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M.L. Kisilak, J.J. Hunter, M.C. W. Campbell, E.L. Iving, L. Huang; Optical Changes in Normal Chick Eyes With Age and in Eyes With Lens–Induced Myopia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1971.
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Purpose: We wish to understand ocular image quality during normal growth and in eyes with lens–induced myopia. Previously, we concluded that the optics of normal and goggled eyes differ for a constant 1.6mm pupil. As the pupil enlarges, blur due to diffraction is expected to decrease while blur due to aberrations will increase, potentially altering image quality with growth. Methods: On the first day post–hatching, 16 chicks were unilaterally fitted with –15D goggles. The other eye acted as a control. On days 0, 2, 4, 7, 9, 10, and 14, goggles were removed for brief periods of time for Hartmann–Shack wavefront measurements (633nm light) and retinoscopy. Hartmann–Shack images were analyzed for the largest common pupil size among birds on a given day and were presumed to be unaccommodated. We defined a new metric of image quality due to aberrations, equivalent blur, as a function of age. Results: For these larger pupils, higher order root mean square wavefront aberrations (horms) in control eyes remained relatively constant with age, while equivalent blur (horms/pupil radius) exponentially decreased (p<0.009). This was driven by changes in both the 3rd and 4th order aberrations. Other measures of image quality due to higher order aberrations also showed a significant improvement with age (p<0.02). Equivalent defocus also decreased significantly. In goggled eyes, equivalent blur decreased exponentially only beyond day 2 (p<0.002), following an initial reduction in defocus. In goggled eyes, horms and equivalent blur values were significantly above those in the control eyes. The time course of equivalent blur from day 2 onwards was not significantly different from control eyes. This effect was due to a significant difference in 3rd order aberrations between goggled and control eyes. Other image quality measures also showed a significant reduction in image quality due to higher order aberrations in goggled eyes (p<0.003) beyond day 2. Conclusions: Image quality due to higher order aberrations improves with age in control eyes, whether or not pupil size is held constant. In goggled eyes, the results are consistent with the reduction of third order aberrations being interrupted by the presence of defocus. Their reduction commences following initial emmetropization of defocus. These results are not consistent with predictions from simple models of scaling of the eyes’ optics with growth or in myopia development, suggestive of visual feedback control.
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