Changes in corneal asphericity after laser in situ keratomileusis.
OBJECTIVE
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.


METHODS
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 (P<.05) in patients with myopia worse than -4.0 diopters at frequencies of 9.2, 12, 15, and 20 cycles per degree.


CONCLUSIONS
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.
Anera
Rosario G
RG
Departamento de Optica, Facultad de Ciencias, Universidad de Granada, Spain. rganera@ugr.es
Jiménez
Jose R
JR
Jiménez del Barco
Luis
L
Bermúdez
Javier
J
Hita
Enrique
E
D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D003315:Cornea / Q000503:physiopathology*; D019781:Corneal Topography; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery*; D011183:Postoperative Complications / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology*