HPX and Schnyder corneal dystrophy: Normally, plasma hemoglobin and heme are removed safely by haptoglobin and hemopexin, but these cytoprotective scavenging proteins are depleted in the plasma of SCD patients and mice (Muller-Eberhard et al., 1968; Wochner et al., 1974; Mollan and Alayash, 2013; Vinchi et al., 2013; Belcher et al., 2014).