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S.M. MacRae, I. Cox; The Effect of Pupil Size, Optic Zone Size and Refractive Error on the Magnitude of Spherical Aberration Induced by LASIK Refractive Surgery . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2670.
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Purpose: It has been reported that LASIK refractive surgery induces significant spherical aberration, particularly with larger pupil sizes found under conditions of low illumination. The purpose of this study was to investigate the interaction between pupil size, optic zone size, and refractive error on the magnitude of spherical aberration induced by LASIK refractive surgery. Methods: Zyoptix wavefront guided LASIK refractive surgery was performed on 340 eyes with myopia up to –7.00D and a range of astigmatism up to –4.00D. Ablation Optic zone sizes of 6.0mm, 6.5mm and 7.0mm diameters were selected at the surgeons discretion depending upon the patient's refractive error and corneal thickness measurements. Wavefront aberration measurements were made using a Bausch & Lomb Zywave following dilation with a mydriatic at the preoperative visit, and 1 week, 1, 3 and 6 months post-op. Zernike co-efficients from each of five measurements made for each eye at each time point were generated across the fully dilated pupil size and averaged. Zernike co-efficients were the recalculated for normalization analysis diameters (or "wavefront aperature diameters" see Table) from 4.5mm to 7.5mm in 0.5mm steps. Results: Induced spherical aberration was calculated by subtracting the preoperative Zernike term for spherical aberration from each of the postoperative timepoint values. A significant increase in positive spherical aberration was found with increasing wavefront analysis diameter, and with increasing degree of myopic correction. However, the postoperative increase in spherical aberration was significantly reduced as optic zone size increased. Conclusions: Although positive spherical aberration is increased with the correction of myopia using LASIK refractive surgery, the magnitude of this increase can be minimized by maximizing the optic zone size of the ablation. Surgeons should be aware that optic zone sizes smaller than the diameter of the naturally dilated pupil will induce significant levels of postoperative spherical aberration, which may lead to reports of decreased night vision performance. 4th Order Aberration (SA) View OriginalDownload SlideView OriginalDownload Slide
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