New research shows an intriguing link between eye health and brain health and could help screen for Alzheimer's disease.
A recent study showed that people who have macular degeneration, glaucoma or diabetic retinopathy are more likely to be diagnosed with Alzheimer's disease than people without these conditions. All three of these conditions are degenerative—meaning they get worse over time. And all three are more common as people age.
The 2018 study, from the University of Washington and the Kaiser Permanente Washington Health Institute, tracked a random sample of people age 65 and older for five years. Participants with one or more of the eye conditions had a 40 to 50 percent greater risk of being diagnosed with Alzheimer’s disease than the others.
Researchers called the difference "not subtle."
The study didn’t look into why people with these eye problems had a higher rate of dementia. It did not prove cause and effect; it showed a connection. There still were many people with the eye conditions who didn't get Alzheimer's disease during the study period.
"From a patient perspective, I don't want people to think, 'Oh, gee, not only am I losing my sight, but I'm also going to develop Alzheimer's.' That's not necessarily the case," said Sunir Garg, MD, a retina specialist at Wills Eye Hospital in Philadelphia.
Dr. Garg said the study highlights how eyes connect to the rest of the body—including the brain—and can be a useful window into general health.
The optic nerve, which connects the eyes to the brain, is essentially brain tissue, he said. The retina, which converts light into vision, is also brain tissue.
Earlier research with mice showed that images of the retina can help identify Alzheimer's disease. So it doesn't surprise Dr. Garg that diseases of the eyes are related to diseases of the brain.
"The more we understand these relationships, the better we can engage with our patients and with our colleagues, and we are able to care of our patients as a whole, and not just their eyes."
One takeaway from the research, Dr. Garg said, is for ophthalmologists to better communicate with a patient’s primary care physician if they diagnose a degenerative eye condition. That communication could help the whole health care team be more alert for signs of dementia. There is no cure for Alzheimer's disease, but some medicines and lifestyle interventions may help people with the disease function well for longer.
The study's results also point out the importance of regular eye exams by an ophthalmologist. These eye conditions usually don’t have symptoms until they're advanced but can be seen by an ophthalmologist during an exam. The American Academy of Ophthalmology recommends a baseline eye exam by an ophthalmologist starting at age 40.