Tear duct resistance measuring system

Abstract

A system for measuring the flow properties of a tear duct, to ascertain its flow resistance, includes a syringe communicating with a cannula to supply liquid to a punctum of an eye, the cannula having a tip to seal to the punctum. A motor is arranged to actuate the syringe. A pressure sensor monitors the pressure of the liquid supplied to the punctum. A monitoring circuit provides an indication of the flow resistance. A feedback circuit controls the motor in accordance with the measured pressure, to maintain a preset liquid pressure, or to ensure that the liquid pressure does not exceed a preset threshold. The system may prevent flow through the other punctum of the eye. If the flow rate of the liquid supplied to the punctum is also monitored, the monitoring circuit is arranged to determine the flow resistance from the pressure and the flow rate.

1 . A system for measuring flow properties of a tear duct, to ascertain flow resistance of the tear duct, the system comprising:
 a syringe with a plunger to generate a flow of liquid, communicating with a cannula to supply liquid into a punctum of an eye to irrigate the tear duct, the liquid being supplied into the punctum at a flow rate, the cannula defining a tip, and being able to seal to the punctum;   a linear actuator to actuate the plunger of the syringe, to generate the flow of liquid;   a pressure sensor to monitor the pressure of the liquid supplied to the punctum;   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 which signals from the pressure sensor are provided, and which provides signals to the linear actuator to control the linear actuator in accordance with the signals from the pressure sensor, to change the flow rate from the syringe either to maintain a preset liquid pressure, or to ensure that the liquid pressure does not exceed a preset threshold;   the linear actuator, the monitoring circuit, and a battery being housed within a casing that incorporates means to mount the syringe on the casing, the casing being ergonomically shaped for hand-held operation with a pen-like grip;   wherein the syringe communicates with the cannula through a flow path defined by a short, rigid tubular element to which the cannula is attached, the short rigid tubular element connecting the cannula to the syringe, and the short rigid tubular element incorporating the pressure sensor; and the system includes a switch in the vicinity of the cannula for convenient use by an operator, the switch enabling activation of the linear actuator and so operation of the syringe;   and wherein the linear actuator is powered by the battery, so that the system may be operated hand-held.   
     
     
         2 . A system as claimed in  claim 1  also comprising means to monitor the flow rate of the liquid supplied to the punctum, and to supply signals representing the flow rate to the monitoring circuit, so the monitoring circuit can determine the flow resistance. 
     
     
         3 . A system as claimed in  claim 1  for use where the eye has a normal tear duct system with two puncta, the system also comprising means to occlude flow through the other punctum of the eye, the occluding means comprising a clip to compress a punctum or adjacent canaliculus between two opposed jaws. 
     
     
         4 . A system as claimed in  claim 2  wherein the flow rate is monitored by monitoring movement of the syringe plunger, or by monitoring the linear actuator. 
     
     
         5 . A system as claimed in  claim 1  wherein the short tubular element also comprises the switch. 
     
     
         6 . A system as claimed in  claim 1  wherein the short tubular element also comprises a one-way valve. 
     
     
         7 . A system as claimed in  claim 1  wherein the system also comprises a source of light directed at the tip of the cannula, to assist the user in identifying the punctum, and to check for liquid leakage during operation. 
     
     
         8 . A system as claimed in  claim 1  also comprising a motor overload detector to detect any overload of the linear actuator. 
     
     
         9 . A system for measuring flow properties of a tear duct, to ascertain flow resistance of the tear duct, the system comprising:
 a liquid reservoir communicating with a cannula to supply liquid into a punctum of an eye to irrigate the tear duct, the cannula defining a tip, and being able to seal to the punctum;   a pump to generate a flow of liquid from the liquid reservoir to the cannula, the liquid being supplied into the punctum at a flow rate;   a pressure sensor to monitor the pressure of the liquid supplied to the punctum;   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 which signals from the pressure sensor are provided, and which provides signals to the pump to control the pump in accordance with the signals from the pressure sensor, to change the flow rate from the pump either to maintain a preset liquid pressure, or to ensure that the liquid pressure does not exceed a preset threshold;   the system also including a casing to enclose or support the pump, the liquid reservoir, the monitoring circuit, and a battery, the casing being ergonomically shaped for hand-held operation with a pen-like grip;   wherein the pump communicates with the cannula through a flow path defined by a short, rigid tubular element to which the cannula is attached, the short rigid tubular element connecting the cannula to the pump, and the short rigid tubular element incorporating the pressure sensor; and the system includes a switch in the vicinity of the cannula for convenient use by an operator, the switch enabling activation of the pump and so initiation of the liquid flow;   and wherein the pump is powered by the battery, so that the system may be operated hand-held.   
     
     
         10 . A system as claimed in  claim 9  also comprising means to monitor the flow rate of the liquid supplied to the punctum, and to supply signals representing the flow rate to the monitoring circuit, so the monitoring circuit can determine the flow resistance. 
     
     
         11 . A system as claimed in  claim 9  for use where the eye has a normal tear duct system with two puncta, the system also comprising means to occlude flow through the other punctum of the eye, the occluding means comprising a clip to compress a punctum or adjacent canaliculus between two opposed jaws. 
     
     
         12 . A system as claimed in  claim 9  wherein the short tubular element also comprises the switch. 
     
     
         13 . A system as claimed in  claim 9  wherein the short tubular element also comprises a one-way valve. 
     
     
         14 . A system as claimed in  claim 9  wherein the system also comprises a source of light directed at the tip of the cannula, to assist the user in identifying the punctum, and to check for liquid leakage during operation. 
     
     
         15 . A system as claimed in  claim 9  also comprising a motor overload detector to detect any overload of the pump.