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S. Garg, W.K. Stell; Inconsistent Effect of Stroboscopic Flicker on Form-Deprivation Myopia in Chicks . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1982.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It has been reported that 10 Hz stroboscopic illumination in the dark (Vingrys et al., 1991 ARVO #2618) or added to normal lighting (Schmid & Wildsoet, 1996 ARVO #3134) inhibits development of form-deprivation myopia. Since this may be due to decreasing corneal curvature (S&W;), stroboscopic flicker might be useful for studying visual/neural regulation of corneal growth. The experiments reported here were intended as preliminaries to such studies. Methods: In three separate experiments, White Leghorn cockerels were fitted monocularly with diffusers made from sandpapered blister-wrap; the fellow eye was an uncovered control. During the light phase of a 12:12 hr L:D cycle, groups of 6 chicks were kept in cages ~6 ft below 64 lux "daylight" fluorescent room lights. In each experiment, one group was exposed to room light only, the other to room light plus a Grass PS22 photostimulator 0.2 m above the cage lid, providing ~30 lux/flash (setting 2) at 10 Hz. Experimental conditions (post-hatching day when stimulation began, number of days' light exposure, hours of light/day) were: (1) P7, 4 da, 9 hr/da; (2) P14, 4 da, 11 hr/da; (3) P7, 4 da, 12 hr/da. On the 5th treatment day chicks were exposed to light for 0, 5, or 4.5 hr respectively, then assessed by streak retinoscopy without cycloplegia, and videokeratometry and 30 MHz A-scan ultrasonography under Halothane/N2O/O 2 anesthesia. Significance of interocular differences (difffuser-open) in flicker vs control groups was assessed by an unpaired 2-tailed Student's t-test (InStat). Results: Exp. #1 - The addition of stroboscopic stimulation increased the effect of form-deprivation (FD) on vitreal chamber depth [(goggled-open)=0.387+0.059 mm (strobe), 0.117+0.035 mm (steady), P=0.0007] and increased refractive error and anterior chamber depth, but decreased the corneal radius of curvature and increased choroidal thickening (all P>0.05). Exp. #2 - Stroboscopic stimulation increased the effects of FD on corneal radius of curvature and anterior chamber depth, and decreased the effects on myopic refractive error, vitreal chamber depth, and choroidal thickness (all P>>0.05). Exp. #3 - Stroboscopic stimulation increased the effects of FD on corneal radius of curvature, vitreal chamber depth, and choroidal thickness, but had no effect on refraction or anterior chamber depth (all P>>0.05). Conclusions: Under conditions of our experiments, the addition of stroboscopic stimulation to room light all day for 4+ days inconsistently, and generally insignificantly, affected the induction of myopic refraction or ocular enlargement by form-deprivation in 1- and 2-week old chicks.
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