Fig. 1.

Schematic representation of the human eye. a Representation of healthy human eye with normal corneal thickness. b Structure of the human cornea. The cornea is a complex tissue comprised of five main layers (from the anterior to posterior margin): corneal epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium. c Human eye with keratoconus with characteristic thinning and cone-like bulging of the cornea