OCTA reveals enlarged foveal avascular zone in preclinical Alzheimer disease

This case-control study evaluated the use of OCT angiography (OCTA) to detect preclinical Alzheimer disease (AD).

Study design

Thirty cognitively normal participants were recruited from the Memory and Aging Project of the Charles F. and Joanne Knight Alzheimer Disease Research Center of Washington University in St Louis. Positron emission tomography (PET) imaging for PiB or ¹⁸F-AV-45 compound and cerebral spinal fluid testing for Aβ43 were used to diagnose 14 patients with preclinical Alzheimer disease. OCTA imaging was compared between the patients with preclinical Alzheimer disease and patients negative for the biomarkers.

Outcomes

Of the 27 patients with PET scans, the 7 with positive findings for preclinical AD had larger foveal avascular zones (FAZ, 0.398 vs 0.288 mm²; P<0.001). Twenty-eight patients completed cerebral spinal fluid testing, of which 10 were positive for preclinical AD. Both the outer foveal measurements (180.8 vs. 189.3 µm; P=0.03) and total foveal thickness were thinner in these patients (245.9 vs. 263.0 µm; P=0.03).

Patients with biomarker-positive results from cerebral spinal fluid or PET exhibited larger FAZ (0.364 vs. 0.275 mm²; P=0.002) but thinner inner foveal layers (66.0 vs. 75.4 µm; P=0.03).

Limitations

The main limitation of the study was the relatively small sample size and lack of longitudinal follow-up. There was also no comment on other potential OCT biomarkers, such as ganglion cell layer thickness or retinal capillary density.

Clinical significance

The observed changes in the foveal avascular zone in biomarker-positive cognitively normal individuals is an exciting finding. It suggests that OCTA could potentially be used as an inexpensive and noninvasive tool to detect and monitor patients with preclinical AD. However, longitudinal studies with larger cohorts are necessary to confirm the utility of OCTA as a meaningful biomarker for this debilitating disease.