Surgeon offsets and dynamic eye movements in laser refractive surgery

PURPOSE: To determine the amount of static and dynamic pupil decentrations that occur during laser refractive surgery. SETTING: The Center of Visual Science and the Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS: The surgeon's accuracy in aligning the pupil center with the laser center axis was measured when engaging the eye-tracker in 17 eyes receiving conventional laser in situ keratomileusis (LASIK) procedures (Technolas 217z; Bausch & Lomb). Eye movements were measured subsequently during the treatment in 10 eyes using a pupil camera operating at 50 Hz. Temporal power spectra were calculated from the eye movement measurements. RESULTS: The mean pupil misalignment by the surgeon at the beginning of the procedure was 206.1 microm +/- 80.99 (SD) (with respect to the laser center). The laser center was typically misaligned below (inferiorly) and to the left (nasally and temporally in left and right eyes, respectively) of the pupil corrected] center. Small amounts of cyclotorsion were observed during the ablation (<2 degrees). The mean magnitude of dynamic pupil decentration from the laser center during treatment was 227.0 +/- 44.07 microm. The mean standard deviation of eye movements was 65.7 +/- 25.64 microm. Temporal power spectra calculated from the horizontal and vertical changes in eye position during the ablation were similar. Ninety-five percent of the total power of the eye movements was contained in temporal frequencies up to 1 Hz, on average, in both directions. CONCLUSIONS: Most eye movements during LASIK are slow drifts in fixation. An eye-tracker with a 1.4 Hz closed-loop bandwidth could compensate for most eye movements in conventional or customized ablations.