Volumetric analysis of early macular edema with the Heidelberg retina tomograph in diabetic retinopathy

Objective: This study describes a new method for the quantification of diabetic macular edema by volumetric analysis with the Heidelberg Retina Tomograph (HRT) scanning laser ophthalmoscope. Design: Topographic images of the macula were obtained in 25 consecutive patients who fitted the inclusion criteria. Twenty age-matched control subjects were randomly selected for a similar examination. Participants: Twenty normal control eyes and 32 eyes of 25 patients with diabetes mellitus were studied. Intervention: Patients with diabetes were examined by HRT and slit-lamp biomicroscopy with a contact lens. On HRT, the volumes above reference plane bound by three consecutive circles centered at the fovea (diameter, 1, 2, and 3 mm) were measured. Measurements were repeated three times in a masked fashion, and the mean measurements were used for the analysis. Main Outcome Measures: Visual acuity, macular edema, and volume above reference plane were measured. Results: There were 19 diabetic eyes with clinical macular edema (deemed positives) and 13 without edema (deemed negatives). Diabetic eyes with macular edema had statistically greater volumes above reference plane than did diabetic eyes without edema (P < 0.001) and greater than the control eyes (P < 0.001) for all three circles. There was no statistically significant difference between volumes measured in eyes without macular edema and control eyes (P = 0.42 for the 1-mm diameter circle; P = 0.72 for the 2-mm diameter circle; and P = 0.19 for the 3-mm diameter circle). For the two smallest circles only, the sensitivity of the HRT was 78.94%, and the specificity was 84.61%. None of the patients missed on the two smallest circles would have been positively identified on the 3-mm diameter circle. Conclusion: The HRT can detect and quantify macular edema in diabetes by volumetric analysis with the method the authors have described. It is sufficient to measure the volumes above reference plane of two circles centered on the fovea and measuring 1 and 2 mm in diameter because the 3-mm diameter circle does not increase the system's sensitivity.