Optophysiology – Spatially Resolved Optical Probing of Retinal Physiology With Functional Ultrahigh Resolution Optical Coherence Tomography

Abstract

Abstract: : Purpose:To introduce a novel optical method, functional ultrahigh resolution optical coherence tomography (F–UHROCT) for non–invasive spatially resolved probing of retinal physiology. Methods:Retinas from anesthetized rabbits were isolated, positioned in a superfusion chamber under a nylon mesh and maintained in oxygenated buffered Ames medium. After dark adaptation the retinas were stimulated with 200 ms long white light flashes. Electrical recordings (ERG) and infrared OCT tomograms were acquired simultaneously, both being triggered by the light stimulation. Retinal profiles were obtained using a fiber based UHROCT system powered by a compact laser with spectrum centered at 1250 nm and bandwidth of 150 nm. The imaged tissue samples were subsequently fixed and embedded to obtain radial serial semithin sections. Results:As confirmed by comparison with histology, UHROCT tomograms of the living rabbit retina acquired prior to light stimulation (axial x lateral image resolution of 3.5µm x 10µm) clearly visualized all major intraretinal layers. Optical recordings acquired before (baseline), during and after application of the light stimulus allowed extracting time–dependent layer–specific changes of retinal optical properties. Changes, being most pronounced in the inner/outer segment region of photoreceptor and in the inner plexiform layer, correlated well with the time course of the ERG recordings. Control experiments, e.g. dark versus light adaptation as well as pharmaceutical inhibition of photoreceptor function clearly confirmed that the cause of the optical signal change detected by F–UHROCT originates in altered physiological states of the retina elicited by the light stimulus. Conclusions:Functional UHROCT enables unprecedented non–invasive probing of retinal physiology, a possible new alternative and compliment to ERG recordings. In addition to providing a non–contact measurement method, F–UHROCT allows for simultaneous, depth resolved imaging of retinal morphology as well as for detecting optical correlates of physiological changes in retinal sublayers.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • photoreceptors