Measuring physiological activity of human photoreceptors in vivo with AO-OCT and AO-SLO-based active eye motion compensation

Abstract

Purpose : Adaptive optics optical coherence tomography (AO-OCT) allows for visualization of individual photoreceptor responses to light stimuli. The physiological response of photoreceptors to light stimulation includes nm-scale structural changes, which can be measured quantitively with phase-resolved OCT. Although phase-resolved OCT can measure these changes in optical path length (OPL), its sensitivity is hindered by eye motion. Active eye motion compensation is implemented allowing measurement of these nm-scale changes at high speeds from targeted retinal locations.

Methods : An AO-OCT system was combined with an adaptive optics scanning laser ophthalmoscope (AOSLO) which was used to identify targets and report the lateral eye motion in real time with low latency at a rate of 960 Hz. These motion traces were sent to a tip-tilt MEMS mirror in the AO-OCT path to steer the beam counter to the eye motion and therefore stabilize it on the retina. The obtained OCT data were compensated for axial bulk motion and the OPL changes of the cone outer segments (OS) were measured over time intervals of 30 ms.

Results : Real-time eye motion compensation enabled acquisition of stable interferograms and consequently high sensitivity to OPL changes in vivo in the human retina. We were able to visualize the elongation of the cone OS in response to light stimulation over a time scale of several seconds.

Conclusions : We demonstrated real time eye motion compensation at a cellular level in the human retina using AOSLO and we measured the physiological activity of cones in response to light stimuli using phase-resolved AO-OCT. This system forms a technology platform that will ultimately allow fast and sensitive measurements of cone function (including mapping of the trichromatic cone mosaic) and the potential for functional measurement of other retinal neurons.

This is a 2020 Imaging in the Eye Conference abstract.

 

Demonstration of active eye tracking on phase sensitive AO-OCT data. a-c) Average Bscans (300 frames averaged). Scale bar is 20 µm. d) AOSLO image of cone mosaic, the yellow line indicates approximate location of OCT Bscan. e-g) Time trace of OCT intensity from the cone OS. h-j) time trace of phase signal from cone OS. k) Time plots of OPL changes due to stimulation (cyan, red, blue, indigo) and control (black).