To determine whether implantation of an intraocular lens (IOL) with a modified prolate anterior surface (Tecnis Z9000, AMO) results in reduced spherical aberration and improved contrast sensitivity after cataract surgery. Hospital NISA Virgen del Consuelo, Valencia, Spain. In an intraindividual randomized prospective study of 30 patients with bilateral cataract, the Tecnis Z9000 IOL was compared with 2 IOLs with spherical surfaces, the AR40e (AMO) and the Stabibag (Ioltech). Ocular aberrations for a 4.0 mm pupil and 6.0 mm pupil were measured with a Hartmann-Shack aberrometer. Quality of vision was measured by visual acuity and contrast sensitivity under mesopic and photopic conditions. Eyes with the Tecnis Z9000 IOL had significantly less spherical aberration and a greater Strehl ratio after surgery. Significant reduction in coma aberration was also found in some cases. Refraction, visual acuity, and contrast sensitivity were not significantly different between the 3 IOL groups. A significant reduction in spherical aberration after Tecnis Z9000 IOL implantation was achieved, but visual acuity and contrast sensitivity were not affected by the aspheric silicone IOL compared to spherical acrylic IOLs.