Light-adapted flicker optoretinograms captured with a spatio-temporal optical coherence-tomography (STOC-T) system

Abstract

For many years electroretinography (ERG) has been used for obtaining information about the retinal physiological function. More recently, a new technique called optoretinography (ORG) has been developed. In one form of this technique, the physiological response of retinal photoreceptors to visible light, resulting in a nanometric photoreceptor optical path length change, is measured by phase-sensitive optical coherence tomography (OCT). To date, a limited number of studies with phase-based ORG measured the retinal response to a flickering light stimulation. In this work, we use a spatio-temporal optical coherence tomography (STOC-T) system to capture optoretinograms with a flickering stimulus over a 1.7 × 0.85 mm2 area of a light-adapted retina located between the fovea and the optic nerve. We show that we can detect statistically-significant differences in the photoreceptor optical path length (OPL) modulation amplitudes in response to different flicker frequencies and with better signal to noise ratios (SNRs) than for a dark-adapted eye. We also demonstrate the ability to spatially map such response to a patterned stimulus with light stripes flickering at different frequencies, highlighting the prospect of characterizing the spatially-resolved temporal-frequency response of the retina with ORG.

Phase-Sensitive Measurements of Depth-Dependent Signal Transduction in the Inner Plexiform Layer

“…It should be noted, however, that only slow changes in optical path length are measured here and that potential high-frequency changes in optical path length cannot be detected with the used volume rate (8 Hz). Furthermore, based on results obtained for photoreceptors by Tomczweski et al ( 22 ), we expect the amplitude of the fast response to be more than one order of magnitude lower and, at these frequencies, it will be difficult to differentiate from heart-beat induced pulsation ( 34 ). Finally, while the observed response is linked to the neuronal activity, the time course of the observed path length changes may differ and show a slower temporal response.…”

“…Additionally, due to the tomographic character of OCT, such variations can be assigned axially and laterally to specific locations with a resolution better than 10 μm, which makes it in principle possible to assign functional changes to single cells. This cellular phase-based functional contrast has so far been demonstrated for the photoreceptor outer segments (OS) with several OCT techniques including Fourier-domain scanning ( 17 – 20 ), line-field ( 21 ), and full-field ( 16 , 22 ) systems. Recently, by using a full-field swept-source OCT (FF-SS-OCT) system, we were able to show functional phase-changes in the inner plexiform layer (IPL) ( 23 ), where the synaptic connections of the bipolar, amacrine, and ganglion cells are located.…”

Chirped frequency flicker optoretinography (fORG) with STOC-T

“…It was conducted following the tenets of the Declaration of Helsinki and the internal regulation of the International Centre for Translational Eye Research (ICTER). To record chirp optoretinograms, we use the STOC-T setup described in detail in our previous works 13,14 . During a single measurement, we record a set of 340 spectral volumes (256 x 256 camera pixels x 512 images), and the data acquisition time is approximately 1.8 s. A visible light source (LED, MNWHL4, Thorlabs) is used as a stimulus, and it is driven with a linearly chirped signal (from 5 Hz to 45 Hz).…”

“…All the presented measurements were performed in the retinal region 5° nasal to the fovea (see Figure 1 for approximate location). Before the start of flicker and data acquisition, the retina was light-adapted, as in our previous work 14 . From the acquired data, we compute the OCT volumes, which are next registered and flattened.…”

Phase-sensitive measurements of depth dependent signal transduction in the inner plexiform layer

“…Additionally, due to the tomographic character of OCT, such variations can be assigned axially and laterally to specific locations with a resolution better than 10 µm, which makes it in principle possible to assign functional changes to single cells. This cellular phase-based functional contrast has so far been demonstrated for the photoreceptor outer segments (OS) with several OCT techniques including Fourier-domain scanning (17)(18)(19)(20), line-field (21), and full-field (16,22) systems. Recently, by using a full-field swept-source OCT (FF-SS-OCT) system, we were able to show functional phase-changes in the inner plexiform layer (IPL) (23), where the synaptic connections of the bipolar, amacrine, and ganglion cells are located.…”