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J.J. Hunter, M.L. Kisilak, M.C. W. Campbell, E.L. Irving, L. Huang; The Chick’s View During Normal Growth and Lens Induction of Myopia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2282.
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Purpose: Diffraction, defocus and higher order aberrations all contribute to changes in optical quality of the chick eye during growth. We have previously shown that negative lenses induce changes in higher order aberrations in addition to myopic defocus. Here, we wish to understand overall image quality during growth with and without goggles. Methods: On the first day post–hatching, 16 chicks were unilaterally fitted with –15D goggles. 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). For the largest common pupil size in each eye for each day, point spread functions (PSFs) were calculated for higher order aberrations (HOA) alone and in combination with astigmatism and defocus terms (2nd order and up) for goggled and control chick eyes. In the case of the goggled eyes, the defocus was that of the eye in combination with the goggle. Modelling shows that the goggles contribute negligible aberrations. Metrics describing the quality of the PSF were calculated using Matlab and were averaged across birds as a function of age and condition. Results: The PSFs showed changes as a function of age and goggling. For control birds, Strehl ratios for 2nd order and up increased exponentially (p<0.02) as a function of age. Entropy and second moment analyses on the PSFs, also showed significant improvements in image quality as a function of age. Improvements were also seen in these 3 metrics for HOA alone. When the vision of the chick through the goggles was analysed, decreasing defocus and constant aberrations coupled with increasing pupil size caused the Strehl ratio to remain relatively constant over the growth period. It was significantly lower than in control eyes. However, entropy and second moment analyses indicated a significant improvement in image quality through the goggle as a function of age. In the goggled eyes, an improvement in Strehl ratio and entropy due to HOA was delayed until after day 2. For subsequent days, there was a significant linear fit with image quality remaining below the control eye until after day 10. However, due to residual defocus, the image quality through the goggle, as measured by Strehl ratio, second moment and entropy, remained poorer than in control eyes on day 14. Conclusions: Strehl ratio, second moment and entropy are useful metrics for characterizing the PSFs. Image quality improved during normal growth. Despite large reductions in defocus, image quality in goggled eyes was significantly poorer than in control eyes during growth.
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