As the infectious agent of the spongiform encephalopathies is present in the cornea of an infected person - and the equipment used in the two contact forms of tonometry is not properly disinfected between tests - the test can spread Creutzfeldt-Jakob disease (CJD).
Researchers at the University of Southern California in Los Angeles say that tonometry is a little recognised spreader of CJD, and that a new test is needed to reduce the risk. Or ophthalmologists should use disposable covers on the tonometry equipment.
Suspicions of a link between CJD and tonometry were first raised as early as 1985, but it took a further 13 years before the hypothesis was proved. After studying 110 CJD cases from 11 States against 114 controls, scientists concluded that the risk of infection increased according to the number of tests done. Someone who had taken five or more tests had a nearly sixfold increased risk of contracting CJD, it was concluded.
Other potential medical causes of CJD include inoculation after injury or during surgery, or from sutures that include animal derivatives (Am J Epidemiol, 1998; 147: S76).