title: Clinical measurement of compensatory torsional eye movement during head tilt.
abstract: OBJECTIVE
  To measure the degree of compensatory torsional eye movement during head tilt using a fundus photography method.
  
  
  METHODS
  We enrolled 55 healthy subjects who were 20-66 years of age. Fundus photographs were obtained in the presumed baseline position and in stepwise head tilt positions to evaluate ocular torsion using a non-mydriatic fundus camera. Horizontal marks on the nose were photographed simultaneously to evaluate head tilt. Images were analysed using Photoshop to measure the degree of ocular torsion and head tilt.
  
  
  RESULTS
  A consistent compensatory torsional eye movement was observed in all subjects during head tilt. The degree of compensatory torsional eye movement showed a positive correlation with the angle of head tilt. Ocular torsional disconjugacy was observed during head tilt, with larger excycloductional eye movement than incycloductional eye movement (4.88 ± 2.91° versus 4.50 ± 2.76°, p < 0.001). In multiple linear regression analysis, the degree of compensatory torsional eye movement was significantly associated with the degree of head tilt (β = 0.191, p < 0.001), and the direction of cycloduction (β = -0.548, p < 0.001).
  
  
  CONCLUSIONS
  The fundus photography method is a non-invasive, accurate and objective tool for measuring compensatory torsional eye movement. Considering the availability of fundus photography in clinical ophthalmology practice, the proposed method can be used as a clinical tool to measure compensatory torsional eye movement.
authors.affiliation: Department of Ophthalmology, College of Medicine, Hanyang University School of Medicine, Seoul, South Korea.
authors.forename: Han Woong
authors.identifier: http://orcid.org/0000-0001-6177-4809
authors.initials: HW
authors.lastname: Lim
authors.affiliation: Department of Ophthalmology, College of Medicine, Hanyang University School of Medicine, Seoul, South Korea.
authors.forename: Ji Hong
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Ophthalmology, College of Medicine, Hanyang University School of Medicine, Seoul, South Korea.
authors.forename: Seung Hun
authors.initials: SH
authors.lastname: Park
authors.affiliation: Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Sei Yeul
authors.initials: SY
authors.lastname: Oh
mesh_terms: D000328:Adult; D000368:Aged; D003941:Diagnostic Techniques, Ophthalmological; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D005654:Fundus Oculi; D019416:Head Movements / Q000502:physiology*; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D010781:Photography; D011187:Posture; D011446:Prospective Studies; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult
keywords: eye movements; fundus photography; head tilt; oblique muscles; ocular torsion