GSTM1 and Schnyder corneal dystrophy: Within the sphere of SCD, many subgroups exist, mainly sickle cell anemia (HbSS), hemoglobin SC disease (HbSC), and hemoglobin sickle-beta-thalassemia (Hb S/β-Thal), (β+ thalassemia or β0 thalassemia) [1].