International Conference ²Computational Mechanics and Virtual Engineering ²



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1st International Conference

²Computational Mechanics and Virtual Engineering ²

COMEC 2005

20 – 22 October 2005, Brasov, Romania







basics of complete biomechanical models for strabismus
Barbu D. Daniela Mariana1, Barbu Gh. Ion2, Luculescu Marius Cristian3

1 „Transilvania” University, Braşov, Romania, e-mail: dbarbu@unitbv.ro

2 „Transilvania” University, Braşov, Romania, e-mail: ibarbu@unitbv.ro

3 „Transilvania” University, Braşov, Romania, e-mail: lucmar@unitbv.ro


Abstract: Diagnosis and treatment of strabismus are based mostly on simple heuristics, shared experience and intuition. Consequently, unusual and complex strabismus cases may be difficult to manage. A description of the mechanisms of binocular coordination – a model – attacks these problems in a new way: experience, intuition and experimental findings go into building and testing the model, and then the model, less impaired by unfamiliarity and complexity, is used in case management. This paper is a review of the most important biomechanical models for strabismus used in scientific world.
Keywords: Eye, Strabismus, Biomechanics, Modeling, Ocular Muscles.

1. INTRODUCTION
Strabismus is a deviation of the eye which the patient cannot overcome without medical or surgical intervention. It can be congenital, acquired (developmental) or can be caused by disease or injury. Onset of congenital strabismus is at birth and onset of the acquired strabismus is after 1 year (average, 2 1/2 years). Generally the divergent eye has not developed normal visual acuity. Medical treatment is directed toward improvement of vision in the "lazy eye" by patching the eye, using eyeglasses or with orthoptics and visual therapy. Surgery is indicated when maximal improvement has been attained by medical methods. Surgical correction of most eye deviations involves lengthening or shortening the extra orbital muscles of the eye, namely the medial and lateral rectus muscles. Many times a series of operations must be done. Surgery for strabismus is generally done early in the life of the afflicted individual to prevent diplopia (double vision) and eventual blindness in the "lazy" eye.

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Figure 1. Forms of strabismus
iagnosis and treatment of strabismus are based mostly on simple heuristics, shared experience and intuition. Consequently, unusual and complex strabismus cases may be difficult to manage. A description of the mechanisms of binocular coordination – a model – attacks these problems in a new way: experience, intuition and experimental findings go into building and testing the model, and then the model, less impaired by unfamiliarity and complexity, is used in case management.
A model-driven approach, able to coordinate broad ranges of laboratory research and clinical experience, can accelerate progress in diagnosis and treatment of strabismus. Without analytical methods it is difficult to develop useful new procedures, particularly for complex, cyclovertical disorders. Such developments have been infrequent. As prosthetic extraocular muscles (EOMs) become practical their use will require judgments for which computational analysis provides the most appropriate guidance.

Actions of the oblique EOMs are complex and dysfunction is often not obvious from inspection of ocular ductions and versions. It is possible that most strabismus is complex, involving abnormal contractile and elastic forces, and path changes in several muscles, their innervations, and their connective tissue suspensions. In many cases of congenital and traumatic strabismus, the primary lesions are obviously multiple and complex. But even in an isolated palsy, there will generally be secondary changes in other muscles: it is well known that muscles adapt to changes in their working length. Innervational changes due to plasticity of neural control centers are less well understood, but are probably important in many disorders. It may be that strabismus diagnoses are typically simple because they are based on limited, poorly-controlled alignment measurements. Such measurements may be the norm because it is impossible to assimilate more adequate data without computational help.



2. Strabismus Models
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