title: Intraocular pressure fluctuations of growing chick eyes are suppressed in constant 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.
authors.affiliation: Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA. Electronic address: CWL5@cornell.edu.
authors.forename: Christina
authors.initials: C
authors.lastname: Wahl
authors.affiliation: Department of Food Science and Technology, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Tong
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Howard C
authors.initials: HC
authors.lastname: Howland
mesh_terms: D000818:Animals; D002645:Chickens / Q000502:physiology*; D002940:Circadian Rhythm / Q000528:radiation effects; D007429:Intraocular Pressure / Q000502:physiology / Q000528:radiation effects*; D008027:Light / Q000009:adverse effects*; D014065:Tonometry, Ocular
keywords: Chick; Constant light; Development; Diel; Growth; Intraocular pressure