What is blindness?

Causes and Symptoms

The major cause of blindness among older adults in the Western world is
glaucoma. The aqueous fluid produced inside the eye fails to drain properly and causes pressure to build up. In extreme cases, the eyeball becomes hard. Without prompt treatment, the outer layer of the optic nerve starts to deteriorate. The patient can still see straight ahead but not off to the side. When the cone of forward vision has narrowed to less than 20 degrees (called tunnel vision), the patient is considered legally blind.

Cataracts
are another common defect of vision among the elderly. The lens of the eye develops dark spots that interfere with light transmission. Cataracts are not caused by an infection or a tumor but instead are a normal part of the aging process, like gray hair. There is no known treatment to retard or reverse the growth of cataracts, though they may be surgically removed.

Macular degeneration
and diabetes mellitus
can cause blindness as a result of hemorrhages from tiny blood vessels in the retina. The macula is a small region in the middle of the retina where receptor
cells are tightly packed together to obtain sharp vision for reading or close work. With aging, blood circulation in the macula gradually deteriorates until the patient develops a black spot in the center of the field of view. Advanced diabetes also causes blood vessel damage in the eye. In serious cases, fluid can leak behind the retina, causing it to become detached. The resulting visual effect resembles a dark curtain that blacks out part of the scene.

Trachoma
is a blinding eye disease that afflicts millions of people in poor parts of the world. It is a contagious infection of the eyelid similar to conjunctivitis (commonly known as pinkeye). If untreated, it causes scarring of the cornea and eventual blindness. Trachoma is caused by a virus that is spread by flies, in water, or by direct contact with tears or mucus.

Many kinds of injuries may cause blindness. Car accidents, sports injuries, chemical explosions, battle wounds, and small particles that enter the eye all can result in a serious loss of vision.

Treatment and Therapy

An indispensable tool in the treatment of serious eye problems is the laser. Its intense light focused into a tiny spot, the laser’s heat can burn away a ruptured blood vessel or weld a detached retina back into place. For
glaucoma patients, medication to reduce fluid pressure in the eye may be effective for a while. Eventually, a laser can be used to burn a small hole through the iris in order to improve fluid drainage. The laser can be used only to prevent blindness, however, and not to restore sight.

Cataracts formerly were a major cause of blindness among older people. Once the eye lens starts to become cloudy, nothing can be done to clear it. Cataract surgery to remove the defective lens and to insert a permanent, plastic replacement has become common. In the United States, more than a million cataract surgeries are performed annually, with a success rate that is greater than 95 percent.

The infectious eye disease called
trachoma has been known for more than two thousand years. Effective modern treatment uses sulfa drugs taken orally, combined with antibiotic eyedrops or ointments. Unfortunately, reinfection is common in rural villages where most people have the disease and sanitation is poor. The World Health Organization has initiated a public health program to teach parents about the importance of cleanliness and frequent eye washing with sterilized water for their children.

Perspective and Prospects

Various techniques have been developed for helping sightless people to live a self-reliant lifestyle. Using a white cane or walking with a trained dog allows a blind person to get around. Biomedical engineers have designed a miniature sonar device built into a pair of glasses that uses reflected sound waves to warn the wearer about obstacles.

The Braille system of reading, using patterns of raised dots for the alphabet, was invented in 1829 and is still widely used. For blind students, voice recordings of textbooks, magazines, and even whole encyclopedias are available on tape. A recent development is an optical scanner connected to a computer with a voice simulator that can read printed material aloud.

The National Federation of the Blind was founded in 1940. Its goals are to assist the blind to participate fully in society and to overcome the still-prevalent stereotype that the blind are helpless. Blind men and women hold jobs as engineers, teachers, musical performers, ministers, insurance agents, computer programmers, and school counselors. As society becomes more sensitive to all forms of disability, opportunities for blind people continue to expand.

Bibliography:

American Foundation for the Blind (AFB). AFB, 2013.

Buettner, Helmut, ed. Mayo Clinic on Vision and Eye Health: Practical Answers on Glaucoma, Cataracts, Macular Degeneration, and Other Conditions. Rochester, Minn.: Mayo Foundation for Medical Education and Research, 2002.

Johnson, Gordon J., et al., eds. The Epidemiology of Eye Disease. 2d ed. New York: Oxford UP, 2003.

Maurer, Marc. “Reflecting the Flame.” Vital Speeches of the Day 57 (Sept. 1, 1991): 684–90.

MedlinePlus. "Cataract." MedlinePlus, Mar. 20, 2013.

MedlinePlus. "Vision Impairment and Blindness." MedlinePlus, Apr. 2, 2013.

Morrison, John C., and Irvin P. Pollack. Glaucoma: Science and Practice. New York: Thieme, 2003.

National Federation of the Blind. NFB, 2013.

Peninsula Center for the Blind. The First Steps: How to Help People Who Are Losing Their Sight. Palo Alto, Calif.: Peninsula Center, 1982.

Sardegna, Jill, et al. The Encyclopedia of Blindness and Vision Impairment. 2d ed. New York: Facts On File, 2002.

Westcott, Patsy. Living with Blindness. Austin, Tex.: Raintree, 2000.