Posterior capsular opacification was evaluated in 46 eyes with an implanted sharp-edged biconvex (BC) lens, 108 eyes with the sharp-edged convex-plano (CP) lens, 160 eyes with the round-edged BC lens and 58 eyes with the round-edged CP lens. In each eye, the intraocular lens had been fixed in the sac after continuous circular capsulorrhexis, with the optic edge completely enclosed by the anterior capsule. Two years postoperatively, the posterior capsules of these eyes were photographed and the degree of opacification was classified as Grade 1 (clear) to Grade 4 (severely opacified). In the sharp-edged BC group, 91% of the eyes were Grade 1; 4% Grade 2; 2% Grade 3; 2% Grade 4. In the sharp-edged CP group, the corresponding percentages were 83, 7, 4, and 6; for the round-edged BC group: 18, 27, 24, and 31; and for the round-edged CP group: 34, 17, 28, and 21. These findings suggest that the most significant factor in prevention of posterior capsular opacification is the sharpness of the optic edge. We believe that the sharp optic edge creates higher pressure on the posterior capsule and acts as a barrier to lens epithelial cell migration.