Results of the Schirmer tear test performed with open and closed eyes in clinically normal horses

BACKGROUND The Schirmer tear test (STT) is widely used in both human and veterinary ophthalmology. Two types of STTs have been developed: STT I and SST II. The STT I measures the basal and reflex tear production and is the most widely used STT. However, several factors influence the STT results such as the person performing the test and the location of the strip placement within the conjunctival sac. The aim of this study was to measure the basal and reflex tear production (STT I) in clinically normal horses with open versus closed eyes. RESULTS Forty clinically healthy horses without any ocular diseases were included. On day 1, the STT I was first performed on all the horses with the eyes open followed by an STT I with closed eyes performed 30 min later. On day 2, all horses had their eyes closed during the first STT and the eyes open during the second test performed 30 min later. The mean value of the STTs performed on open eye was significantly less than the STT performed on closed eye on both days of examination. CONCLUSION This study showed a small but statistically significant difference between STT values obtained with open versus closed eyes in clinically normal horses.