Contributed Session I: Inner limiting membrane peel extends vivo calcium imaging of ganglion cells (RGC) beyond the fovea in non-human primate.

Abstract

Viral expression of the calcium indicator GCaMP in primate RGCs has enabled optical readout of retinal function at a cellular scale in vivo. To date, functional recording has been limited to transduced RGCs close to the foveal pit. In this study we evaluate ILM peel as a strategy to expand the area of transduced RGCs and allow functional recording beyond the fovea in the living eye. 4 eyes of 3 immunosuppressed macaca fascicularis received a 9-12° ILM peel centered on the fovea, followed by intravitreal injection of GCaMP8s 4-8 weeks post-peel. A 660nm flickering visual stimulus drove RGC GCaMP responses which were recorded with fluorescence adaptive optics scanning laser ophthalmoscopy. In all eyes GCaMP was expressed throughout the peeled area, representing a mean 8-fold enlargement in the area of expression relative to a control eye with no peel. Functional responses were obtained from RGCs at max eccentricities of 11.7 o, 8.0 o, 9.7 o, and 13.7 o and could be classified as ON or OFF types up to the edge of the peel. Mean RGC responses in ILM peeled and control eyes of the same animal were comparable at 3.5 o and longitudinal tracking of individual RGCs showed stable responses up to 6 months post-peel. ILM peel substantially expands the region of primate retina accessible for in vivo GCaMP beyond the foveal ring of RGCs. This presents new opportunities for physiological study of the retina and pre-clinical testing of novel therapies in retinal degeneration models.