How Myopia and Glaucoma Influence the Biomechanical Susceptibility of the Optic Nerve Head

​ 1Yong Loo Lin School of Medicine, National University of Singapore, Singapore 2Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 3Eye-ACP, Duke-NUS Medical School, Singapore, Singapore 4Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore 5Department of Ophthalmology, Columbia University, New York, New York, United States 6Laboratory for Biomechanics and Mechanobiology of Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, School of Engineering Medicine, Beihang University, Beijing, China 7Institute for Molecular and Clinical Ophthalmology, Basel, Switzerland ​ PURPOSE. The purpose of this study was to assess optic nerve head (ONH) deformations following acute intraocular pressure (IOP) elevations and horizontal eye movements in control eyes, highly myopic (HM) eyes, HM eyes with glaucoma (HMG), and eyes with pathologic myopia (PM) alone or PM with staphyloma (PM + S). METHODS. We studied 282 eyes, comprising of 99 controls (between +2.75 and −2.75 diopters), 51 HM (< −5 diopters), 35 HMG, 21 PM, and 75 PM + S eyes. For each eye, we imaged the ONH using spectral-domain optical coherence tomography (OCT) under the following conditions: (1) primary gaze, (2) 20 degrees adduction, (3) 20 degrees abduction, and (4) primary gaze with acute IOP elevation (to ∼35 mm Hg) achieved through ophthalmodynamometry.We then computed IOP- and gaze-induced ONH displacements and effective strains. Effective strains were compared across groups. RESULTS. Under IOP elevation, we found that HM eyes exhibited significantly lower strains (3.9 ± 2.4%) than PM eyes (6.9 ± 5.0%, P < 0.001), HMG eyes (4.7 ± 1.8%, P = 0.04), and PM + S eyes (7.0 ± 5.2%, P < 0.001). Under adduction, we found that HM eyes exhibited significantly lower strains (4.8% ± 2.7%) than PM + S eyes (6.0 ± 3.1%, P = 0.02). We also found that eyes with higher axial length were associated with higher strains. CONCLUSIONS. Our study revealed that eyes with HMG experienced significantly greater strains under IOP compared to eyes with HM. Furthermore, eyes with PM + S had the highest strains on the ONH of all groups. ​ Copyright 2023 The Authors iovs.arvojournals.org | ISSN: 1552-5783 ​ ​ Keywords: optic nerve head (ONH), biomechanics, myopia, glaucoma, staphyloma

Author(s): Thanadet Chuangsuwanich,1,2 Tin A. Tun,3,4 Fabian A. Braeu,2,4 Clarice H. Y. Yeoh,1 Rachel S. Chong,4 Xiaofei Wang,6 Tin Aung,1,3,4 Quan V. Hoang,1,3–5 and Michaël J. A. Girard 2,3,7

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