Cellular-scale evaluation of induced photoreceptor degeneration in the living primate eye.

Sarah Walters,William S Fischer,David R Williams,Ethan A Rossi,David A Diloreto,Jennifer Strazzeri,Jennifer J Hunter,William H Merigan,Botond Roska,Christina Schwarz,Robin Sharma,Dasha Nelidova

doi:10.1364/boe.10.000066

Abstract

Progress is needed in developing animal models of photoreceptor degeneration and evaluating such models with longitudinal, noninvasive techniques. We employ confocal scanning laser ophthalmoscopy, optical coherence tomography (OCT) and high-resolution retinal imaging to noninvasively observe the retina of non-human primates with induced photoreceptor degeneration. Photoreceptors were imaged at the single-cell scale in three modalities of adaptive optics scanning light ophthalmoscopy: traditional confocal reflectance, indicative of waveguiding; a non-confocal offset aperture technique visualizing scattered light; and two-photon excited fluorescence, the time-varying signal of which, at 730 nm excitation, is representative of visual cycle function. Assessment of photoreceptor structure and function using these imaging modalities revealed a reduction in retinoid production in cone photoreceptor outer segments while inner segments appeared to remain present. Histology of one retina confirmed loss of outer segments and the presence of intact inner segments. This unique combination of imaging modalities can provide essential, clinically-relevant information on both the structural integrity and function of photoreceptors to not only validate models of photoreceptor degeneration but potentially evaluate the efficacy of future cell and gene-based therapies for vision restoration.

Highlights

Since the advent of the ophthalmoscope in the nineteenth century [1], which provided the first in vivo view of the retina, efforts have continually focused on improving the non-invasive visualization of the many structures and cell classes in the retina
infrared autofluorescence (IRAF) images showed reduced intensity in some areas within the bleb region (Fig. 2(d)); this observation may be confounded by the IRAF reduction that has been observed as a result of AOSLO imaging
It is presumed that cones that are dark in confocal reflectance images, yet show inner segment structure in non-confocal images, are cones that could have compromised outer segment integrity [7]

Summary

Introduction

Since the advent of the ophthalmoscope in the nineteenth century [1], which provided the first in vivo view of the retina, efforts have continually focused on improving the non-invasive visualization of the many structures and cell classes in the retina. Application of optical coherence tomography (OCT) in the living eye afforded a impactful axial resolution increase, allowing individual layers of the retina to be clearly delineated [4,5,6]. These resolution increases revolutionized our ability to visualize many structures in the living retina and our understanding of changes that occur in retinal pathology, both AOSLO and OCT have traditionally relied upon light from an imaging source being directly backscattered to visualize structure. AOSLO imaging methods that use alternative strategies have successfully increased contrast of traditionally hard-to-visualize retinal structures. The intrinsic fluorescence of the retina, whether excited by one-photon [13,14] or two-photon [15,16] techniques, has been exploited to yield increased cellular contrast in several retinal layers

Methods

Results

Conclusion