Spectralis 7 line raster scan1/9/2024 In addition, the high-density raster scan protocol allows for the generation of multiple measurements from a single scan, including rim thickness, rim area, and rim volume. The MDB thickness is calculated from high-density raster scans comprised of 193 B-scans resulting in 100 calculated points along the disc border, whereas the BMO-MRW uses lower density radial scans comprised of 24 B-scans, resulting in 48 calculated points along the disc border. 28– 30, 33 Another fundamental difference between the MDB and the BMO-MRW lies in the image acquisition protocol. The MDB neuroretinal rim parameter is thus defined as the shortest distance between the ILM and the termination of the RPE/BM complex (Fig. Therefore, the termination of the RPE/BM complex may be a more reliable descriptor of the neuroretinal rim border seen in SD-OCT imaging. 32 In addition, the average thickness of the BM is 1 to 5 µm, whereas the axial resolution of the Spectralis SD-OCT machine is 7 µm, making it hard to reliably discern BMO in SD-OCT images. 22, 23, 27 However, although Bruch membrane (BM) may be visible on SD-OCT, it is often indistinguishable from the RPE as noted by an international panel of SDOCT experts. These other 3D parameters include the minimum circumpapillary band, which defines the neuroretinal rim as the distance between the internal limiting membrane (ILM) and the retinal pigment epithelium (RPE), 31 and the BMO-MRW, which defines the neuroretinal rim as the distance between the ILM and the BMO. 28 Like other 3-dimensional (3D) neuroretinal rim parameters, the MDB thickness uses SD-OCT imaging to determine the borders of the neuroretinal rim. 28– 30 The reproducibility of MDB thickness is high, with an inter-test variability of 0.84%. Therefore, this current study utilizes the minimum distance band (MDB) neuroretinal parameter, which is derived from high-density optic nerve scans and which has been shown to be diagnostically better than RNFL thickness, especially in the nasal, temporal, and superonasal regions. 22, 23, 27 To our knowledge, there are no SD-OCT studies which use a high-density scan protocol to evaluate the effects of age, race, and sex on the neuroretinal rim. In contrast, SD-OCT studies which look at the effect of age, race, and sex on the neuroretinal rim are few and are limited to 2 studies which used a low-density scan protocol and evaluated the Bruch membrane opening minimum rim width (BMO-MRW) parameter, which has not been consistently shown to be diagnostically better than the RNFL thickness parameter. 18, 19 However, RNFL thickness measurements through SD-OCT have a high rate of imaging artifacts, and up to 46.3% of RNFL thickness scans have artifacts, which can be caused by decentration errors, posterior vitreous detachments, and epiretinal membranes. 24 Two studies reported that whites had thinner RNFL thickness measurements than other racial groups. 10– 12, 17– 21 Multiple studies reported that sex is not significantly correlated with RNFL thickness, 19, 22, 23 whereas 1 reported that women had thicker RNFL than men. 10– 12, 17– 23 These studies have found that increasing age is associated with RNFL thickness decreases between 0.18 and 0.44 µm annually in normal adult patients. Most SD-OCT studies that look at the effect of age, race, and sex on structural parameters have focused on RNFL thickness. 13– 16 However, clinicians who use neuroretinal rim structural tests need to be aware of how much nerve tissue loss is expected for normal aging and how much racial variation exists in SD-OCT parameters to distinguish normal aging changes and racial variation from glaucomatous changes. 1– 12 As optical coherence tomography (OCT) imaging can show structural changes years before functional visual field (VF) loss, structural tests remain a cornerstone in the evaluation of glaucoma patients. Spectral-domain optical coherence tomography (SD-OCT) has become an integral part of the clinical evaluation for glaucoma because it can objectively measure the neuroretinal rim, the ganglion cell region, and the retinal nerve fiber layer (RNFL), all of which are known to decrease with glaucoma.
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