OBJECTIVE To compare the inhibiting effect on posterior capsule opacification (PCO) of a silicone intraocular lens (IOL) with a sharp posterior optic edge (ClariFlex OptiEdge, Advanced Medical Optics) and a silicone IOL with a round optic edge (PhacoFlex SI-40, Advanced Medical Optics). METHODS Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS This prospective randomized patient- and examiner-masked study comprised 104 eyes of 52 patients with bilateral age-related cataract. All patients had cataract surgery in both eyes and received a sharp-edged IOL in 1 eye and a round-edged IOL in the other eye. Postoperative examinations were at 1 week, 1 and 6 months, and 1 year. Digital slitlamp and retroillumination images were taken of each eye. The amount of PCO was assessed subjectively at the slitlamp and objectively using Automated Quantification of After-Cataract (AQUA) automated-image analysis software. RESULTS The sharp-edged IOL group had significantly less regeneratory and fibrotic PCO 1 month, 6 months, and 1 year after surgery. The mean AQUA PCO score (scale 0 to 10) was 0.71 in the sharp-edged IOL group and 1.40 in the round-edged IOL group (P<.001). The sharp-edged IOL group had less peripheral fibrotic PCO. There was no significant difference between the 2 IOL groups in patient reports of edge glare. CONCLUSIONS The sharp-edged design of the ClariFlex OptiEdge silicone IOL led to significantly less PCO than the round-edged PhacoFlex SI-40 IOL 1 year postoperatively.