Advisory Committee Chair
Kent T Keyser
Advisory Committee Members
Paul D Gamlin
Timothy W Kraft
Joel Pokorny
Rosalyn E Weller
Document Type
Dissertation
Date of Award
2008
Degree Name by School
Doctor of Philosophy (PhD) School of Optometry
Abstract
Historically, the characteristics of the light-evoked neural signals driving the human pupillary light reflex (PLR) have been poorly understood. It was assumed that these light signals originated exclusively from rod and cone photoreceptors, although the measured spectral sensitivity and response dynamics of the PLR were difficult to reconcile with the known properties of rods and cones. Recently, a novel photoreceptive cell class has been discovered in the mammalian retina. These unique retinal ganglion cells not only receive rod and cone inputs, but also express the photopigment melanopsin, and exhibit intrinsic photoresponses independent of rod and cone inputs. These intrinsically photosensitive retinal ganglion cells (ipRGCs) have been shown to project to the pretectum, the retinorecipient area of the brain responsible for the PLR. Initial reports have suggested that ipRGCs contribute significantly to the PLR of rodents, but studies relating this unique cell class to primate PLR are lacking. We have therefore examined the role of the ipRGCs in the primate PLR. Our results show that ipRGCs contribute significantly to the human and non-human primate PLR. We demonstrate that the macaque PLR is still present after the pharmalogical blockade of rod and cone photoreceptors, and that the residual PLR is driven exclusively by the melanopsin-mediated intrinsic response of ipRGCs. We also report that the intrinsic response exclusively drives sustained post stimulus pupilloconstriction in both humans and non- iii human primates. We extended our examination of the human PLR to determine the relative contribution of rod, cone and the intrinsic photoresponses to pupillary constriction during steady-state lighting. We established that the intrinsic response of ipRGCs contributes significantly to the maintenance of half maximal pupilloconstriction in response to light stimuli of 30 seconds or longer, even at low photopic irradiances. Furthermore, we show that the intrinsic response contributes to three- quarter maximal pupilloconstriction in response to light stimuli as short as 2 seconds. We also demonstrate that, although cone photoresponses driving pupilloconstriction quickly adapt, rod photoresponses contribute to the maintenance of pupilloconstriction in response to steady-state light stimuli at both photopic and scotopic irradiances.
Recommended Citation
McDougal, David H., "The Role of Melanopsin Containing Retinal Ganglion Cells in the Pupillary Responses of Human and Non-Human Primates" (2008). All ETDs from UAB. 273.
https://digitalcommons.library.uab.edu/etd-collection/273