VSX1 and keratoconus: Among the best-known genes involved in the development of keratoconus is the VSX1 gene [123], which is also involved in posterior polymorphic corneal dystrophy; the SOD1 gene [124], involved in defense against free radical-mediated damage; ZNF469 [125], the mutation of which leads to fragile cornea syndrome [126]; and the signaling pathway of transforming growth factor (TGF)-8 [127], which plays a role in the regulation of extracellular matrix composition [128].