Larger studies are needed to further test visual contrast sensitivity as a potential biomarker for Alzheimer’s and to probe the underlying biological causes of eye changes in people with the disease. Based on these findings, the authors suggest that visual contrast sensitivity may detect very early-stage Alzheimer’s more easily, less invasively and less expensively than current imaging and spinal-tap methods. In all participants, poorer visual contrast sensitivity was significantly associated with amyloid and tau deposits in certain parts of the brain, as well as a lower temporal lobe volume. People with poorer contrast sensitivity took longer to complete the exam than those with normal contrast sensitivity. They measured visual contrast sensitivity in participants, none of whom had serious eye diseases, using frequency doubling technology. The researchers wanted to know if a test for impaired visual contrast sensitivity could detect Alzheimer’s when amyloid and tau abnormalities are just beginning to occur in the brain. Many people with Alzheimer’s disease have visual problems, such as changes in color vision, and past studies have shown retinal and other changes in their eyes. Participants also had brain scans, including magnetic resonance imaging to measure brain volume, positron emission tomography (PET) to measure amyloid accumulation, and, in 46 participants, PET to measure tau accumulation - all of which can show the earliest brain changes of Alzheimer’s, before memory loss and other symptoms are evident. In the first study, researchers from the Indiana Alzheimer Disease Center, Indianapolis, assessed visual contrast sensitivity - the ability to distinguish objects from their background - in 74 older adults, including 31 cognitively healthy individuals and others at various stages of cognitive impairment. Risacher, Ph.D., Indiana School of Medicine

In the other study, published in Neurobiology of Aging, greater dilation of middle-aged adults’ pupils during cognitive testing was linked to higher genetic risk scores for the disease. In one study, published in Brain Communications, a reduced ability in adults age 50 and older to see differences in flickering light was associated with accumulation in the brain of amyloid and tau, two hallmark proteins of Alzheimer’s. The studies suggest that changes in vision and pupil responses may be effective biomarkers for Alzheimer’s in those at greater risk for dementia. Findings in two separate NIA-funded papers focus on different ways to develop noninvasive, less expensive ways to detect very early-stage Alzheimer’s disease in cognitively healthy people.

Pinpoint eyes