A device for ophthalmic surgery includes a vacuum-pump arrangement for generating a vacuum serving for fixing a suction ring to an eye, an evacuation-path system for transmitting the vacuum to an interface port which permits the separable attachment of a suction-ring instrumentarium including the suction ring, and also a control unit for controlling the vacuum-pump arrangement. In accordance with the invention, the device includes pressure-measuring components for measuring at least the vacuum pressure, the control unit adapted to ascertain a differential pressure between the measured vacuum pressure and an atmospheric pressure. The vacuum-pump arrangement is preferably operated at maximal pumping power in a test-operation mode with suction-ring instrumentarium not attached, in order to ascertain an optimally obtainable relative underpressure in the evacuation-path system. In this way, in the case of fluctuating altitudes of the location of use of the ophthalmic-surgery device and also in the case of fluctuating weather conditions (low pressure, high pressure) it can be ascertained at all times whether the achievable relative underpressure is sufficient.