Results of LASIK Ablation Centration Using Novel Digitized Analysis of Postoperative Scheimpflug Ablation Imaging: Comparison of 2 Excimer Lasers
To objectively evaluate the achieved vs. planned excimer laser ablation centration in relation to the visual axis in eyes subjected to myopic LASIK and compare results from two generations of an excimer laser system.
The study employed 280 eyes subjected to myopic LASIK. Digital image analysis was performed on Scheimpflug sagittal curvature maps (preoperative, postoperative, and their difference). Centration was assessed via digital proprietary software 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: the EyeQ 400Hz excimer laser with a 250 Hz tracker (Group A) and the EX500 excimer laser with a 1056 Hz active tracker (Group B), were compared.
Postoperative spherical refractive error was -0.21 Diopters (+/- 0.3 D) for group A and -0.19 Diopetrs(+/- 0.25 D) for group B. These data, along with the percentage of eyes achieving 20/20, 20/40 for both groups were not statistically significant Average radial displacement of ablation centration in group-A was on average 360 ± 220 μm (range 0 to 1,030 μm), while in group-B 120 ± 110 μm (range 0 to 580 μm). The centration data showed highly significant statistical comparison (P<0.0001).
Faster excimer laser spot delivery frequency, and/or faster response eye tracking with active centration control appears to significantly improve effective ablation centration to the visual axis in myopic LASIK cases. Although these data do not seem to affect the usual metrics such as UDVA and residual refraction, they may affect quality of vision.