Six loci were previously associated with keratoconus (FOXO1, COL5A1, FNDC3B, ZNF469, LOX, and near PNPLA2), and these were associated with central corneal thickness. In addition, strong associations were found near or within genes that code for fibrillar collagens (types I and V), microfibrillar (VI), and peri-fibrillar (XII) structures, implicating impaired cohesion of the collagen matrix in the pathogenesis of keratoconus. This evidence concerns the gene COL5A1 and keratoconus.