Evaluation of tear film breakup time, Schirmer tear test, blink rate and tear ferning test in Shih-Tzu dogs

Abstract

Background: Shih-Tzu dogs are severely affected by lacrimal surface ophthalmic disorders, such as Dry Eye Disease (DED). The objective of this study was to evaluate tear quality in Shih-Tzu dogs. Thirty dogs underwent eyelid blink counting, tear film breakup time (TBUT) test, Schirmer tear test (STT-1), and tear ferning test (TFT). Results: Of the 30 animals evaluated, 28 had STT-1 values within the normal range, with a mean and median of 24.5 and 25 mm/min, respectively. The mean and median of TBUT were 3.8 and 4 seconds, respectively. The majority of TFT classifications suggested ophthalmic alterations, with 61.1% classified as grade III according to the Rolando scale, and 46.4% as grade 3 according to the Masmali scale. In the blink rate, the mean and median values for incomplete eyelid blinks/min (86.9 and 67.5) were higher than for complete blinks/min (22.9 and 12), and this difference was statistically significant (p=0.001). Two dogs had STT-1 values below the reference range, with 10 mm/min in the right eye (RE) and 7 mm/min in the left eye (LE) for the first dog, and 9 mm/min (RE) and 10 mm/min (LE) for the second dog. The TBUT for the first dog was 3 and 4 seconds in the RE and LE, respectively, while for the second dog, it was 3 and 2 seconds in the RE and LE, respectively. Regarding TFT classification, the first dog had type II according to the Rolando scale for both eyes and grade 2 according to the Masmali scale for both eyes, while the second dog had type IV according to the Rolando scale for both eyes and grade 4 according to the Masmali scale for both eyes. In the blink rate, the evaluators observed a mean and median of 9.3 and 6 complete eyelid blinks/min, and 43.6 and 55 incomplete blinks/min for the first dog, and 3.3 and 3 complete eyelid blinks/min, and 43.3 and 44 incomplete blinks/min for the second dog. Conclusions: Under the conditions of this study, despite the animals having STT-1 values within the normal range for the species, there was a high prevalence of type III and grade 3 tear ferning pattern according to the Rolando and Masmali scales, respectively. These patterns are not considered healthy in dogs. Additionally, the dogs exhibited few complete eyelid blinks and a high frequency of incomplete blinks. This finding indicates that the animals, despite having an adequate aqueous fraction, have compromised tear quality and poor spreading of the tear film, which may result in Dry Eye Disease (DED). Further studies are necessary with animals showing STT-1 values below the normal range to better elucidate the abnormalities associated with DED.