High Resolution Wavefront Treatments in Normal Eyes

The University of Ottawa Eye Institute is one of four Canadian centres evaluating the effectiveness of a high- resolution aberrometer (iDesign, Abbott Medical Optics) for wavefront-guided laser vision correction. Although several investigators have used the device diagnostically and/or in unusual cases, this study represents the first standardised use of it to drive clinical treatments. Initially, we are evaluating the aberrometer in normal eyes. To be enrolled in the study, subjects must have best- corrected preoperative acuity of 20/20, no prior surgery and no ocular disease or conditions other than refractive error. The myopia trial is complete. From the clinician’s perspective, the aberrometer works exactly like its predecessor, the WaveScan. However, its capabilities are expected to go well beyond the current technology. For one thing, the resolution is up to five times higher, allowing the aberrometer to capture 600- 1200+ data points, depending on pupil size, rather than the current maximum of 240 data points. The dynamic range of the device is expected to be much broader, as well. Although I have not yet had the opportunity to test its range in highly aberrated eyes, it is theoretically able to image wavefronts from eyes with spherical error of -16.0 D to +12.0, more than 8.0 D of cylinder, and more than 8 μm of RMS error. One of the very interesting questions to be determined in this study is whether high-resolution aberrometry can provide automated refractions on which surgeons can rely without referring back to the subjective, manifest refraction. We have always been impressed with the accuracy of wavefront-derived cylinder refractions and have found that the wavefront refraction is the ideal starting point for quickly obtaining the best manifest. Nevertheless, we often make nomogram or physician adjustments to ensure that the treatment more closely matches the manifest. Better aberrometry could eliminate that step.

Benefits in Practice In addition to wavefront aberrometry, iDesign also incorporates new-technology topography, autorefractometry, pupillometry and keratometry. The immediate benefits of this are the ability to get more precise K readings across the entire cornea and to register topographical maps with the wavefront in order to isolate the source of aberrations. The potential to some day perform treatments that are both wavefront- and topography-guided is very exciting. We already achieve excellent results with wavefront- guided surgery in normal eyes, of course, but one would expect that capturing higher-resolution data from more points on the cornea would at least incrementally improve the precision of visual results in all eyes. The combined myopic data from the trial are currently being analysed and will be reported at the ESCRS meeting. Anecdotally, we are delighted thus far with the clinical results at our centre.

After the conclusion of this trial, we hope to be able to treat high hyperopes and high myopes, who are not part of the current study. But the real potential for this technology is, of course, in treating highly aberrated eyes that are currently difficult or impossible to capture. High-resolution aberrometry offers a great opportunity for refractive surgery. In recent years, we have seen an improvement in outcomes from the move to femtosecond laser flaps, but the excimer laser hardware itself hasn’t changed much. Further gains in precision will likely come from more sophisticated wavefront analysis and treatment planning algorithms.

Dr Jackson is professor of ophthalmology and director of the University of Ottawa Eye Institute in Ontario, Canada. Contact him at: bjackson@ohri.ca.