Reconstructing ocular surfaces by Purkinje images: an exact ray approach.

A method originally developed for corneal topography (using discrete sources and Zernike polynomials) was extended to estimate the geometry of ocular surfaces internal to the eye. The approach was tested in simulation as a candidate method for phakometry. Purkinje images from the anterior surface of an intra-ocular lens (IOL) (aligned and decentered) were simulated using the Navarro eye. The 'full' Navarro eye and a simplified eye were assumed for recovery purposes. Root mean square (RMS) errors and (anterior) IOL radii of curvatures (best-fit spheres) were estimated. The robustness of the method to axial shifts in lens position (both eye models) along with assumed refractive index (simplified eye only) was tested. When axial shifts were ignored, RMS errors for the full eye were sub-micron (<0.8 microm), and radii of curvature errors were approximately 1 microm. Axial shifting increased these errors linearly. The n = 1.32 error curve (simplified eye) matched the full eye error curves closely (for both RMS error and IOL lens radius), although the RMS error curve exhibited some asymmetry for a decentered IOL. The nominal refractive index (n = 1.3305) was sub-optimal in all cases. The resulting method is a potentially useful way to estimate the geometry of the internal ocular surfaces.