Dr Michael English

With a group of others pioneered the first Excimer Laser used in Perth in the mid 90's. Michael is a fellow of the Royal College of Surgeons and the Royal Ausralian and New Zealand Collage of Ophthal-mologists. He is also a fellow of the Royal Collage of Ophthalmology (UK).

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A recent study demonstrates that the wave-front guided LASIK procedure induces significantly less higher-order aberrations, spherical aberration, trefoil and coma that the wavefront-optimised LASIK induced aberrations. Thus, wavefront guided ablations provide the best results for the vast majority of patients with the lowest rate of retreatment over conventional LASIK and wavefront-optimised LASIK.

Reducing aberrations
Studies show that less higher-order aberrations in the eye result in better quality of vision. In the laboratory, Pablo Artal, Ph.D., showed eliminating all higher-order aberrations produces the best visual performance. In addition, studies from Steve Schallhorn, M.D., global medical director of Optical Express, with 140 pilots and 228 clinic patients showed that the best visual performance occurred with the lowest amount of higher-order aberrations. Similarly, pilots who had never had surgery naturally had lower higher-order aberrations.

With wavefront-optimised LASIK, the goal is not to reduce the spherical aberration, but simply not increase it. The treatment basis is sphere and cylinder. Optimized simply means "not intended to induce spherical aberration," and therefore does not address pre-op spherical aberration or any other higher-order aberrations. Numerous studies have shown that by the time most patients reach their 40s, they have positive ocular spherical aberrations. With wavefront-guided LASIK, the goal is to reduce all higher-order aberrations. The spherical aberration target is zero.

Study and results
The purpose of our study was to compare wavefront-optimised and wavefront-guided procedures to determine which is more effective. The retrospective chart review study of 200 IntraLASIK procedures included 100+ IntraLase (Abbott Medical Optics, AMO, Santa Ana, Calif). Wavelight (wavefront-optimised) eyes and 100+ IntraLase Custom Vue (AMO) (wavefront-guided) eyes. Pre-op and post-op wavefront scans were done on all eyes at a 6-mm pupil size. Primary spherical aberrations, primary coma, primary trefoil and total higher-order aberrations were measured.

One hundred and nine Custom Vue eyes and 102 Wavelight eyes were reviewed in 2006 and early 2007. These study results show that wavefront-guided ablation with femtosecond technology is optimal for the majority of patients.

Overall, the wavefront-guided treatment induces significantly less higher-order aberrations, spherical aberration, trefoil and coma than the wavefront-optimised procedure (Figure 1 and 2). There was significantly more variation with the wavefront-optimised eyes. This study indicates that for all higher-order aberration in the wavefront-guided group, about 12% of patients were better, 76% were the same and 12% were worse post-op. With wavefront-optimised, about 8% were better, 51% were the same and 41% were worse. There was significantly greater safety for the patients with the guided procedure. The wave-front-guided procedure had the greater efficacy for total higher-order aberrations and the better safety with the lowest induced aberrations.

We have found that wave-front-guided LASIK has the best chance of maintaining or improving higher order aberrations and therefore has the best chance of providing optimal visual quality.

By Jack T. Holladay M.D.
"Eye World" Published April 2010

Posted 22 July 2010