Retinal vascular characteristics may help clinicians detect glaucoma, according to two recently published studies in the Journal of Glaucoma.1,2 Elevated IOP is considered the main culprit behind optic nerve head damage, but research on POAG patients without elevated pressures has led to speculation on alternative pathophysiologic mechanisms.
The vascular theory of glaucoma considers optic neuropathy to be a result of insufficient blood supply caused by vascular dysregulation. The first study demonstrated correlations of vessel density and spacing between large vessels with total retinal blood flow. The study included 24 patients with POAG and 19 controls, measured on OCT-A, Doppler OCT and automated perimetry. The team’s findings of reduced vessel density in POAG eyes were in agreement with recent studies that demonstrated lower flow index and vessel density in glaucomatous eyes.
“Although the causative relationship between vessel density and total retinal blood flow isn’t known, the following speculation may be considered,” the researchers wrote in their paper. “Retinal capillary non-perfusion (reduced vessel density) due to glaucoma vasculopathy can lead to inadequate tissue oxygenation and cellular dysfunction or death. Consequently, tissue oxygen demand is reduced, resulting in an autoregulatory reduction in oxygen supply (reduced total retinal blood flow).”
Similarly, the second study postulated a relationship between vascular health and glaucoma progression. The researchers used OCT-A to measure macular superficial capillary plexus (SCP) and projection-resolved deep capillary plexus (DCP) vessel densities. They compared the diagnostic accuracy of vessel densities with ganglion cell complex thickness in pre-perimetric glaucoma suspects (26 eyes), glaucoma eyes (161 eyes) and healthy controls, and they found that SCP vessel densities had a better diagnostic accuracy than DCP vessel densities.
“SCP vessel density was consistently lower than DCP vessel density in all eyes, notably in glaucomatous eyes,” the researchers noted in their paper. “This finding is expected because the RNFL and ganglion cell layer, which are structurally damaged in glaucomatous eyes, receive blood from the SCP. In addition, the SCP is believed to have more vascular changes (i.e., blood flow regulation) than the DCP in glaucoma.”
They concluded that DCP vessel density measurements “may not provide critical diagnostic information for glaucoma management as these measurements performed relatively poorly at differentiating between healthy, glaucoma suspect and glaucoma eyes compared with SCP vessel density and ganglion cell complex.”
1. Cano J, Rahimi M, Xu BY, et al. Relationship between macular vessel density and total retinal blood flow in primary open-angle glaucoma. J Glaucoma. 2021. [Epub ahead of print].
2. Nevin E, Manalastas PIC, Zangwill LM, et al. Superficial and deep macula vessel density in health, glaucoma suspect, and glaucoma eyes. J Glaucoma. 2021. [Epub ahead of print].