Subconjunctival anaesthesia for intravitreal injections

Abstract

Sir, We read with interest the paper by Lyall et al,1 who report the results of an observational study of infective endophthalmitis in the United Kingdom following intravitreal anti-VEGF injection. Using 200 patients selected from 10 control centres, the authors identified 3 endophthalmitis patients, compared to 1 control patient, who had received subconjunctival anaesthesia prior to intravitreal injection. Their conclusion that subconjunctival anaesthesia is a significant risk factor for developing infectious endophthalmitis, with an odds ratio of 13.7, was surprising to us. A subconjunctival fluid bleb serves to act as a mechanical barrier between the outside world and the vitreous cavity, and would thereby be expected to reduce the risk of a vitreous wick being exposed to conjunctival flora. To our knowledge, subconjunctival anaesthesia has not been identified as a risk factor for endophthalmitis by any other study. Furthermore, we note the very large confidence interval for the odds ratio (1.07–728.9); however, we recognise that this is a result of studying a rare complication such as post-injection endophthalmitis. We would be interested to know whether subconjunctival anaesthetic was the standard of care in the centres that treated the three patients who developed endophthalmitis, and whether these three patients had any other risk factors for endophthalmitis. In the Medical Retina Unit in Southampton, subconjunctival anaesthesia with 2% lidocaine is standard practice for all patients receiving intravitreal injections. Of the 6000 anti-VEGF injections performed in our unit between January 2012 and December 2012, there have been four instances of post-injection endophthalmitis, representing an incidence of 0.07%, which is not significantly dissimilar from the overall incidence in this or other large studies.2, 3 We are reluctant to change our clinical practice unless there is firm evidence against the use of subconjunctival anaesthesia.