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    Algorithm provides superior results

    Contralateral eye comparison study highlights performance of optimized prolate ablation


    Chicago—Data from 6 months of follow-up in a randomized, contralateral eye comparison study demonstrate LASIK performed using a proprietary "optimized prolate ablation" algorithm (OPA, Nidek) provides superior results compared with a conventional ablation technique, said George O. Waring III, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

    Dr. Waring
    OPA is based on a novel algorithm that integrates information from the preoperative topography and whole eye wavefront for a given eye to create a truly custom, aspheric ablation profile that maintains a prolate cornea. It was compared with a conventional refraction-based ablation profile (Final Fit software, Nidek) in a study enrolling 32 patients.

    Surgery was done by Alaa El-Danasoury, MD, at the Magrabi Eye Hospital in Jeddah, Saudi Arabia. Jack Holladay, MD, Houston, was a co-investigator. All treatments were performed using an excimer laser (EC-5000 CX III, Nidek) and a fourth-generation femtosecond laser (Intra-Lase, Abbott Medical Optics) to create LASIKflaps with an intended thickness of 110 μm.

    Maintaining a prolate cornea

    Figure 1 Right and left eyes of the same patient. The right eye was treated with an optimized prolate ablation algorithm (OPA, Nidek) and shows a prolate topography indistinguishable from baseline, with a cross-section of the power curve showing minimal peripheral steepening (red arrows). The left eye received standard myopic ablation and demonstrates an oblate topography with a "red ring" of peripheral steepening that induces more spherical aberration. The cross-section of the power curve shows this steepening (red arrows).
    Results showed that the OPA software performed successfully in maintaining a prolate cornea over the mesopic pupil in most eyes. It induced significantly less spherical aberration (SA) compared with conventional LASIK, and the OPA-treated eyes benefited with significantly better visual acuity, Dr. Waring noted.

    "All laser refractive surgeons are aware of the issue of fall-off of radial pulse energy delivered to the peripheral cornea due to the oblique beam incidence," said Dr. Waring, emeritus professor of ophthalmology, Emory University, Atlanta, and private practice at Eye1st Vision and Laser, Atlanta.

    "As a result, the prolate cornea is converted to an oblate shape in a standard myopic ablation, and there is induction of spherical aberration that compromises visual quality," Dr. Waring explained. "The OPA approach incorporates an eye-specific compensation matrix to adjust energy delivery in the periphery and also integrates topography in the ablation profile.

    "It, thereby, targets an optimal corneal shape for a given eye, and the results of this study demonstrate the benefit of OPA for delivering better vision," he added.

    Patients in the study were adults with –1 to –8 D of myopia, refractive cylinder <1.5 D, and an estimated residual stromal thickness exceeding 300 μm. The ablations were performed with the first version of the OPA software and the surgeon's personalized nomogram based on previous experience. All eyes were targeted for emmetropia, and with the OPA treatment, spherical aberration RMS was targeted for 0 μm.

    All ablations were performed using iris recognition, online torsion correction, centration close to the visual axis instead of based on the entrance pupil, a large optical zone so that the entire pupil received the full treatment, and a blend zone.


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