Purpose:To analyze the origin of the changes in corneal asphericity (p-factor) after laser in situ keratomileusis (LASIK) and the effect of postsurgery asphericity on contrast-sensitivity function (CSF) under photopic conditions. Setting: Department of Optics, University of Granada, Granada, Spain. Methods:The p-factor and CSF (best corrected before surgery and 1, 3, and 6 months after surgery) were measured in 24 eyes.Results: An increase in the p-factor after LASIK was noted; there was an 87.2% change in the asphericity using the paraxial formula of Munnerlyn and coauthors. Other factors such as decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures, and reflection losses of the laser on the cornea could account for the greater than expected increase (12.8%) in the p-factor. The CSF measurements deteriorated after LASIK; the change was significant (PϽ.05) in patients with myopia worse than Ϫ4.0 diopters at frequencies of 9.2, 12, 15, and 20 cycles per degree. Conclusion:The increase in corneal asphericity after surgery, greater with a higher degree of myopia, and the deterioration in CSF with high myopia justify new ablation algorithms and further study of the variables that could modify the ablation unpredictably.

In this paper, we provide an analytic expression for an adjustment factor in ablation algorithms for photorefractive laser surgery which take into account reflection losses and the nonnormal incidence on the cornea. We evaluate the influence of this factor on certain ocular parameters, calculating alterations in the radius of anterior cornea and corneal asphericity when we use the algorithm given by Munnerlyn’s paraxial formula. Our data indicate that this adjustment factor should be considered in the ablation algorithms that are currently being proposed in customized corneal ablation and that need great accuracy for the correction of eye aberrations.

The present study uses simple reaction time (RT) to examine the temporal response to chromatic changes of the red-green (L-2M) and yellow-blue (S-(LϩM

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Monovision correction by LASIK improved functional near vision in presbyopic patients. Although visual acuity was good for far vision, contrast sensitivity and stereoacuity diminished significantly.