title: Cyclotorsion: a possible cause of residual astigmatism in refractive surgery.
abstract: OBJECTIVE
  To determine whether cyclotorsion occurs when a subject changes from binocular to monocular fixation and to assess positionally induced cyclotorsion.
  
  
  METHODS
  Clinics of the Rotterdam Eye Hospital, Rotterdam, The Netherlands.
  
  
  METHODS
  The axis of astigmatism was measured with the Nidek handheld keratometer in 15 normal subjects under monocular and binocular fixation and in seated and supine positions. The limits of agreement for the repeatability of measurements with the Nidek keratometer were used to identify subjects with statistically significant cyclotorsion.
  
  
  RESULTS
  Two subjects (13%) showed statistically significant excyclotorsion when changing from binocular to monocular fixation in a seated position. In a supine position, 3 subjects (20%) showed excyclotorsion when the fixation changed. Body position itself had no influence on ocular torsion.
  
  
  CONCLUSIONS
  Significant cyclotorsion may occur under monocular viewing conditions. If monocular photorefractive keratectomy procedures are based on binocular keratometry readings, an undercorrection of myopic astigmatism may result. Individuals at risk should be identified before refractive keratectomy is performed.
authors.affiliation: Pediatric Ophthalmology and Strabismus Service, The Rotterdam Eye Hospital, Rotterdam, The Netherlands.
authors.forename: Martha J
authors.initials: MJ
authors.lastname: Tjon-Fo-Sang
authors.forename: Jan-Tjeerd H N
authors.initials: JT
authors.lastname: de Faber
authors.forename: Christine
authors.initials: C
authors.lastname: Kingma
authors.forename: W Houdijn
authors.initials: WH
authors.lastname: Beekhuis
mesh_terms: D001251:Astigmatism / Q000209:etiology*; D003316:Corneal Diseases / Q000150:complications*; D005133:Eye Movements; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy; D011187:Posture; D014102:Torsion Abnormality; D015349:Vision, Monocular