Sir,

We read with interest the article entitled ‘Tonometer disinfection practice in the United Kingdom: a national survey,’1 and agree with the conclusion that guidelines for tonometer disinfection in the United Kingdom are necessary. We would like to comment on the article's surprising finding that 23% of ophthalmology units with training recognition have adopted exclusive use of disposable tonometer prisms despite evidence that there is still a risk of transmission of pathogens when using these,2 and that they are less accurate than a Goldmann prism.3 In the absence of concrete evidence of reduced risk of transfer of viral and bacterial pathogens and controversy about the small theoretical risk of transmission of vCJD,4 we must consider the financial and environmental costs associated with the use of disposable prisms. If we assume that an average ophthalmologist sees 4000 patients per annum, the cost of two non-disposable Goldmann prisms and 36 l of 0.5% sodium hypochlorite solution would be £244 per annum. The cost for Tonosafe disposable prisms for this number of patients would be £2324 (personal communication, Haag Streit). This amounts to a cost per patient of 58.1 pence for the Tonosafe prism and 6.1 pence for the non-disposable prism, a difference in cost per doctor per annum of £2080. Waste produced per 4000 patients using non-disposable prisms is 48 plastic bottles, whereas using disposable prisms results in 5.52 kg of plastic and 1.68 kg of paper waste. There are approximately 2500 consultants, associate specialists, and trainee ophthalmologists working in the United Kingdom (Royal College of Ophthalmologists, personal communication). If all of these were to use disposable Tonosafe prisms, this would result in an approximate added cost to the NHS of £5.2 million per annum and the production of 4.2 tonnes more paper waste, and 13.8 tonnes more plastic waste than if non-disposable prisms were used. Climate change is happening and mankind is believed to be responsible.5 In the absence of a strong case for disposable prism use, guidelines on disinfection can support practice which reduces the risk of cross contamination to acceptable levels, reduces costs and reduces the contribution of ophthalmologists to climate change.

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