Reproducibility of Macular Thickness and Volume Using Zeiss Optical Coherence Tomography in Patients with Diabetic Macular Edema

Abstract

Purpose: To evaluate optical coherence tomography (OCT) reproducibility in patients with diabetic macular edema (DME). Design: Prospective one day observational study. Participants: 212 eyes (107 subjects) with DME involving the macular center by clinical exam and an OCT central subfield thickness ≥ 225 microns. Methods: Retinal thickness was measured with OCT3 and scans evaluated by a reading center. Reproducibility of retinal thickness measurements was assessed and 95% confidence intervals (CI) for a change in thickness were estimated. Main Outcome Measures: Reproducibility of OCT-measured central subfield thickness Results: Reproducibility was better for central subfield thickness than for center point thickness (half-width of the 95% CI for absolute change = 38 versus 50 microns and for relative change 11% versus 17%, respectively, P<0.001). Median absolute difference between replicate measurements of the central subfield was 7 microns (2%). The half-width of the 95% CI for a change in central subfield thickness was 22, 23, 33 and 56 microns for scans with central subfield thickness of < 200, 200–<250, 250–<400 and ≥ 400 microns, respectively. When expressed as percentage difference between two measurements, the half-width of the 95% CI for a change in central subfield thickness was 10%, 10%, 10%, 13% for scans with central subfield thickness of < 200, 200–<250, 250–<400 and ≥ 400 microns, respectively. We were unable to identify an effect on reproducibility of central subfield measurements with respect to the presence of cystoid abnormalities, subretinal fluid, vitreomacular traction, or reduced visual acuity. Reproducibility was better when both scans had a standard deviation of the center point <10.0% (half-width of the 95% CI for change 33 versus 56 microns, P<0.001). Conclusions: Reproducibility is better for central subfield thickness measurements than for center point measurements and variability is less with retinal thickness when expressed as a percent change than when expressed as an absolute change. A change in central subfield thickness exceeding 11% is likely to be real. Scans with a standard deviation of the center point ≥ 10.0% are less reproducible and should be viewed with caution when assessing the validity of an observed change in retinal thickness in patients with DME.