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Jin Wook Jeoung, Hongli Yang, Stuart Keith Gardiner, Yaxing Wang, Seung Woo Hong, Michael J A Girard, Christy A Hardin, Ping Wei, Jayme Vianna, Balwantray C Chauhan, Claude F Burgoyne; Optical Coherence Tomography (OCT) Optic Nerve Head (ONH) Neural Canal Direction, Obliqueness and Minimum Cross-sectional Area in Highly Myopic versus Age-Matched Healthy Eyes. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5552.
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To characterize OCT-detected size, shape and 3D offset of the anterior scleral canal opening (ASCO) relative to Bruch’s membrane opening (BMO) so as to determine ONH neural canal (NC) direction, NC obliqueness and NC minimum cross-sectional area (NCMCA) (Fig.1) in 36 highly myopic (≤ -6D spherical equivalent) and 108 age-matched control subjects.
For each eye, axial length (AL) measurement and ONH OCT imaging (24 enhanced depth, radial B-scans acquired relative to the Fovea-BMO (FoBMO) axis) were performed. Within each OCT data set, BMO and ASCO were manually segmented (Fig 1A), BMO and ASCO fitted planes, centroids and area were calculated (Fig 1B), the NC axis vector was defined by connecting BMO and ASCO centroids; and NC obliqueness was defined by the angle between the NC axis and BMO perpendicular vectors. ASCO/BMO offset magnitude and direction were defined relative to BMO centroid by projecting the NC axis vector and ASCO centroid to the BMO plane (Fig 1B). NCMCA was defined by projecting all BMO and ASCO points onto an NC axis perpendicular plane and quantifying their area of overlap (Fig 1C). The shape of BMO, ASCO and NCMCA was defined by each opening’s long/short axis ratio.
To date, 36 myopic eyes (median AL 27.32 mm, range 26.08 to 30.74 mm) and 108 control eyes (median AL 23.55 mm, range 21.41 to 25.89 mm) have been studied. ASCO/BMO offset direction was nasal in 35 myopic eyes (97.2%), and superior-nasal offset was more frequent in myopic (77.8%) compared to control (58.3%) (P=0.036, chi-squared test) eyes (Fig 2A). Both ASCO/BMO offset magnitude (Fig 2A) and NC obliqueness (Fig 2B), were significantly higher in myopic (287±137 µm and 65.8°±13.9°) compared to control (132±51 µm and 40.5°±16.0°) eyes (each comparison P<0.0001, t-test). While BMO area was significantly larger in myopic (2.33±0.89 mm2) compared to control (1.79±0.35 mm2, P<0.0001) eyes, ASCO and NCMCA were not different. NCMCA was significantly more elliptical in myopic (shape index 2.90±1.07) compared to control (1.55±0.60, P<0.001, t-test) eyes (Fig 2C).
Increased ASCO/BMO offset (most commonly occurring in the superior-nasal quadrant), increased BMO area, increased NC obliqueness and a more elliptical NCMCA underlie the OCT ONH phenotype of the highly myopic eye.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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