Unlocking the Potential of Vessel Density and the Foveal Avascular Zone in Optical Coherence Tomography Angiography as Biomarkers in Alzheimer's Disease

Abstract

Alzheimer's disease is the most prevalent form of dementia. Apart from its traditional clinical diagnostic methods, novel ocular imaging biomarkers have the potential to significantly enhance the diagnosis of Alzheimer's disease. Ophthalmologists might be able to play a crucial role in this multidisciplinary approach, aiding in the early detection and diagnosis of Alzheimer's disease through the use of advanced retinal imaging techniques. This systematic literature review the utilization of optical coherence tomography angiography biomarkers, specifically vessel density and the foveal avascular zone, for the diagnosis of Alzheimer's disease. A comprehensive search was performed across multiple academic journal databases, including 11 relevant studies. The selected studies underwent thorough analysis to assess the potential of these optical coherence tomography angiography biomarkers as diagnostic tools for Alzheimer's disease. The assessment of vessel density and the foveal avascular zone have emerged as a promising avenue for identifying and diagnosing Alzheimer's disease. However, it is imperative to acknowledge that further targeted investigations are warranted to address the inherent limitations of the existing body of literature. These limitations encompass various factors such as modest sample sizes, heterogeneity among study populations, disparities in optical coherence tomography angiography imaging protocols, and inconsistencies in the reported findings. In order to establish the clinical utility and robustness of these biomarkers in Alzheimer's disease diagnosis, future research endeavors should strive to overcome these limitations by implementing larger-scale studies characterized by standardized protocols and comprehensive assessments.

Keywords: Alzheimer’s disease; OCT-A; foveal avascular zone; vessel density.

Figure 1

Retinal vessel densities in healthy individuals (a) and in individuals with Alzheimer’s disease (b). (a) In healthy individuals, the retina is supplied by two sets of vessels, the retinal (superficial, and deep plexus) and the choroidal capillaries. The superficial and deep plexuses are interconnected and vascularize the inner retina, while the outer retina is vascularized by the choroidal capillaries. (b) In patients with Alzheimer’s disease, the vessel density in the superficial and deep retinal plexuses is decreased. RPE is atrophic due to age. RGCs: retinal ganglion cells, IPL: inner plexiform layer (bipolar cells, horizontal cells and amacrine cells), ONL: outer nuclear layer (synaptic layer), RPE: retinal pigmented epithelium. Created with BioRender.com.