Our eyes are the most important sensory organ, as many of our daily actions rely on visual information. Aside from perceiving visual information, our eyes also tell us a lot about our brain, based on how we move them. This is because there is a strong link between eye movement and cognition. As a result, we can measure cognitive changes associated to a specific disease. One key application of eye movement analysis is its use in detecting Alzheimer’s disease.

Overview of Alzheimer’s

Alzheimer’s is a fatal brain disease that destroys brain cells due to a build-up of proteins called tau and beta-amyloid. As brain cells die, the brain begins to shrink, starting from the hippocampus. The hippocampus controls learning and memory, which is why some of the earliest signs of dementia are memory loss, thinking, and decision-making.  Problems with gaze control (the control of the eyes and head) also accompany the earliest signs of dementia. 

The need for early detection

Finding an early diagnosis for Alzheimer’s is important because there are brain changes due to the disease long before symptoms are present. In fact, cognitive impairments appear about 20 years after the disease manifests in the brain. In some cases, Alzheimer’s patients lose their life to the disease without showing any sign of cognitive decline!
In honour of World Alzheimer’s Day, we summarized how researchers are using eye-tracking technology to identify eye movement biomarkers for early diagnosis of Alzheimer’s.

Using eye-tracking for early diagnosis of Alzheimer’s

When it comes to oculomotor testing, saccades and pursuit are the main types of eye movements that researchers analyze. Saccades are rapid eye movements between fixation points and are controlled by the frontal cortex. On the other hand, pursuits describe how our eyes follow a moving stimulus. These tests allow researchers to determine whether an individual has a cognitive impairment associated to a specific region in the brain.

Last year, researchers from Loughborough University found that patients with mild cognitive impairment (MCI) related to memory loss are more likely to develop Alzheimer’s disease. They achieved this by studying how people with Alzheimer’s, amnesic MCI, non-amnesic MCI, and healthy controls performed on anti-saccade tasks. Anti-saccades are a form of oculomotor testing that allows researchers to assess whether someone has a frontal lobe dysfunction. They found that patients who had amnesic MCI had the highest error rates, which were most similar to patients with Alzheimer’s. Their findings were consistent with previous studies which showed that erroneous saccades and increased latency are useful biomarkers for Alzheimer’s disease.

Other studies demonstrated that patients with Alzheimer’s have longer fixation periods compared to healthy controls in visual search tasks and experience difficulty in switching attention and processing stimuli in their field of vision. As a result, this makes it difficult for patients to detect peripheral stimuli in visual search tasks. This can cause patients to overlook important information in their vision.

To elucidate these findings, scientists from the University of College London analyzed the relationship between oculomotor tests and standard cognitive tests in younger individuals with early symptoms of Alzheimer’s. Their results confirmed that eye-tracking metrics are a powerful marker in determining visual cognitive decline. Furthermore, fixation, pro-saccade and smooth pursuit tests were important markers to detect Alzheimer’s.

Future directions

Overall, eye movement analysis in Alzheimer’s disease is a promising road for early diagnosis. By identifying biomarkers for Alzheimer’s, scientists could establish protocols that will help clinicians to not only detect the disease, but also monitor it’s progression. In addition, oculomotor exercises could be used to target and improve cognitive domains that are affected by Alzheimer’s. Lastly, eye-tracking technology has become widely available, and its simplicity in collecting quality data makes it the best candidate for a non-invasive, inexpensive, early diagnostic tool for Alzheimer’s.

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