CTSD and pterygium: The biochemical pathway prospection performed on the KEGG mapper for the pterygium tear proteome is shown in Fig. 2, which represents the estrogen signaling pathway, with altered proteins highlighted: increased levels of KRT13 (Keratin, type I cytoskeletal 13) and HSPA8 (Heat shock cognate 71 kDa protein), and decreased level of CTSD (Cathepsin D).