title: A defined change of polarization axis is detected by variable corneal compensation of the GDxVCC.
abstract: OBJECTIVE
  The aim of the study was to examine whether a defined change of polarization axis (PA) is detected by the variable cornea compensation (VCC) of the GDxVCC. The idea behind was to induce a change of PA by a rotation of the eye and to determine whether the rotation affects the magnitude of retardation and retinal nerve fiber layer measurements.
  
  
  METHODS
  Fifteen normal eyes were examined with the GDxVCC. First scans (cornea and optic nerve head) of the right eye in regular position (0 degree) were performed. These scans are recognized and saved regularly as a right eye by the instrument. Then a second scan set of the same eye was taken: the subjects turned their head upside-down (180 degrees). These scans were recognized and saved as a left eye. For each scan, the instrument calculates the polarization parameter axis and magnitude.
  
  
  RESULTS
  The difference of magnitude was 4.3+/-3.7 nm (0 to 12 nm) and difference of axis was 3.5+/-2.4 degrees (0.1 to 8.1 degrees). There were no significant differences in all measured parameters between the "normal" and the turned eye (all P>0.2; paired t tests).
  
  
  CONCLUSIONS
  A defined change of PA was detected by the VCC of the GDx and the instrument was able to reproduce the polarization parameters of the anterior segment and retinal nerve fiber layer parameters of the same eye in 2 different positions with adequate accuracy.
authors.affiliation: Department of Ophthalmology, University of Dresden, Germany. Eckart.Schmidt@uniklinikum-dresden.de
authors.forename: Eckart
authors.initials: E
authors.lastname: Schmidt
authors.forename: Andreas G
authors.initials: AG
authors.lastname: Boehm
authors.forename: Lutz E
authors.initials: LE
authors.lastname: Pillunat
mesh_terms: D000328:Adult; D001718:Birefringence; D003315:Cornea / Q000502:physiology*; D005260:Female; D006801:Humans; D007834:Lasers; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D009887:Ophthalmoscopy / Q000379:methods*; D009898:Optic Disk / Q000033:anatomy & histology*; D011446:Prospective Studies; D012165:Retinal Ganglion Cells / Q000502:physiology*