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Measurement of tear production and establishment of reference values in guinea pigs (Cavia porcellus) using a modified Schirmer tear test

Background Past studies have shown that 5-mm Schirmer tear tests (STTs) are difficult to interpret in guinea pigs. Modified 2.5-mm STT strips are more adequate for measuring the small volume of tear production in these animals. The aim of this study was to establish reference values for the modified 2.5-mm STT strips. Methods Modified STT measurements were performed in random order in both eyes of 50 guinea pig patients. The wetting of the strip was noted at 30 seconds and at 1 minute. Results The mean±sd STT values for both eyes were 7.58±3.19 mm at 30 seconds and 10.42±3.92 mm at 60 seconds. The median was 8 mm at 30 seconds and 10 mm at 60 seconds for both eyes. Animals under one year of age had lower STT values. STT values at 30 and 60 seconds can both be used. Both eyes should be measured when possible. Conclusion The authors recommend values above 8 mm at 30 seconds and 10 mm at 60 seconds to be considered normal when using a 2.5-mm STT strip. There are ambiguous areas at 5–8 mm and 6–10 mm. If in these ranges the results should be combined with clinical signs and judgement.