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N. G. Strouthidis, H. Yang, J. Grimm, J. Reynaud, C. F. Burgoyne; Three Dimensional (3D) Histomorphometric and Spectral Domain Optical Coherence Tomography (SD-OCT) Disc Margin Anatomy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4786.
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© ARVO (1962-2015); The Authors (2016-present)
To establish how the Neural Canal Opening (NCO) and Border Tissue of Elschnig, rather than the scleral ring, underlie disc margin anatomy in monkey and human eyes.
The NCO (Bruch’s Membrane opening in histomorphometric volumes and Bruch’s Membrane/retinal pigment epithelium complex opening in SD-OCT volumes) was delineated within 40 digital radial sections generated from 3D optic nerve head (ONH) histomorphometric volumes (Downs, et al. IOVS 2007) of 28 normal monkey eyes, from SD-OCT ONH volumes (Heidelberg Spectralis) acquired from 33 normal monkey eyes (15º, 290 x 768 horizontal grid pattern) and from 23 normal human eyes (15º, 145 x 768, horizontal grid pattern). Each volume was co-localized to its disc photograph by matching the retinal vessels within each photograph either to 3D histomorphometric blood vessel reconstructions or to vessel outlines visible within en face SD-OCT images. Border Tissue was delineated where it extended internal to the NCO. A clinician (masked to the delineated points) marked the disc margin onto each photograph whilst viewing the relevant stereophotograph pair. Alignment of the clinician-ascribed disc margin to the NCO and Border Tissue delineations was assessed.
Histomorphometry: Border Tissue configuration relative to the scleral canal opening regionally determined the disc margin. ‘Internally oblique’ Border Tissue extended into the neural canal to join Bruch’s Membrane, making NCO the disc margin. ‘Externally oblique" Border Tissue extended away from the canal, leaving sclera and Border Tissue visible as disc margin. Where Bruch’s Membrane extended beyond Border Tissue it was clinically visible. NCO was the disc margin in all but the inferotemporal region of 1 eye.SD-OCT: NCO was the disc margin for 360° except in 11 monkey eyes where externally oblique Border Tissue was the disc margin temporally. NCO aligned to the temporal and nasal disc margin in the human eyes except in 5 myopic eyes where an exaggerated temporal external obliquity was present. In these cases, the temporal disc margin aligned to the termination of Border Tissue and to the anterior scleral canal opening. NCO was less well visualized by SD-OCT at the poles of human eyes because of obscuration by vessel shadows.
These data for the first time establish that the termination of Bruch’s Membrane, Border Tissue and the anterior scleral canal opening constitute the disc margin within the same eye and that this anatomy is visualized in SD-OCT volumes. Informed by these findings, SD-OCT imaging should enhance the clinical interpretation of the normal and glaucomatous disc.
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