SOD1 and Schnyder corneal dystrophy: This is also true for SCD RBCs in which there is a decreased concentration of both low molecular weight antioxidants such as vitamins A, C and E [29] and the activity/expression of some high molecular-weight antioxidant enzymes, such as SOD [19,45,127], Cat [19,45,128], GR [127] and Gpx [125,128].