A comparison of quantitative mapping and stereoscopic fundus photography grading of retinal thickness in diabetic eyes with macular edema

OBJECTIVE: To evaluate the ability of a retina specialist's grading of 30° color stereoscopic fundus photographs to identify areas of significant retinal thickening as assessed by the Retinal Thickness Analyzer (RTA) and to determine whether this ability was affected by the presence of retinal pathology. MATERIALS AND METHODS: Thirty-two eyes in 29 patients clinically diagnosed as having diabetic macular edema underwent RTA scanning and nonsimultaneous 30° color stereoscopic fundus photography. Retinal thickness maps of the macular area were generated, and regions with significant retinal thickening (≥2 SD above normal values) were identified. A retina specialist reader, masked to the RTA measurements, identified areas with macular edema on the stereoscopic fundus photographs, which subsequently were overlaid on the retinal thickness maps. The sensitivity (percent of significant retinal thickening areas identified by the retina specialist grading the stereoscopic fundus photographs) was calculated separately for areas with and without retinal pathology. Specificity of the stereoscopic fundus photograph grading was assessed similarly. RESULTS: The retina specialist's stereoscopic fundus photography grading identified 78.8% of areas with significant retinal thickening (range over eyes: 20.4%-100%) and was slightly more likely to identify significant retinal thickening when pathology was present (89.6%) than when pathology was not present (78.4%; pooled risk ratio, 1.14 [95% CI=0.54, 2.42]). Specificity of stereoscopic fundus photography grading was 58%, ie, 42% of areas without significant retinal thickening were (incorrectly) identified as edematous by the stereoscopic fundus photograph grading. This misidentification was more likely if pathology was present (76.9%) than if pathology was not present (41.1%; pooled risk ratio, 1.87 [95% CI=1.28, 2.73]). CONCLUSION: This study shows the determination of macular edema by a retina specialist reading color stereoscopic fundus photographs is sensitive but not specific with reference to edema identified by the RTA. Furthermore, the presence of retinopathy tends to cause false-positive readings with reference to edema identified by the RTA. These findings indicate the need to use objective, quantitative methods in clinical studies to detect and monitor macular edema.