[Image properties of spherical as aspheric intraocular lenses]

One reason for the problems that pseudophakic patients have with their mesopic vision is the spherical aberration of the implanted intraocular lens (IOL). Therefore we developed an aspheric IOL that will minimize this aberration. Starting with a 22 diopter lens we checked whether it is possible to keep the aspheric surface of the lens constant while changing the second radius to cover a larger range of needed refractive power. Afterwards we also checked whether the theoretical results correspond to the practically tested image quality.

We analyzed the image quality of the aspheric lenses theoretically by calculating the optimal defocused geometrical spot size. For the ray tracing we used the Gullstrand schematic eye model with an aspheric cornea. The calculated spot sizes were compared to those of a spherical IOL. Subsequently we compared the quality of both lenses by imaging an USAF-test target through a model eye.

We were able to design an aspherical IOL to improve the optical performance up to the limit of diffraction. When the second radius was changed, the spot size enlarged as we expected, but it was considerable smaller than that of the respective spherical IOL. The image quality that we tested with the model eye was considerably better with the aspherical lens than with the spherical lens.

It is possible to improve the optical performance of intraocular lenses by aspherization. The production procedure can be kept simple by aspherizing only one side of the lens. The refractive power can be changed by varying the radius of the spherical side. In our opinion aspheric IOL's should be used especially for cataract patients with a pupil size of 5 mm and more.