title: Region-specific relationships between refractive error and ciliary muscle thickness in children.
abstract: OBJECTIVE
  To determine if there is a relationship between refractive error and ciliary muscle thickness in different muscle regions.
  
  
  METHODS
  An anterior segment optical coherence tomographer was used to measure cycloplegic ciliary muscle thicknesses at 1 mm (CMT1), 2 mm (CMT2), and 3 mm (CMT3) posterior to the scleral spur; maximum (CMTMAX) thickness was also assessed. An autorefractor was used to determine cycloplegic spherical equivalent refractive error (SPHEQ). Apical ciliary muscle fibers were obtained by subtracting corresponding CMT2 values from CMT1 and CMTMAX. Multilevel regression models were used to determine the relationship between ciliary muscle thickness in various regions of the muscle and refractive error.
  
  
  RESULTS
  Subjects included 269 children with a mean age of 8.71 ± 1.51 years and a mean refractive error of +0.41 ± 1.29 diopters. In linear models with ciliary muscle thicknesses and SPHEQ, SPHEQ was significantly associated only with CMT2 (β = -11.34, P = 0.0008) and CMT 3 (β = -6.97, P = 0.007). When corresponding values of CMT2 were subtracted from CMT1 and CMTMAX, apical fibers at CMT1 (β = 14.75, P < 0.0001) and CMTMAX (β = 18.16, P < 0.0001) had a significant relationship with SPHEQ.
  
  
  CONCLUSIONS
  These data indicated that in children the posterior ciliary muscle fibers are thicker in myopia (CMT2 and CMT3), but paradoxically, the apical ciliary muscle fibers are thicker in hyperopia (CMTMAX and CMT1). This may be the first evidence that hyperopia is associated with a thicker apical ciliary muscle region.
authors.affiliation: College of Optometry, The Ohio State University, Columbus, Ohio, USA.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Pucker
authors.forename: Loraine T
authors.initials: LT
authors.lastname: Sinnott
authors.forename: Chiu-Yen
authors.initials: CY
authors.lastname: Kao
authors.forename: Melissa D
authors.initials: MD
authors.lastname: Bailey
mesh_terms: D000293:Adolescent; D002648:Child; D002924:Ciliary Body / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D009130:Muscle, Smooth / Q000473:pathology*; D011446:Prospective Studies; D012030:Refractive Errors / Q000473:pathology*; D012044:Regression Analysis; D041623:Tomography, Optical Coherence
keywords: children's vision; ciliary muscle; hyperopia; myopia; refractive error