Two studies showed that noninvasive eye scans measuring the thickness of the retina can provide a window into the early signs of Alzheimer’s disease, with the goal of providing a quick, inexpensive test for identifying those at a higher risk.
By using optical coherence tomography angiography, or OCT scans, researchers observed cross sections of patients’ retinas, visualizing the changes seen in its smallest blood vessels. They believe that the deterioration of the retina may mirror the disease’s progression in the brain, conveyed across the optic nerve.
The researchers were able to detect alterations in patients with Alzheimer’s, including those with no family history of the disease, and could distinguish between those with Alzheimer’s and those with only mild cognitive impairment. The two studies were presented at the annual meeting of the American Academy of Ophthalmology in Chicago.
"This project meets a huge unmet need," said Sharon Fekrat, a professor of ophthalmology at Duke University and lead author of one of the studies.
Introduced in 2001, light-based OCT scans can take five to 10 minutes and are also used to guide treatments for diseases of the retina and the optic nerve such as glaucoma, age-related macular degeneration and diabetic eye disease.
“It's not possible for current techniques like a brain scan or lumbar puncture to screen the number of patients with this disease,” Fekrat said.
The Duke research team found that Alzheimer’s patients had lost small blood vessels in the back of the eye, and that a specific layer of their retinas were thinner, after comparing their scans to patients with mild cognitive impairment and healthy participants.
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Meanwhile, researchers at the Sheba Medical Center in Israel examined 400 participants with a family history of the disease but no symptoms, and compared their retina and brain scans to people with no family history.
They found that their inner layer of the retina can be thinner, and that brain scans showed early signs of Alzheimer’s in the hippocampus, which helps govern memory. Having both a thinner retina layer and a shrinking hippocampus were associated with poorer scores on a cognitive function test.
"A brain scan can detect Alzheimer's when the disease is well beyond a treatable phase," said the second study’s lead researcher Ygal Rotenstreich, an ophthalmologist at Sheba’s Goldschleger Eye Institute. In addition, the disease is often diagnosed by memory tests or changes in behavior, which are typically seen in advanced stages.
“We need to detect the disease earlier and introduce treatments earlier,” said Fekrat. Even though there is currently no cure, providing earlier diagnoses will most likely assist future therapies and their development, they said.