Macular Ganglion Cell Layer Imaging in Preperimetric Glaucoma with Speckle Noise–Reduced Spectral Domain Optical Coherence Tomography

Abstract

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A Novel Method to Detect Local Ganglion Cell Loss in Early Glaucoma Using Spectral-Domain Optical Coherence Tomography

“…However, Curcio et al also reported that the macular RGC density is not completely symmetrical: the temporal RGC density was slightly lower than the nasal RGC density, whereas the inferior and superior RGC densities were almost equivalent. 1 Nakano et al 13 measured the GCL thickness on SD-OCT images and found identical symmetry between the macular GCL thickness and the RGC density; that is, the temporal GCL was thinner than the nasal GCL, while the superior and inferior GCL thicknesses were almost equivalent. Therefore, we estimated the variability of GCIPL measurements among 360 spokes and found mild variations (maximum difference, 12% of average GCIPL thickness on 360 spokes) among 360 spokes even in healthy eyes.…”

“…Earlier studies using SD-OCT showed similar symmetrical thicknesses of the GCL, IPL, and GCLþIPL of healthy eyes in an elliptical annulus. 7,10,13,19,26 The GCIPL thicknesses on all 360 spokes should be equivalent if the symmetry is perfect; and, consequently, the initial RGC loss limited to a small local area would be detectable as a decrease of the GCIPL thickness on the spokes, leading to minimum GCIPL thickness. Thus, this parameter should theoretically detect early or initial RGC loss with high sensitivity.…”

“…However, the dimension of the outer ring was selected to conform closely to the real anatomy of the macular region, where the GCL is thickest in a healthy eye. 1,13 These parameters were tested in a preliminary analysis using GCIPL maps of 47 healthy eyes. 10,11 We checked the quality of GCIPL segmentation in all of the B-scans in each cube scan by using the criteria of Ishikawa et al 23 In detail, segmentation failures were defined as obvious disruption of the detected border, and/or border wandering (detected border jumping to and from different anatomic structures), within >5% consecutively (i.e., an uninterrupted error) or 20% cumulatively (i.e., adding up all errors amounted to 20% of the image width) of the entire image.…”

“…These advancements include the ability to automatically measure the combined thickness of the RNFL, ganglion cell layer (GCL), and the inner plexiform layer (IPL; these three layers are collectively termed the ''ganglion cell complex'' [GCC]) [7][8][9] ; the combined thickness of the GCL and the IPL [10][11][12] ; and the manual measurement of the thickness of individual layers such as the GCL and RNFL. 13 Earlier studies showed that GCC thickness measurements improved the glaucoma-discriminating ability of the macular measures compared with the total retinal thickness measures. [7][8][9] Despite advancements in the techniques for measuring macular structures, the strategy to detect local loss of the RGCs based on thickness measurements still uses the average and regional thicknesses in the macula.…”

“…We explored a new approach for detecting local loss of macular RGCs by using the lowest ganglion cell-inner plexiform layer thickness (GCIPL) among the 360 spokes (termed ''minimum GCIPL'') based on ganglion cell analysis in a macular elliptical annulus developed on a macular cube scan with OCT software (Cirrus HD-OCT; Carl Zeiss Meditec, Inc., Dublin, CA). Because this method is based on the relatively symmetric macular RGC density, 1 and GCL thickness, 13 it presumably detects the location with most severe RGC loss, which should theoretically represent the location with local RGC loss in early glaucoma. The purpose of this study was to determine whether this new approach effectively discriminates between eyes with early glaucoma and healthy eyes as compared with the conventional average and regional thickness measures.…”