ALDH3A1 and keratoconus: Ultraviolet light (UV) – It is a source of reactive oxygen species (ROS) and it is assumed that excessive exposure to sunlight leads to oxidative damage in KC corneas, in which there is a reduced amount of the enzymes including aldehyde dehydrogenase class 3 (ALDH3) and superoxide dismutase necessary to remove the ROS [23, 14].