Diabetic macular oedema is a major cause of visual loss in patients with diabetes. The Early Treatment of Diabetic Retinopathy Study showed that focal laser photocoagulation reduced moderate visual loss in eyes with clinically significant macular oedema.^1–3 The efficacy of grid photocoagulation for treatment of diffuse diabetic macular oedema was reported in the 1980s.^4–6 Those studies reported resolution of macular oedema and stabilisation or improvement of visual acuity (VA). Eyes treated with conventional grid photocoagulation for diffuse macular oedema, however, developed progressively expanding laser scars that resulted in decreased vision,⁷ subretinal fibrosis⁸ and visual field loss.^6,9 Lee and Olk¹⁰ reported that VA improved in 14.5% and was unchanged in 60.9% of eyes with diffuse macular oedema treated with grid laser photocoagulation. However, the VA decreased by three lines or more in 24.6% of eyes. The limited efficacy of grid laser photocoagulation for treatment of diffuse macular oedema prompted interest in modified methods of grid photocoagulation and other treatments such as steroid injections and pars plana vitrectomy.

In eyes with diffuse diabetic macular oedema, retinal opacification, macular swelling and fluid accumulation prevent …