These 4 Vision Changes Could Be an Early Sign of Alzheimer's, Study Says
If you notice any of them, it may be time for a screening.
Research has long suggested that Alzheimer's disease (AD), the most common form of dementia, can cause changes in eyesight. Yet because Alzheimer's is most commonly associated with cognitive symptoms, the particulars of vision changes in AD patients are less often discussed. A 2017 study published in the journal Nature has shed light on some of the ways that Alzheimer's affects the eyes, outlining four of the most common changes that AD patients experience. Read on to learn which four vision changes they observed through their study—and how they could tip you off to Alzheimer's early in the disease's progression.
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Poor color vision
By comparing the vision and eye structure of 24 people with Alzheimer's and 24 age- and gender-matched people without, the team behind the Nature study identified some surprising ways that AD affects eyesight. Using the Farnsworth and L'Anthony D15 color tests—color arrangement tests commonly used as a measurements of color vision deficiency—they observed that "color vision was significantly affected in AD patients."
They found that the results were "significantly altered in AD patients, corresponding to a worse arrangement of color caps in patients compared to controls. Farnsworth S-Index was also altered in AD subjects suggesting a mild tendency toward protanomaly," a form of red-green color blindness in which the eyes do not detect enough red and are overly sensitive to greens.
Low contrast sensitivity
Contrast sensitivity is your ability to distinguish between fine increments of light versus dark. Tests used to measure contrast sensitivity typically feature letters or images which are darkest at the top of a chart, which then fade toward the bottom where they are at lowest contrast from the background color.
The researchers found that "contrast sensitivity was the most affected parameter in our study." They also noted that these results correlated most directly with structural changes in the eyes.
The team also noted that this particular vision change can be among the first symptoms of Alzheimer's. "Disturbances are present even in the early stages of AD," the researchers wrote.
Reduced visual acuity
Visual acuity is a measurement of one's ability to distinguish shapes at a given distance. Visual acuity tests, such as the Early Treatment Diabetic Retinopathy Study (ETDRS) chart used for this study, probe your ability to recognize smaller and smaller letters on an eye chart. You may recognize this type of test as the most commonly used test in a routine eye exam.
Though research has turned up contrasting data on visual acuity in Alzheimer's patients, several studies, including this 2019 report published in PLOS ONE, have noted that reduced visual acuity is one of several vision changes associated with Alzheimer's disease.
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Structural changes in the eyes
Researchers used non-invasive imaging tests to take structural measurements of people's retinas in both the AD and control groups. "For each scan series of RNFL [retinal nerve fiber layer] measurements, we assessed the average, superior, inferior, temporal, and nasal thickness," the team wrote. They noticed correlations between some of the functional changes in vision among AD patients and the structural changes to their eyes.
"To the best of our knowledge, there are no previously published reports of a correlation between structural changes in the retina of AD patients and alterations observed in contrast sensitivity and color vision," they wrote. However, they found that contrast sensitivity results and color vision in particular "were significantly associated with structural changes, especially macular thickness (not with foveal thickness)."
Further studies are needed to better understand the physiopathology of visual impairment in AD patients. However, their findings suggest that visual function tests and structural changes in the retinas may serve as a sign of "severity and progression in AD."
Speak with your doctor if you notice unexplained changes in your vision—especially if you believe you may be experiencing other symptoms of Alzheimer's.