An eye treatment system having a handpiece, a console, a cassette, and a pump formed by the engagement of the cassette with the console. The pump having a head having a plurality of projections disposed to rotate about an axis, a ramp disposed near the rotating projections, and a resilient channel configured to transfer fluid when engaged by the ramp and the plurality of projections. The ramp having an entrance, a central, and an exit portion. The entrance portion has an arcuate extent over which the projections close the channel as the head rotates. The central portion has an arcuate extent over which the channel is sealed by the projections as the head rotates. The exit portion has an arcuate extent over which the projections open the channel as the head rotates. The arcuate extent of the entrance portion is unequal to the arcuate extent of the exit portion.
