Improvement in Tear Ferning Patterns of Sheep Tears After Addition of Various Electrolyte Solutions

To improve the tear ferning (TF) patterns in sheep tears after the addition of various electrolyte solutions in different proportions. Procedures: Tear samples (20 μL) were collected from the right eyes of seven healthy sheep (5 females and 2 males; age 7–36 months with an average of 17.0 +/- 10.3 months). A tear sample (1 uL) from each sheep was dried on a microscopic glass slide at 22 C and <40% humidity. The TF patterns were graded based on a five-point grading scale in 0.1 increments. Homogenous mixtures were prepared by mixing tears from each sheep (0.5 uL) with various electrolyte solutions in different proportions (1:1, 1:2, 1:4, 1:6, 1:8, and 1:10). A sample of each mixture (1 uL) was dried on a glass slide, and the TF patterns for each mixture were observed, recorded, graded, and compared with those of the corresponding pure sheep tears. In addition, each sheep tear sample (0.5 uL) wase diluted with pure water (0.5 uL) and the TF image were recorded and graded to test the dilution effect. Results: General improvement was noted in TF grades after addition of electrolyte solutions, ranging from 1.7–1.4 to 1.3–0.3 regardless of the ratio between the electrolyte solutions and sheep tears within the mixture. TF grades of sheep tear samples improved significantly after adding different volumes of calcium chloride solution. Similar improvement in TF grades were observed when magnesium chloride hexahydrate and sodium dihydrogen phosphate solutions were used as the electrolytes. Some improvement in TF grades occurred with the addition of potassium chloride to sheep tear samples. There was little improvement in TF grades after addition of sodium chloride solution. Conclusions: TF grades of sheep tear samples improved when mixed with a number of electrolyte solutions at different volumes, in particular with calcium chloride or magnesium chloride solutions. Some improvement in TF grades was seen with sodium dihydrogen phosphate or potassium chloride solution added as the electrolyte. Clearly, divalent electrolytes lead to a greater improvement in TF grades of sheep tear samples as compared with sodium dihydrogen phosphate or monovalent electrolytes.