Newer laser treatments have advantages

Baltimore-Wavefront-optimized and wavefront-guided laser treatments, which may seem new to many patients, now have a 5-year track record and are both significant improvements over conventional laser treatments, said Elliott H. Myrowitz, OD, MPH, here at the Current Concepts in Ophthalmology meeting. Results from both of these newer treatments are comparable, according to recent studies, but each provides varied advantages in achieving visual correction.

Treatment differences

"A normal cornea is aspheric and flattens away from the periphery. Changing the corneal asphericity can cause an increase in spherical aberration," he explained.

"In conventional laser treatments, when the beam hits the peripheral cornea, there is an energy loss away from the center of the cornea. To compensate for this energy loss in the cornea periphery, the number of laser shots is increased. Wavefront-optimized algorithms maintain the natural pre-op corneal curvature by compensating for this effect. The algorithm delivers more shots to the periphery to produce a refractive treatment with minimal increases in spherical aberration," Dr. Myrowitz continued.

Optimizing the treatment also results in a larger optical zone by putting more spots in the periphery to make the transition from the optical zone to the full treatment area, he added.

"Controlling the peripheral ablation profile allows for large, true optical zones and smooth transition zones. In addition, with up to 9-mm treatment diameters, there is minimal induction of nighttime glare and halo," he said. "Peripheral pulse control preserves the overall asphericity while minimizing the induction of higher-order spherical aberration," he added.

Guided versus optimized

Optimized aspheric corneal ablation is based on population analysis, in an attempt to avoid reducing the prolate eccentricity of the cornea, while wavefront-guided treatments are based on the unique aberrations of the individual eye being treated in an attempt to reduce the individual whole-eye aberrations, Dr. Myrowitz explained.

Both wavefront-guided and wavefront-optimized treatments yield high predictability, efficacy, and safety, according to a review study completed by Drs. Myrowitz and Chuck.¹ They found that equally good vision has been obtained with both treatments as measured by Snellen acuity, patient questionnaires, and total residual higher-order aberrations (HOAs).

Supported by studies

In this 2009 paper, Drs. Myrowitz and Chuck also related that wavefront-guided treatments did have better results in spherical aberrations, coma, and contrast sensitivity outcomes. Surgeons who had access to both modalities sometimes noted, " 'Why not just use optimized? It is simpler to do in the clinic.' Some surgeons advocate reserving the use of wavefront-guided for those patients with above average higher-order aberrations," he reported.

Dr. Myrowitz reviewed the results from several studies published from 2009 to 2011 that compared wavefront-optimized and wavefront-guided treatments, and concluded that most of them also found the two treatments comparable:

"The lasers themselves have been upgraded in the past 5 years," Dr. Myrowitz noted. "The whole platform now has improved delivery systems, incorporation of anatomical registration, and higher frequency eye tracking. Teasing apart how much is due to the wavefront-optimized or wavefront-guided algorithms in these better outcomes is hard to say with certainty," he concluded.

References

1. Myrowitz EH, Chuck RS. A comparison of wavefront-optimized and wavefront-guided ablations. Curr Opin Ophthalmol. 2009;20:247-250.

2. Hantera M. Comparison of postoperative wavefront aberrations after NIDEK CXIII optimized aspheric transition zone treatment and OPD-guided custom aspheric treatment. J Refract Surg. 2009;25(10 suppl):S922-926.

3. Ghoreishi SM, Naderibeni A, Peyman A, Rismanchian A, Eslami F. Aspheric profile versus wavefront-guided ablation photorefractive keratectomy for the correction of myopia using the Allegretto Eye Q. Eur J Ophthalmol. 2009;19:544-553.

4. Perez-Straziota CE, Randleman JB, Stulting RD. Visual acuity and higher-order aberrations with wavefront-guided and wavefront-optimized laser in situ keratomileusis. J Cataract Refract Surg. 2010;36:437-441.

5. Hori-Komai Y, Toda I, Yamamoto T, Tsubota K. Comparison of LASIK with the OPDCAT or OATz algorithm using the NIDEK EC-5000CXII excimer laser. J Refract Surg. 2010;26:411-422.

6. Miraftab M, Seyedian MA, Hashemi H. Wavefront-guided versus wavefront-optimized LASIK: A randomized clinical trial comparing contralateral eyes. J Refract Surg. 2011;27:245-250.