This article is more than 5 years old. Information may no longer be current.
Ablation on corneal optical center appears safer than on pupil center, study shows
Eur J Ophthalmol. 2009;19:923-929.
Click Here to Manage Email Alerts
Myopic LASIK with the ablation focused on the corneal optical center may be more effective than ablation focused on the pupil center, according to a study.
The prospective study included 119 eyes of 60 patients who underwent LASIK with a standard spherocylindrical ablation model. The study group included 60 eyes of 30 patients who had ablation fixed on the corneal optical center. The comparator group included 59 eyes of 30 patients with ablation centered on the pupil center.
Investigators measured the distance between the ablation center and corneal vertex normal (DAV) to describe the match of ablated tissue and virgin corneal tissue. They also compared uncorrected visual acuity, best corrected visual acuity, refraction and higher-order aberrations for a 6-mm pupil area between the two groups.
Mean DAV was 0.35 mm in the study group and 0.69 mm in the control group; the difference between groups was statistically significant (P < .05). Study results showed no appreciable difference between the groups' postoperative UCVA and BCVA (P > .05).
Ninety percent of eyes in the study group and 72.88% of eyes in the control group had residual astigmatism within 0.5 D; the difference was statistically significant (P < .01). The study group had a markedly lower increase in root mean square of higher-order aberrations than the control group (P < .01).
The optimal location for ablation centration has long been assumed to be the center of the pupil; however, there are some that have argued that ablations should be centered on the corneal vertex. This study supports the corneal vertex side by demonstrating that there was more induced astigmatism and more induced higher order aberrations in a group with pupil centration compared to a group with corneal vertex centration.
Ablation centration is only an issue for patients with an angle kappa, where the pupil center is different from the corneal vertex. Many patients only have a small angle kappa, so pupil centration will be equivalent to corneal vertex centration, which is probably the reason why many people have continued with pupil centration as problems would only occur in a small percentage of patients. Ablation centration has started to become more of an issue as higher hyperopic treatments are being performed since more hyperopic patients have an angle kappa.
This supports the findings previously reported (Reinstein DZ, Archer TJ, Gobbe M. Centration of Hyperopic Corneal Ablations: Corneal Vertex vs. Pupil Center. AAO Annual Meeting, Atlanta, 9-13 Nov. 2008) for a population of hyperopic patients. All eyes were treated on the corneal vertex and results were grouped into eyes with small and large angle kappa. There was no statistical difference between groups for accuracy, safety, contrast sensitivity, or subjective night vision. Therefore, had the treatments been centered on the pupil in the large angle kappa group, the results would have been worse.
– Dan Z. Reinstein, MD, MA(Cantab), FRCSC, DABO,
FRCOphth
London Vision Clinic, London