Visually-evoked changes in human retinal blood flow measured with OCT

Abstract

Purpose : To image visually evoked changes in the human retinal blood flow using a combined OCT+ERG system and determine the dependence of these changes on the stimulus settings (color, duration, intensity and pattern).

Methods : A research-grade SD-OCT system operating in the 800 nm spectral region was combined with a commercial ERG system for synchronous recordings. A custom visual stimulator was integrated with the OCT retinal imaging probe and connected to the ERG system for precise control of the visual stimuli. Functional retinal data was recorded from healthy subjects using either natural or pharmaceutically induced pupil dilation. A series of concentric circular B-scans centered at the optic nerve head (ONH) were acquired. Blood flow was calculated for each retinal blood vessel from the B-scans using a custom MATLAB algorithm. Total recording time was ~10 seconds with 2s pre-stimulus period. The color, intensity, duration and pattern of the visual stimuli were varied to explore dependence of recorded retinal blood flow changes on these parameters.

Results : Fig. 1 shows results from a test with a green (532 nm), 1s long flicker stimulus with ~17.5 µW optical power at the cornea. An enface view of retinal ONH, generated from volumetric OCT image is shown in Fig 1A. Yellow lines show the approximate location of the circular scans. Fig. 1B shows a circular B-scan with cross-sections of major retinal blood vessels at the ONH. Fig. 1C shows stimulus-induced changes in the blood flow of a single retinal blood vessel over a period of 10s. The black and red lines correspond to the measured raw and filtered blood flow data respectively. The green area marks the timing of the visual stimuli. Blood flow shows a max. of ~70% increase relative to the baseline (dark recording). The onset of measured blood flow change has ~0.5 s delay relative to the onset of visual stimulus, while the max. blood flow change occurs almost simultaneously with the switching off of the visual stimulus.

Conclusions : An OCT+ERG technology and image processing algorithms were developed for conducting studies on functional retinal hyperemia. This technology and study approach have great potential for clinical research on neurovascular coupling in the human retina.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.