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L Llorente, S Marcos, S Barbero, J Merayo-Lloves; How Total and Corneal Aberrations Change With Standard Lasik Surgery for Hyperopia . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2066.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:1)To assess the optical changes induced by LASIK surgery for hyperopia, by measuring total and corneal aberrations. 2)To compare the outcomes for hyperopic to those of myopic LASIK. Methods:Seven hyperopic eyes (mean age: 4012 years; mean cycloplegic spherical equivalent: +3.631.28 D) were measured before and after (8554 days) LASIK. Total ocular aberrations were measured with Laser Ray Tracing, In this technique aberrations are estimated from deviations of captured aerial images corresponding to different entry pupil, which is scanned by an IR laser beam. Corneal aberrations were obtained from videokeratographic corneal elevation maps. Pupil size was 6.51 mm. Wavefront aberrations were described as Zernike polynomial expansions. Root Mean Square wavefront error (RMS) was used as an optical quality metric. Results:1) Total RMS (3rd order and higher) increased after hyperopic LASIK by a factor of 2.10 (std=0.86) on average, and corneal RMS by 1.85 (std=0.77). 2) Both corneal and total pre-op spherical aberration were positive in all eyes and changed toward negative values with surgery. Increments are: -0.680.23 µm for the whole eye, and -0.990.48 µm for the anterior corneal surface. The total and corneal spherical aberration induced by surgery were correlated to intended correction (r=0.64 and r=0.79 respectively) 3) Pre-op internal spherical aberration was ∼0 in five eyes, and increased significantly to positive values in the two most hyperopic eyes, indicating changes in the posterior corneal surface. 4) Third order RMS (coma-like) increased after LASIK by a factor of ∼2 for both total and corneal aberrations. 5) The increase of total RMS with hyperopic LASIK (by a factor of ∼2) is similar to the increase following myopic LASIK, for the same negative amount of spherical error (results from a previous study). However, average post-op spherical aberration was 0.23 µm for myopic and -0.68 µm for hyperopic LASIK. Conclusion:1) Aberrations increase after hyperopic LASIK. 2) Hyperopic LASIK induces negative spherical aberration, while myopic LASIK induces positive spherical aberration. 3) Though the main change occurs on the anterior cornea, final ocular aberrations depend on individual interactions between cornea and lens (differing in hyperopes and myopes) and possible changes on the posterior cornea. 4) Knowledge of total and corneal aberrations helps to evaluate hyperopic surgery outcomes, and will contribute to the design of optimized ablation algorithms.
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