Imaging Light Responses of Foveal Ganglion Cells in the Living Macaque Eye

The fovea dominates primate vision, and its anatomy and perceptual abilities are well studied, but its physiology has been little explored because of limitations of current physiological methods. In this study, we adapted a novel in vivo imaging method, originally developed in mouse retina, to explore foveal physiology in the macaque, which permits the repeated imaging of the functional response of many retinal ganglion cells (RGCs) simultaneously. A genetically encoded calcium indicator, G-CaMP5, was inserted into foveal RGCs, followed by calcium imaging of the displacement of foveal RGCs from their receptive fields, and their intensity-response functions. The spatial offset of foveal RGCs from their cone inputs makes this method especially appropriate for fovea by permitting imaging of RGC responses without excessive light adaptation of cones. This new method will permit the tracking of visual development, progression of retinal disease, or therapeutic interventions, such as insertion of visual prostheses

Functional measurements of retinal phototoxicity using photopigment densitometry and adaptive optics

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2013.Recent advances in high-resolution retinal imaging have led to the discovery of retinal changes caused by light exposures below previously published damage thresholds. These effects were discovered by imaging the retinal pigment epithelium (RPE) with adaptive optics (AO). The changes observed were a transient decrease in RPE autofluorescence (AF reduction) and a disorganization of RPE autofluorescence (RPE disruption). The origins of these changes are not fully understood and their functional consequences have not been previously investigated. Understanding these phenomena is critical for the field of ophthalmic imaging; yet, research to date has been limited to techniques that measure retinal structure and provide little information about function. Photopigment densitometry is a measure of retinal function that can be implemented in a reflectance imaging system and has been used to study the retina for over 60 years. With the advent of near diffraction-limited ophthalmoscopes, which can resolve individual photoreceptors, it is now possible to apply this technique to investigations requiring high spatial resolution. This thesis describes a study that combined high-resolution retinal imaging with photopigment densitometry to investigate the functional consequences of AF reduction and RPE disruption. An adaptive optics scanning laser ophthalmoscope was adapted to measure the density and regeneration rate of the photopigment rhodopsin. Rhodopsin kinetics were measured before and after a series of radiant exposures that caused various degrees of RPE disruption. No measurable change in rhodopsin recovery rate was found at any exposure level and RPE disruption was found to be visible at exposure levels that did not produce a significant reduction in rhodopsin density. However, such a reduction in rhodopsin density was measured at the highest exposure levels. Additionally, a new effect caused by near-infrared (NIR) illumination was discovered: a decrease in infrared autofluorescence (IRAF) measured after exposure to NIR illumination at levels well below recommended limits. Because many retinal imaging systems rely on NIR illumination to avoid potentially harmful exposures at shorter wavelengths, understanding the source of this IRAF reduction is important for both scientific and clinical imaging. This thesis provides the first description of IRAF reduction, as well as an examination of its basic properties

Imaging light responses of foveal ganglion cells in the living macaque eye.

The fovea dominates primate vision, and its anatomy and perceptual abilities are well studied, but its physiology has been little explored because of limitations of current physiological methods. In this study, we adapted a novel in vivo imaging method, originally developed in mouse retina, to explore foveal physiology in the macaque, which permits the repeated imaging of the functional response of many retinal ganglion cells (RGCs) simultaneously. A genetically encoded calcium indicator, G-CaMP5, was inserted into foveal RGCs, followed by calcium imaging of the displacement of foveal RGCs from their receptive fields, and their intensity-response functions. The spatial offset of foveal RGCs from their cone inputs makes this method especially appropriate for fovea by permitting imaging of RGC responses without excessive light adaptation of cones. This new method will permit the tracking of visual development, progression of retinal disease, or therapeutic interventions, such as insertion of visual prostheses

Systems/Circuits Imaging Light Responses of Foveal Ganglion Cells in the

The fovea dominates primate vision, and its anatomy and perceptual abilities are well studied, but its physiology has been little explored because of limitations of current physiological methods. In this study, we adapted a novel in vivo imaging method, originally developed in mouse retina, to explore foveal physiology in the macaque, which permits the repeated imaging of the functional response of many retinal ganglion cells (RGCs) simultaneously. A genetically encoded calcium indicator, G-CaMP5, was inserted into foveal RGCs, followed by calcium imaging of the displacement of foveal RGCs from their receptive fields, and their intensity-response functions. The spatial offset of foveal RGCs from their cone inputs makes this method especially appropriate for fovea by permitting imaging of RGC responses without excessive light adaptation of cones. This new method will permit the tracking of visual development, progression of retinal disease, or therapeutic interventions, such as insertion of visual prostheses. Key words: calcium imaging; in vivo adaptive optics imaging; intrinsic signal imaging; primate fovea; retinal ganglion cell

<it>In-vivo </it>imaging of retinal nerve fiber layer vasculature: imaging histology comparison

Abstract Background Although it has been suggested that alterations of nerve fiber layer vasculature may be involved in the etiology of eye diseases, including glaucoma, it has not been possible to examine this vasculature in-vivo. This report describes a novel imaging method, fluorescence adaptive optics (FAO) scanning laser ophthalmoscopy (SLO), that makes possible for the first time in-vivo imaging of this vasculature in the living macaque, comparing in-vivo and ex-vivo imaging of this vascular bed. Methods We injected sodium fluorescein intravenously in two macaque monkeys while imaging the retina with an FAO-SLO. An argon laser provided the 488 nm excitation source for fluorescence imaging. Reflectance images, obtained simultaneously with near infrared light, permitted precise surface registration of individual frames of the fluorescence imaging. In-vivo imaging was then compared to ex-vivo confocal microscopy of the same tissue. Results Superficial focus (innermost retina) at all depths within the NFL revealed a vasculature with extremely long capillaries, thin walls, little variation in caliber and parallel-linked structure oriented parallel to the NFL axons, typical of the radial peripapillary capillaries (RPCs). However, at a deeper focus beneath the NFL, (toward outer retina) the polygonal pattern typical of the ganglion cell layer (inner) and outer retinal vasculature was seen. These distinguishing patterns were also seen on histological examination of the same retinas. Furthermore, the thickness of the RPC beds and the caliber of individual RPCs determined by imaging closely matched that measured in histological sections. Conclusion This robust method demonstrates in-vivo, high-resolution, confocal imaging of the vasculature through the full thickness of the NFL in the living macaque, in precise agreement with histology. FAO provides a new tool to examine possible primary or secondary role of the nerve fiber layer vasculature in retinal vascular disorders and other eye diseases, such as glaucoma.</p

Intravitreal Injection of AAV2 Transduces Macaque Inner Retina

Intravitreally injected AAV2 transduced inner retinal cells in a restricted region at the macaque fovea. Because macaque and human eyes are similar, the results suggest a need to improve transduction methods in gene therapy for the human inner retina