THURSDAY, Jan. 5 (HealthDay News) -- Daily aspirin use among seniors may double their risk of developing a particularly advanced form of age-related macular degeneration, a debilitating eye disease, a large new European study suggests.

The possible link involves the so-called "wet" type of age-related macular degeneration (AMD), a significant cause of blindness in seniors.

Aspirin use was not, however, found to be associated with an increased risk for developing the more common, and usually less advanced, "dry" form of AMD, according to the report published in the January issue of Ophthalmology.

Although the study team stressed that further research is needed, the findings could cause concern for the millions of older people who routinely take over-the-counter aspirin for pain, inflammation and blood-clot management, and to reduce their risk of heart disease.

"People should be aware that aspirin, often just bought over the counter without prescription, may have adverse effects -- apart from major gastrointestinal and other bleeding -- also for AMD," said lead author Dr. Paulus de Jong.

De Jong is an emeritus professor of ophthalmic epidemiology at the Netherlands Institute for Neuroscience of the Royal Academy of Arts and Sciences, as well as the Academic Medical Center, both in Amsterdam.

Age-related macular degeneration affects the critical central vision required for reading, driving and general mobility. The damage occurs when the retinal core of the eye (the macula) becomes exposed to leaking or bleeding due to abnormal growth of blood vessels.

To examine whether aspirin use might trigger this process, the authors focused on nearly 4,700 men and women over age 65 living in Norway, Estonia, the United Kingdom, France, Italy, Greece and Spain.

In the study, conducted between 2000 and 2003, the researchers looked at blood samples, frequency of aspirin use (though not doses), smoking and drinking history, stroke and heart attack records, blood pressure levels and sociodemographic data.

The team also analyzed detailed images of each participant's eyes, looking for indications of age-related macular degeneration and severity.

Daily aspirin use was associated with the onset of late-stage "wet" age-related macular degeneration, and to a lesser degree, the onset of early "dry" AMD -- even after the researchers took into account age and a history of heart disease, which in itself is a risk factor for AMD.

For late-stage wet AMD only, the association was stronger the more frequently an individual took aspirin.

Early AMD was found in more than more than one-third of participants (36 percent), while late-stage AMD was found in roughly 3 percent, or 157 patients.

Of those with late AMD, more than two-thirds (108) had wet AMD, while about one-third (49) had dry AMD, the researchers found.

More than 17 percent of participants said they took aspirin daily, while 7 percent took it at least once a week and 41 percent did so at least once a month.

About one-third of those with wet AMD consumed aspirin on a daily basis, compared with 16 percent of those with no AMD.

The study authors cautioned that further research is needed on aspirin's possible effects on eye health. Meanwhile, they suggested that doctors generally should not alter their current advice for aspirin use among older patients coping with heart disease risk.

"[But] I would advise persons who [already] have early or late AMD not to take aspirin as a painkiller," de Jong said. "[And] I would advise people with AMD who take small amounts of aspirin for primary prevention -- this means having no past history of cardiac or vascular problems like stroke, and no elevated risk factors for these diseases -- to discuss with their doctor if it is wise to continue doing so. For secondary prevention -- this means after having these elevated risks or disorders -- the benefits of daily aspirin outweigh the risks."

While the study uncovered an association between aspirin use and AMD, it did not prove a cause-and-effect relationship.

This point was also made by Dr. Alfred Sommer, a professor of ophthalmology and dean emeritus at the Bloomberg School of Public Health at Johns Hopkins University in Baltimore. He noted that while the study was "well executed," it should not be seen as definitive proof that aspirin use and AMD are linked.

An observational study of this type "merely calls attention to the fact that such an association may exist, and that it may be causal, but only randomized clinical trials can prove the matter one way or the other," he said.

"Hence, this might or might not be real," Sommer added, "and we will only know that when and if a randomized trial is done."

In the interim, he said the findings should not guide patient behavior.

"It is well known that aspirin [and other NSAIDs] can increase the risk of gastric distress and gastric ulcers," Sommer said. "Like any medicine, it should only be taken if needed. But those taking aspirin to prevent heart disease, particularly those at increased risk of heart disease, definitely do benefit and should not change what they do."

More information

For more on age-related macular degeneration, visit the U.S. National Eye Institute.