Phacoemulsification tip (100), comprising - a rod (108) at least partially straight； - a cutting edge part (112) at the distal end of the rod, wherein the cutting edge part comprises at least a first and second curvature (102,104) and a distal end point (106)； - the tip being configured to be vibrated in ultrasonic torsion when used with a phacoemulsification handpiece (204), which comprises an ultrasonic drive mechanism, whereby the ultrasonic torsional vibration of the tip results in at least two movements, comprising: - a lateral displacement of the tip perpendicular to a collinear axis with a straight shank part and perpendicular to an axis of a curvature of the tip； - a torsion angle along the collinear axis with a straight rod part of the tip； wherein the geometry of the rod and of said at least a first and second curvature is configured to result, during ultrasonic torsional vibration of the tip (100), a lateral displacement of the rod (108), perpendicular to the rod ( 108), of less than about 5 to 25% of the lateral displacement of the distal end point (106) of the tip (100) along the length of the stem extending from the proximal end of the stem to the first curvature of the cutting edge part, in which the lateral displacement (ux) is determined at least partially using the equation, in which: f is the torsion angle of the tip, r is the density of the material of tip, S (z) is a cross-sectional area of the tip along the axis (116) collinear with the stem (108), E is Young's modulus of a point material, Iy (z) is a moment of inertia of a cross section of the tip around an axis perpendicular to the collinear axis with the rod, and l (z) is the lateral displacement along the axis perpendicular to the collinear axis with the rod, and in which the length of the rod is configured to adjust the torsional vibration so that The torsion vibration is in resonance with the ultrasonic drive mechanism to increase the displacement of torsion at the distal end point (106).
