Use of preoperative assessment of positionally induced cyclotorsion: a video-oculographic study

Purpose: Positionally induced cyclotorsion could be an important factor concerning correction of astigmatism in refractive surgery. The method of binocular three dimensional infrared video-oculography (3D-VOG) was used to determine a possible influence of body position on cyclotorsion. Methods: 38 eyes ( 19 healthy subjects, median value of age 25.5) with normal binocular vision were examined using 3D-VOG. This method records ocular motions and positions of both eyes simultaneously in the x, y, and z axis. Cycloposition of the eyes was recorded first in a seated position ( both eyes open, test 1), then in a supine position ( right eye closed, test 2), occlusion of both eyes ( test 3), both eyes open ( test 4). Cyclovergence was calculated as the difference between the right and the left eye positions. Results: The range of cyclotorsion of the right and left eye in all four tests was between 1.13degrees excyclotorsion and 0.34degrees incyclotorsion. There was no statistically significant difference of the median values for torsion for the four test situations. Concerning the influence of body position on cyclotorsion, a statistically significant difference between the different test positions and settings did not exist. Median values for right/left torsion/cyclovergence were: 0.17/ 0.04/ 0.02 ( test 1), 20.31/ 20.71/ -0.16 ( test 2), -1.09/ -0.60/ 0.82 ( test 3), 0.28/ 0.28/ -0.82 ( test 4). Conclusions: Cyclotorsion does not significantly change between seated and supine position in subjects with normal binocular vision and stable fixation. In these subjects, an erroneous refractive surgery due to incorrect measurement of the axis of astigmatism in the seated position and performing the refractive surgery in the supine position, is very unlikely.