The Viscoelastic Properties of Passive Eye Muscle in Primates. I: Static Forces and Step Responses

The viscoelastic properties of passive eye muscles are prime determinants of the deficits observed following eye muscle paralysis, the root cause of several types of strabismus. Our limited knowledge about such properties is hindering the ability of eye plant models to assist in formulating a patient's diagnosis and prognosis. To investigate these properties we conducted an extensive in vivo study of the mechanics of passive eye muscles in deeply anesthetized and paralyzed monkeys. We describe here the static length-tension relationship and the transient forces elicited by small step-like elongations. We found that the static force increases nonlinearly with length, as previously shown. As expected, an elongation step induces a fast rise in force, followed by a prolonged decay. The time course of the decay is however considerably more complex than previously thought, indicating the presence of several relaxation processes, with time constants ranging from 1 ms to at least 40 s. The mechanical properties of passive eye muscles are thus similar to those of many other biological passive tissues. Eye plant models, which for lack of data had to rely on (erroneous) assumptions, will have to be updated to incorporate these properties

The Viscoelastic Properties of Passive Eye Muscle in Primates. II: Testing the Quasi-Linear Theory

We have extensively investigated the mechanical properties of passive eye muscles, in vivo, in anesthetized and paralyzed monkeys. The complexity inherent in rheological measurements makes it desirable to present the results in terms of a mathematical model. Because Fung's quasi-linear viscoelastic (QLV) model has been particularly successful in capturing the viscoelastic properties of passive biological tissues, here we analyze this dataset within the framework of Fung's theory

Transmission Coefficient for Multi-Layered Structures at Arbitrary Incident Angle

Widespread adoption of process inspection is dependent on reduction of cost. In many applications the part geometry may not be known or may be sufficiently complex that it would be desirable to not follow all of the part contours. Fortunately, in cases where refraction of the wave between the coupling fluid and the part is low, relatively complex parts may be scanned without precisely following the part contours. This paper explores a problem where a complex part is scanned with a limited number of degrees of freedom in the scanning system. The close acoustic impedance match between the rubber part and the water coupling fluid allows this to be done efficiently. However, the refraction and attenuation of the wave in the material is still sufficiently high that it may be necessary to correct the amplitude of the received signal to account for the part geometry. Matrix propagator methods are used to create a model which will allow the effect of amplitude variation on the received signal to be explored for the curved specimen. The magnitude of the received signal will be adjusted to be equivalent to a normally incident wave