Tear Film Osmolarity in Horses With Bacterial Conjunctivitis.

Overview

• This study evaluated tear film osmolality and electrolyte concentrations in horses with bacterial conjunctivitis compared to healthy horses.
• The research aimed to establish baseline osmolality data and explore its potential as a non-invasive diagnostic tool for ocular disease monitoring in horses.

Background

• Conjunctivitis is inflammation of the conjunctiva, which can be caused by infectious (viral or bacterial) or non-infectious factors.
• Bacterial conjunctivitis in horses is often caused by bacteria like Staphylococcus and Streptococcus species.
• The severity of bacterial conjunctivitis can vary depending on the specific bacterial species involved.
• Both viral and bacterial conjunctivitis are highly contagious, particularly raising concerns for infecting the unaffected eye.

Objective

• To assess the tear film osmolality in horses affected by bacterial conjunctivitis.
• To establish preliminary baseline values for tear film osmolality and electrolyte composition in healthy horses, facilitating comparison with diseased states.

Methodology

• Subjects included a total of 40 horses, comprising both healthy individuals and those diagnosed with conjunctivitis.
• Tear samples were collected from both eyes using microcapillary tubes, taken three times at five-minute intervals.
• The collected tear samples per horse were pooled to represent an average sample for measurement.
• Laboratory analysis determined the osmolality and concentrations of key electrolytes: sodium, potassium, magnesium, and calcium.
• Statistical analysis involved calculating mean values and standard deviations for each measured variable.

Results

• The average (mean) tear film osmolality in the sampled horses was 283.51 mmol/kg with a standard deviation of 9.33.
• Electrolyte concentrations (mean ± SD) in the tear film were:
  • Sodium: 134.75 ± 10 mmol/L
  • Potassium: 16.3 ± 5.77 mmol/L
  • Magnesium: 3.48 ± 1.97 mmol/L
  • Calcium: 1.06 ± 0.42 mmol/L
• Comparison of electrolyte levels indicated:
  • Sodium concentration in tears closely matched serum sodium levels.
  • Potassium concentration in tears was approximately 4.75 times higher than that in serum, indicating specialized tear film regulation of this ion.

Conclusions

• Measurement of tear film osmolality is a non-invasive, simple, and practical method for obtaining baseline ocular fluid characteristics in horses.
• This parameter shows promise for monitoring changes associated with ocular diseases such as bacterial conjunctivitis.
• However, tear osmolality alone is insufficient for clinical diagnosis and must be used in conjunction with other ocular parameters and diagnostic tests.
• Further controlled studies are necessary to validate tear film osmolality as a reliable biomarker for conjunctivitis in horses.
• Ultimately, developing tear film analysis tools could improve the precision of diagnosis and the comprehensiveness of treatment plans for equine ocular diseases.

Implications for Veterinary Practice

• Veterinarians could potentially use tear film osmolality measurements as a quick screening tool in equine eye care.
• Such measurements may help in early detection of ocular surface disturbances before clinical signs escalate.
• Integrating tear film analysis with microbiological and clinical data could enhance management of infectious conjunctivitis cases, potentially reducing spread and improving outcomes.