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J.J. Hunter, M.C. W. Campbell, M.L. Kisilak, E.L. Irving; Predictions of Blur Sensitivity Improvement in the Growing Chick Eye . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3337.
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© ARVO (1962-2015); The Authors (2016-present)
Mean ocular refraction (MOR) decreases with age in the chick eye by an active process known as emmetropization. We wished to investigate the rates of change of the optical dimensions of the chick eye during the first 14 days after hatching. We compare the predictions of passive and active models of growth based on these changes with measured MOR and image quality in order to determine underlying changes in blur sensitivity.
We have previously reported an improvement in optical quality across both constant and growing pupils in the naturally developing chick eye. We refit data provided by Irving and colleagues on age changes in ocular parameters with significant exponential regressions. The rates of change of pupil radius, anterior cornea radius and ocular equatorial diameter were used to give magnification factors for scaled eye models. We also developed active models. In the first, the retinal position maintained a constant defocus blur. In the second, a constant linear blur due to higher–order aberrations was maintained with increasing eye size. Expected variations in MOR and aberrations with age were derived for each model.
The pupil radius rate of increase is not significantly different from those of any of the other anterior ocular parameters. Our models of passive growth increase in size exponentially with age. The passive model predicts a decrease in MOR as the inverse magnification. For constant retinal blur, MOR decreases as the inverse square of the magnification. The rate of decrease of measured MOR was more rapid, implying an exponential improvement in sensitivity to defocus blur with a time constant ranging between 5.6 & 15.2 days. The passive model predicts an increase in aberrations with age. The active model predicts that the root–mean–square wavefront aberration remains constant and the angular blur on the retina, approximated by equivalent blur (Kisilak et. al., 2005), decreases as the inverse magnification. The experimentally observed improvement in equivalent blur in the developing chick eye implies an improvement in sensitivity to aberration blur, significantly smaller than the rate of change in sensitivity to defocus blur.
Measured changes in defocus and aberration blurs are not predicted by passive models of eye growth. These results suggest an improvement in sensitivity to defocus blur with age. The data are consistent with two different mechanisms of defocus and aberration control and two different blur sensitivities.
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