Optical Coherence Tomography Angiography of Peripapillary Retinal Blood Flow Response to Hyperoxia

Abstract

Purpose: To measure the change in peripapillary retinal blood flow in response to hyperoxia by using optical coherence tomography (OCT) angiography.

Methods: One eye of each healthy human participants (six) was scanned with a commercial high-speed (70 kHz) spectral OCT. Scans were captured twice after 10-minute exposures to normal breathing (baseline) and hyperoxia. Blood flow was detected by the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. Peripapillary retinal blood flow index and vessel density were calculated from en face maximum projections of the retinal layers. The experiment was performed on 2 separate days for each participant. Coefficient of variation (CV) was used to measure within-day repeatability and between-day reproducibility. Paired t-tests were used to compare means of baseline and hyperoxic peripapillary retinal blood flow.

Results: A decrease of 8.87% ± 3.09% (mean ± standard deviation) in flow index and 2.61% ± 1.50% in vessel density was observed under hyperoxia. The within-day repeatability CV of baseline measurements was 5.75% for flow index and 1.67% for vessel density. The between-day reproducibility CV for baseline flow index and vessel density was 11.1% and 1.14%, respectively. The between-day reproducibility of the hyperoxic response was 3.71% and 1.67% for flow index and vessel density, respectively.

Conclusions: Optical coherence tomography angiography with SSADA was able to detect a decrease in peripapillary retinal blood flow in response to hyperoxia. The response was larger than the variability of baseline measurements. The magnitude of an individual's hyperoxic response was highly variable between days. Thus, reliable assessment may require averaging multiple measurements.

Figure 1

The horizontal and vertical scans were registered and merged to obtain one motion- corrected 3D data cube (A). The SSADA algorithm was used to compute flow (B1) and structural (B2) B-scan images. The en face OCT angiogram (C1) is produced by maximum flow projection of the retinal layer and the optic disc. The en face OCT structure (C2) is produced by averaging the signal intensity in each axial scan. The peripapillary region was delineated on the OCT structural image as a 700-μm-wide elliptical annulus extending outward from the optic disc boundary (C2). The peripapillary region of the en face OCT angiogram (D) was used to compute the flow index and vessel density index.

Figure 2

Optic disc en face maximum decorrelation projecton angiograms from a participant with a large response to hyperoxia at baseline (A) and under hyperoxia (B). The images represent a 3 × 3–mm area. The peripapillary region extends from the optic disc (inner green ring) outward for 700 μm (outer green ring). The angiogram after hyperoxia exposure (B) shows a 17% decrease in flow index and a 4% decrease in vessel density.

Figure 3

Line graph displaying the flow index (A) and vessel density (B) average of all peripapillary retinal blood flow measurements from the six participants at baseline and under hyperoxic breathing. Results from the 2 experimental days were averaged.