Factors responsible for tear ferning.

The biochemical agents involved in fern formation on drying tears were investigated by studying the different patterns of ferning of tears from normal and pathological eyes, mucus glycoprotein, saliva, serum, and various salt solutions. We conclude that the ferning phenomenon observed when a drop of tears is allowed to dry at room temperature on a clean microscope slide is to a large extent determined by the electrolyte concentration, especially the ratio of monovalent sodium and potassium ions to divalent calcium and magnesium ions. The presence of a biopolymer is essential, but this need not specifically be mucus as previously thought. The test may therefore be useful clinically in indicating the need for further tear analysis.