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Understanding the Eye-Brain Connection

Alzheimer's losing brain and memory function.

The eyes are often referred to as the windows to the soul. What many don’t realize is that they are also windows into our brain health. Our eyes and brain are deeply connected, and changes in the eyes can often indicate issues in the brain. Here’s why.

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The eyes are wonderfully complex organs, but few realize that they are actually an extension of the brain. As an integral part of the central nervous system (CNS), the eyes are the only part of the body where nervous tissue and blood vessels can be seen directly. The brain and eyes share similar origins in development, similar vasculature or blood vessels, and similar processes that lead to dysfunction.

These similarities are what researchers believe to be the reason why when there’s a breakdown in the brain, it often surfaces in the eye. Though these changes in the retina are good indicators of concern, it’s hard to pinpoint which neurological issue is tied with specific retinal change.

Eye Movements

Along with physical makeup, the eyes and brain share a connection like muscles and other organs where they send communications back and forth. These communications include reporting what the eyes see to the brain and telling the eyes which movements to do and when. Eye movements are controlled by the basal ganglia, a group of brain stem and cerebral cortical structures whose primary function is motor control as well as muscle memory and emotions.

There are 4 basic eye movements:

  • Vestibulo-ocular movements are reflexes that help stabilize the eyes and compensate for head movements. So, when you move your head right, your eyes move left so that what you’re looking at stays in your field of vision.
  • Vergence movements are simultaneous rotations of the eyes to line up the fovea (the most sensitive part of the retina) with an object in view. When you follow your index finger from out in front of you to between your eyes, you use vergence movements.
  • Smooth pursuit movements are what we think of when it comes to eye movements. These are the slow tracking motions that help us stay focused on a moving object.
  • Saccades are the final and, arguably, most complex of eye movements. These movements tell us the most about the brain and are categorized as rapid eye movements that help us change our fixation. These movements are both voluntary and involuntary; they can be large and small movements (scanning a room vs. reading); and they include the movements that occur during the REM sleep cycle.

What Affects Both Eye and Brain Function?

Because of the deep, biological connection between the eyes and brain, there are several factors that impact both. These factors range from illness to simply aging, but they can all be seen in the way eyes and brain function. For example, changes in eye movements are indicative of both aging and cognitive deterioration.

Aging

Of course, our bodies change as we age, and this includes our brains. Some of the more common changes include memory and attention, which tend to become worse with age. As mentioned, eye movements also change with age, with saccades movements changing the most significantly. These movements become smaller, less frequent, and more difficult to initiate as the years go on.

In one study, eye movement analysis demonstrated younger people focus on individual facial features, while older people tend to process the face as a whole. This was relative to task performance, as well, and the older participants performed better when they employed the same strategy as the younger ones. This links the ability of the eyes to function with the ability of the brain to determine what it’s looking at and what to do.

Cognitive Deterioration

Because of the biological connection between the brain and eyes, there are many neurological concerns that present in the eyes/optic nerve, providing direct identification. Concerns like multiple sclerosis, Alzheimer’s, Parkinson’s, and stroke all appear in the eyes as well as the brain. Consequently, if there’s pressure buildup in the brain from a brain tumor or similar issue, there is swelling that can be seen in the optic nerve, notifying health professionals of the neurological concern.

This conclusion reiterates the importance of routine eye and ophthalmic exams. As a more extreme example, an article titled “Eye as a window for glioblastoma multiforme-case reports” recorded 3 cases of glioblastoma patients that presented with optic disc swelling. This prompted the ophthalmologists to order brain scans, revealing the cancerous brain tumor. It’s important to note that there were no ocular symptoms reported at the time, again stressing the importance of maintaining routine eye care.

 

 

Sources

  1. https://dana.org/article/the-eyes-are-windows-into-the-brain/#:~:text=The%20eyes%20are%20a%20window,memory%2C%20and%20decision%2Dmaking.
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4322726/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543080/
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6528662/
  5. https://www.iflscience.com/health-and-medicine/eye-our-window-brain-and-there-s-lot-we-can-tell-it/
  6. https://www.researchgate.net/publication/334298776_Eye_as_a_window_to_the_brain_in_central_nervous_system_diseases
  7. https://www.sciencedaily.com/releases/2016/07/160727103432.htm

One thought on “Understanding the Eye-Brain Connection

  1. That’s really cool that you can tell if someone is at risk for Alzheimer’s from an eye exam. I would want to make sure that I knew if that was a possibility. That way you could be prepared for it and I feel like it wouldn’t be quite as shocking.

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