Optoretinography in wildtype cone photoreceptors of cone-dominant 13-lined ground squirrels and northern tree shrews

Abstract

Purpose : To assess cone function in cone dominant 13-lined ground squirrels (13-LGS) and northern tree shrews (TS) using intensity based optoretinography (iORG).

Methods : The cone mosaic was imaged using AOSLO in 13-LGS (n=4 eyes) and TS (n=4 eyes). Imaging was conducted in November from 13-LGS that had failed to hibernate. For ORG experiments, a 2 μW 30 nm bandwidth stimulus was presented at the peak M cone spectral sensitivity for each species (517nm for 13-LGS and 556nm for TS). Single regions of interest (ROIs) were imaged across 4 trials (2 control & 2 stimulus) of 7 videos each (150 frames), preceded by 3 minutes of dark adaptation. The datasets were processed and registered with custom software (Boston Micromachines, Cambridge, MA.) The iORG signal was extracted from each cone using a method similar to that described in Cooper et al 2020¹. The videos within each trial were registered to each other and a common ROI was extracted across all sessions for a given eye. Cone locations were semi-automatically identified and the change in iORG signal for each cone within a trial was computed as the difference between the average of pre-stimulus frames and peak of 10 frames post-stimulus. The iORG signal from each eye was compared under control versus stimulated conditions.

Results : A total of 4242 cones in 13-LGS eyes, and 4303 cones in TS eyes were analyzed. In 3 of the 4 13-LGS eyes, the variance in stimulus-induced iORG amplitude change was larger than that observed using no stimulus (F=2.723, F=2.640, F=1.137, F=1.085; p<0.0001, p<0,0001, p=0.0115, p=0.11, respectively). All 4 TS eyes showed significantly larger variance in stimulus-induced response compared to no stimulus (F= 4.407, F=2.753, F=4.374, F=2.385; p<0.0001 in all cases). All 8 eyes showed a significant difference in mean iORG amplitude (Wilcoxon-matched paired test), though the difference in average response was lower for 13-LGS eyes (56.9%, 44.2%, 6.3%, 3.1%; mean=27.6%) than for TS eyes (69.8%, 50.6%, 75.7%, 37.0%; mean=58.2%).

Conclusions : These data demonstrate that the iORG can be used to assess cone function in two cone dominant species, with TS cones showing larger responses to stimulation than 13-LGS cones. Future studies during in the 13-LGS active season are needed to assess whether weaker iORG signals observed are due to hibernation-related effects or some other species-specific difference.
1. PMC7771891

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.