes of Vision Disorders

Glaucoma, cataracts, and certain retinal disorders are some conditions that impair vision. Amblyopia, or lazy eye syndrome, is common in children and may occur with strabismus, or crossed eyes. Diabetes and untreated high blood pressure can also affect the eyes as can many drugs.