טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLabin Amichai Moshe
SubjectOptical Analysis of Retinal Glial Cells and their Effect
on Vision
DepartmentDepartment of Physics
Supervisors Dr. Erez Ribak
Professor Emeritus Ido Perlman
Full Thesis textFull thesis text - English Version


Abstract

Light absorption by the photoreceptors of the retina is the first step of the visual process. This absorption of light by the cones and rods is determined by the properties of the visual pigments as well as the spectral, temporal and spatial characteristics of the incident light. There is a ~100 fold difference in sensitivity between rods and cones, which forms the basic mechanism of two parallel visual systems: the cones photopic system, active under well-lit conditions and support color vision, and the rods scotopic system which is active at low light levels and enables night vision. The entire human retinal surface, outside the fovea, is an ensemble of these two photoreceptor arrays.

Another prominent feature of the vertebrate retina is a seemingly ‘inverted’ structure with respect to the light path. The photoreceptors are located at the bottom of the retina, behind five layers of cell bodies and neuronal processes that are expected to cause blurring of the image and reduce the photon flux reaching the photoreceptors to hamper photon absorption, thus their light sensitivity.

It has been recently reported that retinal Müller cells act as light guides serving to transfer light across the retina, from the vitreo-retinal border towards the photoreceptors at the bottom of the retina. However, their optical function and the mechanism in which they serve both cone-mediated vision and rod-mediated vision is poorly understood.

In the study described in this thesis I address this question by using analytical, computational and experimental methods. As a first step, a computational optical model is used to analyse the light guiding properties of Müller cells in the human parafoveal retina, by a direct three-dimensional numerical solution of the Helmholtz equation. The results show that human Müller cells separate white light according to its wavelengths; medium-wavelength light is concentrated onto cones while short- and long-wavelength light leaks to illuminate nearby rods. An independent analytical modal analysis generated similar results and provided insights about the intrinsic optical mechanism. Next, similar theoretical calculations for the guinea pig Müller cells are presented, and compared to imaging experiments in the isolated guinea pig retina. Remarkable agreement is found between the computational - analytical model and the experimental results. These findings are consistent with the hypothesis that the wave guiding properties of Müller cells are wavelength-dependent in a manner that improves cone-mediated vision while minimally impeding rod-mediated vision.