Investigation of rod outer segment disc shedding in vivo in mouse with optophysiological signals measured by OCT

Abstract

Purpose : To investigate rod outer segment disc shedding in mouse retina in vivo and its effects on light-activated optophysiological signals from the outer retina.

Methods : Dark-adapted Balb/c mice retinas were imaged with a custom SLO/OCT system. SLO delivered monochromatic visible light to trigger the opto-physiological signals, while OCT probed the retinal response. The experiments were performed on individual animals at three different times of the day before and after disc shedding takes place. Mice were dark adapted overnight, and between imaging sessions. Volumetric OCT data were aligned to Bruch’s membrane, and further averaged to extract depth scattering profiles. Time-dependent changes of the depth scattering profiles were extracted, and depth positions of the bands quantified by fitting Gaussians to the hyper-reflecting bands of the photoreceptor layer.

Results : Data from a Balb/c mouse exposed to an SLO scan (488 nm) that bleached ~10% of the rhodopsin at three different times of the day are shown in Fig. 1. SLO reflectance imaging (860 nm) enabled the alignment of retina (top row). The depth scattering OCT profiles reveal similar overall trends at the different times of day (2^nd row). However, detailed analysis (Fig. 1, 3^rd and 4^th rows) revealed a difference in the distance between the ELM and Bruch’s membrane (BrM) before bleaching. Moreover, measurement of the outer segment (OS) length at ~130 s after bleaching shows that an ~ 2.2 μm decrease in OS length between 6:30 am and 11:00 am.

Conclusions : Bleaching-activated optophysiological signals in mouse are a novel tool for investigation of retinal function. Here we demonstrated their value in measuring disc shedding in vivo in mice. Two lines of evidence suggest that the variation in the OS layer thickness with time of day arises from rod disc shedding: first, the major thickness changes occur around the times of day when the most disc shedding has been shown to occur; second, the thickness change is close to that expected for a shedding of about 2 μm/day.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Fig.1 Experimental design(lights on at 7am): (top row) SLO image at different times; (2^nd row) the averaged OCT depth profiles before and after light stimulus; (3^rd and 4^th rows) time course of band positions relative to BrM; gray regions where the band positions are poorly resolved due to weak signals; (bottom row) IS and OS length measured at ~130s after light stimulus.