LASIK Ablation Centration: An Objective Digitized Assessment and Comparison Between Two Generations of an Excimer Laser

PURPOSE: To objectively define the effective centration of myopic femtosecond laser-assisted LASIK ablation pattern, evaluate the difference between achieved versus planned excimer laser ablation centration, and compare these results from two different generations of an excimer laser system. METHODS: The study retrospectively evaluated 280 eyes subjected to myopic LASIK. Digital image analysis was performed on Scheimpflug sagittal curvature maps (difference of preoperative to postoperative). Centration was assessed via proprietary software digital analysis of the coordinate displacement between the achieved ablation geometric center and the planned ablation center, which was the corneal vertex. Results from two different excimer laser generations (Eye-Q 400 [140 eyes] and EX500 [140 eyes]; Alcon/WaveLight, Fort Worth, TX) were compared. RESULTS: Radial displacement was on average 360 + 220 mu m (range: 0 to 1,030 mu m) in the Eye-Q 400 laser group and 120 +/- 110 mu m (range: 0 to 580 mu m) in the EX500 laser group (P < .01). The percentage of eyes with displacement of greater than 300 mu m was 52% in the Eye-Q 400 laser group and 4% in the EX500 laser group. CONCLUSIONS: Displacement of ablation pattern may depend on the laser platform used. The improvement in the efficiency of centration indicates that newer generation excimer lasers with faster eye tracking and active centration control appear to achieve a significantly more accurate centration of myopic ablation patterns. The authors propose this novel, objective technique for laser refractive surgeon evaluation may point out significant outcome measures not currently used in standard metrics of refractive laser efficiency.