Optophysiology - Optical Probing of Human Photoreceptor Physiology: Challenges and Limitations

Abstract

Purpose:: To evaluate the feasibility of optophysiology for non-invasive depth resolved optical mapping of physiological photoreceptor response of the human retina in vivo using functional optical coherence tomography (fOCT).

Methods:: Time and frequency domain OCT at 1050 nm for high speed (up to 15000 A-scans per second) ultrahigh resolution retinal imaging has been interfaced to an ophthalmic OCT system equipped for simultaneous ERG measurements. The time resolution of the system is up to 70 µs. In vivo functional OCT and simultaneous ERG measurements have been performed in normal human subjects. After dark adaptation the dilated eyes were measured 3 seconds before and 8 seconds after different light stimuli, which varied in intensity, duration and retinal location. Mixed rod and cone responses were obtained from the dark-adapted eye, as well as isolated cone responses using the same stimulus presented against a rod-saturating background. To reduce the influence of eye motions and physiological noise dedicated post processing techniques for signal extraction have been evaluated.

Results:: Non-contact, optical probing of retinal physiological response with ~5 µm axial and ~20 µm transversal resolution to visual stimulation was demonstrated in vivo in normal healthy eyes using functional ultrahigh resolution optical coherence tomography. Our results describe the relationship between electrophysiological and optophysiological responses in humans. Possible explanation of the detected optophysiological signals in the photoreceptors includes hyperpolarizaton or altered metabolic rates that cause changes in the mitochondrial refractive index.

Conclusions:: A functional extension of ultrahigh resolution OCT (UHR OCT) has been developed, that has the potential to establish this technique as an optical analogue to electrophysiology, by detecting depth resolved variations in optical backscattering caused by physiological tissue changes.

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