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M.L. Kisilak, J.J. Hunter, M.C. W. Campbell, E.L. Irving, L. Huang; Chicks Track –30D Goggles and Large Amounts of Astigmatism Are Induced . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1799.
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We wish to understand ocular image quality during normal growth and in eyes with lens–induced myopia. We are interested in the time course of myopia development. Other groups have found incomplete compensation for high powered lenses. We wish to determine if chicks can track –30D lenses over a longer time period.
On the first day post–hatching, 19 chicks were unilaterally fitted with –30D goggles. The other eye acted as a control. On days 0, 2, 4, 7, 9, 10, 14, 15, 16, 17 & 18, goggles were removed for brief periods of time for Hartmann–Shack wavefront measurements (633nm light) and retinoscopy. Unaccommodated Hartmann–Shack images were analyzed for the largest common pupil size between birds on a given day.
The mean ocular refraction (MOR) of the control eyes significantly exponentially decreased with age (p<0.0001). Goggled eyes also showed a significant exponential decay in MOR with age (p<0.0001). By day 18, we have induced 29D of myopia with the –30D goggles. When compared to previously reported results for birds goggled with –15D and –10D lenses, the initial slopes of MOR change with age are not significantly different until after day 4. The exponential time constant for the –15D goggles was smaller (4.8 days) than for the –30D goggles (11.0 days). Control eyes initially had less than 1D of astigmatism and this decreased significantly with age (p<0.0001). On day 0, astigmatism in eyes goggled with –30D lenses was not significantly different from control eyes. However, it significantly increased with age (p<0.024). An ANOVA of the Jackson Cross Cylinders (JCC) showed that while the JCC0’s were not significantly different, JCC45 was significantly larger in goggled compared to control eyes. In goggled eyes, JCC45 exponentially increased with age reaching a plateau at 1.5D. This result was similar to, but more exaggerated than, that observed for the –15D goggles for which JCC45 plateaued around 0.8D.
Given enough time chicks can accurately track –30D goggles. However, large amounts of oblique astigmatism are induced. This is reminiscent of the results of Irving et al (1992) who reported the induction of up to 4D of astigmatism with the application of –10D lenses following 7 days of +10D lens wear. Defocus compensation for –15D goggles occurs faster than for –30D goggles. There appears to be a maximum rate of eye growth regardless of the inducing lens power.
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