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Esther Moreno-Barriuso, Jesús Merayo Lloves, Susana Marcos, Rafael Navarro, Lourdes Llorente, Sergio Barbero; Ocular Aberrations before and after Myopic Corneal Refractive Surgery: LASIK-Induced Changes Measured with Laser Ray Tracing. Invest. Ophthalmol. Vis. Sci. 2001;42(6):1396-1403.
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purpose. To determine objectively the changes in the ocular aberrations (3rd
order and above) induced by myopic LASIK refractive surgery and its
impact on image quality.
methods. The ocular aberrations of 22 normal myopic eyes (preoperative
refraction ranged from −13 to −2 D) were measured before (2.9 ±
4.3 weeks) and after (7.7 ± 3.2 weeks) LASIK refractive surgery
using a laser ray tracing technique. A set of laser pencils is
sequentially delivered onto the eye through different pupil locations.
For each ray, the corresponding retinal image is collected on a CCD
camera. The displacement of the image centroid with respect to a
reference provides direct information of the ocular aberrations.
Root-mean-square (RMS) wavefront error was taken as image quality
results. RMS wavefront error increased significantly in all eyes but two after
surgery. On average, LASIK induced a significant (P = 0.0003) 1.9-fold increase in the RMS error for a 6.5-mm pupil. The
main contribution was due to the increase (fourfold, P < 0.0001) of spherical aberration. The increase
in the RMS for a 3-mm pupil (1.7-fold) was also significant
(P = 0.02). The modulation transfer (computed for
6.5-mm pupil) decreased on average by a factor of 2 for middle-high
conclusions. (1) Laser ray tracing is a well-suited, robust, and reliable technique
for the evaluation of the change of ocular aberrations with refractive
surgery. (2) Refractive surgery induces important amounts of 3rd and
higher order aberrations. The largest increase occurs for spherical
aberration. Decentration of the ablation pattern seems to generate 3rd
order aberrations. (3) This result is important for the design of
customized ablation algorithms, which should cancel existing
preoperative aberrations while avoiding the generation of new
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