Thursday, April 2, 2009 | 5:41 am

When buying sunglasses, look for those that filter ultraviolet (UV) light, the tumor-producing component of sunshine, and thereby block its entry to the eyes. This helps to prevent cancer of the iris, the colored tissue that surrounds the pupils. UV light is now also thought to be a causative factor in some eye diseases formerly attributed to “aging.”

Thus, the We stern Journal of Medicine (144:454) reports, the cumulative effect of UV on the retina over a period of several decades seems to be a major factor in the development of macular degeneration, one of the most common causes of failing vision, even blindness, in the elderly.

While passing through an eye, however, much of the UV in a sunlight beam gets filtered out by the lens, which, in this way, serves as a shield for the retina. Not surprisingly, therefore, the lens bears some of the brunt of repeated and prolonged exposure to UV, becoming discolored and opaque as the result. Known as cataract, this lens condition produces progressive visual clouding until all that can be sensed is the difference between darkness and light.

Fortunately, these bad effects of UV light upon the retina and lens can be prevented with sunglasses that filter UV from sunlight, thereby stopping it from even entering the eye. However, many sunglasses don’t filter out enough UV light to protect us properly, even when their manufacturer states that they are “UV absorbing.” By itself, that claim can be misleading since any glass or plastic blocks at least some UV.

To properly protect the eyes, we need sunglasses that block out light of all wavelengths below 400 nm (nanometers). As a rule of thumb, lenses that can do this should be dark enough not to let you see your own pupils when looking in a mirror. Glasses that merely block out UV wavelengths below 350 are not good enough. Actually, there is now an instrument that enables professionals to determine if sunglasses can absorb UV sufficiently. This is why you ought to go to an eye professional when purchasing a new pair.


(posted in General health | tagged General health)

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