Macular oedema: the measurements that count

Thickness measurements of the central macular region can be used to differentiate between eyes with and without diffuse clinically significant macular oedema (CSMO), but not between eye with or without foveal CSMO, according to a study published in the February issue of Acta Ophthalmologica Scandinavia.

Lars Loumann Knudsen from the Aarhus University Hospital, Aalborg, Denmark, conducted a study that included 47 normal subjects and 158 ocular examinations of 38 eyes from 22 diabetic subjects with and without CSMO. The central macular region was subdivided into narrow concentric rings around the foveola and the thickness of the individual concentric rings were calculated. Sensitivity and specificity of the CSMO diagnosis were established using the average thickness and the thickness of the concentric rings.

It was found that the average thickness of the central macular region was 165.1 µm in the normal subjects and 192.3 µm in eyes without CSMO. The thickness increased significantly to 198.2 µm in eyes with foveal CSMO and 236.9 µm in eyes with diffuse CSMO. Sensitivity for focal CSMO was 48% with average thickness measurements and 83.6% with concentric rings. The corresponding values for detection of diffuse CSMO were 91.7% and 96.1%, respectively. Specificity was 77.4% with average thickness measurements and 79.7% with concentric rings.

Knudsen concluded that, although thickness measurements can be used to distinguish between eyes with and without diffuse CSMO, it is not as effective at distinguishing between eyes with and without foveal CSMO. He added that sub–analysis based on concentric rings around the foveola does seem to be a useful clinical tool for increasing diagnostic certainty.