Measurement of Anions in Dog Tear Fluid Using Ion Chromatography.

Tear fluid in healthy Beagles contains significantly higher chloride and bromide concentrations than plasma, establishing useful anion reference values.

This study characterized the anion composition of tear fluid in healthy Beagles using ion chromatography, comparing tear anion concentrations to plasma values and evaluating differences between diseased and non-diseased eyes. Six healthy, purpose-bred male Beagles (12 eyes) were enrolled, with tear samples collected via glass capillary tube (minimum 10 µL) and diluted for chromatographic analysis. Key anions measured included chloride (Cl⁻), bromide (Br⁻), nitrate (NO₃⁻), hydrogen phosphate (HPO₄²⁻), and sulfate (SO₄²⁻). Results demonstrated that Cl⁻ and Br⁻ concentrations were significantly higher in tear fluid than in plasma, while SO₄²⁻ was markedly higher in plasma than in tears. HPO₄²⁻ levels were comparable between compartments, and NO₃⁻ was low in both. These findings suggest active ion transport mechanisms regulate the tear film's anion composition rather than simple plasma ultrafiltration. Importantly, no statistically significant differences in anion concentrations were detected between tears from eyes with various diseases and those from non-diseased eyes, though the diseased eye cohort likely represented a heterogeneous group. This work establishes baseline reference values for tear anion concentrations in dogs and validates the use of ion chromatography as a feasible, sensitive tool for canine tear analysis. Future studies in larger, disease-specific cohorts may help clarify whether targeted anion dysregulation plays a role in specific ocular surface disorders in veterinary patients.

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