Spatial location studies on the chemical composition of human tear ferns.

Tear ferns are the patterns formed when tears are allowed to dry on a clean smooth surface. The patterns have been categorised according to confluence of pattern, with less confluent ferns indicative of tear film abnormalities. Little is known about the mechanism that gives rise to this phenomenon. Previous work has concentrated on correlation of alterations in tear film composition on the ferning phenomenon. The present study takes a new approach by analysing the locations of chemical elements in the fern to understand how the ferns form. By means of SEM coupled with EDXA, Na, K and Cl were detected within the fern. Sulphur, indicative of the presence of macromolecules such as mucins and proteins, was only found at the very periphery of the dry tear drop. The results suggest that macromolecules do not play a direct role in the formation of the ferns. A model is put forward to explain the observation whereby proteins and mucins are precipitated selectively by increasing salt concentration at the drop margin.