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Impressum
On the importance of the corneal asphericity in topography-guided treatments-a preliminary study with Wavelight Topolyzer
1,2Jankov M., 1,3Mrochen M. C., 1Seiler T.
1Augenklinik, UniversitätsSpital Zürich, Schweiz; 2Departamento de Oftalmologia, Santa Casa de Sao Paulo, Brasil; 3ETH, Zürich, Schweiz
Objective: To evaluate the clinical importance of aspheric ablation
profiles in topography-guided treatments for the correction of large irregular
astigmatism.
Methods: Topography was measured by a computerised topographer
(Oculus Keratograph, Oculus Optikgeräte GmbH, Wetzlar, Germany) in
10 eyes with large irregular astigmatism of several diopters. The calculation
of clinically used ablation profiles was based on Zernike expansion of
corneal aberration with and without taking the attempted asphericity of
the cornea into consideration.
Results: Not taking the attempted asphericity of the cornea into
consideration for the calculation of ablation profiles results in a systematic
underestimation of the spherical aberration that are pre-existing in a
normal corneal topography. In addition, a gross difference in the spherical
aberration can be found from Zernike expansion.
Conclusion: Higher and lower order optical aberrations calculated
from the Zernike expansion out of the topography data based on the spherical
cornea model can lead to clinically relevant differences in corneal aberrations
measurements. The observed differences are due to the incorrect approximation
of the corneal shape into the spherical rather than realistic aspherical
shape. Zernike coefficients of an aspherical fit of the topographies show
better similarity to the physiological curvature conditions of the cornea
and therefore could be used for the topography-guided corneal laser surgery.