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Dan Z. Reinstein, Timothy J. Archer, Marine Gobbe; Spherical Aberration change as a function of pupil size: a comparison between Small Incision Lenticule Extraction (SMILE) and non-linear aspheric LASIK in moderate to high myopia. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5574.
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© ARVO (1962-2015); The Authors (2016-present)
Comparing the induction of spherical aberration (SA) as a function of pupil size between SMILE and aspherically optimised femto-LASIK for moderate to high myopia.
A case-control retrospective analysis of SA changes between 8 myopic SMILE cases and 22, matched femtosecond flap LASIK cases (-4 to -12.5D). Each SMILE eye was refraction matched with at least 2 LASIK eyes. In SMILE the VisuMax Femtosecond laser (Carl Zeiss Meditec) intrastromally cuts a minimally aspheric refractive lenticule that is removed whole through a 3mm tunnel. LASIK ablations by the MEL80 utilized the Laser Blended Vision (LBV) module - a non-linear aspherically optimised profile. SMILE fully corrected optical zones were 6mm for all but 1 eye treated at 6.5mm; LASIK eyes were optical zone matched. Atlas Placido corneal surface wavefront analysis provided SA values measured at 0.5mm intervals from 3 to 7mm. SA change by zone was calculated from before to after surgery. SA was plotted against pupil size to study the rate of increase of SA with pupil size; the area under the curve represents a measure of total SA over all pupil sizes (RAWS parameter, JRS 2005: 21(9)). Statistical comparison of SA at discrete pupil sizes as well as the RAWS parameter was carried out.
Mean SEQ treated was equal (p=0.731) between the SMILE group (-8.52±2.75D) and the LBV group (-8.04±2.61D). SA increased exponentially with increasing pupil size for both SMILE and LBV. There was no statistically significant difference in SA induction between SMILE and LBV at 3, 4, 5, 6 and 7mm zones (all p>0.2). For the 6-mm zone, mean SA induction was similar (p=0.432) between the SMILE (0.532±0.301 µm) and LBV eyes (0.426±0.177 µm). For the 3-6mm pupil range, RAWS area was similar (p=0.41) between SMILE (581 µm2) and LBV (384 µm2).
SMILE though minimally aspheric, produces similar SA induction to the highly aspherically optimised myopic LBV profile, indicating that the femtosecond flapless procedure leads to less induction of SA than expected for a non-aspheric conventional excimer myopic profile. Further study into aspheric modification of SMILE profiles and stromal profile change are underway to further reduce SA induction in myopic SMILE corrections.
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