Several genes were proposed as candidates for KC, including visual system homeobox 1 (VSX1), superoxide dismutase 1 (SOD1), and collagen, type IV, alpha 3 (COL4A3) and alpha 4 (COL4A4) genes,but their precise role in KC development is not clear [30–32]. This evidence concerns the gene COL4A3 and keratoconus.