Impaired Autoregulation of Retinal Blood Flow in Human Glaucoma Subjects Using Laser Speckle Imaging

Abstract

Purpose : Autoregulation of blood flow is the change in blood flow given a challenge or stimulus and may provide an early biomarker for glaucoma. Hyperoxia causes a relative vasoconstriction in healthy controls that may be impaired in glaucoma. We conducted a cross-sectional interventional study to assess the change in retinal blood flow at baseline and under conditions of induced hyperoxia in a cohort of controls, preperimetric glaucoma (PPG) subjects, and early primary open angle glaucoma (POAG) subjects.

Methods : We recruited three groups: control, PPG, and mild POAG. The XyCAM RI, a retinal blood flow imager, was used to measure retinal blood flow at the optic nerve head (ONH) of both eyes at baseline and during induced-hyperoxia (15 L/min for 10 minutes using a non-rebreather). Dynamic blood flow velocity index (BFVi) metrics were calculated for each patient in each state including the mean, peak and dip blood flow, volumetric rise index, and volumetric skew. Paired t-tests were employed to determine the change in these metrics from baseline to induced hyperoxia.

Results : 39 eyes of 20 subjects were recruited, including 21 eyes of 11 subjects with mild POAG, 8 eyes of 4 subjects with PPG, and 10 eyes of 5 control subjects. 70% of the subjects were female and the average age was 61.0 ± 10.9 years. Control subjects showed a decrease in mean BFVi from 7.7 ± 1.9 a.u. at baseline to 6.7 ± 1.6 a.u. in hyperoxia (p = 0.01), along with reductions in peak (8.2 ± 1.6 a.u. baseline to 7.4 ± 1.3 a.u. hyperoxia, p = 0.01) and dip (6.9 ± 1.6 a.u. baseline to 5.9 ± 1.3 a.u. hyperoxia, p = 0.01). The time to rise and fall, volumetric rise index, and volumetric skew also declined with hyperoxia in controls (p < 0.05). PPG subjects had no significant change in BFVi metrics between baseline and hyperoxia. Mild glaucoma subjects showed a significant (p = 0.01) decrease in the peak BFVi from 8.2 ± 1.6 a.u. at baseline to 7.4 ± 1.3 a.u. in hyperoxia.

Conclusions : In this sample, control subjects exhibited a significant decrease in multiple metrics of BFVi whereas PPG subjects had no significant change in BFVi metrics. Early POAG subjects only had a 9.8% decrease in peak BFVi. The reduced vasoreactivity observed here may be related to impaired autoregulation of blood flow in glaucoma subjects. Further recruitment will allow for improved power to compare the magnitude of change in retinal BFVi metrics across subgroups.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.