A surgical cassette for an ophthalmic surgical system includes an irrigation conduit that is in fluid communication with a handpiece and carries fluid toward a surgical site. An aspiration conduit is in fluid communication with the handpiece and carries fluid away from the surgical site. An aspiration pump creates a vacuum pressure in the aspiration conduit to draw fluid through the aspiration conduit towards a drain reservoir. A reservoir couples with a pressure-vacuum source to manage the reservoir pressure. A valve is in fluid communication with the aspiration conduit and the reservoir and provides one or more channels between the aspiration conduit and the reservoir. One or more pressure sensors detect a pressure associated with the surgical site. A computer controls the valve in response to the pressure detected by the one or more pressure sensors.