Customized aspheric intraocular lenses calculated with real ray tracing

Purpose

To calculate the exact geometry of custom intraocular lenses (IOLs) for pseudophakic eyes and theoretically predict the residual wavefront error by real ray tracing based on Snell's law.

Setting

Centre for Ophthalmology, University Hospital, Tübingen, Germany.

Methods

Individual computer models were constructed based on measurements, including corneal topography and axial length. The geometry of custom spherical, aspheric, toric, and toric aspheric IOLs was calculated in an optimization process with real ray tracing to provide the minimum root mean square wavefront error. The geometric optical properties in terms of residual wavefront error was simulated and approximated by Zernike polynomials.

Results

Data from 45 pseudophakic eyes were used to construct the models. Defocus was almost completely corrected by the spherical IOL and astigmatism, by the toric IOL. The aspheric IOL strongly reduced spherical aberration but only slightly reduced total higher-order aberrations (HOAs); both theoretical predictions corresponded to clinical investigations of wavefront measurements in pseudophakic eyes with a spherical or aspheric IOL.

Conclusions

Real ray tracing calculated the exact geometry of custom IOLs to provide the minimum wavefront error, going beyond simple diopter information. Results show spherical aberration can be significantly reduced with aspheric IOLs. However, the limited possible reduction of total HOAs, even perfectly positioned custom aspheric IOLs, may be a reason for the unclear results in studies assessing the potential benefit to visual performance of currently used aspheric IOLs.