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Tracking of dynamic rotational eye movements during LASIK is especially important for obtaining good ablation results, considering that 29% of eyes can rotate 5Â° or more when the patients shift from the sitting to the supine position.
Dr. Lege based her remarks on experience with a new, fourth-generation eye-tracking system of a proprietary excimer laser platform (Technolas 100, Bausch & Lomb). (See "Online pachymetry, advanced eye-tracking improve LASIK".)
"Many companies have tracking systems that are comparable for the x and y eye trackers, and other companies have systems that allow correction for static cyclotorsion," Dr. Lege said. "This new eye-tracking system includes not only the static control but also a dynamic control of the rotational alignments. This allows us to compensate for active and passive eye movements during the excimer laser ablation and not only in the x and y axis but also torsional and tilting."
She demonstrated that the eye-tracking system compensates for ocular movement and maintains the position of the treatment pattern on the same axis.
Dr. Lege reported results from 1,847 eyes.
"We found that, in 29% of eyes, there was more than a 5° rotation when the patients changed from sitting to the supine position, and 8.3% rotated more than 3° during the treatment," she said. "If there is a mistreatment of 30° , the full cylinder remains. Some eyes even rotated as much as almost 20° during ablation, and those obviously are outliers that benefit most from the new system."
System in use
When in operation, the system shows the on-line pachymetry, the ocular rotation as the procedure progresses, and the compensation for the ocular rotation.
"We found an improvement of about 0.25 D in 14% of cases, and the efficacy improved from 71% to 86%," she said.