The Ocular Motor Periphery

This chapter reviews contributions of orbital tissues and extraocular muscles (EOM) to the control of eye movements. The anatomy of the orbit, fascia, fibromuscular pulleys, and EOM are described and related to the kinematics of 3-D eye rotations. Current concepts of the embryology of the EOM and their unique and diverse characteristics are described, suggesting why they are more vulnerable to certain neuromuscular disorders and less susceptible to others, compared with skeletal muscles. Electrophysiological properties of different EOM fiber types (and their motor neuron innervation) are contrasted, describing new models that attempt to account for nonlinear mechanical properties of the orbit. The substrate and roles of extraocular proprioception in the control of eye movements are summarized and related to clinical disorders affecting EOM. The anatomy of the cranial nerves supplying the EOM is summarized, diagrammed and highlighted to aid diagnosis of common palsies of the oculomotor, trochlear, and abducens nerves.