Optical eye model for photorefractive surgery evaluation

Purpose: To improve the applicability of the Gullstrand's eye model for retinal image evaluation and prediction of photo-refractive surgery outcome. Methods. The Gullstrand's eye model has been modified to allow for variable asphericity of all the refracting surfaces in the model. Formation of the retinal image is studied by means of numerical ray-tracing and by evaluation of modulation transfer function and point/line-spread-function. Results. By comparison of the model line-spread functions with experimental ones taken from the literature, best-fitting values of the asphericity parameters have been derived. The model visual performances are evaluated and compared with other eye models. Application of the model to photo-refractive surgery reveals that proper aspheric curvature in the mid periphery is essential to minimize spherical aberration and guarantee ultimate visual performances in the emmetropic eye, at the limit allowed by diffraction and photoreceptor density in the fovea. Conclusions: The proposed eye model can be useful in vision research as well as in practical applications like the design of ocular lenses and the design of improved algorithms for photorefactive surgery.