New imaging techniques detect early-stage Alzheimer’s disease
Excerpted from page 53 of the November/December edition of AOA Focus.
Earlier this year, research was published showing that eyes can divulge clear signs of prediabetes. Now, a study in JCI Insight has found that the eyes might house a clue to another life-threatening condition: Alzheimer's disease.
The experiment began with researchers examining the postmortem eyes and brains of confirmed sufferers of Alzheimer's disease. They found significantly greater amyloid β-protein deposits in the retina when compared with the organs of subjects without dementia.
To replicate these results in living subjects, scientists devised a technique that combined curcumin supplementation, to act as a fluorescent contrast agent, and a modified scanning laser ophthalmoscope to detect the now-highlighted protein deposits. A proof-of-concept clinical trial was then conducted on 10 Alzheimer's patients and six healthy subjects. All subjects were given a retinal amyloid index number, which measured the curcumin-induced fluorescence that could be seen. The number of visible amyloid β-protein deposits were counted as well. Compared with the healthy subjects, Alzheimer's patients had a 2.1-fold increase in their retinal amyloid index and about twice the number of deposits.
The researchers say these data suggest that amyloid β-protein accumulation in the retina is an early warning sign of Alzheimer's disease, and this type of noninvasive screening might become a relatively easy way to diagnose the condition early and reliably. However, more study is needed to determine whether this technique can detect pre-symptomatic markers of the disease.
Early Alzheimer's detection
As a diabetes eye care specialist, David Masihdas, O.D., a member of the AOA Evidence-Based Optometry Committee and co-chair of the Guidelines for Diabetic Eye Care Committee, has been connecting the dots between eye health and neurodegenerative disease for the past 15 years. (Alzheimer's is sometimes referred to as "type 3 diabetes," a brain-specific form of the disease.)
Although Alzheimer's disease is incurable, Dr. Masihdas sees value in early detection and the lifestyle changes it allows that might slow the progress.
"The main factor of illness is the inflammatory process," he says. "Free radicals contribute to inflammation, and inflammation will contribute to disease. If we can neutralize a free radical in our bodies, we can reduce the risk of the inflammatory process and reduce the time we suffer from disease. If patients are at risk for Alzheimer's, I can put them on a high dose of antioxidants. Over time, I might see a cessation of degradation."
In his practice, if a patient has a family history of dementia, Dr. Masihdas uses optical coherence tomography to look for retinal defects such as nerve fiber layer thinning and ganglion cell degeneration, which are thought to be telltale signs of Alzheimer's disease. As technology progresses, tests become less invasive and more doctors of optometry become well-versed in diagnosing these types of conditions, he can imagine a sea of change in the annual eye exam.
"Unless you start adding other tests to the comprehensive eye exam, you're going to miss some of the neurodegenerative stuff," says Dr. Masihdas. "So, the extent of the exam will have to eventually become different to actually detect some of these conditions."
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