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K. Yew, C.F. Wildsoet; The Usual Effects of High-Power Negative Lens and Diffusers Show Differential Susceptibility to Disruption to the Diurnal Light Cycle . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1979.
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Purpose: Form deprivation (FD) produces exaggerated axial eye growth and myopia, as do negative lenses. A recent study suggested that these negative lens and FD effects involve different mechanisms. (Kee et al, IOVS 2001;42:575). It seems likely that negative lenses of sufficiently high power may act as FD stimuli just as high-power positive lenses. This issue was investigated, making use of an altered lighting regimen similar to that used by Kee et al. Methods: Three treatments: -5D and -30D lenses, and opaque white diffusers, were monocularly applied to 4-day-old chicks, and worn for 2 weeks (n>6 per group), under two lighting regimens: Normal ,12/12 hr light/dark (N); Interrupted night , 15 min/hour light during the dark phase (IN). Axial dimensions and refractive errors (RE) were measured every 2 days for 2 weeks, by high frequency A-scan ultrasonography and photoretinoscopy respectively, under halothane anesthesia. Data were analyzed by repeated measures ANOVA, followed by Tukey-Kramer post-hoc test. Interocular differences in vitreous chamber depth (VCD), axial length (AL) and RE data in age of 8 and 15 days are shown. Results: The normal (N) -30D and the diffuser groups developed similar amounts of myopia, with the -5D group showing significantly less change (RE, VCD, AL: p<0.001). Compared to N/ -30D group, the IN/ -30 group showed significantly less myopic (p<0.001). The effect the -30D lens was significantly reduced by the IN paradigm which had no significant effect on either the –5 D or diffuser treatment effects. Conclusions: The data suggest that the -30D lenses and diffusers activate different mechanisms; though they showed similar growth effects under normal diurnal conditions, they showed differential sensitivity to light at night. The differential sensitivity of the -5D and -30D lenses further suggests that different mechanisms underlie the responses to low and very high power negative lenses. View OriginalDownload SlideView OriginalDownload Slide
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