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Inside Eyetube.net | Feb 2014

High-Resolution Wavefront Aberrometry

This technology is most beneficial for the measurement and correction of astigmatism.

The popularity of wavefront-guided laser vision correction is growing. Now, with the use of more precise aberrometry, surgeons can provide their patients with maximal refractive outcomes. One of the latest technologies, the iDesign (Abbott Medical Optics Inc.), uses high-resolution aberrometry to enhance surgical precision.

Results from a recent study demonstrated that, even without nomogram adjustments, the iDesign performs better than an earlier technology, the WaveScan Wavefront System (Abbott Medical Optics Inc.). Like its predecessor, the iDesign aberrometer uses a Fourier reconstruction algorithm and Hartmann-Shack technology, but it has a greater dynamic range, captures five times as many lenslet data points (up to 1,200 depending on pupil size), and incorporates a corneal topographer, among other new features.

ANALYSIS

We evaluated results from 1,201 eyes of 641 patients with low to moderate myopia (manifest spherical equivalent [MSE], -0.25 to -6.00 D) undergoing primary LASIK at Optical Express centers in the United Kingdom. All eyes had at least 1-month follow-up, and all flaps were created with the iFS femtosecond laser (Abbott Medical Optics Inc.). Results were compared with a large matched cohort of more than 27,000 eyes (14,589 patients) treated with WaveScan aberrometry in 2012 and 2013.

At 1 month, 95.3% of eyes in the iDesign group had an MSE within ±0.50 D of intended correction, and 99.5% were within ±1.00 D. Not only was this more predictable than the comparison group (Figure 1), but also the correlation coefficient of attempted-versus-achieved MSE (0.96) indicated a tight spread of the results. Compared with the standard aberrometry (WaveScan) group, the iDesign group also had fewer outliers, as depicted by double-angle plots (Figure 2). Additionally, in a subgroup of patients who underwent astigmatism correction, the axis shift did not exceed ±5° in 64% of those patients in the iDesign group versus 59% in the WaveScan group.

As a result of the improvements in predictability and the ability to accurately correct cylinder, monocular UCVA at 1 month was 20/20 or better in 96% of the iDesign eyes and 20/16 or better in 84%, compared with 94% and 80%, respectively, in the WaveScan group (Figure 3). The results achieved with iDesign represent the best cylinder correction I have ever seen following laser vision correction.

PATIENT-REPORTED OUTCOMES

We also reviewed patient-reported outcomes (PROs), an important metric in the upper ranges of what this technology is capable of. PROs help us understand whether patients experience a difference in quality of vision and whether the procedure has met their expectations.

Patients reported greater satisfaction with iDesign-driven treatments compared with WaveScan-driven treatments (97.3% vs 95.2%). About half of the patients in the iDesign group said their vision was much better than expected. They also reported less difficulty with postoperative starbursts, glare, and halos (Figure 4). Complaints of severe difficulty with visual symptoms were low in both groups.

CLOSER TO PERFECTION

With modern technology, most patients—especially those with low to moderate myopia—have the potential to achieve better than 20/20 vision postoperatively, and many can come close to the limits of human vision at 20/12.5 or 20/10 vision. However, achieving maximal results routinely requires good technology, good processes for screening candidates, and the ability to measure beyond 20/20 in the first place.

At the high end of the visual acuity spectrum, gains are small and incremental, but still worth celebrating. Getting closer to 100% of patients achieving 20/20 visual acuity and more patients achieving 20/16 or better is what will continue to drive patient satisfaction, referrals, and a stronger laser vision correction market. We must also reduce the variability and increase the predictability of our results, so that every patient achieves the high-quality optics and vision that we want him or her to have.

One remaining cause of variability is the healing response. Improvements in ablation profiles have helped to modulate the healing response. Consistent, uniform healing reduces variability and maximizes the chance of achieving visual outcome goals. Personalized nomograms that take into account differences in healing response based on age, for example, also help to improve predictability.

Many surgeons have well-developed nomograms, so it is encouraging to see good early results in our study, even without nomogram adjustments. We can expect to see further improvement and tightening of the standard deviation as surgeons begin to modify their nomograms with the iDesign aberrometer. A better capture of the true ocular wavefront from more data points also reduces variability in the correction, as we see in the cylinder correction data.

ADDITIONAL BENEFITS

Easier capture with the iDesign improves the flow of patients through the preoperative work-up. We have treated hundreds of complex eyes with the iDesign, although these were not included in our analysis. In these cases, image capture is much easier than with previous generations of aberrometers. The iDesign also has a greater dynamic range, making it possible to design treatments for more highly aberrated eyes and perform diagnostic captures of eyes with keratoconus and other conditions that are not suitable for laser vision correction.

The interface of the aberrometer has been refined, and the device incorporates multiple measures, including wavefront aberrometry, full-gradient topography, autorefraction, pupillometry, and keratometry (K). The ability to measure corneal curvature and automatically incorporate K into the treatment design eliminates the step of manually entering K readings. While the iDesign has not yet replaced topography in our clinics, it will be interesting to see how this capability may be utilized in the future.

CONCLUSION

As we move into a new era of high-definition wavefront, I am excited to see how our results continue to improve.

Steven C. Schallhorn, MD, is the Global Medical Director of Optical Express. Dr. Schallhorn states that he is a paid consultant to Abbott Medical Optics Inc. He may be reached at tel: +1 619 920 9031; e-mail: scschallhorn@yahoo.com.

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