The Royal College of Ophthalmologists' National Ophthalmology Database Study of Cataract Surgery: Report 13, monitoring post-cataract surgery endophthalmitis rates-the rule of X.

backgroundCataract surgical safety has improved over recent decades, with endophthalmitis rates before 2006 typically 0.13-0.15% compared with the most recent UK national estimate of 0.02%. There remains, however, substantial variation in reported rates from different centres. Due to the low event rate, this disparity may not be noticed and opportunities to improve therefore be missed. We propose a method of monitoring post-cataract endophthalmitis rates that would help centres with higher rates identify this.

methodsA statistical tool, available to download or use online, permits comparison of local endophthalmitis rate with the estimated UK rate of 0.02%. Centres are encouraged to maintain a register of endophthalmitis cases, and when the number reaches a threshold (X cases), either in a certain time period or in a fixed number of procedures, then the centre can consider itself as an outlier and trigger local investigations to improve infection control.

resultsExample outputs are offered, such as for a unit doing 5000 cataracts annually, a value of X is suggested such that the third case of endophthalmitis (X = 3) in a 12-month period would give 85% confidence, the fourth case 90% confidence and the fifth case 95% confidence that the true endophthalmitis rate for that unit was higher than the national average.

conclusionsThis statistical tool provides a basis for units to set a threshold number of cases of endophthalmitis within a given period that would trigger local processes, thus helping inform local monitoring processes for this rare but potentially catastrophic complication of cataract surgery.