Non-invasive imaging of the eye could be used to detect early signs of Alzheimer disease, two studies presented at the annual meeting of the American Academy of Ophthalmology in Chicago this week have suggested.

In one study, researchers evaluated the retinal layer thickness in asymptomatic offspring of patients with Alzheimer disease in order to identify early retinal biomarkers for the condition.

The researchers, led by Ygal Rotenstreich, MD, of the Goldschleger Eye Institute at Sheba Medical Center, Tel Aviv, Israel, found that the inner layer of the retina is thinner in people with a family history of Alzheimer disease. In addition, brain scans of those patients showed that the hippocampus, the part of the brain first affected by Alzheimer disease, had already begun to shrink.

“Inner retinal layer thickness is associated with cognitive function and hippocampal volume and may present a novel biomarker for very early detection of Alzheimer disease,” Rotenstreich and colleagues concluded during their presentation of the data

In another study, researchers found that changes in retinal microvasculature as detected by optical coherence tomography angiography (OCT-A) could be an early sign that a patient is progressing toward Alzheimer disease

This study, led by Sharon Fekrat, MD, and Dilraj Singh Grewal, MD, both of Duke University in Durham, found that patients with Alzheimer disease had significantly reduced vessel density and perfusion density compared to patients with mild cognitive impairment (MCI), which suggests these changes could mirror small-vessel cerebrovascular changes and provide clinicians with a non-invasive biomarker for the diagnosis of Alzheimer disease.

The study enrolled eligible patients with Alzheimer disease and MCI aged ≥ 50 years from the Duke Memory Disorders Clinic as well as community-based healthy volunteers also aged ≥ 50 years without subjective memory complaints. Subjects with confounding factors were excluded. Study subjects were imaged with OCT-A and underwent cognitive evaluation with the Mini Mental State Examination.

The researchers analyzed a total of 70 eyes from 39 Alzheimer disease patients, 72 eyes from 37 MCI patients, and 254 eyes from 133 healthy controls (one eye per subject). They found that subjects with Alzheimer disease had decreased vessel density and perfusion density compared with controls (P < .0001) and patients with MCI (P < .01) within both the 3- and 6-mm Early Treatment Diabetic Retinopathy Study (ETDS) subfields.

Patients with Alzheimer disease also had thinner ganglion cell layers compared with the control (P = .002) and MCI (P = .05) groups, while retinal nerve fiber layer thicknesses were similar.

The researchers also found that subjects with MCI had lower perfusion density than controls in both 3-mm (P = .021) and 6-mm (P = .04) subfields.

“Changes in the retinal microvasculature may mirror small-vessel cerebrovascular changes in Alzheimer disease,” the researchers concluded during their presentation. “These parameters may serve as surrogate non-invasive biomarkers for the diagnosis of Alzheimer disease.”

They suggested that future studies are needed to determine whether these kinds of tests will be able to detect the progression of mild cognitive impairment to Alzheimer disease. The availability of such a test would meet a huge unmet need, according to Dr. Fekrat, who pointed out that, with current techniques such as positron emission tomography and spinal taps, it is impossible to screen the huge numbers of people at risk for the condition.