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Chronobiology International
The Journal of Biological and Medical Rhythm Research
Volume 26, 2009 - Issue 2
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Short Communication

Circadian Intraocular Pressure Rhythms in Athletic Horses under Different Lighting Regime

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Pages 348-358 | Received 29 Jul 2008, Accepted 08 Oct 2008, Published online: 07 Jul 2009
 

Abstract

The present study was undertaken to investigate the existence of intraocular pressure (IOP) rhythms in athletic thoroughbred horses maintained under a 24 h cycle of light and darkness (LD) or under constant light (LL) or constant dark (DD) conditions. We identified an IOP circadian rhythm that is entrained to the 24 h LD cycle. IOP was low during the dark phase and high during the light phase, with a peak at the end of the light phase (ZT10). The circadian rhythm of IOP persisted in DD (with a peak at CT9.5), demonstrating an endogenous component in IOP rhythm. As previously shown in other mammalian species, horse IOP circadian rhythmicity was abolished in LL. Because tonometry is performed in horses for the diagnosis of ophthalmologic diseases, such as glaucoma or anterior uveitis, the daily variation in IOP must be taken into account in clinical practice to properly time tests and to interpret clinical findings.

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