A comparative study between four different OCT devices has shown pronounced differences in retinal thickness values. Results of the study, published in the journal Retina (2011, Vol. 31, No. 1, pp 48-55) suggest that due care should be exercised in respect of monitoring and quantifying therapeutically induced effects. The research, conducted at the Medical University of Vienna, Austria, indicated that different segmentation algorithms of thickness measurement software may in part explain the divergence between devices. Given the increasing importance of OCT data in treatment indication and follow-up for cases of diabetic macular edema (DME), the findings provide important information for both practicing clinicians and sponsors of clinical trials.