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

Abstract

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 263 participants in a trial comparing two photocoagulation techniques for DME. Correlation coefficients (r) were calculated comparing RT measured 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) microm in the lowest level of the photographic scale to 517 (455, 598) microm 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.

Trial registration: ClinicalTrials.gov NCT00071773.

Figures

Figure 1

Comparison of ETDRS (black) and OCT (white) macular grids. When centered on the macula, the solid circles and radial lines divide the area within the grid into nine subdivisions (subfields): one central, four inner, and four outer. The central and four inner subfields combined comprise the inner zone. The diameter of the ETDRS grid is four standard disc diameters, and its area is 16 disc areas. In the ETDRS, the historical precedent for considering the diameter of the average normal disc to be 1500 μm was adopted, resulting in designations of 6000, 3000, and 1000 μm for the diameters of the three solid circles. With the advent of photodynamic therapy and digital fundus photography, 1800 μm has been adopted as a more realistic estimate of the diameter of the average normal disc. With this convention, the diameters of the ETDRS grid may be expressed as 7200, 3600, and 1200 μm, whereas those of the OCT grid remain 6000, 3000, and 1500 μm.

Figure 2

Distribution of retinal thickness in the central subfield by ETDRS DME severity level at baseline. The boxes indicate 25th to 75th percentiles and the whiskers the 10th and 90th percentiles. Solid line: median; dashed line: mean.

Figure 3

Distribution of retinal thickness in the central subfield by ETDRS DME severity level at 12 months. The plots are as described in Figure 2.

Figure 4

Distribution of baseline to 12-month change in retinal thickness in the central subfield by change in ETDRS DME severity level. Negative change in OCT values indicates decrease in thickening.