How reliable is the Schirmer tear test for measuring cat tear

Abstract

OBJECTIVE: To assess reliability of the Schirmer tear test-1 (STT-1) for measurement of tear production in cats in various environments, investigate whether sympathetic stimulation impacts measurements, and determine whether meaningful conclusions regarding lacrimation in cats can be drawn from STT-1 measurements obtained with STT strip placement for < 1 minute. ANIMALS: 176 cats examined in a private practice (n = 100), a feral cat clinic (56), or a veterinary teaching hospital (20). PROCEDURES: The STT-1 was performed in both eyes of each cat. Measurements were recorded at 10- or 30-second intervals for 1 minute. Cats at the teaching hospital were tested once in a quiet examination room (unstimulated conditions) and once in the same room with loud prerecorded noises (stimulated conditions), with a 30-minute interval between tests and evaluation of cats' heart rates before and after STT-1. Data were analyzed with parametric statistical tools and a nonlinear mixed-effect model. RESULTS: 30- and 60-second STT-1 measurements were significantly correlated (= 0.94). The STT-1 measurements did not differ under nonstimulated versus stimulated conditions, despite significant changes in heart rates that indicated sympathetic stimulation. A hyperbolic model of STT-1 kinetics was validated, allowing for extrapolation of measurements obtained in < 60 seconds and generation of reference values (95% predictive intervals) for various test durations. Median (95% predictive interval) 30- and 60-second STT-1 measurements were 9.1 mm (4.8 to 15.6 mm) and 14.3 mm (8.2 to 22.3 mm), respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The STT-1 was a reliable diagnostic test in all settings; results were not affected by sympathetic stimulation, and a shorter duration of testing could be considered in selected cases.