An in vivo creep test and mechanical modeling in strabismus

Abstract

Many patients come afoul by the over correction or under correction of the eye muscles after strabismus surgery. This is related to the individual properties of anyone's distinct eye muscles. Therefore it is necessary to have accurate information about the living soft tissues in simulations and the proper modeling of the human eye muscles. In vivo properties of the eye muscles have not been explored sufficiently. There are many problems in experimental works such as a lack of a standard methodology and disagreements between model and experimental data. The aim of this work is to exhibit an in vivo measurement in strabismus surgery to study the viscoelastic properties of the horizontal eye muscles and present a three element model which consists of a spring in parallel with a Maxwell element which was composed of a dashpot and a spring in series. The test was performed on 2 women and 5 men under general anesthesia.Three different loads (10, 15, and 20 grams) were applied onto the medial rectus over a maximum time period of up to 10 seconds. The response of the linear and nonlinear three element model was fitted to the obtained creep graphs. The results showed a good fitness in both the linear and nonlinear model. Since the living soft tissues generally exhibit nonlinear behavior, these results can indicate that the experiment have done in linear range.It would be useful to predict any patient's eye muscle performance after strabismus surgery.