Your eye is an intricate structure that efficiently performs many tasks: It receives and transmits thousands of visual messages per minute, automatically adjusts to changing light conditions, focuses incoming light, and produces its own fluids—inside and outside the eye—for lubrication, cleansing, and fighting off infection. Healthy eyes perceive the world both centrally and peripherally. Your central vision enables you to read this page, while your peripheral vision lets you see the person entering a door to your right, without turning your head. Moreover, though each eye sees separately, both eyes together produce "binocular" vision—that is, the brain perceives a single image, thus giving you three-dimensional depth perception and a coherent picture of your surroundings.
You have millions of neurons—anywhere from 17 to 18 million—in each eye, and these are what help you see. The average person without an eye disorder loses about 20 percent of those neurons by age 90. Even so, there's still enough left to keep us reading and walking without too much difficulty even at age 90 and beyond.
The most common eye diseases in people over age 50 are cataracts, glaucoma, age-related macular degeneration, and diabetic retinopathy. Fortunately, if you have one of these eye disorders and are treated early enough, the progression can often be slowed or even halted. Because most eye disorders cause no symptoms in their early stages, many people are unaware when one first develops. That's why periodic visits to an eye-care specialist are crucial to detect conditions early enough to allow for effective treatment.
You can also take steps to protect your eyes as you age. A healthy diet can provide the nutrients your eyes need, although the research linking nutrition and vision remains a work in progress. Supplements can help some people with age-related macular degeneration.
To help open your eyes to the complex factors affecting your gift of sight and what you can do to keep seeing clearly, consult Protecting Your Aging Eyes.