Please mark your calendars for our March Vision Science Research Seminar Series (VSRSS) lecture, which will take place March 22nd, in OPT 1129, at 3:30 pm. Dr. Bill Stell will present a lecture entitled, "Myopia - The Long and Short of It".
William (Bill) Stell, PhD, MD
Department of Cell Biology & Anatomy, Graduate Department of Neuroscience, and Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary.
What is myopia? What causes it? What can be done about it?
This presentation will focus on childhood or “school” myopia, which occurs spontaneously, has no obvious cause, and is largely benign. However, since the prevalence of school myopia is increasingly high in the developed world – up to 90% of young adults in some Asian cities – it is a significant concern. Furthermore, the costs are significant – on the order of $1 billion annually in Canada alone – and still we have no therapy to prevent its onset or retard its progression.
What causes school myopia? Traditional beliefs in genetics or excessive accommodation due to reading and near-work, and more recent theories involving accommodative fatigue and prolonged negative defocus, have been found wanting.
It is difficult to study myopia experimentally in human subjects or primate models. However, we know from non-primate animal studies that myopia is easily inducible by “form-deprivation” or negative defocus; that the regulatory mechanism is mainly intrinsic to the eye and local; that the protective effect of unrestricted vision is additive with time; that many retinal transmitter systems participate in a cascade of signals from retina –> RPE –> choroid –> sclera; and that induced animal myopia, like spontaneous human myopia, is mainly axial (vitreous), not refractive (cornea, lens).
The best evidence suggests that spontaneous human, as well as induced animal myopia, is not inherited but environmental – that it is caused by insufficient exposure to stimuli that promote development of emmetropia. The essential stimuli include light of sufficient intensity as well as specific spatiotemporal properties, which in turn stimulate the release of dopamine, nitric oxide, and other retinal transmitters and neuromodulators. It is still a mystery how these prevent myopia, but the retinal mechanism(s) may be shared with changes in neural circuit function that accompany light-adaptation.