Elderly individuals with cognitive impairment may be more likely than those with intact cognitive function to have early age-related macular degeneration (AMD), according to findings from the Cardiovascular Health Study published in the Archives of Ophthalmology.

"Alzheimer's disease and AMD have long been hypothesized to share a common pathogenesis based on several lines of evidence," Dr. Tien Yin Wong of the University of Melbourne, Australia, and co-authors write. These include similar tissue changes, common circulatory risk factors, and perhaps a shared genetic profile. Clinical and epidemiological studies of this association are lacking, however.

To further investigate, Wong's group conducted a "large, ethnically diverse, population-based" study that included 2008 subjects, ages 69 to 97 years, from four counties in the U.S. All of the participants underwent retinal photography and assessment of cognitive function between 1997 and 1998.

The average scores on the Digit Symbol Substitution Test (DSST), a simple but sensitive test to evaluate cognitive function, were lower among the 324 subjects diagnosed with AMD than those without AMD, Wong and colleagues report.

After controlling for sociodemographics, risk factors, and apolipoprotein E genotype (gene associated with Alzheimer's disease), the subjects who scored in the bottom quarter of the DSST were twice as likely to have early AMD.

However, a diagnosis of dementia or Alzheimer's disease, according to detailed neuropsychological testing, was not significantly associated with early AMD.

Still, the authors note, in analyses excluding the 135 subjects with dementia, the association between DSST score and early AMD remained statistically significant.

These findings, along with other data, "provide further support that AMD and cognitive impairment may share similar complex pathogenesis and risk factors," the researchers conclude.