A system for regulating pressure in an ophthalmic surgical system comprising: a sleeve coaxially received over a needle so as to define a flow passage between the sleeve and the needle through which irrigation fluid is communicated to a surgical site, and a needle passage through which fluid is aspirated from the surgical site, the sleeve and needle for insertion into a medium through an incision of a predetermined size; a container configured to provide an adjustable infusion pressure for urging a flow of irrigation fluid within the container to the sleeve, for infusion to the surgical site; a vacuum source configured to establish a vacuum for urging an aspiration of fluid from the surgical site through the needle passage; a sensor for providing a signal indicative of the vacuum being applied; a flow sensing or estimating device for providing a signal indicative of a flow rate of fluid being aspirated from the surgical site; and a controller configured to receive an input of a needle size, a sleeve size, and the incision size, and to estimate an intraocular eye pressure based on the infusion pressure less a pressure drop due to a predetermined resistance to the fluid flow, which fluid flow does not include any predicted leakage flow and wherein the controller is configured to obtain a more refined estimate of the intraocular eye pressure based on the infusion pressure and a combination of the sensed fluid flow rate and a predicted leakage rate of fluid exiting the incision selected from a look-up table based on the needle size, the sleeve size, and the incision size, wherein the controller uses the refined estimate to control fluid flow to maintain a desired intraocular pressure. a sleeve coaxially received over a needle so as to define a flow passage between the sleeve and the needle through which irrigation fluid is communicated to a surgical site, and a needle passage through which fluid is aspirated from the surgical site, the sleeve and needle for insertion into a medium through an incision of a predetermined size; a container configured to provide an adjustable infusion pressure for urging a flow of irrigation fluid within the container to the sleeve, for infusion to the surgical site; a vacuum source configured to establish a vacuum for urging an aspiration of fluid from the surgical site through the needle passage; a sensor for providing a signal indicative of the vacuum being applied; a flow sensing or estimating device for providing a signal indicative of a flow rate of fluid being aspirated from the surgical site; and a controller configured to receive an input of a needle size, a sleeve size, and the incision size, and to estimate an intraocular eye pressure based on the infusion pressure less a pressure drop due to a predetermined resistance to the fluid flow, which fluid flow does not include any predicted leakage flow and wherein the controller is configured to obtain a more refined estimate of the intraocular eye pressure based on the infusion pressure and a combination of the sensed fluid flow rate and a predicted leakage rate of fluid exiting the incision selected from a look-up table based on the needle size, the sleeve size, and the incision size, wherein the controller uses the refined estimate to control fluid flow to maintain a desired intraocular pressure.