Trace Element Levels in Canine Tear Film

Objective: To evaluate the levels of trace elements in the tear film of healthy dogs. Animals Studied: Twenty-five healthy Labrador retrievers. Procedures: Tear samples were collected from the ventral conjunctival fornix of each dog using a Schirmer tear test strip. Elemental analysis was conducted using the particle-induced X-ray emission (PIXE) method with a 1.7 MV Pelletron accelerator. Trace element levels were compared across all dogs using the Kruskal–Wallis test with post hoc Tukey analysis and between male and female dogs using the Mann–Whitney test. Results: The study included 14 neutered males and 11 spayed females, with a mean (±SD) age of 19.8 ± 3.1 months (range 14.3–26.5, median 18.8 months). Elemental analysis of tear samples revealed the presence of calcium (Ca), chloride (Cl), iron (Fe), phosphorus (P), potassium (K), sodium (Na), and sulfur (S). The median ± SEM peak area levels were highest for Cl (69 530 ± 1432) and K (5782 ± 514), followed by S (3545 ± 772), Na (3387 ± 159), P (1408 ± 160), Ca (593 ± 85), and Fe (276 ± 206). Compared to males, female dogs had significantly higher peak areas for S (2272 ± 549 vs. 4389 ± 1484, p = 0.037) and Ca (536 ± 76 vs. 800 ± 148, p = 0.029). Conclusions: This study provides a detailed assessment of the trace element composition in the tear film of healthy dogs. These findings enhance our understanding of canine ocular surface physiology and may have potential implications for the diagnosis and management of ocular surface diseases in dogs.