Research On Key Mathematical Models In Excimer Laser Vision Correction

Excimer laser corneal refractive surgery and wavefront technology have developed rapidly these yeas. Now, wavefront-guided laser vision correction becomes the hotspot in corneal refractive surgery. Applying the technology of CAD/CAM, This paper has studied modeling technologies in excimer laser vision correction. Research results of the paper have been directly used by homemade Excimer laser aberration correction system. Main research achievements of this paper are as following:1. The modulation transfer function (MTF) for a large pupil is computed from the wavefront aberration. The influence of the wavefront aberration on the MTF is analyzed. Using the wavefront aberration map and the MTF, interaction between aberrations to improve or reduce visual performance is discussed.2.A model for wavefront reconstruction from slopes of reflected wave is presented. Properties of zernike polynomial with normalization factor is studied thoroughly. According to the geometry of slope measurements for the subjective wavefront optometer, a wavefont reconstruction model using zernike polynomial with normalization factor is put forward. Based on Householder transformation and Gram-Schmidt orthogonalization method, two methods for working out unknown zernike coefficients are bring forward. The error propagation parameter for the wavefront reconstruction model is deduced.3. Key models in traditional laser vision correction are presented. Corneal surfaces in eyes with regular astigmatism are thought to be toroidal surfaces. Based on mathematical models for corneal surfaces before and after treatment, a corneal ablation model is given for such refractive errors as spherical myopia, compound myopic astigmatism, and simple myopic astigmatism. A similar corneal ablation model is also given for such refractive errors as hyperopia, compound hyperopic astigmatism, and simple hyperopic astigmatism. Ablation models on all kinds of refractive errors are simulated on computer. A blend zone model is presented and the optical zone diameter or the transition width can all be adjusted in this model.4. Key models in wavefront-guided laser vision correction are presented. Based on the relationship between the change of the cornea thickness and optical path length, the ablation profile for the correction of wavefront aberration is presented and simulated on computer. The process of scanning-spot excimer laser is studied and simulated on computer. Models for calculation of residual wavefront aberration on situations of lateral decentration and torsional misalignment are brought up. This will be helpful in studying the influence of decentration on wavefront correction result.5. Using these mathematic models discussed in the paper, the homemade Excimer laser aberration correction system has been manufactured with cooperation of Su Zhou 66 Vision Tech Co., Ltd. Now the system has been applied to clinical practice. Clinical results showed that: the Excimer laser aberration correction system can remarkably improve visual performance when treating ametropia; the system can...