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Liang Zhang, Mani Baskaran, Tin Aung, Nicholas Strouthidis, Michael J A Girard; A Novel Virtual Fields Method to Measure the Biomechanical Properties of Human Optic Nerve Head Tissues. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3557.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a novel and fast virtual fields method (VFM) to measure the patient-specific biomechanical properties of optic nerve head (ONH) tissues.
Our method was designed to extract the biomechanical properties of human ONH tissues (choroid, peripapillary sclera, prelamina, and lamina cribrosa), given their full-field IOP-induced deformations. The latter can be derived through 3D tracking of in vivo optical coherence tomography (OCT) images (Girard et al., J R Soc Interface. 2013; 10:20130459). To verify our technique, we first generated ‘artificial’ ONH deformation data from predetermined (known) ONH tissue biomechanical properties using finite element analysis (Figure 1a-b). Using such deformations, if we are able to match back the known biomechanical properties, it would indicate that our VFM (Pierron, F., & Grédiac, M. 2012. Springer Science & Business Media) technique is accurate. We assumed that the prelamina, the choroid and the lamina cribrosa can be described with a single stiffness parameter (elastic moduli: Ep, Ec and El); the peripapillary sclera can be described with 2 stiffness parameters representing the stretch-induced stiffening of the collagen fibers (c3 and c4), and 2 microstructural parameters representing the main orientation (θp) and the degree of alignment (k) of the collagen fibers. The ‘artificial’ IOP-induced ONH deformations were fed into the VFM algorithm (custom written in C++) to extract back the biomechanical properties. The computational speed of VFM was then compared to that of a gold standard stiffness measurement method (inverse finite element).
From the given ONH deformations, VFM successfully matched back the biomechanical properties of ONH tissues with high accuracy and efficiency. For all parameters, the percent errors were less than 1% (Figure 1c). Our method was also able to recover the highly-aligned circumferential organization of the collagen fibers in the peripapillary sclera. Finally, VFM was found 60 times faster than gold-standard stiffness measurement methods.
VFM may be capable of measuring the biomechanical properties of human ONH tissues with high speed and accuracy. It has potential in identifying patient-specific ONH biomechanical properties in the clinic if combined with OCT.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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