טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLabin Amichai Moshe
SubjectVision Effects Caused by Retinal Structure
DepartmentDepartment of Physics
Supervisor Dr. Erez Ribak
Full Thesis textFull thesis text - English Version


Abstract

The human vision system is one of the most complex and important biological systems of the human body. The retina is the light sensitive tissue and it converts the incoming light into an electrical signal. The cells in the retina are organized in a seemingly reverse order: the photoreceptors, responsible for the acquisition of incoming light are located at the bottom behind a five layered structure. This reverse structure gave the retina its name: “The inverted retina”, and posed a major optical problem in understanding human vision.

The work described in this thesis presents the effort to confront the inverted retina problem within the framework of optical physics and computational methods. The light propagation processes in the different layers and cells of the retina have been analyzed thoroughly, both from a single cell point of view and as a collective phenomenon. For that purpose I have developed and expanded an algorithm from another field (the Beam Propagation Method) in order to account for the retina’s special structure and data properties. The analysis was concentrated on the role of the glial cells array as a whole. The results had presented a surprising picture: The electromagnetic field coupling into the neighbor glial cell shows that for small incidence angles (up to 50), corresponding to a smaller pupil as in day time (photopic) vision, the amount of leaked energy is low, <3%. More significant coupling occurred for higher incidence angles, when the pupil is wider (night, or scotopic, vision). Another significant result obtained was that for wavelengths in the center of the visible spectrum (0.5-0.6 ?m), a lower coupling was calculated, even for higher arrival angles and conserved an optimal image resolution. These results provide evidence for a natural optical parallel waveguide array, which preserves almost perfectly images obtained under the constraints of the pupil diameter, eye-ball radius and the visible wavelengths. The seemingly illogical inverted structure of the retina, which was thought as contradiction to its optical purpose, was revealed for the first time to have developed as an optimal structure designed for improving the sharpness of images.