This study requires four groups of 8,750 patients - 35,000 in all - to demonstrate reductions of currently reported rates of endophthalmitis (approximately 0.3%) in patients where no intraocular antibiotics are used, or where they are used by the subconjunctival route. Other studies using intraocular vancomycin have reported results as low as 0.05%, but these studies were not standardised or controlled and the results were anecdotal. In addition, vancomycin should not be used for routine prophylaxis and should only be used as the antibiotic of 'last resort'.