title: Muscle path length in horizontal strabismus.
abstract: BACKGROUND
  Sarcomere adaptation has been proposed as a mechanism for the adjustment of rectus muscle length in regulating binocular alignment. The purpose of this study was to investigate whether horizontal rectus muscle paths have abnormal lengths in subjects with intermittent or alternating strabismus.
  
  
  METHODS
  High-resolution, surface coil magnetic resonance imaging was obtained in 2 mm thick axial planes in strabismic patients who had not undergone prior surgery and normal control subjects. The lengths of horizontal rectus muscle paths were measured digitally in central gaze for the fixating eye only and compared.
  
  
  RESULTS
  A total of 12 strabismic subjects and 13 controls were included: 8 subjects had esotropia averaging 30(Δ), and 4 had exotropia averaging 47(Δ). The sample had 80% power to detect muscle path length changes of at least the typical surgical doses appropriate to strabismus surgery for correction of the mean deviations in each group, had such changes existed. Mean (± standard deviation) medial rectus path length was 35.0 ± 4.1 mm in controls, not significantly different from 36.3 ± 1.7 mm in exotropia (P = 0.56) or 35.8 ± 2.9 mm in esotropia (P = 0.62). Mean lateral rectus path length in controls was 35.7 ± 4.0 mm, not significantly different from the values of 39.6 ± 3.8 mm in exotropia (P = 0.09) and 37.8 ± 3.3 (P = 0.19) mm in esotropia.
  
  
  CONCLUSIONS
  Horizontal rectus muscle path lengths are not significantly abnormal in commonly encountered intermittent or alternating esotropia and exotropia.
authors.affiliation: Jules Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles.
authors.forename: Ronen
authors.initials: R
authors.lastname: Rabinowitz
authors.affiliation: Jules Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles; Department of Neurology, University of California, Los Angeles; Department of Bioengineering, University of California, Los Angeles; Department of Neuroscience Interdepartmental Programs, University of California, Los Angeles. Electronic address: jld@jsei.ucla.edu.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Demer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004948:Esotropia / Q000175:diagnosis*; D005099:Exotropia / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000473:pathology*; D015348:Vision, Binocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult