title: The Calibration of the Corneal Light Reflex to Estimate the Degree of an Angle of Deviation.
abstract: OBJECTIVE
  To measure the conversion factor for the size of an angle of deviation from the clinical photographs of the corneal light reflex.
  
  
  METHODS
  In this cross-sectional study, 19 normal subjects with 20/20 visual acuity were photographed with a digital camera while staring at targets placed five prism diopters (PD) apart from one another on a screen. The subjects were tested at a distance of 1 meter (m) and 4 m from a screen. Measurement of the corneal light reflex displacement for each fixed target was obtained from the photographs. The calibration of the corneal light reflex displacement in millimeters (mm) against the angle of deviation in PD was then analyzed with repeated measure linear regression analysis.
  
  
  RESULTS
  At 1 m, the values of 0.047 mm/PD and 0.058 mm/PD were obtained as the conversion factor from reflex displacement to deviated angle for the nasal side and temporal side respectively. At 4 m, the values were 0.050 mm/PD and 0.064 mm/PD for the nasal side and the temporal side respectively. There were significant differences between the values obtained at the different distances, regardless of nasal or temporal side.
  
  
  CONCLUSIONS
  Conversion factors were presented for estimating the strabismic angle at different distances and gazes. For clinical practice, the use of photographs to estimate the strabismic angle should use different values for different distances and strabismic types.
authors.forename: Supaporn
authors.initials: S
authors.lastname: Tengtrisorn
authors.forename: Sitthi
authors.initials: S
authors.lastname: Tangkijwongpaisarn
authors.forename: Somporn
authors.initials: S
authors.lastname: Burachokvivat
mesh_terms: D000328:Adult; D001767:Blinking / Q000502:physiology*; D002138:Calibration; D003315:Cornea / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D010781:Photography / Q000379:methods; D013285:Strabismus / Q000175:diagnosis* / Q000503:physiopathology