According to certain embodiments, a surgical cassette for an ophthalmic surgical system comprises 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. Each sensor detects 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 to mitigate a pressure or volume change.