A system for measuring the flow properties of a patient's tear duct (14, 15, 16, 18), to ascertain the flow resistance of the tear duct, the system comprising: - a means to generate a flow of liquid, communicating with a cannula to supply liquid into a punctum (12, 13) of the patient's eye to irrigate the tear duct so the liquid flows through the tear duct from the punctum (12, 13) to the nasal passage, the cannula defining a tip, and being able to seal to the punctum (12, 13); - a motor to actuate the flow-generating means; - a pressure sensor to monitor the pressure of the liquid supplied to the punctum (12, 13); - a monitoring circuit to which signals from the pressure sensor are provided, arranged to provide an indication of the flow resistance from those signals; and - a feedback circuit to control the motor in accordance with signals from the pressure sensor, either to maintain a preset liquid pressure, or to ensure that the liquid pressure does not exceed a preset threshold; - wherein the flow-generating means communicates with the cannula through one or more components that define a flow path, the flow path being defined at least in part by a short, rigid tubular element of length less than 150 mm to which the cannula is attached; and the system includes a switch to allow actuation of the flow generating means; and wherein either: (a) the short, rigid tubular element is attached to the outlet of the flow generating means so as to connect the flow generating means to the cannula, the system is portable, the motor is powered by a battery, and the switch is in the vicinity of the cannula for convenient use by an operator, so the system may be operated hand-held by the operator using one hand; or: (b) the flow-generating means and the motor are adapted to be mounted on a microscope, the flow path is defined at least in part by a flexible tube, the flexible tube is sufficiently long that the short, rigid tubular element can be held and manipulated by the operator using one hand, to insert the cannula into a patient's punctum (12, 13) while the operator views the patient's eye through the microscope, and the switch is in the short, rigid tubular element for convenient use by the operator, so it can be operated by the fingers holding the short tubular element. - a means to generate a flow of liquid, communicating with a cannula to supply liquid into a punctum (12, 13) of the patient's eye to irrigate the tear duct so the liquid flows through the tear duct from the punctum (12, 13) to the nasal passage, the cannula defining a tip, and being able to seal to the punctum (12, 13); - a motor to actuate the flow-generating means; - a pressure sensor to monitor the pressure of the liquid supplied to the punctum (12, 13); - a monitoring circuit to which signals from the pressure sensor are provided, arranged to provide an indication of the flow resistance from those signals; and - a feedback circuit to control the motor in accordance with signals from the pressure sensor, either to maintain a preset liquid pressure, or to ensure that the liquid pressure does not exceed a preset threshold; - wherein the flow-generating means communicates with the cannula through one or more components that define a flow path, the flow path being defined at least in part by a short, rigid tubular element of length less than 150 mm to which the cannula is attached; and the system includes a switch to allow actuation of the flow generating means; (a) the short, rigid tubular element is attached to the outlet of the flow generating means so as to connect the flow generating means to the cannula, the system is portable, the motor is powered by a battery, and the switch is in the vicinity of the cannula for convenient use by an operator, so the system may be operated hand-held by the operator using one hand; or: (b) the flow-generating means and the motor are adapted to be mounted on a microscope, the flow path is defined at least in part by a flexible tube, the flexible tube is sufficiently long that the short, rigid tubular element can be held and manipulated by the operator using one hand, to insert the cannula into a patient's punctum (12, 13) while the operator views the patient's eye through the microscope, and the switch is in the short, rigid tubular element for convenient use by the operator, so it can be operated by the fingers holding the short tubular element.