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Ya Xing Wang, Hongli Yang, Haomin Luo, Seung Woo Hong, Stuart Keith Gardiner, Jin Wook Jeoung, Joseph Caprioli, Shaban Demirel, Christopher A Girkin, Jeffrey M Liebmann, Christian Y Mardin, Harry A Quigley, Alexander F Scheuerle, Balwantray C Chauhan, Claude F Burgoyne; Optical Coherence Tomography (OCT) Anterior Scleral Canal Opening (ASCO) Tilt and Rotation relative to Bruch’s Membrane Opening (BMO) and Peripapillary Scleral Bowing (PSB) in Healthy Eyes. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5516.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize OCT ASCO/BMO tilt, rotation and PSB in 362 healthy human eyes.
One eye of each subject underwent OCT imaging (Spectralis, 12° circle scan and 24 enhanced depth, ONH radial B scans), relative to the Fovea-BMO (FoBMO) axis. For each eye, BMO, ASCO and the peripapillary scleral surface were manually segmented and RNFL and MRW were computed. For BMO and ASCO, a long axis, centroid and fitted plane were determined. The neural canal (NC) axis was defined by the vector connecting BMO and ASCO centroids (Fig 1A). NC direction was determined by projecting the NC vector onto the BMO plane relative to the FoBMO axis. ASCO/BMO tilt magnitude was defined by the angle between the BMO and ASCO normal vectors. Its direction was determined by translating the ASCO normal vector to the BMO centroid and projecting it onto the BMO plane. ASCO/BMO rotation was determined by the angular displacement of the superior ASCO long axis relative to the superior BMO long axis (Nasal (+), Temporal (-)) (Fig 1B). PSB slope was calculated within each B-scan within a bilinear model of the scleral surface that provided inner (juxta-scleral canal) and outer slopes relative to a single inflection point (Fig 1C). Correlations between ocular, demographic, ASCO/BMO, PSB slope, RNFL and MRW parameters were assessed.
Mean (range) ASCO/BMO tilt and rotation were 1.15±0.72° (0.04–4.97°) and 3.3±24.5° (-90–+84°), respectively. As tilt increased, its direction was more commonly nasal and more closely approximated the NC direction (P=0.001) (Fig 2A). In eyes with nasal ASCO tilt, a greater tilt angle correlated with increased inferior MRW (P=0.002, R2=0.16). Temporal ASCO rotation was associated with longer axial length, larger ASCO tilt, greater ASCO-BMO offset. Nasal ASCO rotation was associated with higher IOP and thicker RNFLT in the nasal and nasal-inferior sectors (all P<0.008) (Fig 2B). Sectoral PSB slopes were greatest inferior-temporally, increased with age, and age effects were greatest nasally (all P<0.001, GEE)), (Fig 2C).
Our study establishes OCT anatomic relationships between ASCO/BMO tilt, rotation, PSB and NC direction, which can be used to provide OCT–based guidelines for clinically evaluating optic disc tilt and torsion in healthy, myopic and glaucoma eyes.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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