Simulation of oculomotility in craniosynostosis patients

Abstract

Craniosynostosis syndromes can be associated with missing extraocular muscles, or muscles with abnormal insertions, and so provide useful test cases for assessing our understanding of the mechanics of the extraocular muscles. Patient with craniosynostosis syndromes often show eye movements in which a horizontal movement by one eye is accompanied by upshoot or downshoot in the other eye.An hypothesis which has been put forward to explain these movements is that the muscles in the patients are excyclorotated and that the upshoots and downshoots follow directly from the application of Hering’s law of equal innervation. We modelled the mechanics of the excyclorotated muscles and verified this hypothesis. However, excyclorotation of the orbit often occurs in combination with anomalous muscle anatomy in craniosynostosis syndromes. In keeping with this finding, we have found that surgical transposition of the rectus muscles is insufficient by itself to correct the anomalous eye movements, but that transposition in combination with weakening of the obliques is effective.