Fast Facts about Sun and our Eyes

One of the great wonders of the human body is the ability of damaged cells to be repaired or replaced. Red blood cells, for instance, live for about 120 days. Each day, about 1% of your red blood cells retire to be replaced by a fresh generation. The lens of the eye is a notable exception. The cells of the lens of the eye are never replaced; the proteins of the lens are never replenished. The lens cannot repair itself; damage accumulates over a lifetime.

Cataracts are the result of gradually accumulating damage to the proteins of the lens. The most important source of this damage is exposure to ultraviolet (UV) radiation, especially while one is young.

Behind the lens lies the retina, the thin lining of the back of the eye. The retina is the eye’s miracle. This patch of tissue, about the size and thickness of a postage stamp, is able to dissolve and create a new image every tenth of a second.

Today in the United States, retinal diseases are the leading cause of blindness. Macular degeneration, the accumulation of damage in the retina, is the leading cause of blindness from retinal disease. Slowly, over the years, the macula is irreversibly damaged by exposure to UV radiation. About one third of adults over age 65 experience this steady decline of central vision, not correctable by glasses.

Excessive exposure to sunlight during early childhood is harmful to the eyes. Sunlight contains harmful UV radiation.

The risk for retinal damage from the sun’s rays is greatest in children less than 10 years old, although the consequences usually do not become apparent until well after they are adults.

All children should be taught to wear sunglasses, especially between 10 AM and 2 PM, when ultraviolet exposure is the most dangerous. This is true even for children with darker eye colors, even though their darker pigments afford partial protection. Of course, children with light-colored eyes need sunglasses all the more.

Ultraviolet exposure is at its peak when children are at high altitudes, snow-covered landscapes, bright sandy beaches, or near reflective bodies of water.

All sunglasses are not the same. Effective sunglasses should block both UVA and UVB radiation. The sunglasses must be measured to block 99% to 100% of UVA or UV400 (400 nm is the wavelength of UVA radiation). Thankfully, all sunglasses block UVB radiation.

Large lenses that fit close to the eyes are best. Those that block visible blue light are even safer.

Expensive brand names and polarizing lenses are no guarantee.

Ordinary sunglasses make the situation WORSE! The dark lenses cause the pupils to dilate, allowing more of the dangerous UVA radiation to damage the lens and the retina.

Last medical review on: September 01, 2001
About the Author
Photo of Alan Greene MD
Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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