Tear ferning test in healthy dogs

Abstract

Purpose: To evaluate and compare three tear sampling methods using two grading scales for administering the tear ferning test (TFT) to healthy dogs.

Methods: In total, 90 dogs (180 eyes) were subjected to tear sampling using millimetered strips, reused after the Schirmer tear test (STT) (Schirmer group, SG). Then, the dogs were subdivided into three groups according to sampling approach: micropipette (MPG), microcapillary (MCG), and Schirmer sample 2 (S2G). The collected tears were dried on a clean microscope glass slide at room temperature and humidity. The ferning patterns were observed under a polarized light microscope and classified according to the Rolando and Masmali grading scales.

Results: Although all three methods were feasible, the STT was easier to perform in clinical settings. Type I and Grade 1 were the most commonly observed (64.17% and 61.7%, respectively) regardless of collection method. There was no significant difference between the STT median values and the TFT classifications.

Conclusions: The TFT is appropriate for dogs and can be performed using the three suggested sampling methods, with a higher frequency of Type I and Grade 1. Thus, it is possible to use both grading scales in the classification of tear ferning in dogs.

Keywords: Schirmer test; grading scale; microcapillary; micropipette; ocular surface; tear film.