A recent study examining the relationship between functional and structural markers of normal tension glaucoma (NTG) and measures of retinal vasculature integrity identified new biomarkers to supplement those found on OCT-A, which they noted is “largely restricted to quantification of perifoveal vessel density.”
The study included 31 patients with NTG after medication washout. The researchers evaluated their IOP and visual fields and performed both OCT and OCT-A. They measured macular ganglion cell complex, inner macular thickness and circumpapillary RNFL on OCT and perifoveal vessel density, foveal avascular zone perimeter and multispectral fractal dimensions on OCT-A.
Eyes with more severe cases of glaucoma demonstrated a significantly smaller macular ganglion cell complex, thinner circumpapillary RNFL thickness and lower perifoveal vessel density. For every 1% decrease in perifoveal vessel density, the researchers noted a decrease of 0.4 decibels in macular density.
Eyes with lower perifoveal vessel density and patients with systemic hypertension tended to have lower multispectral fractal dimensions, the researchers found. They also noted that lower perifoveal vessel density was significantly associated with a thinner inner macular thickness, smaller macular ganglion cell complex and lower macular density but not with multispectral fractal dimensions.
Multispectral fractal dimensions, a measurement of capillary branching complexity, were of particular interest to the researchers, since changes in this measure have been noted in patients with hypertension and lacunar stroke. They believe it plays a role in the pathogenesis of glaucoma in terms of ocular blood flow.
Though the sample size was small and it focused on NTG rather than advanced glaucoma (to accommodate medication washout), the researchers concluded that their work provides further evidence that glaucoma leads to changes in the retinal vasculature.
“Perifoveal vessel density was significantly reduced in NTG and was diminished in eyes with worse macular density,” the researchers wrote in their paper. “Macular vessel branching complexity was not related to severity of visual field loss but was lower in NTG patients with systemic hypertension.”
Cheng KKW, Tan BL, Brown L, et al. Macular vessel density, branching complexity and foveal avascular zone size in normal-tension glaucoma. Sci Rep. 2021;11:1056.