Tear production in dogs with epiphora and corneal epitheliopathy

Measurement of tear volume by phenol red thread tear test (PRT), Schirmer's tear test (STT-1) and Schirmer's tear test with topical anesthesia (STT-2), and vital staining with a combination of fluorescein and rose Bengal of the cornea were performed in dogs with normal eyes and those with epiphora. The breeds included the Shih-Tzu (n = 26), and five other breeds (n = 50). The PRT, STT-1 and STT-2 results from the five breeds of normal dogs were 26.9 +/- 3.0 mm, 17.4 +/- 4.3 mm, and 8.8 +/- 3.2 mm, respectively. The PRT, STT-1, and STT-2 results for the Shih-Tzu eyes were (mean +/- standard deviation): 28.2 +/- 4.3 mm, 19.5 +/- 4.1 mm, and 9.2 +/- 4.5 mm, respectively. In the five breeds, corneal epitheliopathy, as evidenced by the retention of topical fluorescein and rose Bengal, occurred in 97% of dogs with epiphora and in 55% of the dogs without epiphora. Also in the dogs with corneal epitheliopathy the STT-2-value was low (4.0 +/- 2.8 mm) compared with those eyes without corneal epitheliopathy (8.8 +/- 3.1 mm). In the Shih-Tzu breed the STT-2 results were not significantly different between those dogs with corneal epitheliopathy and those with normal corneas. In the non-Shih-Tzu breeds the decrease in basic tear secretion, as measured by the STT-2, is associated with the corneal epitheliopathy.