Topographical Correlation Between Macular Layer Thickness and Clockwise Circumpapillary Retinal Nerve Fiber Layer Sectors in Patients with Normal Tension Glaucoma

Purpose: To define topographical areas of the macula in optical coherence tomography (OCT) scans by identifying regions in which macular retinal nerve fiber layer (mRNFL) and ganglion cell-inner plexiform layer (mGCL + IPL) thickness was highly correlated with clockwise circumpapillary RNFL (cpRNFL) thickness in patients with normal tension glaucoma (NTG). Methods: This study included 101 eyes of 101 patients with mild or moderate NTG. CpRNFL, mRNFL, and mGCL+ IPL thickness were assessed with spectral-domain OCT (3D OCT-2000). The region of interest (6 x 6mm square) was centered on the fovea and layer thickness was measured at each point on a 10 x 10 grid. Spearman's rank correlation coefficient was determined between each temporal clockwise sector (7, 8, 9, 10, 11 o'clock) of the cpRNFL and each grid point in the mRNFL and mGCL+ IPL. Grid points were defined as correlated to specific clockwise sectors when the correlation coefficient was more than 0.4. To validate the areas comprised by these points, they were superimposed on a swept-source OCT image (12 x 9mm, EnView software, Topcon) showing the anatomical trajectory of nerve fiber defects. Results: Macular areas with a high correlation coefficient (r >= 0.4, p<0.05) to clockwise cpRNFL were identified. The number of grid points in the mRNFL and mGCL+ IPL correlated to specific clockwise cpRNFL sectors was, respectively, 40 and 18 (7 o'clock), 41 and 22 (8), 33 and 44 (9), 39 and 39 (10), and 18 and 19 (11) (r = 0.40-0.79). Interestingly, the distribution of mRNFL sectors closely matched the RNFL defects in the OCT image, although the mGCL+ IPL sectors differed and were closer to the fovea than the mRNFL sectors. Conclusion: The identification of these topographical macular areas, and the different layouts in the mRNFL and the mGCL+ IPL, may increase the accuracy of clinical research on NTG.