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Melanie Campbell, Kaitlin Bunghardt, Marsha Kisilak, Elizabeth Irving; Comparing Rates of Emmetropization and Diurnal Rhythms Before and After Goggle Removal in Chick. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5177. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We have shown, in chicks recovering from either negative or positive lenses, that the rapid reduction in spherical refractive error is due in part to an increase in the amplitude of its sinusoidal variation. Here we investigate whether this alteration occurs before or after goggle removal. Short term changes in mean ocular refraction (MOR) are measured immediately before and after goggle removal following 6 days of emmetropization to lens induced myopia.
Twelve birds, unilaterally treated with a -15D goggle on the day of hatching, were raised on a 14h/10h light dark cycle. On day 6, at 8:30 am, 4 hourly Hartmann Shack and A scan ultrasound axial length measurements began, ending on day 9. The goggle was permanently removed after the day 7 830am measurement. MOR was analyzed for the largest common pupil and slopes were taken over the first 4 hours on days 6 and 7. Linear variations were subtracted and residual sinusoidal variations were fitted before and after goggle removal. Comparisons were made to previously presented results of control birds. Paired t tests were used, p≤0.05 for significance.
On day 6, sinusoidal amplitudes and periods of control and goggled eyes did not differ significantly and goggled eyes were not different from eyes of control birds on day 7. Acrophases on day 6 for control eyes were significantly clustered, and significantly different from those of goggled eyes that were not significantly clustered (Rayleigh test). On day 6, average MOR slopes for each of goggled and control eyes did not differ from 0 or from each other. Average initial slopes for day 7 (-0.08 D/Hr and 0.84 D/Hr for control and treated eyes) were significantly different from each other. Values for the control eyes did not differ from 0 or from day 6. The immediate rate of emmetropization of the previously goggled eye differs significantly from that prior to goggle removal.
After 6 days of unilateral emmetropization to a -15D goggle, the rate of change of MOR approached 0 in both eyes. The amplitude, period and phase of the diurnal variation of MOR in the goggled eye did not differ from the control eye. The timing of the first peak of the diurnal variation differed. On goggle removal, within the first four hours, the direction of emmetropization changed significantly. Sinusoidal changes appear to occur following goggle removal.
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