Sir,

The theoretical risk of prion transmission has led to the widespread use of disposable prism tonometers.1 This has led to the marketing of products such as TONOSAFE (Haag-Streit UK), who state in their product information that ‘disposable prisms are convenient, effective method of reducing the risk of cross infection between patients and eliminating the need to clean and disinfect prisms.’2 The actual prisms have been shown to enable accurate pressure measurement and to be sterile.3, 4 The potential risk of transmission of microbial contamination of the holder for disposable applanation prisms has yet to be reported (see Figure 1).

Figure 1
figure 1

Illustration of TONOSAFE prism and holder.

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Case report

In the light of this, an audit of handwashing was performed during a general ophthalmology checkup. This involved plating of ophthalmologist's fingers, after handwashing, following the interaction with patients. The sterile holder (TONOSAFE) was also plated after use with each successive patient (n=10). The next day, the process was repeated, but the holder was disinfected with alcohol wipes between patients (as was standard in the traditional Goldmann tonometer).

Normal skin flora was grown on doctor's blood agar plates. This included Staphyloccocus aureus and coagulase-negative Staphylococcus. These organisms were shown to be present on the plates of the holder even after the first patient (see Figure 2). We believe that they had transferred from patient to holder through the doctor's hands. Alcohol wiping of holder removed all organisms.

Figure 2
figure 2

Blood agar plate from plating of holder showing the growth of Staphylococcus aureus following the evaluation by Staphareux.

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Comment

Disposable tonometers have been advocated as a better replacement for Goldmann tonometers as they ‘eliminate the need to clean and disinfect prisms.’2 This audit has shown that bacteria can be transferred to the holder and are transferred between patients through the clinicians' hands (despite handwashing). The transmission of S. aureus (including MRSA) presents a potential risk for infection control, particularly in the elderly population.5 Although this is unlikely to be of pathological significance, these results contradicts the manufacturer's claims regarding their product.

We believe that even the disposable holders should be cleaned with alcohol wipes between patients to reduce this risk. The original reason for introducing disposable prisms was to eliminate transfer. These results indicate that this risk has not been averted.