Repeatability of Spectralis OCT measurements of macular thickness and volume in diabetic macular edema.

Objective: We estimated coefficients of repeatability for Spectralis optical coherence tomography (OCT)-derived automated retinal thickness and volume measurements in subjects with center-involving diabetic macular edema (DME).

Methods: A total of 50 eyes of 50 consecutive patients with center-involving DME underwent four consecutive "fast" volume scans at a single session using one OCT device operated by one of two experienced operators. Bland-Altman coefficients of repeatability (CR) were calculated for automated retinal thickness measurements in the nine Early Treatment of Diabetic Retinopathy Study (ETDRS) subfields, center point thickness, and total macular volume. Scans were evaluated for significant automated retinal boundary detection error and revised estimates for CR calculated with these scans excluded.

Results: CR in the central subfield was 8.03 μm (95% confidence interval [CI] 7.70-8.35 μm). In other subfields, CR ranged from 6.54 to 18.25 μm. Scan sets from 13 subjects had significant boundary detection error; reanalysis with these excluded yielded a CR for the central subfield of 7.44 μm with CR for all other subfields <8 μm.

Conclusions: Retinal thickness measurements in subjects with DME obtained using Spectralis OCT are considerably less variable than has been reported with other devices. Changes in central subfield thickness >8 μm can be considered more indicative of true clinical change rather than measurement variability. This finding informs clinical practice and clinical trial design.