OCT-Detected Optic Nerve Head Neural Canal Direction, Obliqueness, and Minimum Cross-Sectional Area in Healthy Eyes

Abstract

To assess anterior scleral canal opening (ASCO) offset relative to Bruch's membrane opening (BMO) (ASCO/BMO offset) so as to determine neural canal direction, obliqueness, and minimum crosssectional area (NCMCA) in 362 healthy eyes. DESIGN: Cross-sectional study. METHODS: After optical coherence tomography optic nerve head and retinal nerve fiber layer thickness (RNFLT) imaging, BMO and ASCO were manually segmented. Planes, centroids, size, and shape were calculated. Neural canal direction was defined by projecting the neural canal axis vector (connecting BMO and ASCO centroids) onto the BMO plane. Neural canal obliqueness was defined by the angle between the neural canal axis and the BMO plane perpendicular vector. NCMCA was defined by projecting BMO and ASCO points onto a neural canal axis perpendicular plane and measuring the area of overlap. The angular distance between superior and inferior peak RNFLT was measured, and correlations between RFNLT, BMO, ASCO, ASCO/ BMO offset, and NCMCA were assessed. RESULTS: Mean (SD) NCMCA was significantly smaller than either the BMO or ASCO area (1.33 (0.42), 1.82 (0.38), 2.22 (0.43) mm 2 , respectively), and most closely correlated to RNFLT (P < .001, R 2 [ 0.158). Neural canal direction was most commonly superior-nasal (55%). Mean neural canal obliqueness was 39.4 8 (17.3 8). The angular distance between superior and inferior peak RNFLT correlated to neural canal direction (P £ .008, R 2 [ 0.093). CONCLUSIONS: ASCO/BMO offset underlies neural canal direction, obliqueness, and NCMCA. RNFLT is more strongly correlated to NCMCA than to BMO or ASCO, and its peripapillary distribution is influenced by neural canal direction.

Longitudinal Observation of Border Tissue Configuration During Axial Elongation in Childhood

“…The tensile stress in the temporal ONH during myopic axial elongation can lead to permanent externalization and elongation of the temporal border tissue. 22 , 28 Recently, Hong et al 29 investigated the 3D neural canal direction and obliqueness by assessing the ASCO offset relative to BMO. From a cross-sectional observation of 362 healthy eyes, an increase in the AXL was associated with ASCO/BMO offset magnitude, direction, and neural canal obliqueness.…”

Microstructure of Nonjuxtapapillary Microvasculature Dropout in Healthy Myopic Eyes

“…1A, 1B). 8,[18][19][20] However, the peripapillary tissues comprise several layers with different elasticities 21,22 (e.g., retina, BM, choroid, and sclera) that extend to the ONH tissues in different ways. When the stretching tension exceeds the combined elastic limit of the tissues, it is likely that the less-elastic tissue with a weaker connection to the ONH will be the first to become disrupted or dislocated.…”

Peripapillary Choroidal Vascularity Index and Microstructure of Parapapillary Atrophy

“…Recently, the anterior scleral canal opening (ASCO) was introduced as a stable anatomic landmark, although it is often challenging to segment ASCO accurately. 9,42 As OCT visualization and segmentation improves, segmenting the ASCO will be helpful in further clarifying the anatomy of the parapapillary ONH structure. Finally, this study quantified the choroidal vasculature, but not the blood flow itself.…”