On Tuesday, October 6, 2015, Dr. Debora Nickla, New England College of Optometry presents “Circadian Rhythms and Emmetropization” as part of the College’s Light InSight Lecture Series.
Abstract: All circadian rhythms are entrained by the cycle of light and dark, so that light at crucial times phase-shifts rhythms to a precise 24-hour period. Light can also have “acute” effects, such as melatonin release, that are also phase-dependent. “Circadian disruption” is defined as a perturbation of the endogenous circadian rhythmicity, and includes both phase and amplitude characteristics of biological processes that exhibit an endogenous, 24 hour rhythm, and encompasses such disturbances as phase shifts and/or the acute effects on an “output” of the clock. In chickens, monkeys, and humans, eyes elongate more during the day than at night, in approximate anti-phase to a rhythm in choroidal thickness. Circadian disruptions in these diurnal rhythms are strongly associated with alterations in ocular growth patterns and refractive development in chicks and monkeys: their phases and/or amplitudes are altered in eyes growing too fast, in response to form deprivation (no image) or minus lens-induced hyperopic defocus, or too slowly, in response to plus lens-induced myopic defocus. This presentation will describe how “time of day” (phase) is crucial in determining the growth responses of eyes to various visual stimuli such as retinal defocus, or normal “in focus” vision at night. I will show that stimuli that cause eye growth stimulation at certain times of day are associated with disruptions in the rhythms in eye length and choroid thickness, while those that do not alter growth are not. Finally, I will present preliminary data showing that the effects of the growth-inhibiting drugs atropine and dopamine agonists are more effective when given at one time than another, arguing that anti-myopia therapies in children should consider time of day as a variable