Prions are small proteinaceous infectious agents known to cause central nervous system infections in both animals and humans. Interest in the pathogenesis of these diseases has grown since the emergence of bovine spongiform encephalopathy (BSE or "mad cow disease") in the United Kingdom and several other countries in Europe. Ingestion of meat products from animals infected with BSE has resulted in transmission of the disease to humans as a variant form of Creutzfeldt-Jakob Disease (vCJD). CJD has a long asymptomatic incubation period, is untreatable, and universally fatal. Hence concern has arisen over other possible routes of disease transmission. Because it is known that prions are found in low levels in the corneas of animals with experimentally induced prion disease, and that a case of human CJD transmission by corneal transplantation has occurred, the question of possible prion transmission through the reuse of diagnostic fitting of contact lenses has surfaced. This article reviews prion diseases of animals and humans, and the data regarding the presence and location of prions in the eye. Issues inherent in the question of corneal and contact lens transmission are discussed. Although some key information has yet to be derived, it appears that the chance of obtaining prion disease through contact lens use is negligible.
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