Tear ferning test in horses and its correlation with ocular surface evaluation

To describe the tear ferning test (TFT) in healthy horses and its correlation with other parameters for evaluating the ocular surface.

Thirty male and female adult healthy horses (60 eyes), of no defined breed.

Tear sample was collected with a microcapillary tube, placed on the surface of a glass slide, and allowed to dry at room temperature. The crystallization pattern was classified according to Rolando (Chibret International Journal Ophthamology, 1984; 2, 32). The program STEPanizer(©) stereology tool, version 1.0, was utilized for counting points on the digitally captured crystallization image. A conjunctival biopsy was performed.

Tear ferning test was classified as Type I in 18 eyes (30%), Type II in 31 eyes (51.7%), and Type III in 11 eyes (18.3%), at a mean temperature of 27.3 ± 1.5 °C and relative humidity of 61.5 ± 5.7%. In the Type I crystallization, the count varied between 27 and 36 points (mean: 33.27 ± 2.40), in Type II between 22 and 31 points (25.42 ± 1.95), and in Type III between 13 and 25 points (16.82 ± 3.76). There was no statistical difference or correlation between the right and left eyes, nor was there a statistically significant influence (P < 0.05) on TFT by the factors evaluated. The mean goblet cells values were 50 ± 11.4 cells/field. All samples showed the presence of lymphocytes, plasmocytes, and eosinophils.

Tear ferning test is easy to perform, without risks to the patient. Once standardized for horses, associated or not with the program STEPanizer(©) stereology tool, it is an additional method for evaluating the ocular surface.