Retinal and Vascular Findings in Optical Coherence Tomography in Healthy Cognitive Patients With Alzheimer Disease Biomarkers: A Systematic Review and Meta-Analysis

PURPOSE: This systematic review and meta-analysis aimed to explore differences in optical coherence tomography (OCT) findings between cognitively healthy individuals with Alzheimer disease (AD) biomarkers and healthy controls. METHODS: A thorough literature review was conducted on February 6, 2023, in PubMed, Embase, Cochrane Library, LILACS, and DANS EASY Archive. Studies that involved cognitively healthy individuals with AD biomarkers undergoing OCT or OCT angiography were included. The risk of bias was assessed using validated tools. A narrative synthesis and meta-analysis were performed with standardized mean differences and I2 heterogeneity assessments. RESULTS: Seventeen studies comprising 601 participants with positive AD biomarkers and 881 controls were included. The reviewed studies varied in design, with notable findings indicating a reduction in retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) thickness, alongside an increase in inner plexiform layer (IPL) thickness. In addition, OCT angiography revealed reduced vascular density and an enlarged foveal avascular zone-however, variations and inconsistencies in results led to inconclusive outcomes for RNFL and GCL-IPL meta-analyses. CONCLUSION: In summary, cognitively healthy individuals with positive AD biomarkers demonstrated RNFL, GCL thinning, and IPL thickening trends. Future longitudinal studies using standardized methods are critical to validate these OCT changes as potential early indicators for AD.