Comparison of optical coherence tomography in diabetic macular edema, with and without reading center manual grading from a clinical trials perspective.

PURPOSE: To analyze the value of reading center error correction in automated optical coherence tomography (OCT; Stratus; Carl Zeiss Meditec, Inc., Dublin, CA) retinal thickness measurements in eyes with diabetic macular edema (DME).
METHODS: OCT scans (n=6522) obtained in seven Diabetic Retinopathy Clinical Research Network (DRCR.net) studies were analyzed. The reading center evaluated whether the automated center point measurement appeared correct, and when it did not, measured it manually with calipers. Center point standard deviation (SD) as a percentage of thickness, center point thickness, signal strength, and analysis confidence were evaluated for their association with an automated measurement error (manual measurement needed and exceeded 12% of automated thickness). Curves were constructed for each factor by plotting the error rate against the proportion of scans sent to the reading center. The impact of measurement error on interpretation of clinical trial results and statistical power was also assessed.
RESULTS: SD was the best predictor of an automated measurement error. The other three variables did not augment the ability to predict an error using SD alone. Based on SD, an error rate of 5% or less could be achieved by sending only 33% of scans to the reading center (those with an SD >or= 5%). Correcting automated errors had no appreciable effect on the interpretation of results from a completed randomized trial and had little impact on a trial's statistical power.
CONCLUSIONS: In DME clinical trials, the error involved with using automated Stratus OCT center point measurements is sufficiently small that results are not likely to be affected if scans are not routinely sent to a reading center, provided adequate quality control measures are in place.