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E. Schmidt, A.G. Boehm, L.E. Pillunat; A Defined Change of Polarization Axis Is Detected by Variable Corneal Compensation of the GDxVCC . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2503.
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Purpose: Aim of the study was to examine whether a defined change of polarization axis (PA) is detected by the variable cornea compensation 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 RNFL measurements. If it could be shown that the measured axis is rotated to the same amount as the eye and magnitude and RNFL parameters are unaffected this would prove the proper operativeness of the variable corneal compensator. Methods: 15 normal eyes were examined with the GDxVCC. First scans (cornea and optic nerve head) of the right eye in regular position (position 0°) were performed. In this position the 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 (position 180°). These scans in the 180° position of the right eye were recognized and saved as a left eye by the instrument. A 180° rotation of a right eye results in the same relative position of the optic nerve head and the macula of a left eye. For each scan the instrument calculates the polarization parameter axis and magnitude of the AS. For the left eyes the procedure was adopted accordingly. Results: Difference of Magnitude of AS was 4.3 ± 3.7 nm (range 0–12 nm) and difference of axis was 3.5 ± 2.4° (range 0.1°–8.1°). 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 the polarization axis was detected by the variable cornea compensation of the GDxVCC. The instrument was able to reproduce the polarization parameters of the AS of the same eye in two different positions with adequate accuracy. The measured axis was rotated to the same amount as the eye was rotated and the magnitude and RNFL parameters were unaffected. This suggests a proper operativeness of the variable corneal compensator of the GDxVCC.
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