Comparison of time-domain OCT and fundus photographic assessments of retinal thickening in eyes with diabetic macular edema

Purpose. To explore the correlation between optical coherence tomography (OCT) and stereoscopic fundus photographs (FP) for the assessment of retinal thickening (RT) in diabetic macular edema (DME) within a clinical trial. Methods. OCT, FP, and best corrected visual acuity (VA) measurements were obtained in both eyes of 265 participants in a trial comparing two photocoagulation techniques for DME. Correlation coefficients (r) were calculated comparing RT mea- sured by OCT, RT estimated from FP, and VA. Principal variables were central subfield retinal thickness (CSRT) obtained from the OCT fast macular map and DME severity assessed by a reading center using a seven-step photographic scale combining the area of thickened retina within 1 disc diameter of the foveal center and thickening at the center. Results. Medians (quartiles) for retinal thickness within the center subfield by OCT at baseline increased from 236 (214, 264) fxm in the lowest level of the photographic scale to 517 (455, 598) in the highest level (r = 0.67). However, CSRT interquartile ranges were broad and overlapping between FP scale levels, and there were many outliers. Correlations between either modality and VA were weaker (r = 0.57 for CSRT, and r = 0.47 for the FP scale). OCT appeared to be more reproducible and more sensitive to change in RT between baseline and 1 year than was FP. Conclusions. There was a moderate correlation between OCT and FP assessments of RT in patients with DME and slightly less correlation of either measure with VA. OCT and FP provide complementary information but neither is a reliable surrogate for VA.