Circadian intraocular pressure rhythms in athletic horses under different lighting regime.

This research investigates the patterns of intraocular pressure (IOP) in athletic horses under different light conditions. The findings suggest that IOP in horses follows a circadian rhythm which is affected by the 24-hour cycling of light and darkness and these findings are vital for timing and interpreting clinical tests for eye diseases in horses.

Understanding the Circadian Rhythm of Intraocular Pressure

• The researchers aimed to explore the existence of IOP rhythms in athletic thoroughbred horses. Intraocular pressure refers to the fluid pressure inside the eye. Any alterations in this pressure can lead to severe eye disorders such as glaucoma or uveitis.
• The study subjects were exposed to three different lighting conditions – a standard 24-hour cycle of light and darkness (LD), constant light (LL), and constant dark (DD).
• The study found that the IOP circadian rhythm follows the 24-hour LD cycle. This implies the IOP was low during darkness and high during light with the highest peak at the end of light phase (ZT10).

Impact of Constant Lighting on IOP Rhythms

• The research further established that the circadian rhythm of the IOP continued to persist in constant darkness (peak at CT9.5), implying an inherent component in IOP rhythm. This innate component could independently function without the guidance of light or dark cycles.
• However, the rhythm was abolished in constant light conditions, mimicking the patterns identified in other mammalian species.

Clinical Implications

• The identified daily variation in intraocular pressure is critical because tonometry, a diagnostic tool for eye diseases like glaucoma and anterior uveitis in horses, heavily relies on these pressure measurements.
• Knowing the IOP’s circadian rhythm will help in effectively planning the timing of these tests and correctly interpreting the test results, leading to better diagnoses and treatments of ophthalmologic diseases in horses.