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The Eyes May Show Early Alzheimer's

- Monday, August 15, 2011

The eyes are a window into the brain for many disorders, and Alzheimer's disease may be no exception.

In a pilot study, retinal scans to measure blood vessel thickness at the back of the eye showed strong correlations with the level of beta-amyloid deposits in the brain.

At a press briefing in advance of his formal presentation at the International Conference on Alzheimer's Disease (ICAD), Frost said the retinal scans could be a relatively easy and cheap way to screen people for preclinical Alzheimer's disease.

He reported early findings from a study which is tracking some 500 individuals as they age.

Some earlier studies have linked retinal abnormalities to cognitive dysfunction. For example, in a large 2009 study, patients with mild cognitive impairment were reported to be at almost 40% higher risk for age-related macular degeneration after controlling for other risk factors.

In the current study, participants were classified as having normal cognition, mild cognitive impairment (MCI), or Alzheimer's disease according to clinical assessments. A total of 146 were included in the current study: 110 healthy, 13 with MCI, and 13 with Alzheimer's disease.

The retinal scans measured central retinal arterial and venous diameters, with the arterio-venular ratio (AVR) as the primary indicator of possible Alzheimer's pathology.

Study participants also underwent PET scans.

Frost reported correlations between the retinal and PET scan data for 46 of the healthy controls, nine MCI patients, and three with Alzheimer's disease.

Preliminary findings from the study indicated that AVR values correlated significantly with amount of plaque build-up.

Perhaps the most important finding was that, in the cognitively normal individuals, the AVR values differed according to plaque build-up.

These values were significantly higher in the 15 individuals with large burdens relative to the 31 with low plaque levels.

Frost said the correlations were driven primarily by differences in retinal venous thickness.

William Klunk, of the University of Pittsburgh, who moderated the press briefing, said a test like this would probably be most useful as a preliminary screen.

Right now, the most accurate tests for detecting early or preclinical Alzheimer's disease require cerebrospinal fluid samples and PET scans. But these may be too expensive and invasive for broad screening of individuals with nonspecific symptoms or who only have risk factors for the disease.

"This test [the retinal scan] is on the end of easier to accomplish, completely noninvasive, and relatively inexpensive," he said.

However, "it's not going to have a perfect correlation to pathology in the brain," he added, although it could be very useful for identifying individuals who would possibly need more elaborate testing.

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