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Refractive Surgery | Jul 2011

Feature Story: Customized Ablations for Better Visual Outcomes

More than 20 years have passed since LASIK was first performed, and the procedure continues to undergo refinement today. In the recent past, mechanical microkeratomes have been widely supplanted by femtosecond lasers, and conventional ablations have given way in many practices to customized ablations. Both advances contribute to the improved visual outcomes our patients achieve today.

Customized ablations should be the standard for all patients undergoing refractive surgery. Our goal as refractive surgeons is to reduce—or at least not to increase—ocular aberrations after the refractive procedure. Achieving visual quality better than 20/20 is not the goal; the target should be preservation of 20/20 with good visual quality under all conditions, including night driving. I believe that wavefront-guided treatment is the best option to attain these parameters. However, the differences in postoperative aspheric profiles and visual outcomes with wavefront-guided and wavefrontoptimized treatments are controversial, and unfortunately there is very little peer-reviewed literature that demonstrates the difference between treatment results after wavefront-guided and wavefront-optimized treatments.

Today’s wavefront-guided algorithms have been adjusted to compensate for the higher-order aberrations (HOAs) induced by photoablation and flap creation, allowing us to decrease preoperative HOAs without inducing new ones. Alternatively, wavefront-optimized treatments aim to prevent the induction of aberrations and keep the natural prolate shape of the cornea. The ability to maintain the preoperative corneal structure lies within the relationship between asphericity, spherical aberrations, and quality of vision.

REVIEW OF THE LITERATURE

Edward E. Manche, MD, at Stanford University, reported that patients achieved better results with wavefront-guided LASIK compared with wavefront-optimized LASIK.1 Dr. Manche and colleagues performed wavefront-guided LASIK in one eye and wavefrontoptimized LASIK in the contralateral eye of 90 patients. At 1 week, more wavefront-guided patients had achieved visual quality of 20/20 or better (90% vs 78%), and at 3 months the results were still better in the wavefront-guided versus wavefront-optimized group.

In another study, Scott D. Barnes, MD, of the Warfighter Refractive Eye Surgery Clinic in Fort Bragg, North Carolina, compared UCVA after wavefront-optimized and wavefront-guided PRK.2 One month after surgery, 47% of wavefrontguided PRK patients achieved a UCVA of 20/15, and 92% achieved a UCVA of 20/20. In the wavefront-optimized patients, 25% achieved a UCVA of 20/15 and 72% a UCVA of 20/20 at 1 month. At 3 months, 76% of wavefront-guided and 55% of wavefront-optimized patients achieved a UCVA of 20/15, and 100% and 91%, respectively, achieved a UCVA of 20/20. At 6 months, 47% and 25% of wavefront-guided and wavefront-optimized PRK patients, respectively, achieved a UCVA of 20/15, whereas 92% and 72%, respectively, achieved a UCVA of 20/20. After 6 months, the results started to become similar.

From results such as these, we deduce that wavefrontguided ablations produce faster visual recovery with a higher level of predictability compared with wavefront-optimized ablations. However, in either form, customized ablations lead to a significant decrease in enhancement rates. Compared with conventional treatments, wavefront-guided ablations significantly improve patients’ contrast sensitivity, reduce glare and halos, and improve functional night vision.3

CONSIDERATIONS

Should all patients be offered the option of custom ablation, and if so, is the extra cost associated with wavefront treatments justified for only a potential improvement in visual quality? We still do not know the answers to these questions; however, we do know that wavefront-customized treatments produce a more substantial effect in the following groups: patients with large pupils, as they are more sensitive to higher-order aberrations; patients with greater than 0.3 μm preoperative total HOAs; and patients with hyperopia and mixed astigmatism.

The extra cost and the extra surgical time needed for customized treatments can be potential limitations. I suggest defining one price for the procedure, whether conventional or wavefront-guided, and using aberrometry to assess all patients before surgery. Therefore, any patient who is a good candidate can elect custom treatment based on medical, not financial, arguments. After all, is it not our ethical mission to choose the best solution for each patient in terms of safety and efficacy?

PREFERENCE

Each surgeon must believe in his or her preferred method and concept of treatment. This belief is acquired through personal experience and the use of evidencebased medicine. Unfortunately, custom ablation is poorly documented in the peer-reviewed literature. This partly explains why the distribution of this technique is so heterogeneous. Another reason is that refractive surgeons who adopt these technologies must learn the new language of aberrations and how to manipulate more sophisticated treatment protocols than were needed for conventional or topography-guided ablations.

There are several options for wavefront-guided LASIK, but we prefer the Advanced CustomVue procedure (Abbott Medical Optics Inc., Santa Ana, California). I use wavefront-guided treatments in the majority of my patients, with the exception of cases with a discordance of more than 10° of axis or more than 1.00 D of cylinder between aberrometric refraction and manifest refraction. I also avoid wavefront-guided treatments in patients with thin corneas. In these cases, conventional treatment is preferred because it saves more tissue.

The CustomVue’s iris registration software centers and aligns the treatment independent of pupil center migration and compensates for cyclotorsional movement, providing more precise ablation placement. Fourier algorithms are equivalent in accuracy to 20th-order Zernike measurements, and variable spot scanning and variable repetition rate technologies reduce thermal effects on the cornea. These software developments allow us to perform the Advanced CustomVue procedure quickly and effectively, maximize patient safety, and ensure precise ablation.

In a retrospective study of approximately 30,000 eyes treated with the Advanced CustomVue wavefront-guided ablation profile, 91.8% had a UCVA of 20/20 or better and 71.6% a UCVA of 20/16 or better at 1 month postoperative. 4 David Tanzer, MD, recently reported that, of 300 eyes treated with myopic LASIK on the same platform, 84% were 20/12.5 or better at 1 month after surgery.5

CONCLUSION

There is currently considerable contrast between centers dedicating 90% of their ablations to wavefront-customized treatment and others that are still performing only conventional treatments. We can expect a decrease in this discrepancy as prospective studies comparing the two profiles of ablation enter the literature, but also due to educational programs dedicated to teaching aberrometry from a practical point of view.

Béatrice Cochener, MD, is a Professor and the Chairman of the Ophthalmology Department at Brest University Hospital, France, and President of the French Academy of Ophthalmology. Professor Cochener states that she is a clinical investigator for Alcon Laboratories, Inc., Bausch + Lomb, Abbott Medical Optics Inc., PhysIOL, and Thea. She may be reached at tel: +33 2 98 22 34 40; e-mail: beatrice.cochener@ophtalmologie-chu29.fr.

  1. Ophthalmology Times Web site.Charters L.LASIK outcomes compared.http://www.modernmedicine.com/modernmedicine/ Modern+Medicine+Now/LASIK-outcomes-compared/ArticleStandard/Article/detail/698223. Accessed May 12,2011.
  2. Barnes SD.Comparing wavefront guided and wavefront optimized LVC.EyeWorld.2010;5(Supp):14.
  3. Schallhorn SC,Tanzer DJ,Kaupp SE,et al.Comparison of night driving performance after wavefront-guided and conventional LASIK for moderate myopia.Ophthalmology.2009;116(4):702-709.
  4. Schallhorn SC,Venter JA.One-month outcomes of wavefront-guided LASIK for low to moderate myopia with the Visx Star S4 laser in 32,569 eyes.J Refract Surg.2009;25(Suppl):S634-641.
  5. Tanzer DJ.Bringing LASIK to the next level with advanced femtosecond technology:A clinical comparison.Paper presented at:The XXVII Congress of the ESCRS;September 15,2009;Barcelona,Spain.

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