PURPOSE To determine if the three-dimensional eyeball shape is associated with the positions of the central retinal vascular trunk (CRVT) and the externally oblique border (EOB) in the optic nerve head (ONH).
DESIGN Prospective cross-sectional study
PARTICIPANTS: Fifty-six (56) subjects (112 eyes) with a diagnosis of glaucoma or glaucoma suspect
METHODS: The three-dimensional shape of the eyeball on 3D-MRI scans was classified according to the dimension of the longest diameter: axial dimension (prolate sphere), group 1; horizontal dimension (horizontally oblate sphere), group 2; and vertical dimension (vertically oblate sphere), group 3 . The deviation of the CRVT, as a surrogate of lamina cribrosa (LC) shift, was measured from the center of the Bruch's membrane opening (BMO) demarcated by OCT imaging, with the horizontal midline as 0° and the superior location as a positive value . The angular location of the longest EOB was also measured . MAIN OUTCOME MEASURE Positions of CRVT and EOB according to the three-dimensional shape of an eyeball
RESULTS: Among 112 eyes, 54 (48 %) had a prolate shape (group 1), 23 (21 %) a horizontally oblate shape (group 2), and 35 (31 %) a vertically oblate shape (group 3). The angular deviation of the CRVT differed among the groups: to the nasal side in group 1, to the temporal side in group 2, and along the vertical meridian in group 3 . In cases of asymmetric eyeball shape, the CRVT was deviated toward the undergrown side from the overgrown side, regardless of grouping . The angular location of the longest EOB was in the direction opposite to the CRVT position (P <0.001). A generalized estimating equation analysis revealed that the temporal location of the CRVT was associated with older age (P = 0.001), nasal location of the longest EOB (P <0.001), and oblate shape of the eyeball (P <0.001, group 2; P = 0.007, group 3).
CONCLUSIONS The position of the CRVT and EOB were associated with the three-dimensional eyeball shape . Considering that infant ONH morphology is highly uniform, various modes of eyeball expansion during growth can result in diverse directionalities of offset between the LC and BMO in adults.