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Updated: Jul 31, 2026

Assessing Transmissible Spongiform Encephalopathy Species Barriers with an In Vitro Prion Protein Conversion Assay
Published on: March 10, 2015
Minimising the risk of prion transmission by contact tonometry
S Z Amin1, L Smith, P J Luthert
1Institute of Ophthalmology, Department of Pathology, Bath Street, London EC1V 9EL, UK.
Aims:
The unknown prevalence of variant Creutzfeldt-Jakob disease (vCJD) in the UK population has led to fears of horizontal transmission through routine medical procedures. The potential risk of transmission via contact tonometry was examined.
Methods:
The total amount of protein carried over by tonometer tips after applanation of patients was assessed.
Results:
Tonometer tips had an inherent ability to carry proteinaceous material. There was a large variability in the load carried over between individual patients. Rinsing tonometer tips in water reduced protein carryover. Wiping the tonometer tips also reduced carriage, though less dramatically.
Conclusion:
There is a small theoretical risk of transmission of vCJD by contact tonometry through reuse, but this should be reduced if the prisms are washed and wiped. In the light of these findings a protocol for the management of reusable tonometer prisms is recommended.
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