According to a new study, the first signs of Alzheimer's disease may appear in your eyes.

The eyes are more than a window to the soul, they are a reflection of a person's cognitive health. Research has been exploring how the eye may help in diagnosing Alzheimer's disease before symptoms begin. A recent study examined donated tissue from the retina and brains of 86 people with different degrees of mental decline. The study is the first to provide in-depth analyses of the protein profiles and molecular, cellular, and structural effects of Alzheimer's disease in the human retina and how they correspond with changes in the brain and cognitive function. This study found that changes in the retina correlated with changes in parts of the brain called the entorhinal and temporal cortices, a hub for memory, navigation and the perception of time. The study collected retinal and brain tissue samples over 14 years from 86 human donors with Alzheimer's disease and mild cognitive impairment. Researchers compared samples from donors with normal cognitive function to those with mild cognitive impairment and those with later-stage Alzheimer's disease. They found significant increases in beta-amyloid, a key marker of Alzheimer's disease, in people with both Alzheimer's and early cognitive decline. Microglial cells declined by 80% in those with cognitive issues, and markers of inflammation were also found. Tissue atrophy and inflammation in cells in the far periphery of the retina were most predictive of cognitive status. These findings may eventually lead to the development of imaging techniques that allow us to diagnose Alzheimer's disease earlier and more accurately.