title: Extraocular muscles in patients with infantile nystagmus: adaptations at the effector level.
abstract: OBJECTIVE
  To test the hypothesis that the extraocular muscles (EOMs) of patients with infantile nystagmus have muscular and innervational adaptations that may have a role in the involuntary oscillations of the eyes.
  
  
  METHODS
  Specimens of EOMs from 10 patients with infantile nystagmus and postmortem specimens from 10 control subjects were prepared for histologic examination. The following variables were quantified: mean myofiber cross-sectional area, myofiber central nucleation, myelinated nerve density, nerve fiber density, and neuromuscular junction density.
  
  
  RESULTS
  In contrast to control EOMs, infantile nystagmus EOMs had significantly more centrally nucleated myofibers, consistent with cycles of degeneration and regeneration. The EOMs of patients with nystagmus also had a greater degree of heterogeneity in myofiber size than did those of controls, with no difference in mean myofiber cross-sectional area. Mean myelinated nerve density, nerve fiber density, and neuromuscular junction density were also significantly decreased in infantile nystagmus EOMs.
  
  
  CONCLUSIONS
  The EOMs of patients with infantile nystagmus displayed a distinct hypoinnervated phenotype. This represents the first quantification of changes in central nucleation and myofiber size heterogeneity, as well as decreased myelinated nerve, nerve fiber, and neuromuscular junction density. These results suggest that deficits in motor innervation are a potential basis for the primary loss of motor control.
  
  
  CONCLUSIONS
  Improved understanding of the etiology of nystagmus may direct future diagnostic and treatment strategies.
authors.affiliation: Department of Ophthalmology, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: Kathleen T
authors.initials: KT
authors.lastname: Berg
authors.forename: David G
authors.initials: DG
authors.lastname: Hunter
authors.forename: Erick D
authors.initials: ED
authors.lastname: Bothun
authors.forename: Rosalia
authors.initials: R
authors.lastname: Antunes-Foschini
authors.forename: Linda K
authors.initials: LK
authors.lastname: McLoon
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000368:Aged; D000818:Animals; D002648:Child; D002675:Child, Preschool; D005125:Eye Banks; D005260:Female; D000882:Haplorhini; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000473:pathology; D009210:Myofibrils / Q000473:pathology / Q000502:physiology; D009469:Neuromuscular Junction / Q000473:pathology / Q000503:physiopathology; D020417:Nystagmus, Congenital / Q000473:pathology* / Q000503:physiopathology*; D009801:Oculomotor Muscles / Q000294:innervation / Q000473:pathology* / Q000503:physiopathology*