Schirmer strip wetting length varies by commercial manufacturer.

Objective: To determine whether wetting length of Schirmer tear test (STT) strips varies by commercial manufacturer of test.

Animals Studied: Ten normal female beagle cross-breed dogs.

Procedures: Schirmer tear test strips from four commercial manufacturers were used to assess wetting lengths in-vitro when exposed to a set volume of water over 1 minute. Digital photography was used to assess the total surface area of Schirmer strips from each manufacturer. Schirmer tear test type 1 was performed on normal dogs over 1 minute with STT strips from the same four commercial manufacturers in a randomized crossover design. ANOVA was used to detect differences between strips from different manufacturers.

Results: Significant differences in wetting length were found between STT strips from different manufacturers in-vitro (P < .0001) and in-vivo (P < .0001). STT wetting lengths for the in-vitro experiments (mean ± SD) were 21.2 ± 0.8 mm (Amcon Laboratories), 27.8 ± 2.7 mm (Merck Animal Health), 30.0 ± 1.7 mm (HUB pharmaceuticals), and 31.5 ± 2.3 mm (Gulden Ophthalmics). STT wetting lengths for the experiments in live dogs (mean ± SD) were 17.5 ± 3.4 mm (Amcon Laboratories), 24.8 ± 3.9 mm (Merck Animal Health), 26.5 ± 3.7 mm (HUB pharmaceuticals), and 24.0 ± 3.9 mm (Gulden Ophthalmics). The surface area of STT strips were found to vary between different manufacturers.

Conclusions: Schirmer tear test type 1 results in dogs are affected by choice of STT strip commercial manufacturer. It is proposed that guidelines are created for the standardization of future STT strip production.