Tonometer may expose patients to mad cow prions, Scottish report states

Corneal cells can remain on tonometer tips even after rigorous cleansing, thereby making it possible for Creutzfeldt-Jakob disease to be passed from one patient to another, researchers in Scotland assert. Other researchers, however, raise questions about the practical possibility of transmission through this route.

Baljean Dhillon and colleagues in Edinburgh collected retained materials from reusable Goldmann tonometer prisms to determine the presence of residual cells. The researchers studied cytology specimens from 69 patients. Patients using eye drops shed significantly more corneal epithelial cells (average 156 cells) than patients not using eye drops (average 14 cells), they found.

The authors hypothesize in the July issue of British Journal of Ophthalmology that variant Creutzfeldt-Jakob disease (CJD), or mad cow disease, cells might be transferred after tonometer testing, potentially exposing thousands of patients to the disease yearly.

The BJO Online also published an e-letter in response to the article, reviewing the literature in light of the authors’ findings. Jodhbir S. Mehta and colleagues note in the letter that the risk of transmission from tonometer tips may be “more theoretical than practical” at present. Only one confirmed CJD case has been reported after corneal transplantation, and the prion load in tonometer testing “can hardly be compared” to that from a full-thickness corneal graft, the authors note.