Vision Basics

WHAT ARE CATARACTS AND HOW DO THEY FORM?

Light enters the eye through the pupil, the round, black opening at the center of the iris. Behind the pupil is the lens, which catches the incoming light and focuses it onto the retina at the back of the eye.

A cataract is formed when protein fibers in the lens change shape and clump together, clouding the normally transparent lens. This is similar to the process that turns the protein in egg albumin from clear to white when cooked. In fact, most well-developed cataracts look milky white, although in some cases, the lens can turn yellow or brown instead.

Cataracts develop slowly, over a period of years. But even before a cataract can be seen from the outside, vision can become blurry or cloudy — like looking through a fogged windshield. Other possible symptoms include worsened night vision, faded color vision, and starburst or halo effects around bright lights. Because cataracts can be surgically removed, these symptoms are only temporary — after surgery you may need glasses to see detail, but your sight will be clear.

No one knows exactly what causes eye proteins to clump and create a cataract. Many scientists blame unstable molecules known as free radicals, which can wreak havoc throughout the body, causing destruction and disease wherever they go through a complex chemical process called oxidative stress. And what creates free radicals? Well ... the single greatest cause is just being alive. Natural metabolic processes from normal body functions like breathing and digesting food generate lots of free radicals, and unless they are neutralized, they build up over time. (A powerful tool to neutralize free radicals are antioxidants; learn more in How Food Affects Cataracts. That's why our bodies seem to deteriorate slowly with age — it's the accumulated damage from years of free radical attacks.

Two other major causes of free radicals are smoking and ultraviolet radiation from sunlight. This is the reason all cataract-prevention strategies must include a commitment to stop smoking and reduce exposure to sunlight. Cataracts can also be caused by surgery for other eye problems, traumatic eye injury, or long-term use of corticosteroids. In very rare circumstances, genetic anomalies can create cataracts in newborn babies or infants.

WHAT IS MACULAR DEGENERATION AND HOW DOES IT OCCUR?

The retina is the part of the eye that receives light and images from the world and sends them to the optic nerve to be processed in the brain. The macula is the center of the retina — and the most sensitive part. It fine-tunes focus at the center of our visual field, the area that allows us to recognize faces, read words on a page, and discern detail in anything we look at. Macular degeneration, then, is a deterioration of the macula, gradually leading to central blindness. Peripheral vision remains clear, so it isn't a total lack of sight but the loss of detailed vision.

There are two types of macular degeneration: dry (also called atrophic), caused by a gradual breakdown of light receptors; and wet (also called exudative), caused by leaks in the blood vessels of the retina, which in turn cause scarring and tissue death. With both types, people usually notice vision distortions first, such as straight lines appearing wavy, along with difficulty reading and recognizing faces. As more and more receptors die, central vision disappears. Fortunately, major advances have been made in treating the wet form of macular degeneration. For example, doctors can now prescribe injectable drugs that stop the leaky blood vessels from growing. There is currently no medical treatment for dry macular degeneration.

Macular degeneration happens most often in people over age 70, primarily women. Although it can run in families, no one knows what causes macular degeneration, or how to stop it once it begins.