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L. H. Yoo, H. Kim, V. Gupta, J. L. Demer; Quasi-linear Viscoelastic Behavior of Bovine Extra-ocular Muscles. Invest. Ophthalmol. Vis. Sci. 2009;50(13):647.
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© ARVO (1962-2015); The Authors (2016-present)
There has been no prior comprehensive analytical model of the nonlinear viscoelastic stress-strain behavior of extraocular muscles (EOMs). The present study describes the nonlinear, history-dependent viscoelastic properties and elastic stress-strain relationship of the EOMs using a quasi-linear viscoelastic (QLV) model.
From each of the six oculorotary EOMs obtained fresh from a local abattoir, longitudinally oriented specimens were taken from different regions and subjected to uniaxial tensile, relaxation, and cyclic loading testing using an automated load cell under temperature and humidity control. Twelve samples were subjected to uniaxial tensile loading with 1.7%/s strain rate until failure to characterize elastic function within the mechanical model. Sixteen specimens were subjected to relaxation studies over 1,500 seconds to describe time-dependent viscoelastic behavior exhibited by EOMs. Cyclic loading was performed to validate predictions of the QLV model characterized from uniaxial tensile loading and relaxation data.
Uniform and highly repeatable stress-strain behavior was observed for 12 specimens extracted from various regions of all EOMs. Since the results from tensile tests and relaxation tests of all six EOMs were similar, mechanical properties for each of the six EOMs were assumed to be same. Results from 16 different relaxation trials illustrated that most stress relaxation occurred during the first 30-60s for 30% extension. Elastic and reduced relaxation functions were fit (nonlinear least square fit) to the data, from which a QLV model was assembled and compared with cyclic loading data. Predictions of the QLV model agreed with observed peak cyclic loading stress values to within 8% for all specimens and conditions.
Close agreement between the QLV model and both relaxation and cyclic loading data validates model quantification of EOM mechanical properties, and will permit development of accurate overall models of mechanics of ocular motility and strabismus.
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