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J.O. Hjortdal, T. Møller-Pedersen, A. Iversen; Corneal Aberrations after PRK and LASIK for Myopia. Results from a Prospective Randomised Trial . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2637.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate whether corneal aberrations are different after PRK and LASIK for moderate myopia. Methods: One eye of 45 subjects with myopia ranging from –6 to –8 dioptres (subjective spherical equivalent) and less than 1 dioptre of subjective refractive astigmatism was included in the study. Each eye was randomised to PRK or LASIK treatment. Ablation was performed with the Meditec-Asclepion MEL-70 G-scan flying-spot excimer laser using a 6-mm optical zone size and the same algorithm for PRK and LASIK treatments. Re-treatments were not allowed during the follow-up period. Subjective refraction and corneal topography (TMS-1, Tomey) was measured before, and 1, 3, 6, and 12 months after surgery. Corneal wave front analyses including Zernike polynomial decomposition was performed with the Zemax-EE optical analysis software (Focus, Tucson, AZ). Results: Subjective spherical equivalent refraction was reduced from –7.12±0.57 D and –6.91±0.57 D before surgery to –1.31±0.71 and –1.42±1.16 one year after surgery in the PRK and LASIK groups, respectively. Corneal aberrations (RMSCentroid; 4 mm pupil) excluding defocus, increased overall from 0.49+0.22 µm and 0.51±0.20 µm before surgery to 0.55±0.20 µm and 0.59±0.19 µm one year after surgery in the PRK and LASIK groups, respectively (NS). One year after surgery, spherical aberration was 2 to 3 times higher and coma-like aberrations 2 times higher than the pre-operative levels. Other higher-order aberrations did not increase significantly. There was no significant difference between LASIK and PRK treated eyes. Corneal aberrations (including defocus) at one year after surgery increased more than four-fold when a 4 to 6 mm increase in pupil size was simulated. This pupil-dependent increase was mainly caused by defocus (myopia) and spherical aberration and was similar in the LASIK and PRK treated eyes. Conclusions: Corneal aberrations caused by spherical aberration and coma-like aberrations increase similarly after LASIK or PRK for myopia. Symmetrical aberrations caused by spherical aberration and defocus are the main causes of degrading optical quality with increasing pupil size. Aspherical refinements of laser treatment algorithms should improve the optical quality after PRK or LASIK.
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