Macular degeneration may be on the decline

A disabling eye condition that typically strikes in older age may be less common than in the past, suggests a large new study.

Researchers estimate that macular degeneration — which involves damage to the center of the retina, making it difficult to see fine details — affects less than seven percent of the U.S. population aged 40 and older.

A study from the early 1990s had put that number at more than nine percent.

Age-related macular degeneration (AMD) is the leading cause of severe visual impairment in persons over 65 years of age, a group that is growing in numbers because of increased life expectancy,” lead researcher Dr. Ronald Klein of the University of Wisconsin in Madison, told Reuters Health in an e-mail.

To gauge AMD’s current impact, Klein and his colleagues looked at high-resolution pictures of the eyes of 5,553 U.S. adults, aged 40 or older, who participated in the 2005-2008 National Health and Nutrition Examination Survey.

Based on the digital photographs taken of both eyes, the researchers found that 6.5 percent of the participants had signs of some level of AMD, including tiny yellow or white deposits in the retina, pigment changes and deterioration of the retina and surrounding tissue.

Less than one percent had late disease, the advanced stage in which eyesight is more severely affected.

These figures translate to an estimate of 7.2 million people in the U.S. having any degree of AMD and 890,000 of those with advanced disease, report the researchers in the Archives of Ophthalmology.

In contrast, the 1988-1994 Third National Health and Nutrition Examination Survey estimated that 9.4 percent of people in this same age group had some level of AMD.

If that rate was correct and remained unchanged, it would mean some 18 million Americans should be showing signs of AMD today. The new estimates therefore represent a reduction of more than 30 percent in rates of AMD, the authors note.

The reason for the apparent decline is not completely clear.

“It may reflect changes over time in smoking behavior, diet, the use of antioxidant vitamins and zinc, and other factors associated with AMD,” Klein said.

The researchers did find that current rates of the condition increased with age and also differed by race, with African Americans at a lower risk for AMD than whites.

These racial differences, too, are not well understood. However, the authors point to the potential influence of harmful and protective genes that are more or less common in different racial and ethnic groups. Rates of smoking, high blood pressure, exercise and other relevant risk factors also vary in different populations.

A better understanding of why AMD’s frequency is falling in the older population, and doing so differentially, he said, could help inform new prevention strategies that could lead to further reductions.

It may also clarify whether current public health programs designed to increase awareness of the relationships between exposures and the disease are working.

“While AMD prevalence is declining, it is still a common condition in the population,” Klein added.

SOURCE: Archives of Ophthalmology, online January 10, 2011.

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