“On Label” but “Out of the Box”

Since the development of conventional Munnerlyn formula-based excimer laser vision correction two decades ago, new treatment strategies have been developed to improve refractive outcomes. Early strategies relied on preoperative manifest refraction, thus, two eyes with the same sphero-cylindrical correction would receive the exact same treatment. Although these conventional treatments provided satisfactory results, higher-order aberrations (HOA) were not taken into consideration.

These challenges led to the development of ocular wavefront technology, which has proven vital to our understanding of HOA and their effect on point-spread function, modulation transfer function, and resultant retinal image quality. In recent years, aspheric ablation profiles have been developed in an attempt to preserve the natural, aspheric shape of the cornea. The Allegretto WaveLight (Alcon, Inc, Ft. Worth, TX), utilizes a wavefront-optimized (WFO) treatment, taking advantage of previously published pre- and postoperative wavefront data to improve radial ablation efficiency and pre-compensate for induction of spherical aberration. One of the ongoing challenges faced is determining which laser profile best fits an individual patient’s needs. The following are two studies conducted to help answer these questions.

Wavefront-optimized Vs. Wavefront-guided LASIK for Myopia

In a prospective, randomized, contralateral trial comparing LASIK using WFO and wavefront-guided (WFG) technology for the treatment of myopia, 25 patients (50 eyes) enrolled in the study (Durrie D, unpublished data). Each patient received LADAR 6000 (Alcon, Inc, Ft. Worth, TX) WFG treatment in one eye and Allegretto WFO in the other. Uncorrected distance visual acuity (UCDVA) was recorded preoperatively and then at one day, one week, one month, and three months postoperatively. Manifest refraction spherical equivalent (MRSE) and HOA were recorded preoperatively and one and three months postoperatively. No patient was lost to follow-up.

Table 1. Direct Comparison of Alcon LADAR 6000 Wavefront-Guided and Allegretto WaveLight Wavefront-Optimized Laser Surgery Source: Daniel S. Durrie, MD

Results demonstrated that WFO provided statistically significantly superior results in terms of rapid visual recovery, with nearly two-thirds of WFO eyes enjoying an UCDVA >20/20 at postoperative day one, and more than 75% of eyes were >20/20 by one week (Table 1). The difference in UCDVA between treatment groups decreased over time, reaching statistical insignificance at 3 months. Refractive predictability showed no statistically significant difference in 3-month MRSE in both treatment groups. With regards to HOA, the wavefront-optimized treated eyes had a statistically significant increase in induced spherical aberration compared to eyes undergoing wavefront-guided treatment (Figure 1). Eyes with higher levels of preoperative spherical aberrations appeared to have higher levels of induced postoperative spherical aberration. Future analysis is necessary to confirm these early observations. There were no statistical differences among vertical or horizontal coma.

Figure 1. Spherical Aberration Over Time by Treatment In patients with myopia, wavefront-optimized eyes had a statistically significant increase in induced spherical aberration compared to eyes undergoing wavefront-guided treatment. Source: Daniel S. Durrie, MD

Comparing Hyperopic LASIK Outcomes with Conventional and Wavefront-optimized Ablations

In a prospective, randomized, single-center clinical trial, 51 consecutive eyes underwent LASIK for the treatment of hyperopia (+0.50 D to +4.50 D). Eyes were divided between groups treated with conventional Alcon LADAR 4000 (n=25) and WFO Allegretto WaveLight 200 Hz (n=26). The refractive and visual outcomes, induced spherical aberrations, and contrast sensitivity were analyzed (Durrie D, unpublished data).

At postoperative week 1, 31% of eyes treated with a conventional profile had UCDVA of 20/20 or better compared to 77% of eyes receiving WFO treatment (P=0.0020). By 6 months, UCDVA was 20/20 or better in 72% and 84% of the conventional and WFO groups, respectively (P=0.3254) (Table 2). At 6 months, the MRSE was -0.21 ± 0.47 D and 0.16 ± 0.27 D (P=0.6469) whereas the cylinder was -0.41 ± 0.47 D and -0.17±0.27 D (P=0.0332) for the conventional and WFO groups, respectively. Induced spherical aberration was -0.54 ± 0.32 µ and -0.42 ± 0.21 µ for the conventional and WFO groups, respectively (P=0.1195). The respective change in mesopic and photopic area under the log contrast sensitivity function was -0.05 ± 0.29 and -0.05 ± 0.23 for the conventional group and 0.08 ± 0.39 and 0.08 ± 0.41 for WFO (P=0.1970).

Table 2. Direct Comparison of Alcon LADAR 4000 and WaveLight Allegretto 200 Hz Laser Surgery *P <0.05 for conventional vs. wavefront-optimized treated eyes at 1 week. Source: Daniel S. Durrie, MD

Both WFO and conventional ablation predictably and safely correct low to moderate hyperopia. WFO showed superior results with regards to rapid visual recovery and residual cylinder. Although not statistically significant, a trend towards less induced negative spherical aberrations and improved mesopic and photopic contrast sensitivity was noted with WFO treatment.

Considerations for Choosing Treatment

It is important to consider the ablation profile when individualizing patient treatment. With the Allegretto WaveLight Laser, the surgeon has the option of both wavefront-guided and wavefront-optimized treatment. For most patients with root mean square (RMS) <0.3 µ, WFG offers no advantage over WFO treatment. For patients with a RMS > 0.3 µ, the WFG profile is better able to reduce both the pre-existing and induced HOA when compared to WFO treatment.

Case Presentation Case 2: A 64-year old white male with a manifest refraction of +5.00 -5.00 x 180º giving 20/20 visual acuity wants perfect near and distance vision. Topography confirmed that the astigmatism lies in the cornea. Daniel S. Durrie, MD: A bioptic approach was taken. First, the patient underwent LASIK using the Allegretto WFO with a target of +2.5 D. He subsequently underwent a refractive lens exchange with a ReSTOR IOL. At one-month follow-up, he saw 20/20 at distance and near. Do not hesitate to take a bioptic approach in patients with high levels of astigmatism. Currently, toric IOLs do not come in high enough powers to correct more than 2.5 D of astigmatism and LRIs lose predictability with larger corrections. Residual astigmatism interferes with postoperative visual quality, especially when using multifocal IOLs, therefore accuracy is vitally important. The Allegretto WaveLight is effective in eliminating significant levels of astigmatism and should be considered in all patients who have >3 D of astigmatism at the corneal plane.