Aims To explore the parameters that influence injection frequency in patients treated with intravitreal bevacizumab (ivB) for diabetic macular oedema. Injection frequency was considered as a surrogate marker of persistent or recurrent oedema.

Methods A post hoc analysis of the patients randomised to the ivB arm of a prospective, randomised controlled trial (A prospective randomized trial of intravitreal bevacizumab or laser therapy in the management of diabetic macular edema (BOLT study)) was done to assess the factors that may determine the injection frequency at 12 and 24 months. The injection response patterns were classified based on the specific time point at which the macula was first defined as ‘dry’.

Results Eyes with better baseline visual acuity less frequently had persistent oedema and had fewer recurrences in the second year. All eyes with baseline subretinal detachment showed persistent macular oedema at 24 months. None of the other factors assessed influenced injection frequency or response in the first or second year.

Conclusions Good long-term response is predicted by resolution of macular oedema by 4 months. However, approximately 20% of patients with persistent oedema at 12 months achieved a dry macula and 50% gained more than 15 letters at 24 months with sustained treatment, suggesting that oedema at 4 or 12 months should not be used as a stopping criterion for treatment.