Dr. Greene’s Answer:
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. This same story of replenishment, replacement, and repair is repeated in almost every part of your body.
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.
The lens is intended to focus and transmit light to the back of the eye. Sometimes tiny, cloudy spots form in the lens. These can spread to turn the entire lens milky white, scattering the incoming light and blocking vision. People with this condition sometimes feel as if they were looking at the world through a waterfall, which is why the ancient Greeks named these cloudy changes cataracts, or waterfalls.
This condition has blinded more people throughout the ages than any other problem of the eye. Senile cataracts, those that develop slowly with advancing age, are the most common cataracts. They 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. Today cataracts can be treated with surgery and artificial lenses.
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. Look across the room and marvel at how quickly your retina creates new images.
The retina is woven of brain cells. It is the part of the brain that faces the world around us. Its efforts are more intense than those of any other part of the brain. No other tissue in the body uses oxygen or food at such a rate. The hardest working region of the retina is called the macula. The macula is the part of the retina that lies directly in the path of light rays focused by the lens.
Today in the United States, retinal diseases are the leading cause of blindness. Unlike cataracts, little can be done to treat them. Unlike the lens, the retina is irreplaceable. 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.
Teaching your children to wear sunglasses may be more important than giving them a college fund.
All children should be taught to wear wide-brimmed hats and 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.
Most people wear sunglasses to reduce glare. This is trivial compared to the long-term protection they afford for the precious ability to see. Parents can set a good example for their children by wearing sunglasses at the appropriate times.
All sunglasses are not the same. Effective sunglasses should block both UVA and UVB radiation. Large lenses that fit close to the eyes and partially wrap around the sides of the face are best. Those that block visible blue light are even safer. Thankfully, all sunglasses block UVB radiation. A great many sunglasses, however, do not afford UVA protection. Expensive brand names and polarizing lenses are no guarantee. The sunglasses must be measured to block 99% to 100% of UVA or UV400 (400 nm is the wavelength of UVA radiation).
Ordinary sunglasses without full UV protection 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.
Of course, children will break and lose sunglasses with remarkable rapidity. Thankfully, suitable sunglasses are quite cheap. I bought another pair yesterday for under five dollars that blocked blue light and had 100% UV400 protection.
Expensive brands may be more stylish, but they confer no advantage when it comes to eye health.