Wavefront-guided, wavefront-optimized platforms for LASIK and PRK yield comparable results

Results from two prospective, randomized fellow-eye studies on PRK and LASIK show good efficacy and predictability with wavefront technology.

Refractive surgery has been shown to induce changes in corneal asphericity. LASIK especially increases coma and spherical-like aberrations in larger myopic treatments. This may partially explain why patients with postoperative 20/20 vision complain about their quality of vision.

Usually the increase in spherical aberration is minimal, thus not affecting vision. In cases complicated by surface irregularities, more worrisome higher-order aberrations such as coma and trefoil can occur, causing a decrease in contrast sensitivity or night vision. While conventional refractive surgery treats lower-order aberrations, newer wavefront-guided refractive surgery treats both lower- and higher-order aberrations.

Wavefront-guided refractive surgery uses three-dimensional measurements of an individual’s cornea to create a customized ablation profile. This profile is used to provide a spatially varying correction, in contrast to conventional LASIK, which provides a simple correction of focusing power or astigmatism.

There are currently two types of wavefront surgery, wavefront-optimized and wavefront-guided. Wavefront-optimized tries to minimize the induction of aberrations in the eye during surgery. Wavefront-guided treatments use a wave of light to measure the exact optical abnormalities across many points. These aberrations are not normally corrected with glasses. In theory, wavefront-guided treatment offsets existing aberrations while minimizing the induction of any new aberrations.

Background

We recently conducted two prospective, randomized fellow-eye studies comparing wavefront-optimized surgery to wavefront-guided surgery for both LASIK and PRK. While there have been multiple published studies comparing these modalities for LASIK, this is the first known comparison between wavefront-guided and wavefront-optimized techniques in PRK.

Our study comparing wavefront-guided to wavefront-optimized LASIK included 44 eyes of 22 patients, while the study comparing wavefront-guided to wavefront-optimized PRK included 46 eyes of 23 patients. We randomized treatment in one eye with the wavefront-optimized WaveLight Allegretto 400-Hz Wave Eye-Q laser (Alcon). The fellow eye was assigned treatment with the wavefront-guided VISX CustomVue STAR S4 IR excimer laser with ActiveTrack iris registration (Abbott Medical Optics).

Results

Our findings support the conclusions of previous research that both the wavefront-optimized and wavefront-guided platforms are effective and predictable in LASIK and PRK. In both groups there was no statistically significant difference between the groups for uncorrected distance visual acuity and corrected distance visual acuity at 1 or 3 months postoperatively. Using wavefront-optimized or wavefront-guided LASIK resulted in 91% of eyes achieving 20/20 acuity or better at 3 months. In the PRK study, 87% of the wavefront-optimized and 91% of the wavefront-guided eyes achieved 20/20 uncorrected distance visual acuity at 3 months.

Spherical aberration is a rotationally symmetric aberration in which the light rays that pass through the central pupil focus at a different distance than the rays that pass through the marginal pupil. Normally, a certain quantity of positive spherical aberration is present, which is considered physiological. By using wavefront aberrometry we were able to measure these aberrations preoperatively and postoperatively.

The wavefront-guided LASIK group showed a non-significant decreasing trend in higher-order aberration values postoperatively. In contrast, there was a significant 4% increase in mean total higher-order aberration root-mean-square or sum total of higher-order aberrations in the wavefront-optimized LASIK group.

Both PRK groups showed an increasing trend in all higher-order aberrations at 3 months postoperatively, with a statistically significant twofold and threefold increase in spherical aberrations. Although there was a statistically significant increase in spherical aberration for both groups, there was no significant difference when comparing these changes between the wavefront-guided and wavefront-optimized platforms (P = .320).

In comparison to LASIK, which did not show any significant change of contrast sensitivity, the wavefront-guided PRK group showed a small statistically significant advantage exclusively at 12 cycles per degree at 1 month following surgery, but no significant changes at 3 months.

Conclusion

Although PRK was first to market, with U.S. Food and Drug Administration approval in 1995, it was quickly overtaken by LASIK. However, the increased publicity of potential complications of LASIK such as post-LASIK ectasia, flap-related problems and increased occurrence of dry eye has brought about a renewed interest in surface treatments such as PRK. This resurgence has continued with the introduction of wavefront-guided refractive surgery.

In our current study, we found that utilizing a wavefront-guided profile for LASIK reduces higher-order aberrations at 3 months compared to wavefront-optimized LASIK. We also showed a trend of increasing higher-order aberrations in both wavefront-guided and wavefront-optimized PRK eyes, both inducing a statistically significant increase of spherical aberrations. This contrasts with a previous study we conducted that demonstrated an increase in higher-order aberrations in both wavefront-guided LASIK- and PRK-treated eyes, but with wavefront-guided PRK inducing statistically fewer higher-order aberrations than wavefront-guided LASIK at 6 months.

In conclusion, at 3 months postoperatively, our findings support previous research that the VISX CustomVue wavefront-guided platforms and the WaveLight Allegretto wavefront-optimized platform are both highly efficacious and predictable in PRK and LASIK. We hope to report long-term data soon, following changes in higher-order aberrations and contrast sensitivity that may improve over time, especially with PRK.

References:

• Bottos, KM. Leite MT, Aventura-Isidro M, et al. Corneal asphericity and spherical aberration after refractive surgery. J Cataract Refract Surg. 2011;37(6):1109-1115.
• Calossi, A. Corneal asphericity and spherical aberration. J Refract Surg. 2007;23(5):505-514.
• Levinson BA, Rapuano CJ, Cohen EJ, et al. Referrals to the Wills Eye Institute Cornea Service after laser in situ keratomileusis: Reasons for patient dissatisfaction. J Cataract Refract Surg. 2008;34(1):32-39.
• Moshirfar M, Churgin DS, Betts BS, et al. A prospective, randomized, fellow eye comparison of WaveLight Allegretto Wave Eye-Q versus VISX CustomVue STAR S4 IR in laser in situ keratomileusis (LASIK): analysis of visual outcomes and higher order aberrations. Clin Ophthalmol. 2011;5:1339-1347.
• Moshirfar M, Churgin DS, Betts BS, et al. Prospective, randomized, fellow eye comparison of WaveLight Allegretto Wave Eye-Q versus VISX CustomVueTM STAR S4 IR in photorefractive keratectomy: analysis of visual outcomes and higher-order aberrations. Clin Ophthalmol. 2011;5:1185-1193.
• Moshirfar M, Schliesser JA, Chang JC, et al. Visual outcomes after wavefront-guided photorefractive keratectomy and wavefront-guided laser in situ keratomileusis: Prospective comparison. J Cataract Refract Surg. 2010;36(8):1336-1343.

• Majid Moshirfar, MD, can be reached at the John A. Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132; 801-581-2352; email: majid.moshirfar@hsc.utah.edu.
• Disclosure: Funding was provided from Research to Prevent Blindness. The authors have no financial interests in any materials or products discussed here or any other financial disclosures.