Ablations should be centered based on intraoperatively measured angle kappa

In this study, the authors investigated the prevalence of angle kappa in hyperopic eyes and its effect on the refractive outcomes of excimer laser vision correction.

Study design

This retrospective multicenter study analyzed 170 hyperopic astigmatic eyes of 112 patients who had initial microkeratome and wavefront-optimized LASIK with hyperopic regression. Patients who had preoperative cycloplegic refraction greater than 1 D when compared with the manifest refraction or with less than 6 months of follow-up were excluded.

Treatment groups were defined based on the magnitude of preoperative angle kappa (low was <0.25 mm, moderate was 0.25 to 0.50 mm and high was >0.50 mm) and evaluated pre and post operatively. The ablation was performed on the surgeon-defined visual axis intraoperatively.

Outcomes

Postoperative corrected distance visual acuity (CDVA) was worse for patients with high angle kappa compared with the moderate angle kappa group. The surgeon’s perceived angle kappa of the patient intraoperatively was statistically smaller than the preoperative measured angle kappa in the group of eyes with preop angle kappaa of 0.25 mm or greater. The magnitude of angle kappa had no effect on efficacy or safety of hyperopic treatments.

Limitations

The biggest limitation is that the treatment centration was subjectively defined by the surgeon rather than using objective methods. The angle kappas were separated into discrete groups, which decreases the ability to determine where angle kappa becomes clinically significant. The surgeon defined the desired ablation center as 100% offset from the acquired pupil center at the beginning of each treatment and did not study anything less, which has been shown in previous studies to be the true visual axis.

Clinical significance

Knowing that the preoperatively measured angle kappa may be larger intraoperatively is helpful, but this may be equipment specific. When counseling patients, physicians should keep in mind that a high angle kappa can decrease CDVA. It is important to note that centering an ablation too nasally on a patient with a high angle kappa can be optically detrimental.