Characterization of Ocular Tissues Using Microindentation and Hertzian Viscoelastic Models

Abstract

Relaxation testing by microindentation is a powerful method for characterization of time-dependent behaviors of a wide range of ocular and orbital tissues using small specimens, and provides data suitable to define finite element models of a wide range of tissue interactions.

Atomic force microscopy determination of Young׳s modulus of bovine extra-ocular tendon fiber bundles

“…Unlike other ocular and orbital tissues (Yoo et al, 2009; Yoo et al, 2011d), single fibers from EOT exhibit much higher stiffness and purely elastic, rather than viscoelastic, behavior. From previous investigations on viscoelastic characteristic of orbital/ocular tissues, it was reported that Young’s modulus of most of orbital tissues does not exceed 120kPa (Yoo et al, 2011d).…”

“…From previous investigations on viscoelastic characteristic of orbital/ocular tissues, it was reported that Young’s modulus of most of orbital tissues does not exceed 120kPa (Yoo et al, 2011d). Perhaps the purely elastic behavior of EOT facilitates the extreme eye movements also known as saccades, which are not only the fastest movements achieved by any part of the body, but are regulated by neural commands that appear optimized to minimize the time required to shift from one eye position to the next (Kirchner and Thorpe, 2006).…”

“…This obviously unrealistic assumption might cause erroneous simulation results, and highlights the need to obtain actual data on EOTs. Investigators in the field have employed various techniques to accurately determine the biomechanical properties of other orbital tissues, including conventional tensile elongation (Collins et al, 1981; Quaia et al, 2009a; Robinson et al, 1969; Simonsz, 1994; Yoo et al, 2009) and micro/nano indentation (Yoo et al, 2011c; Yoo et al, 2011d) methodologies. Despite studies in some tissues (Boyce et al, 2007; Quaia et al, 2009a; Quaia et al, 2009b; Yoo et al, 2011a; Yoo et al, 2009; Yoo et al, 2011b; Yoo et al, 2011c; Yoo et al, 2011d), however, many material parameters of orbital tissues have yet to be defined.…”

Simulation of Active Eye Motion Using Finite Element Modelling

“…The mechanical properties assumption for these two parts are reported in Table 1. These assumptions are employed from Schutte et al 2006 and seems to be proper according to experimental reports by Yoo et al 2011 . Moreover, eye ball Young modulus and Poisson's ratio are also assumed based on the data reported by Schutte et al 2006 and its density is calculated to be 1270 kg/m 3 according to the data stated by Robinson 1981 . As stated before, Schutte et al 2006 considered EOMs as a simple orthogonal elastic material which is always passive.…”

“…Many of these features are not studied till now. Meanwhile reliable available experimental data about the eye parts mechanical characteristics are limited details can be found in works by Schoemaker et al 2006, Robinson et al 1969and Yoo et al 2011 . We are intended to obtain some information which are not convenient through the conventional experiments through our model.…”