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M. L. Kisilak, M. C. W. Campbell, K. Bunghardt, E. L. Irving; In Chick, Optical Blur and Abnormal Lighting Conditions Increase Components of Astigmatism and the Amplitude of Their Diurnal Oscillation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1720.
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© ARVO (1962-2015); The Authors (2016-present)
In chick, an animal model of refractive error development, there are several potential optical signals to eye growth during emmetropization, including astigmatism. We have previously reported that astigmatism increases in the presence of large optical blur, preferentially in the oblique direction. Here, we report on other changes in the components of astigmatism as a result of a variety of altered visual experiences.
Components of astigmatism were calculated from Hartmann Shack patterns for seven groups of chicks raised with a 14 h light/10 h dark cycle (LD). Four of these were unilaterally goggled with lenses of differing powers and 3 groups developed naturally. Measurements were made at least a day apart on a normal group and 3 groups of birds unilaterally goggled with differing powers. For the 5th group, recovery from myopia induced by a -15D lens removed at the time of the first measurement on day 7 was monitored. At the beginning of day 4, the 6th group (initially naturally developing) was placed in constant darkness (DD) and light exposure was minimized. For these groups and a normal group (LD), measurements were made on both eyes at 8 time points on days 7 and 8. Linear fits were subtracted from the time dependent data of individual birds. Residual data were then fit with sinusoidal and damped sinusoidal functions.
In control eyes, larger values of blur due to either JCC0 or JCC45 decrease with age, and these components oscillate with a diurnal rhythm. The magnitude of JCC components and their amplitudes of oscillation are larger in DD birds, with some evidence of damping. In goggled eyes, blurs due to JCC0 and JCC45 increase with differing time courses for the two components. In eyes recovering from optical blur, the magnitude of JCC components and their diurnal amplitude increased, preferentially in JCC0. Periods remained not different from 24 hours for both JCC components for all eyes except previously goggled eyes, which had a period for JCC45 not significantly different from 12 hours.
Astigmatism increases in the presence of visual blur and in the dark. In addition, the amplitude of its diurnal rhythm increases. Increases in the amplitude of diurnal oscillations may be linked to an increase in the amount of astigmatism. This may indicate that normal visual experience reduces astigmatism and its amplitude of diurnal oscillation.
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