Abstract

Purpose : To develop a combined optical coherence tomography and electroretinography (OCT+ERG) system for imaging visually evoked functional changes (neuronal and blood flow) in the human retina.

Methods : A commercial ERG system was combined with a research-grade SD-OCT system operating in the 800 nm spectral region for synchronous recordings of visually evoked changes in the retinal neuronal function and retinal blood flow (RBF). The OCT system has compact fiberoptics design and offers ~2.5 µm axial resolution and sensitivity of ~99 dB for 1.1 mW optical power incident on the cornea and image acquisition rate of 250,000 A-scans/s. 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 after pupil dilation (1 drop of Tropicamide) and ~20 min dark adaptation. Circular OCT B-scans, centered at the optic nerve head (ONH), were acquired over 10s time with 2s pre-stimulus period. Blood flow was calculated for each retinal blood vessel. The color, intensity, duration and pattern of the visual stimuli were varied to explore dependence of recorded retinal blood flow changes on these parameters. ERG recordings were processed and analyzed using well-established approaches.

Results : Figure A shows a diagram of the OCT+ERG system. Figure B shows changes in the RBF measured from 3 blood vessels (red, green and blue curves) in response to a visual stimulus with the following parameters: green color (532 nm), 1s long flicker stimulus with ~17.5 µW optical power at the cornea. The black curve is a “dark recording” (absence of visual stimulation). All curves show low amplitude oscillations in the measured RBF that correspond to a heat rate of 60 – 75 bpm. A small reduction of the RBF is observed for a short duration, commencing with the stimulus onset, followed by large increase in the RBF that peaks after the stimulus is switched off. The RBF returns to baseline within ~ 1.5 s after the positive peak value. Figure C shows example ERG recordings.

Conclusions : An OCT+ERG technology and image processing algorithms were developed for simultaneous recording of changes in the retinal neuronal function and RBF. 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 Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.