Common Bug May Up Risk
of Age-Related Vision Loss

NEW YORK (Reuters Health) - New findings suggest that a frequent cause of age-related vision impairment may be linked to a common bacterial infection.

U.S. researchers discovered that people with age-related macular degeneration (AMD) tended to carry higher levels of antibodies targeted against the bacterium Chlamydia pneumoniae than those without AMD. Such targeted antibodies are a sign of past infection.

Although the reason for this relationship is not yet clear, the findings suggest that infection with C. pneumoniae may cause changes in the body that increase a person's risk of developing AMD, according to the study authors.

They report the results in the April issue of the Archives of Ophthalmology.

AMD occurs when light-sensitive cells in the macula, the tissue at the center of the retina, break down. This can make it difficult to read, drive or perform other activities that require fine vision.

An estimated one-third of Americans age 75 and older have AMD.

C. pneumoniae normally infects the respiratory system, but it's also suspected of promoting certain chronic illnesses. Research has shown that infection with the bug may promote heart disease by producing inflammation in blood vessels. Some experts believe that this inflammation could damage the blood vessel lining and potentially contribute to artery blockages.

In addition, this inflammation could disturb unstable artery blockages and help trigger a heart attack or stroke.

As evidence for a role of C. pneumoniae in blood vessel disease, researchers have found that people with the artery-clogging disease atherosclerosis have higher levels of antibodies against the bacterium than people without the condition.

In addition, there's evidence that AMD and atherosclerosis share some risk factors, including smoking and high blood pressure. And some researchers suspect that chronic inflammation may contribute to AMD.

During the current study, Dr. Murat V. Kalayoglu of the Massachusetts Eye and Ear Infirmary in Boston and colleagues examined blood samples from 43 visitors to a VA hospital eye clinic, 25 of whom had AMD.

According to the researchers, "patients with (AMD) were more likely to have higher levels of anti-C. pneumoniae antibodies compared with patients without (AMD)."

This association remained after the researchers accounted for patients' age and smoking habits.

In contrast, antibodies against two other bugs the researchers tested appeared no more often in the blood of people with AMD.

Kalayoglu and colleagues suggest that C. pneumoniae may increase the risk of AMD by directly infecting eye tissues or increasing the production of substances that promote inflammation.

They caution, however, that the people included in the study were mostly male and had several other illnesses -- suggesting that the same results may not apply to the general population.

Given the potential role of C. pneumoniae in cardiovascular problems, investigators are currently studying whether bacteria-fighting antibiotics could help treat artery disease.

Kalayoglu and the Massachusetts Eye and Ear Infirmary have a proprietary interest in some of the study data, according to the report.

SOURCE: Archives of Ophthalmology 2003;121:478-482.

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