In vivo optoretinography reveals photoreceptor inner segment ellipsoid as the signal source of the second hyperreflective OCT band of outer retina

Abstract

Purpose : This study is to verify anatomic and physiological correlates of the second (2^nd) hyper-reflective band in optical coherence tomography (OCT) of the outer retina.

Methods : Wild type mice (C57BL/6J) were used for this study. A custom-designed OCT was employed for dynamic near-infrared (NIR) imaging of the retina activated by a visible light flicker stimulation. Stimulus-evoked intrinsic optical signal (IOS) changes at individual retina layers were measured. Spatiotemporal properties of the IOS changes at the photoreceptor outer segment (OS) and inner segment (IS) were investigated. Comparative analysis of structural OCT reflectance and functional IOS change at the photoreceptor intersegment ellipsoid (ISe) was implemented to evaluate the signal source of the 2^nd hyper-reflective OCT band of the outer retina.

Results : Rapid IOS change was observed at the OS right away after the stimulation (Fig. 1), and the early OS-IOS was predominantly distributed at the boundaries connected to the IS and RPE. On contrary, the IS-IOS showed a time delay and a relatively slow time course. The IS-IOS distribution perfectly matched the location of the 2^nd OCT band of the outer retina. High-speed OCT recording disclosed robust OS-IOS within 2 ms, and the IS-IOS showed a time delay of ~ 12 ms relative to the stimulus onset. The average OCT intensity of IS showed a gradual increase after the retinal stimulation, while the intensity of OS remained the same.

Conclusions : The consistency of the spatial distribution of the stimulus-evoked IS-IOS and the 2^nd OCT band supports the ISe, which has abundant mitochondria, as the signal source of the 2^nd OCT band of the outer retina.

This is a 2021 ARVO Annual Meeting abstract.

 

Fig. 1. (A) OCT intensity (A1) and IOS activity (A2) M-scan maps. Three white arrows, from top to bottom along the direction of the inner retina to outer retina, show the top boundary of 2^nd (ISe), the connection between the 2^nd band and OS, and the connection between OS and RPE, respectively. in the intensity M-scan and corresponding IOS M-scan. (B) OCT intensity (B1) and IOS-activity (B2) waveform of the M-scan at different time points. (B3) The early phase of B2. Green arrows show that the IOS change at the boundaries of the OS was stronger than the IOS change in the middle of the OS. The red arrow shows a peak response seen at ~3.5 seconds at the ISe (2^nd) band.