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Published on: January 12, 2015
Diurnal illumination patterns affect the development of the chick eye
1Section of Neurobiology and Behavior, Cornell University, 14853, Ithaca, NY, USA. tl24@cornell.edu
Insights
Young chicks need at least 4 hours of uninterrupted darkness daily to prevent abnormal eye development caused by constant light (CL) effects. This daily dark period must occur at the same time to ensure normal ocular development.
Area of Science:
- Ophthalmology
- Developmental Biology
- Chronobiology
Background:
- Continuous light (CL) exposure disrupts normal ocular development in young chicks.
- CL effects include corneal flattening, shallow anterior chambers, and progressive hyperopia.
Purpose of the Study:
- Determine the minimum diurnal light cycle requirements to prevent CL effects.
- Investigate the role of the dark period duration and timing in preventing ocular developmental abnormalities.
Main Methods:
- Chicks were reared under various light-dark cycles, including constant light and cycles with 1 to 12 hours of darkness.
- The duration and timing of a 4-hour dark period were manipulated to assess their impact on CL effects.
- Fourier analysis was used to correlate illumination patterns with observed ocular changes.
Main Results:
- CL effects were prevented when the daily dark period was 4 hours or longer.
- Below 4 hours of darkness, CL effects were dose-dependent and inversely correlated with the 1 cycle per day (CPD) illumination amplitude.
- Complete suppression of CL effects required a single, continuous 4-hour dark period administered daily at the same time.
Conclusions:
- A minimum of 4 hours of uninterrupted darkness per day, provided consistently, is essential for normal ocular development in chicks.
- The light-dark cycle interacts with an oscillating system, influencing ocular development.
- These findings highlight the critical role of structured light-dark cycles in preventing developmental eye disorders.
Abstract:
Exposure to continuous illumination disrupts normal ocular development in young chicks, causing severe corneal flattening, shallow anterior chambers and progressive hyperopia ('constant light (CL) effects'). We have studied the minimum requirements of a diurnal light cycle to prevent CL effects. (1) Seven groups of 10 chicks were reared under a 0 (constant light, CL), or 1, 2, 3,4, 6, or 12/12 h (normal) light-dark cycles. It was found that CL effects were prevented if the dark period was 4 h or longer. Below 4 h, the effects were dose-dependent and inversely correlated with the amplitude of the Fourier component of illumination at 1 cycle per day (CPD). (2) Three groups of 20 chicks were exposed to 4 h of darkness distributed differently over 24 h to vary the amplitude of the Fourier component at 1 CPD. It was found that complete suppression of the CL effects required that the 4 h of darkness were given in one block and at the same time each day. Our results show that normal ocular development in the chick requires a minimum of 4 h darkness per day, provided at the same time of the day without interruption, and suggest that the light-dark cycle interacts with a linear or weakly nonlinear oscillating system.
