The same plaques that build up in the brains of people with Alzheimer's disease also accumulate in the retinas of their eyes, new research suggests.
And this retinal plaque shows up earlier than the cell-damaging stuff in the brain, meaning images of the eyes could lead to earlier diagnosis of the disease, the researchers say.
Abnormal brain deposits of so-called beta-amyloid plaques, which damage cells and interrupt cell-to-cell communications, are considered a hallmark of Alzheimer's. However, because noninvasive brain-imaging technologies can't yet show such changes, the most definitive diagnosis of Alzheimer's disease comes only after an autopsy.
Accumulating research suggests Alzheimer's disease damages the brain well before the outward mental impairment shows up. So if doctors could catch Alzheimer's in this pre-symptomatic stage, they could start early treatments to help at least slow the mental slide.
In the new study, scientists discovered characteristic amyloid plaques in retinas from deceased Alzheimer's disease patients. The plaques were found not only in patients who definitely had the disease, but also in the retinas of some people who were suspected of having early-stage Alzheimer's disease.
Then, the researchers genetically modified a set of mice to develop Alzheimer's. To look for plaques, the team injected a fluorescent compound called curcumin, a natural component of the spice turmeric, into the mice's bloodstream. The compound crossed the blood-retinal barrier and bound to the retinal plaques, making them visible when viewed under a microscope.
Images revealed the retinal plaques in the mice developed at a pre-symptomatic stage, before the plaque appeared in the brain.
The researchers also found a correlation between retinal and brain plaques as the disease progressed in the mouse models. When subjected to an immune system-based therapy that reduces brain plaques, the mice showed reduced amounts of plaque in the retinas to the same extent. That suggests the retina could be a reliable indicator for assessing the brain's response to therapy.
Together, these findings establish the potential of direct retinal beta-amyloid plaque imaging in live subjects as a tool for early on Alzheimer's Disease.