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Intraocular pressure fluctuations of growing chick eyes are suppressed in constant light conditions
Christina Wahl1, Tong Li2, Howard C Howland3
1Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA.
Insights
Intraocular pressure (IOP) in chicks fluctuates with normal light-dark cycles but is suppressed under constant light. Recovery of normal IOP patterns after constant light exposure takes longer than one week.
Area of Science:
- Ophthalmology
- Chronobiology
- Animal Science
Background:
- Intraocular pressure (IOP) is a critical factor in ocular health.
- Light-dark cycles are known to influence physiological processes in many species.
Purpose of the Study:
- To investigate the impact of different lighting conditions on intraocular pressure (IOP) in developing domestic chicks.
- To determine the effect of constant light (CL) and a return to normal light-dark cycles (N) on IOP fluctuations.
Main Methods:
- Measurements of IOP were taken at 12-hour intervals in domestic chicks under three lighting conditions: normal (N), constant light (CL), and a switch from CL to N (CLN).
- IOP was recorded at noon and midnight under N and CLN conditions, and at corresponding intervals under CL.
Main Results:
- Chicks under normal light (N) exhibited significant IOP fluctuations between light (25 mm Hg) and dark (17.5 mm Hg) periods, established by 4 days of age.
- Constant light (CL) suppressed IOP fluctuations, maintaining a steady pressure around 17 mm Hg.
- Chicks switched from CL to N required over one week to re-establish normal IOP fluctuations.
Conclusions:
- IOP naturally fluctuates in hatchling chicks under normal light-dark conditions.
- Constant light exposure suppresses these natural IOP fluctuations.
- Recovery of normal IOP fluctuation patterns after prolonged constant light exposure is a gradual process, taking more than a week in normal light conditions.
Abstract:
We report measurements of intraocular pressure (IOP) in growing domestic chicks at 12 h intervals, with three different lighting conditions. One group of chicks was raised in 12 h light and 12 h darkness (N), another in constant light (CL), and the third group was initially exposed to CL for three weeks then returned to N for either one week or four weeks (CLN). Pressures were measured in the middle of the light and dark periods (noon and midnight) for N and CLN birds, and at corresponding 12 h intervals for CL birds (also noon and midnight). The IOP of N chicks fluctuated from a light period average value of 25 mm Hg ( ±1.3 SD), to a dark period average value of 17.5 mm Hg ( ±1.1 SD mm Hg; P < 0.0001). These pressures were established by 4 days of age. At 7 weeks, (N) IOP continued to fluctuate: light values were 21.7 mm Hg (±1.2 SD), and dark values were 18.3 mm Hg ( ±0.7 SD). The IOP of CL birds did not fluctuate, remaining steady at 17 mm Hg ( ±1.4 SD). Chicks exposed to CL for 3 weeks required more than one week in N to re-establish (N) IOP values. We conclude that IOP fluctuates in hatchling chicks under N light conditions, that fluctuation is suppressed in CL light conditions, and that IOP recovery from 3 weeks suppression in CL requires more than one week in N light conditions.
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