Abstract

P 233

The effect of the asphericity of myopic laser ablation profiles on the induction of wavefront aberrations

Jens Bühren1, Lana Nagy2, Geunyoung Yoon2, Scott MacRae2, Krystel Huxlin2
1Klinik für Augenheilkunde, Goethe-Universität Frankfurt am Main, Frankfurt/Main; 2Center for Visual Science, University of Rochester, Rochester, NY, USA

Objective
The goal of the study is to compare the effects of laser profile asphericity on the induction of lower- and higher-order aberrations and susceptibility to decentration.
Methods
Four (Poly-)Methylmethacrylat (PMMA) lenses received an ablation for -6 D with an optical zone (OZ) of 6mm (217, Bausch & Lomb).  One lens was treated with a conventional profile; for the 3 other lenses profiles of different asphericity were used.  Based on previous data from our cat model, an induction of primary spherical aberration (primary SA, Z(4,0)) of 0.346 µm was expected to be induced by a treatment of -6 D (6 mm OZ and pupil diameter [PD]).  To pre-compensate for induced spherical aberration, an additional Z(4,0) amount of -0.346 µm (1n), -1.038 µm (3n) and -2.076 µm (6n) was included in the profile.
The curvature of the PMMA lens was measured using surface profilometry (TalySurf, Taylor & Hobson), and wavefront changes were computed from curvature differences after ablation (9 mm PD, Matlab 7.1).  A computer model (Matlab 7.1) was used to simulate decentration of a sub-pupil of 6 mm relative to the measured WFE difference in 100 µm steps.
Results
With all aspheric profiles, Z(4,0) was under-corrected with a correction efficacy between 20 und 27%.  The 6n profile induced least SA (RMS from Z(4,0) und Z(6,0)).  The higher the amount of negative Z(4,0) in the profile, the less SA was induced and the lower were the under-correction of refractive error and coma induction due to decentration.
Conclusions
1. Aspheric ablation profiles induced less SA than the standard profile.  The pre-compensation of SA induction was effective but subject to marked under-correction.  2. SA induction and under-correction on PMMA lenses could be explained by loss of laser energy in the periphery.  3. Treatments with aspheric profiles were less susceptible to OZ decentration.

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