The authors describe a multi-centre prospective observational study of 293 participants that underwent cataract surgery who all had diabetic retinopathy without definite central-involved macular oedema. Forty-five clinical sites took part throughout the United States. Patients were eligible if there was cataract with surgery scheduled within 28 days of recruitment. Central subfield thickening was measured on optical coherence tomography (OCT), if the thickness was less than 250 microns on time domain OCT or less than 310 on spectral domain OCT. Criteria included visual acuity of light perception or better, and presence of microaneurysms on clinical examination. The study showed that 16 weeks after cataract extraction there is an increased risk of developing central involved macular oedema if there is the presence of non-central involved diabetic macular oedema (DME) immediately prior to cataract surgery or any history of previous treatment for DME.