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T.H. Krzizok, R.C. Becker, H. Wassill; A New Method to Assess Positionally Induced Cyclotorsion and its Meaning for Refractive Surgery . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1932.
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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 was used to determine a possible influence of body position on cyclotorsion. Methods: 38 eyes from 19 healthy subjects (mean age 25.5 ± 6.8 years) ) with normal binocular vision were examined using the method of three-dimensional video-oculography (3D-VOG). With the help of the black pupil technique and especially the iris' image (iris segment analysis), this non-invasive method can record ocular motions and positions of both eyes simultaneously in the x, y and z-axis thus allowing a 3-D positional analysis with free gaze directions and head tilts for measuring not only horizontal and vertical, but also torsional deviations. Cycloduction of the eyes was recorded first in a seated position with both eyes open (test 1), then twice in a supine position, beginning with the right eye closed (test 2), then with closure of both eyes (test 3) followed by a third measurement with both eyes open (test 4). Each of these 4 tests was recorded for 1 minute allowing measurement of 3000 single positions. Cyclovergence was calculated as the difference between the right and the left eye positions. Results: Examinations took 4 minutes in total for each subject and a torsion quality higher than 0.8 could be achieved for all measurements representing data with a high quality level with a minimum of false positive or false negative values. Concerning the influence of body position on cyclotorsion, a statistically significant difference between the different test positions and settings did not exist. In the supine position with opening of both eyes, cycloduction was less irregular compared to the supine position with both eyes closed, but was still differing more from zero than in the seated position. In a supine position with closure of only one eye, cycloduction was more irregular and differed more from zero compared to the seated position. Median values for Right Torsion/ Left Torsion/ Cyclovergence: 0.17/ 0.04/ 0.02 (test 1), -0.31/ -0.71/ -0.16 (test 2), -1.09/ -0.60/ 0.82 (test 3), 0.28/ 0.28/ -0.82 (test 4). Conlusions: Because we did not find a statistically significant influence of body position on cyclotorsion in persons with normal binocular vision, the measurements of astigmatismus, corneal topography and aberration in the seated position are also correct for the supine position. Further investigations will be performed to examine if this applies also to persons without normal binocular vision in case of strabismus, anisometropia etc.
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