A system (30) for measuring the flow properties of a tear duct (14, 15, 16, 18) to ascertain its flow resistance comprises a syringe (32) communicating with a cannula (46) to supply liquid to a punctum (12, 13) of an eye (10) the cannula (46) having a tip (47) to seal to the punctum (12, 13). A motor (34) is arranged to actuate the syringe (32). A pressure sensor (42) monitors the pressure (P) of the liquid supplied to the punctum (12, 13) and a monitoring circuit (50) provides an indication of the flow resistance In addition a feedback circuit (50) controls the motor (34) in accordance with the measured pressure (P) either to maintain a preset liquid pressure or to ensure that the liquid pressure does not exceed a preset threshold. The system may also include means to prevent flow through the other punctum of the eye for example a plug (60, 62) or a clip (65, 73). If the flow rate (F) of the liquid supplied to the punctum (12, 13) is also monitored the monitoring circuit (50) is arranged to determine the flow resistance (R) from the pressure (P) and the flow rate (F).
