In this article, the authors discuss how WF?guided and WF-optimized LASIK performed on hyperopic patients can provide similar results in terms of safety, contrast sensitivity and refractive error.
Wavefront-guided vs wavefront-optimized LASIK in hyperopes: is there a winner?
The first eye-to-eye comparison of WF-guided and WF-optimized LASIK for the primary treatment of hyperopia
By Dr Christopher S. Sáles, MPH and Dr Edward E. Manche
Although effective at correcting simple spherocylinder refractive errors, conventional laser refractive surgery can have the undesirable effect of inducing spherical aberrations and reducing quality of vision. In conventional LASIK, laser pulses delivered to the periphery ablate less tissue than centrally delivered pulses because of their oblique angle of incidence on the corneal surface. This renders the cornea more oblate than prolate, thereby inducing more spherical aberration. Wavefront (WF)-based treatments attempt to compensate for this phenomenon with more sophisticated ablation patterns.1–5
WF-based treatments can be classified into two broad categories: WF-optimized and WF-guided algorithms. The WF-optimized approach considers an eye’s refractive error and preoperative keratometry, in conjunction with the variable ablation depths of peripherally delivered pulses, to apply a precalculated aspheric treatment that aims to limit induced spherical aberrations. The WF-guided approach renders a customized treatment plan based on an eye’s unique preoperative aberrometry with the intent of not only minimizing induced postoperative aberrations but also reducing or eliminating preoperative higher order aberrations (HOAs).
We conducted a prospective, randomized, eyeâto-eye pilot study comparing WF-guided with WF-optimized treatments in hyperopes. The primary outcome measures included uncorrected distance visual acuity (UDVA), refractive stability, predictability, contrast sensitivity, HOAs, loss of corrected distance visual acuity (CDVA) and a validated quantitative questionnaire. There were no statistically significant differences between the groups for any of the variables studied after 12 months of follow-up (all P>0.05). Both WF-guided and WF-optimized ablations were found to be safe, effective and predictable for the treatment of hyperopia with or without astigmatism. At 12 months, >90% of eyes in both groups had achieved ≥20/20 vision, and there were no statistically significant differences between the group’s mean CDVAs under <5% and <25% contrast sensitivity conditions (all P>0.05).
Eleven participants with hyperopia with or without astigmatism were randomized to receive either WF-guided LASIK with the VISX Star CustomVue S4 IR (Abbott Medical Optics, Santa Ana, California, USA) or WF-optimized LASIK with the WaveLight Allegretto Eye-Q 400 Hz (Alcon Inc., Hüenberg, Switzerland) in their dominant eye and the alternative in their other eye.
“...WF-guided and WF-optimized LASIK performed on hyperopic patients, with or without astigmatism, can provide similar results...”
Patients underwent a comprehensive preoperative evaluation, including <5% and <25% contrast sensitivity (Precision Vision, La Salle, Illinois, USA), slitâlamp biomicroscopy, Goldmann applanation tonometry, infrared pupilometry (Neuroptics, Irvine, California), dilated fundus examination, manifest and cycloplegic refraction using Early Treatment Diabetic Retinopathy Study (ETDRS) charts, computerized corneal topography and WF aberrometry. Wavefront aberrations were measured preoperatively and postoperatively with a physiological pupil under controlled scotopic conditions using the WaveScan aberrometer (Abbott Medical Optics, Santa Ana, USA, California, USA), which was also used to plan WF-guided treatments. All surgeries were performed at Stanford University Eye Laser Center by a single surgeon (E.E.M.). LASIK flaps were created using the 150 kHz IntraLase iFS (Abbott Medical Optics, Santa Ana, USA, California, USA). A 9.2-mm-diameter superior hinge with a 105-μm programmed flap depth setting was used, and intraoperative ultrasonic pachymetry (Sonogage, Cleveland, Ohio, USA) was performed in all cases. Patients were prospectively evaluated at postoperative months 1, 3, 6 and 12. At each evaluation, patients completed a questionnaire that has been employed in previous contralateral eye studies by Dr Manche.6–8
The questionnaire quantifies each of the following parameters on a grading scale of 0 (no symptoms) to 10 (severe symptoms): glare under night and day conditions, haze, halos, clarity under night and day conditions, dry eye symptom frequency and severity, foreign body sensation, vision fluctuation and ghosting. LASIK surgeries were performed in a bilateral simultaneous fashion to negate any learning curve with regard to the survey.
Although the series is limited, with only 11 participants, to the best of our knowledge this is the first eyeâto-eye comparison of WF-guided and WF-optimized LASIK for the primary treatment of hyperopia. In 22 eyes, WF-guided LASIK did not offer any statistically significant advantages over WF-optimized LASIK for the parameters studied at postoperative months 1, 3, 6 and 12, including UDVA, CDVA, contrast sensitivity, astigmatism, spherical equivalence, HOAs, efficacy, predictability and safety (all P>0.05). However, one must consider the alternative hypothesis that there was insufficient power to detect differences of potential clinical importance between the groups.
Previous studies of myopes have concluded that WF-guided approaches may yield small but statistically significant advantages compared with WF-optimized approaches. Our own study published in Ophthalmology found that WF-guided treatments performed with the WaveLight Allegretto demonstrated slightly superior predictability, better mean UDVA and less trefoil compared with WF-optimized treatments performed with the same machine.9 The absence of such differences after WF-guided and WF-optimized LASIK in hyperopes raises the question whether surgically induced HOAs are affected differently by WF algorithms in hyperopes compared with myopes.
Based on this small, prospective, comparative series of 22 eyes, we conclude that WF-guided and WF-optimized LASIK performed on hyperopic patients with or without astigmatism can provide similar results with respect to the parameters of safety, contrast sensitivity and refractive error. It is possible that WF-guided treatments offer some advantages over WF-optimized treatments, but this series lacked sufficient power to detect such differences if they were present. It will be of interest to see whether future studies with larger samples confirm our postulates, which should be interpreted with caution.
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