Hyperoxia-induced reactivity of ocular blood flow is altered in glaucoma

Abstract

Purpose : Hyperoxia induces vasoconstriction of cerebral and retinal blood vessels. Monitoring of ocular blood flow (OBF) by using laser speckle contrast imaging (LSCI) allows us to noninvasively and rapidly characterize this hyperoxia-induced vascular reactivity. We aim to assess the differences in response of OBF to hyperoxia in healthy and glaucoma patients and identify OBF features that may have diagnostic value.

Methods : LSCI data was collected at a frame rate of 82 Hz for 6 seconds, from 3 groups of human eyes: 21 eyes of 11 glaucoma (GL), 7 eyes of 4 preperimetric glaucoma (PPG), and 10 eyes of 5 healthy control (HC) subjects, using the XyCAM RI (Vasoptic Medical, Inc., MD, USA) under baseline (preO₂) and hyperoxia (postO₂) conditions. Hyperoxia was induced by having patients inhale 100% oxygen for 10 minutes after baseline data acquisition. To capture OBF directed towards the peripapillary region, we considered a crescent-shaped region of interest adjacent to the optic disc on its temporal side as shown in Fig. 1. Dynamic metrics like peak blood flow velocity index (BFVi), dip BFVi, volumetric rise index (VRI), volumetric fall index (VFI), pulsatility ratio were obtained from pulsatile OBF waveform. BFVi values were also heartrate-adjusted (HRA) to capture the effect of autoregulation on OBF rather than systemic heartrate-mediated regulation. Group-wise means of the dynamic metrics and ratios of postO₂ to preO₂ metrics were statistically compared using Student t-tests.

Results : As shown in Table 1, dip BFVi was significantly (p < 0.05) lower in PPG and GL eyes than HC eyes at baseline, but its fractional change from baseline to hyperoxia condition was not significantly different. However, postO₂/preO₂ ratio of HRA dip BFVi was significantly (p < 0.05) higher in GL (1.01 ± 0.24) and PPG (1.03 ± 0.14) than in HC (0.87 ± 0.13). These suggest an impairment in autoregulation of OBF associated with glaucoma. Hyperoxia-induced change in pulsatility ratio was similar across groups, though GL and PPG groups showed a larger variance than HC. Hyperoxia-induced fractional reduction in VRI and VFI was also greatest in HC.

Conclusions : Characterizing hyperoxia-induced changes in OBF may provide a novel biomarker for glaucoma. Additional studies with larger sample sizes are needed to validate our preliminary findings.

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