Identification of diabetic macular oedema using retinal thickness measurements

Abstract

Identification of clinically significant macular oedema (CSMO) involves human depth perception, which is subject to a degree of uncertainty. However, although the ability to obtain objective thickness measurements of the central macular region may be advantageous, the topography of the macular region suggests that average thickness measurements represent a simplification of the topographic profile of the region. This study explored the applicability of additional sub-analysis of central macular thickness measurements. The study included 47 eyes of 47 normal subjects and 158 ocular examinations of 38 eyes from 22 diabetic subjects with and without CSMO. All eyes underwent central macular thickness measurements using retinal thickness analysis equipment. Eyes of diabetes subjects were classified as being without CSMO (n = 53), with focal CSMO (n = 50) and with diffuse CSMO (n = 55). The central macular region was subdivided into narrow concentric rings around the foveola, using a new invention, and the thicknesses of the individual concentric rings were calculated. The sensitivity and specificity of the CSMO diagnosis were established using the average thickness and the thicknesses of the concentric rings. The average thickness of the central macular region was found to be 165.1 microm in eyes of normal subjects and 192.3 microm in eyes without CSMO. It increased non-significantly to 198.2 microm in eyes with focal CSMO and significantly to 236.9 microm in eyes with diffuse CSMO. Sensitivity for focal CSMO was 48.0% with average thickness measurements and 83.6% with concentric rings. 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. Thickness measurements of the central macular region can be used to distinguish between eyes with and without diffuse CSMO, but not between eyes with and without focal CSMO. Additional sub-analysis based on concentric rings around the foveola seems to be a useful clinical tool that increases diagnostic certainty in these eyes.