March 4, 2004 -- Smokers are four times more likely to become blind because of age-related macular degeneration than those who have never smoked. But most smokers don't realize their risk, new research shows.
Age-related macular degeneration is a severe and progressive condition that results in loss of central vision. It results in blindness because of the inability to use the part of the retina that allows for 'straight-ahead' activities such as reading, sewing, and even driving a vehicle. While all the risk factors are not fully understood, research has pointed to smoking as one major and modifiable cause.
"While most people recognize many adverse health hazards of tobacco smoking, they remain largely unaware of its link with blindness," writes Simon P. Kelly, MD, an ophthalmic surgeon with Bolton Hospitals in Great Britain. His editorial appears in this week's British Medical Journal.
"More than a quarter of all cases of age-related macular degeneration with blindness or visual impairment are attributable to current or past exposure to smoking," Kelly writes.
Only a few modestly effective treatments are available for this condition, and not all people benefit from them. In fact, when people continue to smoke after the treatments, it's likely that they will adversely affect the outcome, he says.
In his editorial, Kelly cites several studies backing up his alarm.
Three studies involving 12,470 patients all showed that people who currently smoked had a three to fourfold increased risk of macular degeneration compared with people who had never smoked.
In the studies, Kelly also found what's known as a "dose-response relationship" -- the longer people smoked and the more packs of cigarettes they smoked, the greater their risk of blindness from age-related macular degeneration.
Biologically, what's likely happening is that the retina suffers from oxidative damage from smoking. This is damage created by unstable molecules or toxins called free radicals that cause damage to cells. That damage is too great to be offset by protective measures such as antioxidants in the diet, he explains.
Other studies show that when a smoker quits, the eyes are protected from further damage. "Former smokers have an only slightly increased risk of age-related macular degeneration, compared with never smokers," he writes.
The reversibility of this condition in one eye "has important implications" for prevention of damage to the second eye, says Kelly.
SOURCE: Kelly, S. British Medical Journal, March 6, 2004; vol 328: pp 337-338.