Iris registration is a good compensator of cyclotorsion

Compensation of cyclotorsion using iris registration can be helpful in decreasing misalignment of the axis of correction and in improving the overall outcome of LASIK, according to a study to be published in the April 2008 issue of the Journal of Cataract & Refractive Surgery.

Hyojin Kim and Choun-Ki Joo performed the study, to evaluate the degree and direction of ocular cyclotorsion according to body position and flap creation before LASIK, at Kangnam St Mary's Hospital, Seoul, Republic of Korea.

The rotational position and degree were measured in 140 eyes of 70 patients with myopia or myopic astigmatism. Preoperatively, an iris image of each eye was examined using the Visx WaveScan Wavefront System (AMO) iris-registration feature with the patient seated. A Visx Star S4 laser (AMO) was used to measure cyclotorsion on the images before flap creation with the patient supine. The iris image was measured again after flap creation with the patient supine. The hinge of the LASIK flap was placed on the superior side and by rotating from the right to left side.

The mean cyclotorsional misalignment was 2.59 degrees±1.91 (SD) (right eye, 2.67±2.00 degrees; left eye, 2.51±1.98 degrees). Twenty eyes (13.0%) had cyclotorsion greater than 5 degrees. Seventy-six eyes (54.3%) had excyclotorsion. After flap creation, 107 eyes (76.4%) and 27 eyes (19.3%) rotated in the direction of identity and opposition, respectively. In eyes with cyclotorsion of identical direction, the mean increase was 1.27±0.99 degrees and 1.19±1.08 degrees in the excyclotorsion direction and incyclotorsion direction, respectively.

From these results, the authors concluded that compensation of cyclotorsion using iris registration can be helpful in decreasing misalignment of the axis of correction and in improving the overall outcome of LASIK.