PRNP and scrapie: However, minimal amounts of PrP-scrapie were detected in the cornea of patients with sporadic or variant Creutzfeldt-Jakob disease, human prion disorders, leading to the classification of cornea as low risk in comparison to the retina and optic nerve that were considered highly infectious (Armitage et al., 2009; Armstrong, 2006; Head et al., 2003).