PurposeOur aim was to evaluate the impact of intravitreal ranibizumab pretreatment on the outcome of vitrectomy surgery for advanced proliferative diabetic retinopathy. The objective was to determine the feasibility of a subsequent definitive trial and estimate the effect size and variability of the outcome measure.Patients and methodsWe performed a pilot randomised double-masked single-centre clinical trial in 30 participants with tractional retinal detachment associated with proliferative diabetic retinopathy. Seven days prior to vitrectomy surgery, participants were randomly allocated to receive either intravitreal ranibizumab (Lucentis, Novartis Pharmaceuticals UK Ltd, Frimley, UK) or subconjunctival saline (control). The primary outcome was best-corrected visual acuity 12 weeks following surgery.ResultsAt 12 weeks, the mean (SD) visual acuity was 46.7 (25) ETDRS letters in the control group and 52.6 (21) letters in the ranibizumab group. Mean visual acuity improved by 14 (31) letters in the control group and by 24 (27) letters in the ranibizumab group. We found no difference in the progression of tractional retinal detachment prior to surgery, the duration of surgery, or its technical difficulty. Vitreous cavity haemorrhage persisted at 12 weeks in two of the control group but none of the ranibizumab group.ConclusionRanibizumab pretreatment may improve the outcome of vitrectomy surgery for advanced proliferative diabetic retinopathy by reducing the extent of post-operative vitreous cavity haemorrhage. However, the effect size appears to be modest; we calculate that a definitive study to establish a minimally important difference of 5.9 letters at a significance level of P<0.05 would require 348 subjects in each arm.