Objective Neuroretinal rim assessment based on the clinical optic disc margin (DM) lacks a sound anatomic basis for 2 reasons: (1) The DM is not reliable as the outer border of rim tissue because of clinically and photographically invisible extensions of Bruch’s membrane (BM) inside the DM and (2) nonaccountability of rim tissue orientation in the optic nerve head (ONH). The BM opening-minimum rim width (BMO-MRW) is a parameter that quantifies the rim from its true anatomic outer border, BMO, and accounts for its variable orientation. We report the diagnostic capability of BMO-MRW. Design Case control. Participants Patients with open-angle glaucoma (n = 107) and healthy controls (n = 48). Methods Spectral-domain optical coherence tomography (SD-OCT) with 24 radial and 1 circumpapillary B-scans, centered on the ONH, and confocal scanning laser tomography (CSLT) were performed. The internal limiting membrane (ILM) and BMO were manually segmented in each radial B-scan. Three SD-OCT parameters were computed globally and sectorally: (1) circumpapillary retinal nerve fiber layer thickness (RNFLT); (2) BMO-horizontal rim width (BMO-HRW), the distance between BMO and ILM in the BMO reference plane; and (3) BMO-MRW, the minimum distance between BMO and ILM. Moorfields Regression Analysis (MRA) with CLST was performed globally and sectorally to yield MRA1 and MRA2, where “borderline” was classified as normal and abnormal, respectively. Main Outcome Measures Sensitivity, specificity, and likelihood ratios (LRs) for positive and negative test results (LR+/LR−). Results The median (interquartile range) age and mean deviation of patients and controls were 69.9 (64.3–76.9) and 65.0 (58.1–74.3) years and −3.92 (−7.87 to −1.62) and 0.33 (−0.32 to 0.98) dB, respectively. Globally, BMO-MRW yielded better diagnostic performance than the other parameters. At 95% specificity, the sensitivity of RNFLT, BMO-HRW, and BMO-MRW was 70%, 51%, and 81%, respectively. The corresponding LR+/LR− was 14.0/0.3, 10.2/0.5, and 16.2/0.2. Sectorally, at 95% specificity, the sensitivity of RNFLT ranged from 31% to 59%, of BMO-HRW ranged from 35% to 64%, and of BMO-MRW ranged from 54% to 79%. Globally and in all sectors, BMO-MRW performed better than MRA1 or MRA2. Conclusions The higher sensitivity at 95% specificity in early glaucoma of BMO-MRW compared with current BMO methods is significant, indicating a new structural marker for the detection and risk profiling of glaucoma.

Objective To characterize optic nerve head (ONH) anatomy related to the clinical optic disc margin with spectral domain optical coherence tomography (SD-OCT). Design Cross-sectional study. Participants Open-angle glaucoma patients with focal, diffuse and sclerotic optic disc damage, and age-matched normal controls. Methods High-resolution radial SD-OCT B-scans centered on the ONH were analyzed at each clock hour. For each scan, the border tissue of Elschnig was classified for obliqueness (internally oblique, externally oblique, or non-oblique), and presence of Bruch’s membrane overhang over border tissue. Optic disc stereo-photographs were co-localized to SD-OCT data with customized software. The frequency with which the disc margin identified in stereo-photographs coincided with (1) Bruch’s membrane opening, defined as the innermost edge of Bruch’s membrane; (2) Bruch’s membrane/border tissue, defined as any aspect of either, outside Bruch’s membrane opening or border tissue; or (3) border tissue, defined as any aspect of border tissue alone, in the B-scans was computed at each clock hour. Main Outcome Measures SD-OCT structures coinciding with the disc margin in stereo-photographs. Results There were 30 patients (10 with each type of disc damage) and 10 controls, with median (range) age 68.1 (42–86) and 63.5 (42–77) years respectively. Although 28 (93%) patients had 2 or more border tissue configurations, the most predominant one was internally oblique, primarily superiorly and nasally, frequently with Bruch’s membrane overhang. Externally oblique border tissue was less frequent, observed mostly inferiorly and temporally. In controls, there was predominantly internally oblique configuration around the disc. While the configurations were not statistically different between patients and controls, they were among the 3 glaucoma groups. At most locations the SD-OCT structure most frequently identified as the disc margin was some aspect of Bruch’s membrane and border tissue, outside Bruch’s membrane opening. Bruch’s membrane overhang was regionally present in the majority of glaucoma patients and controls, however, in most cases not visible as the disc margin. Conclusions The clinically perceived disc margin is most likely not the SD-OCT detected innermost edge of Bruch’s membrane. These findings have important implications for the automated detection of the disc margin and estimates of the neuroretinal rim.

BMO-MRW quantifies the neuroretinal rim from a true anatomical outer border and accounts for its variable trajectory at the point of measurement.