June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Circadian Rhythms of Intraocular Pressure and Core Body Temperature Persist in Continuous Dim Light
Author Affiliations & Notes
  • Diana C Lozano
    College of Optometry, University of Houston, Houston, TX
  • Andrew T E Hartwick
    College of Optometry, The Ohio State University, Columbus, OH
  • Michael D Twa
    College of Optometry, University of Houston, Houston, TX
  • Footnotes
    Commercial Relationships Diana Lozano, None; Andrew Hartwick, None; Michael Twa, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 5821. doi:https://doi.org/
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      Diana C Lozano, Andrew T E Hartwick, Michael D Twa; Circadian Rhythms of Intraocular Pressure and Core Body Temperature Persist in Continuous Dim Light. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5821. doi: https://doi.org/.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: To compare and contrast the circadian rhythms of intraocular pressure (IOP) and body temperature in Brown Norway rats when housed in standard light-dark(LD) and continuous dim light(LL) conditions (40-90 lux).

Methods: An intraperitoneal temperature sensor was implanted and body temperature measurements were obtained every 5 minutes until the end of each experiment. IOP was measured every two-hours over 26-hours using a rebound tonometer. These two physiological functions were evaluated when the animals were housed in LD and after the animals had been housed in LL for 1 and 4 weeks (Group 1; n=4 animals) or for 7 weeks (Group 2; n=7 animals). Circular statistics (length of the mean resultant vector [R], circular variance [S], and Rayleigh’s test) were used to determine the distribution of temperature and IOP peak times.

Results: Body temperature in LD was lowest during the light-phase (36.9±0.1°C), highest during the dark-phase (37.5±0.2°C), and peaked near the middle of the dark phase (17.5±1.9 Zeitgeber Time). IOP in LD was lowest during the light-phase (16±2 mmHg), highest during the dark-phase (30±7mmHg), and peaked near the middle of the dark-phase (16.6±1.2 Zeitgeber Time). In LD, the vector length for temperature and IOP were larger than 0.96, circular variances were less than 0.04, and Rayleigh’s test (P<.001) supported that the times were concentrated around the middle of the dark-phase. However, temperature and IOP peaked at different times when the animals were place in LL. In Group 1, the time difference was -4.6±1.0h after 1 week of LL and IOP peak times were still concentrated around the same time (R=0.98; S=0.02; Rayleigh’s P=.01). The time difference was +9.5±6.8h and IOP peak times were more spread around the clock after 4 weeks in LL (R=0.21; S=0.79; Rayleigh’s P=.85). In Group 2, the time difference was +6.2±8.4h after 7 weeks in LL and IOP peak times were spread out evenly around the clock (R=0.11; S=0.89; Rayleigh’s P=.92). The maximum range of IOP measurements was 14±3mmHg under LD conditions; this range dampened (8±1mmHg) after 1 week in LL and stayed dampened after 4 weeks in LL (8±2mmHg; Group 1). For Group 2, the maximum range dampened to 6±1mmHg after 7 weeks in LL.

Conclusions: Persistent, but dampened, circadian rhythms of IOP and temperature were measured in continuous dim light and the results showed that they are not synchronized by the same central oscillator.

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