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I was intrigued to hear about an experimental test that could detect signs of Alzheimer’s disease by imaging the retina at the back of the eye. Researchers have found, at least in mice, that beta amyloid plaques can be detected in the retina before they gunk up the brain and interfere with memory and other mental functions.

They’ve also found amyloid plaques in the retinas during autopsies of eight Alzheimer’s disease patients and in five living patients who had dementia and other symptoms indicative of the disease—but not in five healthy individuals of the same age who also participated in a 2010 study published in the journal NeuroImage. Dr. Keith L. Black, chair of neurosurgery at Cedars-Sinai Hospital in Los Angeles, who helped conduct the initial studies, told me he and his colleagues are now gearing up for larger studies in humans to see if the imaging technique—which uses curcumin, a compound in the spice turmeric which binds to the amyloid and makes it visible on the imaging test—really does hold promise for the early detection of Alzheimer’s disease.

But using the eyes as a window to detect our overall health is nothing new. Ophthalmologists can detect everything from clogged arteries to diabetes to liver disease when they conduct routine eye exams since the body’s organ systems are all linked. Changes in blood vessels, hormonal systems, and the vast network of nerves all can be seen by examining the internal structures of the eye during an exam.

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In addition to eye diseases like glaucoma and macular degeneration, here are some other health issues that can be revealed during an eye exam.

1. Diabetes. Small blood vessels in the back of the retina that leak blood can be a sign of diabetes. “I’d say about 5 percent of the exams I conduct detect small hemorrhages in the blood vessels in the retina,” said Dr. Sherleen Chen, director of the comprehensive ophthalmology service at Mass Eye and Ear. The problem itself requires treatment to prevent permanent vision loss as well as the underlying conditions causing the hemorrhages.

2. Clogged arteries. A blockage in smaller veins in the retina can occur when larger retinal arteries have been clogged by artery plaque. This shows up as retinal occlusion on an eye exam. Atherosclerosis in the retina can signal clogged arteries elsewhere in the body as well as uncontrolled hypertension, said Chen, and may require a cardiology workup.

3. Allergies. Dark under-eye circles can be a sign of aging, but sometimes they’re the mark of an allergy known as allergic shiners. They result from clogged sinuses that cause blocked blood flow in the nasal passages surrounding the eye and—along with persistent nasal congestion—may be a sign that you need to see an allergy specialist.

4. Liver disease. Yellowing in the whites of the eye can indicate a buildup of bile or jaundice, which could indicate liver disease. Some people, though, make excess bile—and have slightly yellowish eyes—due to mild benign jaundice known as Gilbert’s disease. A routine blood panel can distinguish one from the other.

5. Autoimmune diseases. Bulging protruding eyes are a sign of overactive thyroid, an autoimmune condition called Grave’s disease.

6. Cancer. Sometimes the first signs of cancer metastases can be picked up on an eye exam, said Chen. And lesions on the retina can signal Gardner syndrome, a genetic disorder that causes numerous colon polyps, raising the risk of colon cancer.

7. High cholesterol. A thin white or gray ring around the edge of the eye’s cornea indicates a deposit of fat and cholesterol, which is common in older folks. When found in those under age 65, a blood test is probably warranted to measure cholesterol levels.