Daily rhythm of tear production in normal horse.

The research article investigates the daily rhythm of tear production in healthy horses, examining the differences between left and right eyes and between male and female horses under varying light and dark conditions.

Research Methodology

• The study consisted of 18 horses – nine male and nine female. These subjects were subjected to three separate light and dark schedules: an equal 12-hour light and 12-hour dark cycle, consistent 24-hour light exposure, and constant 24-hour darkness.
• The researchers used Schirmer tear tests to measure tear production. This test was administered every 4 hours over each 24-hour period, under the different light and dark conditions.

Research Findings

• A circadian rhythm of tear production was observed in the horses during the balanced 12-hour light and dark cycle, as well as during the continuous darkness. The term “circadian rhythm” describes physical, mental and behavioral changes that roughly follow a 24-hour cycle, responding primarily to light and darkness.
• The researchers found a statistically significant difference in tear production when comparing the left and right eyes of the horses, as well as between male and female horses.

Conclusions

• The study concluded that the timing of tear evaluation plays a significant role in diagnosing tear film disorders. This suggests that tear production is not constant throughout the day, and has peak times of production influenced by environmental light conditions.
• The notable differences found between tear production in left and right eyes and between genders also imply that these factors should be considered in ophthalmic exams for horses. This could potentially inform more effective and accurate diagnoses of eye conditions.

Relevance and Application

• This research has significant implications for the diagnosis and treatment of equine eye conditions. Understanding the natural daily rhythm of tear production in horses and its influential factors could guide clinicians in scheduling tests and interpreting results more effectively.
• This study also suggests that a change in the light-dark cycle could impact tear production in horses – which is of interest for horse caretakers and vets especially in regions or times of year with extreme differences in day and night length.