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The possible link between the eyes and Alzheimer’s disease

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Is there a link between the eyes and Alzheimer’s disease?

Eye researchers are investigating whether certain eye or vision tests can detect changes in the brain associated with Alzheimer’s even before the onset of memory problems. This early detection would allow management and therapies to be started early, potentially slowing down progression of dementia. 

How would vision changes detect early Alzheimer’s?

Different parts of the brain are affected as Alzheimer’s develops. Some scientists now believe the vision-related parts of the brain may be affected in early stages of Alzheimer’s and that memory loss may develop only after the disease progresses. 

If this is the case, it is possible that specialized eye or vision tests might be able to detect early signs of Alzheimer's disease, even before memory issues develop.

These findings, in addition to several recent studies showing the potential of blood-based tests for Alzheimer’s disease, may allow doctors to identify and detect those early changes in vision, even before cognitive function is impaired. Although there is no cure for Alzheimer’s, early diagnosis and treatment can help manage symptoms and improve quality of life.

Is there an eye test to check whether someone will develop Alzheimer’s?

No, there is not an eye test that will tell you whether or not you will develop Alzheimer’s. This disease is not caused by a single factor, but results from the interaction of several genes, aging, environment and lifestyle. Because of this, it is difficult to predict someone’s risk of developing the disease. 

A blood test for the APOE-e4 gene is sometimes used to identify people at increased risk of developing Alzheimer’s. This genetic factor is only one consideration among many and is mainly used in clinical research studies. It does not indicate whether someone will go on to develop the disease or whether they already have it.

What is Alzheimer’s disease, and how does it affect vision?

Alzheimer's disease is the most common cause of dementia. Dementia is a general term that describes the presence of cognitive impairments that have reached a level where they interfere with a person’s normal daily activities. 

Dementia is not a specific disease, and it can have a number of different causes. Alzheimer's disease is the most common cause or type of dementia, accounting for the majority of cases. 

Alzheimer’s impacts a person’s memory, behavior and overall ability to think. Symptoms worsen over time, interfering with their daily life activities.

Vision problems can sometimes indicate Alzheimer’s and other forms of dementia. People with the disease may have difficulty with:

  • Face recognition

  • Color perception

  • Depth perception 

They can also have poor vision in low-contrast settings. These problems are common because Alzheimer’s can disrupt the areas of the brain that process vision.

Poor vision, caused by aging or eye disease, can also decrease the stimulation of the brain's visual pathways. This can speed up the decline in cognitive function. Research has shown that there is a higher risk of dementia in people with:

READ MORE: Some eye conditions may increase your risk of dementia

How eye exams may detect early changes in the brain

To date, no single in-office test can determine Alzheimer’s risk. Doctors currently use patient histories, memory tests, and thinking assessments, as well as lab and imaging tests, to diagnose Alzheimer’s. Scientists hope to combine vision and eye tests with these other medical tests to detect changes in the brain at earlier stages in the disease. 

The link between the brain and eyes begins when a baby develops in the mother’s womb. An important part of this connection includes the retina and optic nerve — structures in the eye that process light signals and relay them to the brain. They are formed from brain tissue and are part of the central nervous system.

Since the eyes and brain are closely connected, certain tests may be able to help eye doctors spot changes in the eyes and vision that could indicate early signs of Alzheimer’s. These include:

Optical coherence tomography

Optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) are non-invasive tests that take cross-section images of your retina. Studies have found that changes in the retina are linked to dementia development and progression. The retina is the thin light-sensitive tissue in the back of the eye that changes light into signals for the brain.

Doctors hope to use imaging technology — such as OCT and OCTA — to detect early changes in the retina and blood vessels to identify people in the early stages of Alzheimer’s disease.

Detection of beta-amyloid plaques in the eye

Recent studies have also suggested that the formation of beta-amyloid plaques is one of the primary causes of Alzheimer's disease. These plaques are found in the brain and may also accumulate in the retina and lens of the eye. Testing for the presence of these plaques in the eye may one day help doctors identify the disease early. 

Visual sensitivity testing

Another recent study found that some people who scored lower on certain visual sensitivity tests went on to develop dementia years later. It is theorized that this is because Alzheimer’s may impact the part of the brain that processes vision before it affects memory.

A person’s visual sensitivity is their ability to notice and register an image quickly and correctly. If a person’s visual sensitivity declines, they may struggle with simple visual tasks. These include recognizing objects and faces, reading, and recalling how to get around familiar places. Issues with visual sensitivity may also be early indicators of cognitive decline.

If this type of testing can help identify early signs of Alzheimer’s, it may be possible to start management therapies early and potentially slow down the progression of the disease.  

Contrast sensitivity testing 

This type of testing has also been studied as a potential indicator of the risk of future dementia. Contrast sensitivity is the ability to see contrast in low light. Some research has found that poor contrast sensitivity is linked with amyloid and tau proteins in the brain. These are typically found in the brain in Alzheimer’s.

Tips to improve your eye and brain health

Scientists don't know exactly what causes Alzheimer’s. However, you can make several lifestyle changes to help keep your eyes and brain healthy. You should:

  1. Exercise regularly (at least 150 minutes a week).

  2. Make healthy diet choices, including whole grains, lean protein, and plenty of fruits and vegetables.

  3. Maintain a healthy weight.

  4. Get annual checkups so your doctor can help you manage any health conditions.

  5. Don’t smoke.

  6. Establish a healthy sleep schedule (at least seven hours a night).

  7. Keep your stress level under control.

  8. Keep your mind active by trying new things and taking part in community activities.

  9. Establish and maintain a support network of family and friends.

  10. Schedule annual routine eye exams.

Schedule an eye exam

Researchers continue to look for links between the eyes and the brain, hoping to gain insight into diseases such as Alzheimer’s. Someday, comprehensive eye exams may not only help prevent eye diseases but also help detect early signs of Alzheimer’s. This means management can start early too. 

Meanwhile, scheduling routine eye exams can help keep your eyes healthy and your vision clear. This, in turn, supports a healthy brain.

READ NEXT: AMD and other eye conditions associated with Parkinson’s Disease

Alzheimer’s disease seen through the eye: Ocular alterations and neurodegeneration. International Journal of Molecular Sciences. February 2022.

Visual impairment and risk of dementia in 2 population-based prospective cohorts: UK Biobank and EPIC-Norfolk. The Journals of Gerontology: Series A. April 2022.

How your vision can predict dementia 12 years before it is diagnosed – new study. The Conversation. April 2024.

10 early signs and symptoms of Alzheimer’s and dementia. Alzheimer's Association. Accessed May 2024.

Alzheimer’s blood test performs as well as FDA-approved spinal fluid tests. Washington University School of Medicine in St. Louis. February 2024.

Alzheimer's vs dementia - What is the difference? UCLA David Geffen School of Medicine. June 2023.

Alzheimer's disease genetics fact sheet. National Institute on Aging. March 2023.

Medical tests for diagnosing Alzheimer's. Alzheimer's Association. Accessed May 2024.

What is Alzheimer's disease? Alzheimer's Association. Accessed May 2024.

Eye conditions linked to heightened risk of dementia. BMJ. September 2021.

How is Alzheimer's disease diagnosed? National Institute on Aging. December 2022.

Eye as a window to the brain in central nervous system diseases. Medical Journal of Dr. D.Y. Patil Vidyapeeth. July–August 2019.

What is optical coherence tomography? EyeSmart. American Academy of Ophthalmology. April 2023.

Multimodal coherent imaging of retinal biomarkers of Alzheimer’s disease in a mouse model. Scientific Reports. May 2020.

What happens to the brain in Alzheimer's disease? National Institute on Aging. January 2024.

Role of retinal amyloid-β in neurodegenerative diseases: Overlapping mechanisms and emerging clinical applications. International Journal of Molecular Sciences. February 2021.

Alzheimer's disease amyloid-β pathology in the lens of the eye. Experimental Eye Research. August 2022.

Visual contrast sensitivity is associated with the presence of cerebral amyloid and tau deposition. Brain Communications. February 2020.

10 healthy habits for your brain. Alzheimer’s Association. Accessed May 2024.

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