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 μm 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 μm from baseline and a CPT of at least 300 μm, 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 μm from baseline and a CPT of at least 300 μm, 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.