Schirmer tear test and strip meniscometry in healthy cats

Abstract

Background: The surface of the eye is covered by the preocular tear film, which is critical for maintaining a normal, healthy, visual, and comfortable vision. The Schirmer tear test (STT) and, more recently, strip meniscometry (SM) are used to evaluate tear production.
Aim: To establish the normal values for STT and SM in healthy cats and to discover the correlation between these tests.
Methods: A total of 25 mixed breed cats, aging from 8 months to 13 years of both genders (10 females and 15 males) were included in the study. All the cats were assigned to the study as being both clinically and ophthalmologically healthy. For the SM test, the tip of the strip was used to evaluate the meniscus without touching the eyelid or the cornea for 5 seconds. After a full tear washout period of 10 minutes, the STT was performed using a standard STT strip.
Results: In the right eyes, the mean ± standard deviation (SD) of SM was 4.32 ± 2.27 mm/5 seconds, and in the left eyes it was 5.04 ± 2.24 mm/5 seconds (for both eyes combined: 4.68 ± 2.26 mm/5 seconds), with a median of 4 in both eyes; the reference values ranged from 4.04 to 5.32 mm/5 seconds. No significant differences were recorded in the SM between the right and left eyes of the cats when using the SM (p > 0.05). When the STT was used, the mean ± SD for the cats’ right eyes was 12.16 ± 4.04 mm/minute, and for the left eyes, it was 12.76 ± 4.1 mm/minute (for both eyes combined: 12.46 ± 4.20 mm/minute), with a median of 13.50 for both eyes. Reference values were calculated and ranged from 11.27 to 13.65 mm/minute. No significant differences were recorded between the STT for the right and left eyes (p > 0.05).
Conclusion: Both tests can, therefore, be used to assess tear production in cats. For more precise results, SM should be evaluated according to the cat’s eye position—whether it is a brachiocephalic cat or a normaloid cat—and according to the age. In all cases, STT and SM should be evaluated according to the animal’s clinical status and the results of other diagnostic tools.