Eye health may aid in early diagnosis of Alzheimer’s and dementia, research shows

Some studies make the argument that retinal health can be a prognostic indicator of brain functions, writes Syed Jamal. (Sherman Smith/Kansas Reflector)

The eye has been referred to as a window to the soul. The eye can also be a window to your brain.

The eye is well connected to the brain. The back of your eye, known as the retina, is like a film on which images form before being sent to the brain via the optic nerve.

As such, awareness and maintenance of eye health in older adults, especially those above 65, seems to be critical in light of recent studies suggesting an association between eye health and the risk for developing Alzheimer’s and dementia.

Lately, there have been some persuasive studies that seem to establish the argument that retinal health can be a prognostic indicator of brain functions: the ability to remember names and events, to smell flowers, to recognize faces of loved ones.

A recent study tested retinal and brain tissue samples from 86 people over a 14-year period in normal donors, donors with mild cognitive declines and donors with late-stage Alzheimer’s. It found significantly elevated levels of beta amyloid and a large decline in microglial cells (immune cells of the nervous system) in people with cognitive problems. Microglia help repair injury, maintain neuronal network and do injury repair .

Beta-amyloid is a breakdown product of APP — a membrane protein broken down by enzymes into a variety of products. Beta-amyloid is a marker for both Alzheimer’s and early cognitive decline.

Inflammation in the far region of the retina can also be a predictor of cognitive decline.

Another study uses a new technique called Optical Coherence Tomography (OCT) that reveals information about retinal thickness and predicts the chances of an individual getting mild cognitive impairment and Alzheimer’s disease.

OCT sends infrared beam of light to the tissue of interest and then combines the scattered light with a reference beam. There are interference patterns used to generate scans that give scattering properties of the tissues along the path of the beam. The beam of light is moved along the tissue to produce a succession of scans. The technology is used measure blood flow to the retinal vessels. It can detect reductions in blood flow to the optic papilla or disc.

The optic disc can be seen as a round and yellowish pink structure by the ophthalmoscope, the instrument used to look at the retina, optic nerve and blood vessels supplying the retina. The optic disc is also known as the blind spot because it lacks photoreceptors. (We’re all reminded to check our blind spots while changing lanes on the roads while driving.)

The optic disc is the entry point for the optic nerve as well as the blood vessels that feed the eye. It is most commonly affected by glaucoma , in which the high blood pressure of the fluid pushes on the optic disc. The retinal artery, a branch of the internal carotid artery, and its tributaries supply blood to the retina and other parts of the eye.

A meta-analysis of 11 studies found that Alzheimer’s patients had reduced retinal thickness. In fact, the entire retinal layer is affected in these patients, and this abnormality can’t be solely due to aging. Although the biology of the degenerative processes that lead to structural changes in the brains of Alzheimer’s patients is still being unraveled, some scientist believe that the same degenerative processes also affect the neural layers of the retina.

Limitations of the study included the facts that the sample size wasn’t large enough to allow generalization of results and that seven different types of OCT instruments were used. If you are using different types of instruments, your results won’t be as reliable. I also suspect that seven persons using seven different instruments would introduce more bias into your results.

However, these findings help make a strong case for more studies and alert primary care clinicians to ask patients over age 45 about their eye health. If providers suspecting any problems, they can refer patients to the eye doctor.

These are exciting times for eye research, as the advent of artificial intelligence and big data — combined with advanced imaging techniques — has led to the emergence of oculomics. That’s a field that strives to find ophthalmic biomarkers for other diseases in the body. But that’s another column.

Syed Jamal teachers college-level chemistry, biology and anatomy/physiology and researches phytoremediation and cancer biology. Through its opinion section, Kansas Reflector works to amplify the voices of people who are affected by public policies or excluded from public debate. Find information, including how to submit your own commentary, here .

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