Looking for clues about the health of your brain? You might want to pay a visit to your eye doctor. Research increasingly links common eye conditions — glaucoma, age-related macular degeneration, and diabetic retinopathy — to risk for Alzheimer’s and other forms of dementia, Harvard Health Publishing says.

What’s interesting about the study results, says Dr. Albert Hofman, chair of epidemiology at the Harvard T.H. Chan School of Public Health, is that cataracts, another common age-related eye condition, had no apparent connection to dementia risk. This gives scientists an important clue about the cause of dementia and Alzheimer’s disease, he says.

“My view, and one of the possible explanations that the authors present, is that these three eye diseases and Alzheimer’s and dementia have a joined etiology” — that is, a common causative factor. “All are linked to cardiovascular disease,” says Dr. Hofman.

Glaucoma is a condition marked by increased pressure in the eye that can lead to vision loss. It has been linked to high blood pressure, diabetes, and poor blood circulation.

Age-related macular degeneration involves breakdown of the macula, the part of the retina responsible for sharp central vision. It has also been linked to heart disease.

Diabetic retinopathy occurs in people with diabetes when high levels of blood sugar damage blood vessels in the retina. There are strong links between diabetes and cardiovascular problems.

Cataracts — clouding of the lenses of the eyes — are more likely to develop as people age. However, they don’t appear to increase the risk of cardiovascular disease, Alzheimer’s disease, or other types of dementia.

The Adult Changes in Thought study, which began in 1994, included 5,400 dementia-free adults. Participants were followed until they decided to leave the study, died, or developed dementia. Research published in Alzheimer’s & Dementia in 2019 analyzed data drawn from the Adult Changes in Thought study. This time, the researchers focused on 3,800 of those participants, both with and without eye disease at the start of the study. Some 792 of them went on to develop dementia.

Study authors found that people with age-related macular degeneration were 20% more likely to develop dementia compared with people who did not have the eye disease. People with diabetic retinopathy were 44% more likely to develop dementia than those without. People in the study with a recent glaucoma diagnosis — but not participants with established disease — had a 44% higher rate of dementia. It’s not clear why there was a difference between people with new or existing disease.