Innervated Myotendinous Cylinders Alterations in Human Extraocular Muscles in Patients With Strabismus

PURPOSE: To analyze innervated myotendinous cylinders (IMCs) in the extraocular muscles (EOMs) of normal subjects and strabismic patients. METHODS: The rectus muscles of 37 subjects were analyzed. Distal myotendinous specimens were obtained from 3 normal subjects, 20 patients with acquired strabismus, 11 with infantile strabismus, and from 3 with congenital nystagmus, and were studied by using light microscopy. Some specimens (6 rectus muscles) were also examined by transmission electron microscopy. RESULTS: IMCs were found in the distal myotendinous regions of EOMs. The IMCs of patients with acquired strabismus showed no significant morphological alterations. However, significant IMCs alterations were observed at the distal myotendinous junction of patients with congenital strabismus and congenital nystagmus. CONCLUSIONS: This study supports the notion that IMCs in human EOMs function mainly as proprioceptors, along with effector properties, and a disturbance of ocular proprioceptors plays an important role in the pathogenesis of oculomotor disorder. We suggest that a proprioceptive feedback system should be stimulated and calibrated early in life for the development of binocular vision.

The Morphological Differences of Proprioceptors in Extraocular Muscles among Congenital, Acquired Exotropia and Congenital Nystagmus

PURPOSE: To evaluate morphological differences in proprioceptors in extraocular muscles between congenital exotropia, acquired exotropia and congenital nystagmus. METHODS: Nine medial recti including the myotendinous junction were resected using medial rectus resection in three congenital and five acquired exotropia patients. Two medial recti and two lateral recti were resected using the modified Kestenbaum procedure in two congenital nystagmus patients. The muscle tissues were examined under a light microscope following examination with a transmission electron microscope. RESULTS: In the congenital exotropia group, the electron microscopic findings showed degenerative changes in proprioceptors, such as decreased microtubules, axonal shrinkage and decreased myelin thickness. In the acquired exotropia group, the neural structures in the myotendinous junction were well maintained. There were no neural structures in the myotendinous junction in the congenital nystagmus group. CONCLUSIONS: Depending on the type of strabismus, there may be morphological differences in proprioceptors of extraocular muscles.