Detection of cyclotorsional rotation during excimer laser ablation in LASIK

Positionally induced cyclotorsion could be an important factor in the correction of astigmatism during refractive surgery. We analyzed the change in cyclotorsional rotation during excimer laser ablation in LASIK surgery using the NIDEK Torsion Error Detector (TED).

One hundred ten patients (192 eyes) who underwent LASIK for myopic astigmatism, using the NIDEK Advanced Vision Excimer Laser (NAVEX) were measured for cyclotorsion during surgery using the TED system. The manifest refraction of these patients was -6.80+/-2.74 diopters (D) (range: -1.00 to -13.75 D). The iris pattern of the patient's eyes in the supine position was recorded via a CCD camera in the EC5000CXII excimer laser system, and it was compared to the iris pattern acquired during OPD-Scan measurement in the sitting position.

During laser ablation, the degree of cyclotorsional rotation detected by TED was 1.33+/-1.88 degrees (range: -6.33 to 2.99 degrees) clockwise and 1.00+/-1.79 degrees (range: -3.70 to 7.34 degrees) counterclockwise. The absolute degree of torsion error detected by the TED system was 2.33+/-1.16 degrees (range: 0 to 6.21 degrees).

The effectiveness of the cylinder treatment can be reduced due to torsion errors. The degree of cyclotorsion constantly changes during laser ablation. Therefore, a monitoring system should be developed for the measurement of torsion error, and this will enable the maximum possible correction of the error during laser ablation.