Optic Disc Margin Anatomy in Patients with Glaucoma and Normal Controls with Spectral Domain Optical Coherence Tomography

Abstract

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.

Histological changes of high axial myopia

“…The region without the Bruch's membrane (and correspondingly, without retinal pigment epithelium and choriocapillaris) has been called parapapillary gamma zone. 20,22,23 This gamma zone was significantly correlated with high axial myopia, with the prevalence of gamma zone steeply increasing at a cutoff value of B26.0 mm of axial length (in histologically fixed globes). Interestingly, parapapillary gamma zone was not related with the presence of glaucomatous optic nerve damage.…”

“…As the presence of the Bruch's membrane is essential for the presence of retinal pigment epithelium cells and choriocapillaris, the secondary macular defects in the Bruch's membrane were associated with a complete loss of retinal pigment epithelium cells and choriocapillaris, and an almost complete loss of the large choroidal vessel layer and photoreceptors. 20 These macular Bruch's membrane defects can histologically be differentiated from myopic chorioretinal atrophic areas in the macular region with a complete loss of retinal pigment epithelium cells and choriocapillaris, but with the Bruch's membrane present, similar to the histology of geographic atrophy in the framework of age-related macular degeneration.…”

“…Highly axially myopic eyes showed, however, defects in the Bruch's membrane in the macular region. 20 These macular defects in the Bruch's membrane in highly axially myopic eyes may be called secondary defects as compared with the primary defect in the Bruch's membrane in the region of the optic nerve head. As the presence of the Bruch's membrane is essential for the presence of retinal pigment epithelium cells and choriocapillaris, the secondary macular defects in the Bruch's membrane were associated with a complete loss of retinal pigment epithelium cells and choriocapillaris, and an almost complete loss of the large choroidal vessel layer and photoreceptors.…”

The comparison of manual vs automated disc margin delineation using spectral-domain optical coherence tomography

“…[23][24][25] The disc margin is anatomically complex and studies have shown that the clinically identified disc margin is often based on more than one tissue structure. [26][27][28] It has been demonstrated that this variability can lead to a clinical disc margin assessment that may over-and/or underestimate the amount of remaining rim in any given optic disc region. 27,29 SDOCT technology allows crosssectional visualization of the neural canal opening, which provides a distinct advantage in identifying disc margins compared to traditional stereoscopic examination.…”

Glaucoma Diagnosis: Past, Present and Future

“…Its anatomy determines what structure is perceived clinically as the edge of the optic disc. According to their research, Reis, et al 8 found that the clinically visible disc margin corresponds to border tissue of Elschnig or both Bruch's membrane with underlying border tissue. Less frequently, it corresponds to termination of Bruch's membrane.…”