gms | German Medical Science

A part of a system for coupled biomechanics-optics simulation is presented, which will be used for preoperative estimation of the vision quality after refractive surgical acts. The following contribution shows results of special methods of the optical part of the system on the basis of simulation examples.

Very similar to human vision is the simulation of the optical imaging of an object pattern onto a surface which is comparable to the retina concerning the shape and the resolution. Series of images are produced by variation of optical parameters within simulation cycles. The variants of these parameters might be the object distance, shape of the cornea or the length of the eye bulb. For objective validation the calculated images are analyzed, using digital filters with regard to the individual sharpness. The real eye exhibits not only rotational symmetry concerning the surfaces (e.g. astigmatism). Therefore it is essential to accomplish image analysis by means of anisotropic contrast filtering, to be able to determine the corresponding optical parameters, i.e. the power and angle of astigmatism. Additionally wavefront analysis is performed to investigate higher order aberration of the virtual eye. In this field algorithms are applied, which are described by Tscherning (known as Tscherning Wavefront Analyzer) and by Liang (known as Hartmann-Shack sensor).

Simulation using optical imaging and wavefront analysis has been applied to calculated corneal surfaces and to those geometries of corneas, which have been acquired topographically from real patient's eyes.

The shown methods are appropriate to simulate the optical behaviour of a human eye. Furthermore the results of the biomechanical simulation (deformation of the tissue) can be used as input to the optical part of the system. So an assessment of the influence of corneal tissue after simulated refractive surgery on optical properties is possible.