COL4A4 and keratoconus: Collagen type IV gene, alpha-4 (COL4A4), is located in the region 2q35–q37 with a gene span composed of 113 kb and 48 exons.[18,19] Type IV collagen is not expressed in cornea in the normal condition and its presence indicates a corneal pathology; therefore, type IV collagen can be a potential candidate in the pathogenesis of KC.