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A. Barutchu, S.G. Crewther, M.J. Murphy, D.P. Crewther; Can Low Frequency Flickering Light Alter Compensatory Processes to Lens Induced Defocus? . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1985.
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Purpose: Recently, it has been suggested that spatial-temporal modulation of environmental contrast and flickering light may play a role in refractive development. Thus, the aim of this study was to investigate effects of flickering light on refractive compensation to monocular lens induced defocus in hatchling chicks. Methods: Eighty chicks were reared from days 4-10 post-hatching with a 12 hour light/dark cycle, with monocular -10 D, 0 D, or +10 D lens or no lens. During the day cycle, chicks were exposed to either constant luminance or flickering light at 1 Hz frequency (330 ms duration with a logarithmic rise and fall). Refractive state and ocular dimensions were measured using retinoscopy and A-scan ultrasonography on day 10. Results: Under constant light conditions, chicks compensated to lens induced defocus in a sign dependent manner (-10 D: -9.72 ± 0.72; 0 D: -.94 ± .95; +10 D: 8.39 ± 0.88). By comparison flickering light induced a myopic shift in all eyes with lenses (p<.01), i.e., -10 D lenses overcompensated to -13.7 ± 3.86, 0 D lenses went to -4.38 ± 4.83 and +10 D lenses to -4.66 ± 6.29. Eyes without lenses went to -1.75, ± 3.46. Ocular dimensions followed the refractive state. Interestingly, flickering light led to an increase in anterior chamber depth for all lens conditions (p<.01). Conclusions: Results suggest that light, flickering at 1 Hz, promotes a myopic shift, ocular growth and anterior chamber elongation. Furthermore, the unexpected refractive and ocular changes to 0D lenses, suggests that slight degradations in image quality coupled with flickering light may have an adverse affect on refractive development. As flickering light also appears to have an impact on the anterior segment of the eye, in order to further our understanding of the interrelationship between refractive development and flickering light, future research needs to consider corneal curvature.
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