Tear film osmolality and electrolyte composition in healthy horses.

The research explores the osmolality and electrolyte composition of tear films in healthy horses, providing preliminary guidelines for comparison in subsequent studies related to eye diseases in horses.

Study Design and Methodology

• The study involved 15 healthy adult horses, from which tear samples were collected and analyzed.
• A detailed ophthalmic examination was performed on each horse, inclusive of a slit-lamp biomicroscopy, indirect ophthalmoscopy, and a Schirmer tear test.
• Tear samples were collected from both eyes of each horse, using microcapillary tubes, thrice at five-minute intervals.
• These samples were pooled for each horse and then subjected to analysis involving osmolality and electrolyte concentration measurements.

Findings and Conclusions

• The mean tear film osmolality was 283.51 mmol/kg, and the mean concentrations of different electrolytes, namely sodium, potassium, magnesium, and calcium were also recorded.
• The sodium concentration in the tear film was found to be similar to that in the serum, while the potassium concentration was roughly 4.75 times that of the serum.
• The study concluded that the collected results could serve as preliminary guidelines for tear samples from horses suffering from keratopathies (corneal diseases).
• The research emphasized the convenience and non-invasive nature of measuring tear film osmolality in horses.
• An unexpected observation was that the tear film concentration of divalent cations (ions with a charge of +2) was greater than anticipated – in fact, higher than the concentrations in tear films of rabbits and humans.
• These findings were deemed potentially useful in diagnosing and monitoring hyperosmolar ocular surface disease in horses – a condition involving an elevated osmolality of the tear film and ocular surface damage.

Implications and Future Research

• By establishing baseline data for tear film electrolyte composition and osmolality in healthy horses, the study provides a reference point for diagnosing and monitoring horse eye diseases, paving way for advanced treatments.
• The observed high concentration of divalent cations could lead to subsequent research to further investigate this phenomenon, and any potential implications it may have on eye health or disease pathology in horses.