The best solution for minimizing induced ocular abberations after refractive surgery
Our knowledge about ocular aberrations and how they increase after laser refractive surgery has enabled us to find solutions for this problem. For example, in myopic corrections, the effect of peripheral laser pulses is diminished due to their oblique angle of incidence. In this case, less peripheral ablation induces more spherical aberration.
To solve this problem, in wavefront-optimized algorithms, more laser pulses or energy are applied in the corneal periphery. Wavefront-optimized algorithms are based on the concept that an aspheric profile for laser ablation will maintain the prolate corneal shape, and attempts to prevent the induction of spherical aberrations.1
The first published study on using wavefront technology was 'Wavefront-guided laser in situ keratomileusis: early results in three eyes' by Mrochen et al.2 Results showed up to 2 lines increase of best spectacle-corrected visual acuity, which improved to 20/10 in all 3 eyes. The uncorrected visual acuity was 20/10 in two eyes, and 20/12.5 in 1 eye 1-month postoperatively. Afterwards, many articles showed the efficacy of this approach with more or less interesting results.
Wavefront-guided and wavefront-optimized procedures attempt to minimize induced aberrations in different ways, and both approaches have their own advantages and disadvantages. Therefore, comparing these two approaches in patients receiving primary laser refractive treatment for myopia and astigmatism can help us determine the best candidate for each method.
Nonetheless, comparative studies and clinical trials which compare these two treatment modalities are scant. For a definite and better comparison of these two approaches, we designed a prospective randomized comparative study of wavefront-optimized LASIK and wavefront-guided LASIK.
We enrolled 41 patients with up to 7.00 D of myopia and up to 3.00 D of astigmatism.3 One eye of each patient was randomly assigned to wavefrontguided and the other eye for wavefront-optimized LASIK, and results were assessed in terms of visual and refractive results, as well as changes in higher order aberrations and contrast sensitivity.
The LASIK flap was created using a Hansatome XP microkeratome (Bausch + Lomb Surgical, Irvine, California) that produces a 120 micron superior hinge flap. For both modalities, the WaveLight Concerto excimer laser (WaveLight Laser Technologie AG, Erlangen, Germany) with a 0.95mm spot size and 500Hz repetition rate was used.
We selected a 6.5 mm optical zone with a 1.25mm blend zone in all cases, and the undilated pupil centre was selected for ablation centration. Aberrometry was performed using the Allegretto Wave analyzer (WaveLight Laser Technologie AG) after pharmacologic pupil dilation, and contrast sensitivity was tested using the CSV-1000 chart (VectorVision, Dayton, Ohio, USA) at 3, 6, 12 and 18 cycles per degree (cpd),while the patients were wearing their spectacles.