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Thanadet Chuangsuwanich, Xiaofei Wang, Tin A Tun, Sripad Krishna Devalla, Dan Milea, Quan V Hoang, Tin Aung, Michael J A Girard; Adduction Induces Abnormally Large Optic Nerve Head Strains in Normal Tension Glaucoma Subjects. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1005.
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© ARVO (1962-2015); The Authors (2016-present)
To assess optic nerve head (ONH) strains (i.e. deformations) following adduction, abduction, and IOP elevation in healthy, primary open angle glaucoma (POAG), normal tension glaucoma (NTG), and highly myopic eyes.
We recruited 74 subjects, which comprised of 36 POAG, 26 NTG, 6 highly myopic, and 6 healthy subjects. For each subject, we imaged the ONH using Spectral-domain optical coherence tomography (OCT) under the following conditions: (1) primary gaze, (2) 20o adduction, (3) 20o abduction, and (4) primary gaze with acute IOP elevation (to ~40 mmHg) achieved through ophthalmodynamometry. For each OCT volume, we automatically segmented the prelaminar tissue (PLT) and the lamina cribrosa (LC) using deep learning. We also digitally aligned the OCT volumes obtained from (2)-(4) to the baseline volume (1) before performing digital volume correlation (DVC) analysis to quantify IOP- and gaze-induced PLT and LC displacements for all scenarios. The resulting displacement fields obtained from the DVC analysis were then used to calculate the effective strain (a local measure of tissue deformation) that was compared across groups.
We observed a uniform posterior displacement of the LC under IOP elevation (Figure 1a). Adduction produced a slight ONH tilt and caused shearing of the ONH tissues (Figure 1b). Across all subjects, adduction generated high strains (3.4 ± 1.2%) in the ONH tissues on the same order of magnitude as those induced by an IOP of 40 mmHg (3.8 ± 1.5%), while abduction generated significantly lower strains (2.8 ± 0.9%). Interestingly, POAG subjects exhibited the highest strains from IOP elevation (4.2 ± 1.6%, Figure 2a). Conversely NTG and highly myopic subjects exhibited the highest strains from adduction (NTG: 3.6 ± 1.6%and Myopia: 4.6 ± 2.3% - both of which were significantly higher than POAG: 3.2 ± 1.3% and healthy subjects: 2.9 ± 0.9%; p < 0.05, Figure 2b).
We found that adduction produced high strain in vivo – this is especially true for NTG and myopic subjects. POAG subjects tend to be more sensitive to IOP elevation as compared to changes in gaze. These preliminary results are part of a larger study that may help us elucidate the role of biomechanics in glaucoma pathogenesis.
This is a 2020 ARVO Annual Meeting abstract.
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