Date Published: June 7, 2018
Publisher: Public Library of Science
Author(s): Maria P. Bambo, Beatriz Cameo, Ruben Hernandez, Enrique Fuentemilla, Noemi Güerri, Blanca Ferrandez, Vicente Polo, Jose M. Larrosa, Luis E. Pablo, Elena Garcia-Martin, Sanjoy Bhattacharya.
To evaluate the diagnostic ability of macular ganglion cell (mGCL) and macular retinal nerve fiber (mRNFL) layers, to detect early glaucomatous eyes, using the new segmentation software of Spectralis optical coherence tomography (OCT) device (Heidelberg Engineering).
A total of 83 eyes from 83 subjects were included in this observational, prospective cross-sectional study: 43 healthy controls and 40 early primary open-angle glaucoma (POAG) patients. All participants were examined using the Horizontal and Vertical Posterior Pole protocols, and the peripapillary RNFL (pRNFL) protocol of Spectralis OCT device. The new automated retinal segmentation software was applied to horizontal and vertical macular B-scans to determine mGCL and mRNFL thicknesses in each one of the 9 sectors of the Early Treatment Diagnostic Retinopathy Study circle. Thickness of each layer was compared between groups, and the sectors with better area under the receiver operating characteristic curve (AUC) were identified.
mGCL was significantly thinner in the POAG group, especially in outer and inner temporal sectors (p<0.001); and mRNFL was significantly thinner in the POAG group in the outer inferior and the outer superior sector (p<0.001). Diagnostic accuracy of inner macular layers was good, and in general mGCL was superior to mRNFL. pRNFL obtained the best diagnostic capability (AUC, 0.886). Horizontal and vertical Posterior Pole protocols performed similarly. Inner macular layers using either horizontal or vertical B-scans, especially temporal sectors of mGCL, have good diagnostic capability to differentiate early glaucomatous eyes from control eyes; however, pRNFL has the highest diagnostic sensitivity for glaucoma detection.
The advent of new spectral domain optical coherence tomography (SD-OCT) technology has allowed a more rapid acquisition of retinal images at a higher axial-image resolution, enabling better identification of individual retinal layers . Consequently, there has been an increasing interest in the importance of evaluating inner macular layers in glaucoma diagnosis . Recent studies have demonstrated that macular damage occurs early in the disease process  and structural changes in the macula can thus precede detectable visual field (VF) loss .
Analysis was finally performed on 40 early POAG eyes of 40 participants and 43 healthy eyes of 43 normal participants. The demographic and clinical characteristics and pRNFL thicknesses of each group are summarized in Table 1. There were no differences in age, gender and spherical equivalent between groups. As expected, MD was significantly worse in the glaucoma group (MD, -3.06±1.86 dB) than in normal participants (MD, -0.33±1.47 dB).
The present study analyzed the diagnostic ability of two individual inner macular layers (mRNFL and mGCL) obtained using a new segmentation software, with Posterior Pole protocols (one performed with 61 horizontal B-scans and the other with 19 vertical B-scans) of Spectralis SD-OCT. Previous authors had evaluated the role of macular inner layers in glaucoma, but using horizontal scanning protocols only [4–7] or after a manual segmentation of SD-OCT B-scans . This is the first study to compare the ability of new automatic segmentation software for Spectralis SD-OCT in the macular area, with both horizontal and vertical scan Posterior Pole protocols. The results showed that some sectors of inner macular layers have similar diagnostic capability than the classical peripapillary RFNL to differentiate early glaucomatous eyes from control eyes, and outer ETDRS sectors performed better than inner sectors for diagnosis. In general, mGCL was superior to mRFNL to discriminate glaucoma subjects, but pRNFL shown the best diagnostic accuracy.