title: Adaptability of the Immature Ocular Motor Control System: Unilateral IGF-1 Medial Rectus Treatment.
abstract: OBJECTIVE
  Unilateral treatment with sustained release IGF-1 to one medial rectus muscle in infant monkeys was performed to test the hypothesis that strabismus would develop as a result of changes in extraocular muscles during the critical period of development of binocularity.
  
  
  METHODS
  Sustained release IGF-1 pellets were implanted unilaterally on one medial rectus muscle in normal infant monkeys during the first 2 weeks of life. Eye position was monitored using standard photographic methods. After 3 months of treatment, myofiber and neuromuscular size, myosin composition, and innervation density were quantified in all rectus muscles and compared to those in age-matched controls.
  
  
  RESULTS
  Sustained unilateral IGF-1 treatments resulted in strabismus for all treated subjects; 3 of the 4 subjects had a clinically significant strabismus of more than 10°. Both the treated medial rectus and the untreated ipsilateral antagonist lateral rectus muscles had significantly larger myofibers. No adaptation in myofiber size occurred in the contralateral functionally yoked lateral rectus or in myosin composition, neuromuscular junction size, or nerve density.
  
  
  CONCLUSIONS
  Sustained unilateral IGF-1 treatment to extraocular muscles during the sensitive period of development of orthotropic eye alignment and binocularity was sufficient to disturb ocular motor development, resulting in strabismus in infant monkeys. This could be due to altering fusion of gaze during the early sensitive period. Serial measurements of eye alignment suggested the IGF-1-treated infants received insufficient coordinated binocular experience, preventing the establishment of normal eye alignment. Our results uniquely suggest that abnormal signaling by the extraocular muscles may be a cause of strabismus.
authors.affiliation: Graduate Program in Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States 2Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States.
authors.forename: Christy L
authors.initials: CL
authors.lastname: Willoughby
authors.affiliation: Washington National Primate Research Center, Seattle, Washington, United States 4Department of Ophthalmology, University of Washington, Seattle, Washington, United States.
authors.forename: Jérome
authors.initials: J
authors.lastname: Fleuriet
authors.affiliation: Washington National Primate Research Center, Seattle, Washington, United States.
authors.forename: Mark M
authors.initials: MM
authors.lastname: Walton
authors.affiliation: Washington National Primate Research Center, Seattle, Washington, United States 4Department of Ophthalmology, University of Washington, Seattle, Washington, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Mustari
authors.affiliation: Graduate Program in Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States 2Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States.
authors.forename: Linda K
authors.initials: LK
authors.lastname: McLoon
mesh_terms: D000818:Animals; D003692:Delayed-Action Preparations; D004195:Disease Models, Animal; D004343:Drug Implants; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000494:pharmacology*; D008251:Macaca; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000378:metabolism; D009413:Nerve Fibers, Myelinated / Q000473:pathology; D009801:Oculomotor Muscles / Q000187:drug effects* / Q000294:innervation / Q000473:pathology; D013285:Strabismus / Q000139:chemically induced* / Q000473:pathology; D015348:Vision, Binocular / Q000187:drug effects
chemical_list: D003692:Delayed-Action Preparations; D004343:Drug Implants; D007334:Insulin-Like Growth Factor I; D018995:Myosin Heavy Chains