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M. C. Campbell, K. Bunghardt, M. L. Kisilak, E. L. Irving; Potential Optical Signals to the Direction of Defocus Change Rapidly Following an Increase in Defocus Blur. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3928.
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© ARVO (1962-2015); The Authors (2016-present)
During emmetropization in animal models, eye growth rates change rapidly in response to imposed optical blur in order to keep the eye in focus. The optical signals to this change are not well understood. We wished to determine whether there were rapid changes in the optical blur on the retina, following an increase in defocus blur, which could enhance optical signals to the direction of defocus.
On the day of hatching, 7 chickens were goggled unilaterally with a -15D goggle. On day 7, 3 hours into the daylight cycle, goggles were removed permanently. Hartmann-Shack measurements were obtained at 8 time points over the next 32 hours, with a minimum of 4 hours between measurements. Hartmann-Shack images were analyzed at each time point for the largest common pupil size across birds and across time points. Components of refractive error and higher-order root mean square aberrations (HORMSA) were calculated. After linear fits were subtracted from the time dependent data of individual birds, residual data were fit with a sinusoidal function.
When the goggle was removed, HORMSA and Jackson cross cylinder components (JCC0 and JCC45) were not significantly different between control and previously goggled (defocused) eyes. Spherical refraction (MOR) changed linearly in 6 of 7 goggled eyes, with a superimposed, significant sinusoidal oscillation in 4 eyes. MOR was fit with a significant sinusoid in 4 control eyes. JCC0 and JCC45 each had significant sinusoidal oscillations in 4 control eyes and in 3 goggled eyes. Five and 3 eyes showed significant sinusoidal variation of HORMSA in control and goggled eyes, respectively. Within hours of goggle removal, optical properties of the treated eyes (in addition to defocus) differed from those of the control eyes. MOR and JCC0 oscillated with significantly larger amplitudes in the defocused eye than in the control eye. MOR and JCC0 amplitudes increased on average by 0.6D and 0.25D, respectively. HORMSA were significantly larger in the defocused eye than the control eye, beginning 4 hours after goggle removal, giving a larger blur on the retina.
Putative optical signals to the direction of defocus which appeared to increase in the defocused eye include increased oscillations in each of MOR and JCC0 and an increase in HORMSA. The rapid changes observed in the optical properties of eyes in response to increased defocus blur may increase directional signals needed to allow a rapid emmetropization response of the eye.
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