Topography-guided LASIK compensates for angle kappa to yield better outcomes

"Published papers and a study of ours that is currently in press establish that angle kappa is significant in hyperopic patients and especially in eyes with moderate to high levels of hyperopic error," explained Dr. Kanellopoulos, associate professor of ophthalmology, New York University, New York. "Since the measurements obtained to determine the ablation for LASIK are centered on the line of sight, not on the pupil center, the hyperopic treatment must adjust for angle kappa to avoid complications related to a decentered ablation zone.

"That concept is supported by our experience with the topography-guided technique, which, when compared with our previously published series of standard hyperopic treatment, had better outcomes in terms of less induced astigmatism, better quality of vision, and a lower regression rate," he said.

"To accommodate the decentered ablation, the flap should also be decentered. That can be challenging using a mechanical microkeratome, but is facilitated by using the . . . femtosecond laser (IntraLase, Advanced Medical Optics/IntraLase Corp.) for flap creation," Dr. Kanellopoulos said.

Preoperatively, the population had a mean ± SD sphere of +3.08 ± 1.56 D and mean cylinder of +1.80 ± 1.01 D. At last follow-up, mean sphere was –0.10 D (range, –0.75 to +0.75 D) and mean cylinder was +0.15 D (range, 0 to +0.50 D).

Mean uncorrected visual acuity improved from 20/78 preoperatively to 20/23 and mean best spectacle-corrected visual acuity improved from 20/28 to 20/23. Wavefront analysis revealed a 35% reduction in aberrations, and contrast sensitivity improved 25%. Refraction shifted by a mean of +0.32 D between months 1 and 12.

"These results were very rewarding and generally similar to those achieved with our standard wavefront-optimized treatment using [the] excimer laser in a published series of 120 eyes," Dr. Kanellopoulos said. "However, the topography-guided treatment has better predictability-in our standard treatment group mean sphere was +0.6 D and mean cylinder was +0.65 D, and the regression rate is lower as well. That latter benefit may be due to less treatment-induced astigmatism."