Purpose To determine the rate of progression of eyes with subclinical diabetic macular edema (DME) to clinically apparent DME or DME necessitating treatment during a 2-year period. Methods In all, 43 eyes from 39 study participants with subclinical DME, defined as absence of foveal center edema as determined with slit lamp biomicroscopy but a center point thickness (CPT) between 225 and 299 lm on time domain (Stratus, Carl Zeiss Meditec) optical coherence tomography (OCT) scan, were enrolled from 891 eyes of 582 subjects screened. Eyes were evaluated annually for up to 2 years for the primary outcome, which was an increase in OCT CPT of at least 50 lm from baseline and a CPT of at least 300 lm, or treatment for DME (performed at the discretion of the investigator). Results The cumulative probability of meeting an increase in OCT CPT of at least 50 lm from baseline and a CPT of at least 300 lm, or treatment for DME was 27% (95% confidence interval (CI): 14%, 38%) by 1 year and 38% (95% CI: 23%, 50%) by 2 years. Conclusions Although subclinical DME may be uncommon, this study suggests that between approximately one-quarter and one-half of eyes with subclinical DME will progress to more definite thickening or be judged to need treatment for DME within 2 years after its identification.

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The Diabetic Retinopathy Clinical Research Network Clinical Sites that participated on this protocol: Sites are listed in order by the number of subjects enrolled into the study. The number of subjects enrolled is noted in parenthesis preceded by the site location and the site name.