Vascular Biomarkers from Optical Coherence Tomography Angiography and Glaucoma: Where do we stand in 2021?

Abstract

Biomarkers of ocular blood flow originating from a wide variety of imaging modalities have been associated with glaucoma onset and progression for many decades. Advancements in imaging platforms including optical coherence tomography angiography (OCTA) have provided the ability to quantify vascular changes in glaucoma patients, alongside traditional measures such as retinal nerve fiber layer thickness (RNFL) and optic nerve head (ONH) structure. Current literature on vascular biomarkers, as measured by OCTA, indicates significant relationships between glaucoma and blood flow and capillary density in the retina and ONH. The data currently available, however, is highly diverse and lacks robust longitudinal data on OCTA vascular outcomes and glaucoma progression. Herein we discuss and summarize the relevant current literature on OCTA vascular biomarkers and glaucoma reviewed from December 14, 2020 through March 1, 2021. Associations between OCTA vascular biomarkers and clinical structural and functional glaucoma outcomes as well as differences between glaucoma patients and healthy controls are reviewed and summarized. The available data identifies significantly decreased flow density, flow index, and vessel density in the ONH, peripapillary vascular layer, and macula of glaucoma patients compared to controls. Whole image vessel density is also significantly decreased in glaucoma patients compared to controls and this outcome has been found to correspond to severity of visual field loss. OCTA vascular biomarkers alongside clinical structural outcomes may aid in assessing overall risk for glaucoma in patients.