Topography-based intraocular lens power selection.
OBJECTIVE
To provide mathematical tools for selecting intraocular lens (IOL) power for normal eyes and for "odd" eyes, particularly after corneal refractive surgery.


METHODS
Universitats-Augenklinik, Mainz, Germany.


METHODS
First, IOL power is selected based on the radii and numerical eccentricity of the cornea, extracted from corneal topography in a consistent numerical model of the cornea. To fine-tune the result, the visual impression is simulated by blurred Landolt rings superimposed on the retinal receptor grid. The calculation uses numerical ray tracing of the whole pseudophakic eye comprising all monochromatic errors. The error contributions of the influencing parameters, such as anterior and posterior corneal shape and corneal thickness, are quantified in detail. The method is verified in IOL power selection for normal eyes and for eyes after corneal refractive surgery.


RESULTS
The main difference between normal corneas and corneas after refractive surgery results from different asphericities. Normal corneas are prolate, with typical numerical eccentricities of 0.5, whereas corneas after laser surgery for myopia are oblate. This causes the main difference (hyperopic shift up to 2.0 diopters) in IOL power selection. Shifts in the posterior corneal radius and corneal thickness are of minor importance.


CONCLUSIONS
Intraocular power selection after corneal refractive surgery should be based on all the information corneal topography provides.
Preussner
Paul-Rolf
PR
Universitäts-Augenklinik, Mainz, Germany. pr.preussner@uni-mainz.de
Wahl
Jochen
J
Weitzel
Daniela
D
D002387:Cataract Extraction; D003315:Cornea / Q000473:pathology / Q000601:surgery; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D007910:Lenses, Intraocular; D008433:Mathematics; D008962:Models, Theoretical; D055095:Optics and Photonics; D054140:Refractive Surgical Procedures