Figure 4. Scanning electron micrographs of the ferning pattern of camel tear film, human tear film, and Refresh Plus lubricant. A, B: Part of the camel tear film showing primary (pf), secondary (sf), tertiary (trf), and fine ferning; C, D: Human tear film containing primary (pf) secondary ferning (sf) and fine ferning. E, F: Refresh Plus ferning showing primary and secondary branching. 1 = First layer, 2 = Second layer, 3 = Third layer, 4 = Fourth
layer, 5 = Fifth layer, CR = Crystals, PF = Primary ferning, SF = Secondary ferning, TRF = Tertiary ferning.