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S. N. Kiely, J. Kanaris, M. J. Murphy, L. C. Giummarra, A. Mortimer, D. P. Crewther, S. G. Crewther; The Effects of Temporal Luminance Modulation on Compensation to Defocus. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1734.
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Recent research has demonstrated a myopic shift in compensation to positive and negative lens induced defocus (LID) in the presence of low frequency ramped flicker. This study investigated a new method of temporal modulation of the environment via light emitting diodes at varying frequencies under asymmetric Fast ON (perceptual darkening) or Fast OFF (perceptual brightening) light profiles. The aim of this study was to assess the effect of this reversible paradigm at different frequencies on refractive state and ocular growth.
166 chicks were randomly assigned to either Fast ON/Slow OFF or Fast OFF/Slow ON flickering light profiles at a frequency of 1 or 4 Hertz or a standard 12/12 hour light cycle. Chicks were fitted with ±10D lenses or no lens and raised days 5-9 under one of each of the lighting conditions. Biometry (Retinoscopy & A-Scan Ultrasonogrpahy) was performed at day 9 post-hatching and eyes were then prepared for immunohistochemistry.
A significant effect of frequency (particularly 1 Hz) and of lens on compensation to LID was observed. A significant effect of light on refraction was observed as well as a significant interaction effect of light, lens and frequency; however no significant difference between the Fast ON and Fast OFF paradigms occurred for other measures of ocular dimensions. Alterations of growth patterns occurred in the presence of defocus as no lens eyes showed little change.
Low frequency flicker is sufficient to induce a myopic shift in refractive compensation in the presence of LID. The small difference between the effects of Fast OFF and Fast ON suggest that the transient temporally ramped flicker itself rather than the direction of movement of the sawtooth light profile is more important in inducing a refractive response. This highlights the importance of the photoreceptors in coding for changes in luminance as well as driving changes in ionic and fluid movement across the entire retina. The difference in the pattern of growth between the frequencies indicates a time dependency in the ability of the outer retina to convert changes in ion flow into a meaningful growth response.
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