Abstract
The degree of myopia is represented by a global index, such as refractive error or axial length. However, the progression of myopia mainly develops in the posterior eyeball. Therefore, it is reasonable to assume that the evaluation of myopia should be confined to the posterior segment, where most of the growth and lengthening occurs. Swept source optical coherence tomography software can reconstruct the scans to the coronal view of the posterior pole, which provides additional anterior-posterior depth (z axis in the Cartesian coordinates) that is not provided with the common fundus photograph. We deduced that the parameter of deepest point of the eyeball (DPE) as a surrogate for posterior pole configuration. Between myopes with and without normal tension glaucoma (NTG) with similar axial length, myopes with NTG had deeper and more distant location of the DPE from the optic disc. The difference of the DPE position between the myopes with and without NTG may have implications for the larger optic disc tilt and torsion characteristic of myopes with NTG. Furthermore, these data suggest that myopes with NTG go through excessive posterior scleral remodeling, which may result in vulnerable optic nerve head.
Highlights
Unlike secondary high myopia due to congenital glaucoma, the axial elongation of primary myopia develops primarily in the posterior part of the eyeball[9,10]
In an attempt to resolve this deficiency, we recently introduced a method to describe the three-dimensional structure of the posterior pole and used it to verify the relationship with the optic disc tilt and torsion[16]
Identifying the deepest point could be a significant factor affecting the ONH configuration because the optic disc would likely be leaned towards the direction of the deepest point of the eyeball (DPE), and the degree of curvature would be proportional to the depth of the DPE, which showed a strong association in the non-glaucomatous emmetropic and myopic eyes[16]
Summary
Unlike secondary high myopia due to congenital glaucoma, the axial elongation of primary myopia develops primarily in the posterior part of the eyeball[9,10]. Our group previously investigated the posterior pole with various conventional imaging tools such as common fundus photograph or swept-source optical coherence tomography (SSOCT) or B-scans and attempted to find an association with the ONH configuration[13,14,15]. These tools were limited by providing only two-dimensional measurements of the posterior pole, and could not assess the posterior pole as a three-dimensional structure.
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