Abstract
Background: Healthy vision in humans and animals requires a stable tear film. The environmental factor could affect the status of the tear film. Therefore, assessing the tear film in animals is essential to avoid visual system disturbance.
Aim: The current research used a noninvasive device to evaluate the tear meniscus height (TMH) and lipid layer pattern (LLP) in domestic cats. In addition, the scores were compared with those of humans with healthy eyes.
Methods: Fifty-four domestic cats (28 males and 26 females; mean ± SD = 13.9 ± 18.2 months) were randomly selected and included in the study. The cats were healthy, without any ocular disorders or diseases. Fifty-four healthy eye subjects (27 males and 27 females; mean ± SD = 25.6 ± 5.1 years) were randomly recruited and took part in the study for comparison. EASYTEAR View+ was used, for the first time, to assess the tear film parameters on the right eye of each subject. The examiner allowed a 5-minute gap between the tests. Each test was performed by the same examiner three times, followed by calculating the mean scores.
Results: Significant differences (Mann–Whitney U test) were found in the median scores of LLP (P = 0.009) between cats and subjects with healthy eyes. The median TMH score was higher in cats (0.18 mm) than in humans (0.14). However, no significant difference (Mann-Whitney U Test, P = 0.210) exists in the TMH scores between cats and humans. The LLP analysis indicated that a dense white-blue lipid layer (grade 4 or D; lipid layer thickness, LLT, = approximately 80 nm) was predominant in both cats (N = 24, 44.4%) and humans (N = 29, 53.7%). In comparison, variable colors lipid layer (grade 5 or E; LLT = 90–140 nm) was a minority in cats (N = 5, 9.3%) and common in humans (N = 16, 29.6%). The statistical analysis indicated medium correlations between cats' TMH and LLP scores (r = 0.431, P < 0.01) and between age and TMH scores in humans (r = 0.440, P < 0.01). In addition, it indicated a weak correlation (r = 0.291, P < 0.05) between the LLP scores in cats and humans.
Conclusions: Assessing animals' tear film is essential to avoid any ocular disorders. EASYTEAR View+ is efficiently used to evaluate domestic cats' tear meniscus height and lipid layer patterns. Cats have thicker lipid layers and longer tear meniscus height comparable to those reported for humans with healthy eyes.

Key words: Domestic cats, Tear film, Dry eye, Tear meniscus height, Lipid layer patterns