Simultaneous functional imaging the physiological response of neuronal and photoreceptor layers to varying stimuli in living human retina

Abstract

Purpose : Non-invasive functional retinal imaging, especially of neuronal activity in humans, is of tremendous interest. Recently we have shown that the activation of photoreceptor cells (PRCs) and of the ganglion cell layer/inner plexiform layer (GCL/IPL) can be observed simultaneously by phase-sensitive full-field swept-source optical coherence tomography (FF-SS-OCT). The spatial correlation of the response to the two retinal layers was successfully measured. Based on the different physiological function, different reactions of PRCs and the GCL/IPL are expected to varying optical stimulus condition. Especially stimulation with different flicker frequencies should lead to specific reactions in the GCL/IPL.

Methods : FF-SS-OCT is able to detect sub-wavelength morphological changes of different retinal layers by phase evaluation, because high phase stability is reached by parallel illuminating the field-of-view. Using an ultrafast area camera (FASTCAM SA-Z, Photron) volume rates of up to 100 Hz were achieved. For data acquisition wavelengths between 816 and 867 nm were used, which are outside the sensitivity range of the human retina. Phase extraction was improved by using a cross-spectrum algorithm similar to the Knox-Thompson method in astronomic speckle interferometry. Time-modulated visible light with frequencies between 0 and 50 Hz was used to stimulate the retina. The study was approved by the ethic boards of the University of Lübeck.

Results : Using our newly developed cross-spectrum algorithm, a quantitative evaluation of the PRC and GCL/IPL response over 8 seconds was possible. The outer segments of the PRCs followed the stimulation at low frequencies. At higher frequency their response stayed constant. In contrast, a pronounced frequency dependence of the GCL/IPLresponse was observed. GCL/IPL first showed an increasing amplitude of the intrinsic optical signals (IOS), which than leveled of and decreased.

Conclusions : Using FF-SS-OCT with an improved phase evaluation algorithms allows not only to map functional connections between PRC and GCL/IPL, but also to quantify the response in both layers. It is expected to become a valuable tool in diagnostics and basic research.

This is a 2020 ARVO Annual Meeting abstract.