[Influence of body position on ocular cycloposition in patients without binocular vision]

Positionally induced cyclotorsion could be an important factor concerning correction of astigmatism in refractive surgery. Previous studies have shown no influence of body position on cycloposition in healthy subjects with normal binocular vision.

10 subjects (median value of age 44.2 years) without binocular vision due to an organic eye disease or to strabismus were examined using three-dimensional video-oculography (3D-VOG). This non-invasive method can record changes in the position of both eyes simultaneously in the x-, y- and z-axes. The cycloposition of the eyes was recorded first in a seated position with both eyes open (test 1), then in a supine position with the right eye closed (test 2), then in a supine position with occlusion of both eyes (test 3), and then in a supine position with both eyes open (test 4). In each of these 4 situations, the eyes were recorded for 1 minute. Cyclovergence was calculated as the difference between the right and the left eye positions.

The range of cycloposition of the right and left eye in all 4 tests was very small. 95 % confidence intervals for cycloposition of the right and left eyes and for cyclovergence: cycloposition right eye/cycloposition left eye/cyclovergence: 0.72;0.76/- 0.07;0.01/0.71;0.79 (test 1), 0.23;0.29/0.19;0.33/- 0.81;- 0.63 (test 2), - 0.92;0.7/- 0.51;- 0.37/- 0.79;- 0.45 (test 3), 0.14;0.52/- 0.07;0.31/0.59;0.21 (test 4). There was no statistically significant difference of the cycloposition between the 4 test situations.

The cycloposition of the eyes does not significantly change between seated and supine positions of the body, either in subjects with, or without binocular vision. This means for refractive surgery that a correction of astigmatism, to be performed in the supine position of the patient, can be based on a measurement of the axis of astigmatism obtained in the seated position.