A new study shows that smokers are at substantially increased risk for developing age-related macular degeneration and even blindness. The research, by scientists in Japan and the United States, shows that Japanese smokers face four times the risk of age-related macular degeneration, or AMD, than non-smokers.
In AMD, the light-sensing cells in the retina die off over time, causing progressive vision loss.
The disease is much more common in Japanese men than women, but sex difference may really just reflect the fact that men in that country smoke more than women, according to the researchers.
"The bottom line for people worried about age-related macular degeneration is that there is a modifiable risk factor that is very, very strong, and that's smoking," said Dr Peter Gehlbach, an ophthalmologist at Johns Hopkins University in Baltimore, and a co-author of the study.
"It may well be that a significant portion of macular degeneration is the result of prior significant exposure to cigarette smoke," Gehlbach said.
Just less than a third of Americans over 75 have AMD, according to the National Institutes of Health. The condition takes two forms, a quick-onset "wet" type, marked by leaky blood vessels in the retina, and, more commonly, a "dry" version that progresses slowly.
Although macular degeneration has no cure, several treatments, including drugs and surgery, can delay its progression. The wet form in particular can respond to medications such as Roche's Lucentis, which acts by preventing the formation of abnormal blood vessels in the eye.
In a recent study, another Roche drug called Avastin proved to be equal to Lucentis at preventing vision loss, although possibly with greater risk for side effects.
Avastin, which is not approved for AMD, but is the most frequently injected drug for treating the condition, costs about $50 a dose, compared to $2,000 for Lucentis.
Previous studies have looked for a link between smoking and AMD, with mixed results.
The Japanese study, published in the journal Ophthalmology, included 279 men and women with AMD and 143 people without the disease.
Tobacco use had the strongest association with blindness, with 75% of AMD patients smoking compared to only 40% of the comparison group.
After taking other differences into account, smokers had four times the risk of AMD relative to non-smokers. They also had a nearly fivefold increase in risk of developing a vision disorder called polypoidal choroidal vasculopathy, which also leads to bleeding in the retina.
Having high blood pressure and being overweight also seemed to be associated with a greater risk of AMD, although to a lesser extent than smoking.
A study like the current one doesn't prove that smoking causes AMD, but scientists believe that it is likely to be the case.
Simon Kelly, an eye surgeon at Royal Bolton Hospital in England, and author of two reviews of the link between smoking and vision loss, said the latest study supports the connection.
"The public health need is now, in my opinion, to highlight this link of smoking and [AMD] to patients and the public all over the world. In Europe we are calling on governments to put the message 'smoking causes blindness' on tobacco products."
Kelly, who was not involved in the new study, said that in his experience, smokers seem willing to quit the habit when warned of the risk of blindness later in life.
"We have found that such a message has traction amongst teenagers," he added.