ICAD: Eyes Spot Early Alzheimer's

Posted on Sep 15, 2011 in Health Optimization

By John Gever

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

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, said Shaun Frost, a doctoral student in the e-Health Research Center operated by the Australian national research organization CSIRO.

At a press briefing here 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 what many researchers regard as preclinical Alzheimer’s disease.

He reported early findings from the longitudinal Australian Imaging, Biomarker and Lifestyle study, which is tracking some 500 individuals as they age. Its design is similar to the U.S.-based Alzheimer’s Disease Neuroimaging Initiative.

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 with the Pittsburgh Compound B tracer that binds to beta-amyloid plaque burdens in the brain.

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 plaque burdens, Frost said.

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

These values were significantly higher in the 15 individuals with large burdens relative to the 31 with low plaque levels (P=0.001).

Mean AVRs in the cognitively normal participants with high burdens were similar to those seen in the MCI patients, though lower than in the patients with overt Alzheimer’s disease.

Correlation coefficients for plaque burden and AVR were significant both in MCI patients and in the healthy controls with large plaque burdens, despite the small size of these groups. For the high-burden healthy controls, Frost reported an r2 value of 0.317 (P=0.03).

The correlation was even stronger for the MCI patients (r2=0.721, P=0.03).

Frost said the correlations were driven primarily by differences in retinal venous thickness. Arterial thickness was not significantly different between Alzheimer’s patients and cognitively normal participants.

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

“We have different levels of tests, and they have different levels of expense, difficulty, and complexity [as well as] specificity and sensitivity,” he told MedPage Today. “It’s always a trade-off.”

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 for whom the more elaborate testing would be appropriate.