PURPOSE: To determine whether implantation of an intraocular lens (IOL) with a modified anterior aspheric surface results in reduced spherical aberration and improved contrast sensitivity after cataract surgery. DESIGN: Prospective, comparative, interventional case series. METHODS: In an intraindividual randomized prospective study of 25 patients with bilateral cataract, an IOL with a modified anterior surface (Tecnis Z9001; Advanced Medical Optics, Santa Ana, California, USA; group 1) was compared with biconvex lens with spherical surfaces (ClariFlex; Advanced Medical Optics; group 2). Ocular aberrations for a 5.0-mm pupil and 6.0-mm pupil were measured with Hartmann-Shack aberrometer. Quality of vision was measured by visual acuity and contrast sensitivity under mesopic and photopic conditions. All patients were followed up for three months. RESULTS: No statistically significant difference in postoperative uncorrected and best-corrected distance vision acuity after a follow-up of three months existed between the groups. Postoperative contrast sensitivity testing revealed significant differences between the groups under photopic and mesopic conditions. These differences reached statistical significance under photopic conditions at three spatial frequencies and under mesopic conditions at all spatial frequencies. When analyzing higher-order aberrations, the difference between the groups was statistically significant at the 5.00-mm and 6.00-mm pupil diameters, with the group 1 inducing less higher-order aberration and also less spherical aberration compared with group 2. CONCLUSIONS: Results show the Tecnis Z9001 IOL with a modified anterior aspheric surface induced significantly less higher-order aberration and spherical aberration compared with the ClariFlex IOL. Contrast sensitivity revealed better values under photopic and mesopic conditions with the Tecnis Z9001 IOL.