A Modified Schirmer Tear Test in Clinically Normal Horses: Measurement at 30 Seconds versus 60 Seconds

•A strong linear correlation was observed between STT30 and STT60 values•Age, eye or sex does not significantly affect STT30 or STT60 values•Shortening the STT time may be useful in non-cooperative horses This study sought to compare the Schirmer Tear Test (STT)-1 results at 30 (STT30) versus 60 (STT60) seconds in healthy horses. This study included a total of 56 healthy horses. STT-1 was performed in both eyes, right eye first, and the wetting lengths were measured in STT30 and STT60. To evaluate the reduction of the initial reflex phase, the wetting length velocity was measured during the first 30 seconds. The effects of eye, age, weight, sex, and ambient temperature and humidity on STT values were evaluated. Mean (standard deviation) STT30 and STT60 were 19.06 (3.88) and 24.26 (4.50) mm. There was a linear correlation between the STT 30 and STT60, expressed according to the following equation: STT60 = 2.20 + 1.18 × STT30 (P = .001). STT30 or STT60 values did not vary between the sexes or correlate with age, weight, ambient temperature, or humidity. In conclusion, STT30 allows for an accurate, reliable, and applicable diagnosis of tear production compared with the standard STT60 value. The proposed method is shorter and may be a suitable alternative to the 1-min test.