Do cats cry more at night?

2 September 2019 – News

Tear film production is a parameter to evaluate while performing a complete ophthalmic examination -Aa Schirmer tear test (STT) is commonly used in veterinary medicine to determine whether they eye produces enough tears to keep it moist.

Studies in humans and dogs correlate STT values with circadian rhythm but, to the author’s knowledge, there hadn’t been a similar study in cats.

This article describes a pilot study in which 20 healthy cats living indoors were exposed to 14h of daylight and 10h of dark. A STT strip was placed in the lower conjunctival fornix of each cat for one minute and tear production was measured every 4 hours, in both eyes, over 2 days.

The highest mean values were obtained at midday and the lowest during afternoon. In contrast, the lowest STT in dogs is at night.  An explanation for this difference between cats and dogs could be the nocturnal character of felines. The study also highlighted that variations of 5mm/min occurred throughout the day.  This could be clinically significant in animals with low tear production test values.

This study shows that it is important to considering the timing of STT evaluation and suggests that further studies taking into account seasonal variations, breed, human interaction and stress, should be considered.

Faghihi H, Rajaei SM, Ansari mood M, Williams DL. Pilot evaluation of the circadian rhythm of tear production in a population of healthy adult cats. Vet Ophthalmol. 2019;00:1–5. https://doi.org/10.1111/vop.12673