Backgroud/aims The purpose of this study was to determine the incidence of, and risk factors dictating, progression of subclinical macular oedema (SCME) to clinically significant macular oedema (CSME) in patients with diabetes.

Methods This was a retrospective, observational case-controlled study at the Veterans Administration (VA) Boston Healthcare System. The study group included subjects with central subfield macular thickness (CSMT) of 200–300 μm, measured by optical coherence tomography, compared with a control group with foveal thickness of <200 μm, matched for age, sex and duration of diabetes. Main outcomes measured were progression to CSME by clinical examination.

Results A total 124 eyes of 73 diabetic patients from the greater Boston area were included in this retrospective study. The study group comprised 52 eyes of 37 diabetic patients with SCME in one or both eyes. The control group included 72 eyes of 36 patients without macular oedema. Sixteen eyes of 13 subjects (35%) progressed to CSME in the study group, compared with six eyes of four subjects (11%) in the control group. Stepwise logistic regression analysis confirmed that prior history of CSME increased the risk of progression (OR 3.69, CI 1.10 to 12.31, p=0.03). Logistic regression analysis also depicted a 15% increase in odds of progression with each 10 μm increase in CSMT (OR 1.15, CI 1.03 to 1.28, p=0.01).

Conclusions The results and statistical analyses of this retrospective study suggest that a significant number of patients with SCME ultimately progress to CSME compared with controls. A significant association with prior history of CSME, advancing age and graded increases in CSMT was found.