Background/aims To compare the visual outcome in early versus deferred surgery in patients with idiopathic epiretinal membrane (ERM) and good presenting visual acuity and mild symptoms.

Methods This study is a randomised clinical trial. 53 eyes of 53 patients with symptomatic ERM and best-corrected visual acuity (BCVA) at presentation ≥65 early treatment diabetic retinopathy study (ETDRS) letters were randomised to immediate surgery (20 eyes) or to watchful waiting (33 eyes) for 1 year. Primary end-point was BCVA after 12 months. Secondary end-points were central macular thickness and the number of patients that crossed over from the watchful waiting arm to the surgery arm due to deteriorated symptoms.

Results Mean BCVA after 12 months in the watchful waiting group (81 letters) were not significantly different from patients undergoing immediate surgery (82.5 letters, p=0.647). During 1 year of follow-up, eight patients in the watchful waiting group (24%) crossed over to surgery and these patients gained a mean of 3.1 letters (SEM 1.38). Patients randomised to immediate surgery gained approximately one line. Watchful waiting patients who remained without surgery were stable. The visual acuity gain after surgery is slow and gradual until 9 months postoperatively. There were no serious complications such as retinal detachment or infectious endophthalmitis.

Conclusions Vitrectomy for early symptomatic ERM is beneficial in preserving excellent vision. A watchful waiting approach with 1 year of follow-up is safe in the sense that this group does not lose five ETDRS letters in waiting. Deferral of surgery by regular monitoring of patients is a safe approach.

Trial registration numbers H-C-2008-026 and NCT00902629.