Purchase this article with an account.
K. Bunghardt, M. C. W. Campbell, M. L. Kisilak, E. L. Irving; Constant Dark has Differential Effects on Diurnal Rhythms of Refractive Error, Length and Pupil Size in Normal Chicks. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1733.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
In chick, an animal model of refractive error development, normal ocular growth requires a diurnal light cycle. Changes in diurnal rhythms in axial length have been reported in differing lighting conditions. We previously found diurnal rhythms in refractive error and pupil size in normal lighting, which changed in the presence of defocus blur. Here we determine the influence of light on mean ocular refraction (MOR), pupil size and length to the retina, by comparing rhythms in normal light dark cycles and constant dark.
Nine chicks developed naturally with a 14 h light/10 h dark cycle (LD). Eight chicks were raised on the same light/dark cycle until the beginning of day 4 at which time they were placed in constant dark (DD). Components of refractive error were calculated for a constant pupil size from Hartmann Shack measurements on both eyes at 8 time points on days 7 and 8. Light exposure of DD birds was minimized. Lengths were measured using A-scan ultrasound from the cornea to the retinal surface. Linear fits were subtracted from the time dependent data of individual birds. Residual data were then fit with sinusoidal and damped sinusoidal functions.
Periods were not different from 24 hours for pupil size and MOR variation in both groups. In DD eyes, pupil size amplitude of oscillation was significantly smaller with fewer significant sinusoidal fits than in LD eyes and damped sinusoids gave better fits for 10 of 16 DD eyes but not LD eyes. This implies that pupil size has a weak circadian component with an exdogenous, light dependent rhythm. For MOR, only the average phase and acrophase of sinusoidal fits were significantly different between DD and LD eyes. Fewer DD eyes had significant sinusoidal fits but damped sinusoids were better fits in only 2 DD eyes. Thus MOR variation appears to be endogenous and light entrained. For variation of length to the retinal surface, the average period shifted from 14 (LD) to 21hrs in DD birds with a larger standard deviation. This may result from the known phase shift in DD eyes of the rhythm of overall length relative to choroidal rhythm. Although length amplitude of oscillation was significantly smaller in DD eyes, damped sinusoids did not give improved fits.
The remaining but altered circadian rhythms in pupil size, length to the retina and MOR after 3 days in the dark indicate that the rhythms are partially endogenous. Each is differently affected by light, indicating that its influence is complex.
This PDF is available to Subscribers Only