A New Method for the Determination of the Mechanical Properties of the Vitreous

Abstract

In order to determine the mechanical properties of the vitreous which are characteristic for the extraction of foreign bodies, an oscillatory method was devised. The mechanical properties are described by a spring constant – relevant for the rubber elastic behaviour – and a friction constant characterizing the dissipative interaction inside the vitreous. The appropriateness of the data is demonstrated by the capability to predict the distance-time behaviour in strong, pulsed magnetic fields of ferromagnetic foreign bodies implanted into the vitreous of pig eyes.

The Mechanical Properties of the Vitreous of Pig and Human Donor Eyes

“…The experi ments were done with spheres of 0.5 mm diameter. The equivalent data obtained for pig eyes have been reported in the previous paper [6]. Com parison shows that the data are very similar.…”

“…The reasonable agreement between the observed distance-time behaviour of spheres moving in the inhomogeneous field of a strong pul sed magnet (see the previous paper) [6] with the calculated values shows that the description with a damping constant which is proportional to the cross-sectional area is rather accurate. For the large forces employed in the experiments the elastic interactions between sphere and vitreous body only plays a minor role.…”

“…In order to find out whether extended storage had any influence on the mechanical properties, the spring constant D0 -extrapo lated to zero elongation -was studied as a function of the storage time. The measured spring constant D0, obtained from a computer analysis of the resonant curves (as, e.g., shown in figure 2 of the previous paper [6], has been plotted in figure 1 as a function of the storage time. The solid line represents the averaged data, and the broken lines indicate the possible deviation in slope.…”

“…In the previous paper [6] a method has been described which allows the determination of the mechanical properties of the vitreous under con ditions which occur during magnet extraction. The method depends on periodic oscillations of a steel sphere under external excitation from which a spring constant D and a damping factor rz can be deduced.…”

A finite element infant eye model to investigate retinal forces in shaken baby syndrome

“…The ciliary body is modeled as a tension-only membrane, where the tensile strength is assigned a value of 11 MPa [26]. The current vitreous used in this investigative study utilizes an elastic model where the vitreous is considered "rubber-elastic" [39]. Utilizing the damping and stiffness values, the natural frequency and the damping ratio, from human specimens, are converted to an equivalent modulus of elasticity and damping coefficient for finite element modeling.…”