Abstract:
Systems and methods for treating an ocular condition includes a heating chamber comprising a material expandable when heated and comprising a flow passage having an inlet and an outlet. A heating element is arranged and disposed to introduce heat in the heating chamber. A flexible diaphragm separates the heating chamber from the flow passage, and is moveable between a first position and a second position to change a volume of one of the pump chamber and flow passages in response to a temperature change in the heating chamber.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to pressure/flow control systems and methods for use in treating a medical condition. In some instances, embodiments of the present disclosure are configured to be part of an IOP control system for the treatment of ophthalmic conditions. 
         [0002]    Glaucoma, a group of eye diseases affecting the retina and optic nerve, is one of the leading causes of blindness worldwide. The chamber pressure of the eye is known as intraocular pressure (IOP). Most forms of glaucoma result when IOP increases to pressures above normal for prolonged periods of time. IOP can increase due to high resistance to the drainage of the aqueous humor relative to its production. Left untreated, an elevated IOP causes irreversible damage to the optic nerve and retinal fibers resulting in a progressive, permanent loss of vision. This may be due to a direct effect of the raised pressure upon the optic nerves and/or the effect of chronic under-perfusion of the nerve head. 
         [0003]    The eye&#39;s ciliary body continuously produces aqueous humor, the clear fluid that fills the anterior segment of the eye (the space between the cornea and lens). The aqueous humor flows out of the anterior chamber (the space between the cornea and iris) through the canalicular and the uveoscleral pathways, both of which contribute to the aqueous drainage system. The orbital globe of the eye is an essentially non-compliant sphere, allowing IOP to be influenced by a change in volume of the contents of the orbit, including both the anterior segment and the posterior segment. Thus, the delicate balance between the production and drainage of aqueous humor can influence the IOP of the eye. 
         [0004]      FIG. 1  is a diagram of the front portion of an eye  10  that helps to explain the processes of glaucoma. In  FIG. 1 , representations of the lens  110 , cornea  120 , iris  130 , ciliary body  140 , trabecular meshwork  150 , Schlemm&#39;s canal  160 , the anterior segment  165  including both the anterior chamber  170  and the posterior chamber  175 , the posterior segment  178 , the sclera  180 , the retina  182 , the choroid  185 , the limbus  190 , the suspensory ligaments or zonules  195 , the suprachoroidal space  200 , and the conjunctiva  202  are pictured. Aqueous fluid is produced by the ciliary body  140 , which lies beneath the iris  130  and adjacent to the lens  110  in the anterior chamber  170  of the anterior segment of the eye  165 . This aqueous humor washes over the lens  110  and iris  130  and flows to the drainage system located in the angle of the anterior chamber  170 . The posterior segment  178  is filled with a gel-like substance called vitreous humor. Normal regulation of IOP occurs chiefly through the regulation of the volume of aqueous humor. Similarly, however, changes in the volume of fluid (e.g., vitreous humor) within the posterior segment can affect IOP. 
         [0005]    After production by the ciliary body  140 , the aqueous humor may leave the eye by several different routes. Some goes posteriorly through the vitreous body behind the lens  110  to the retina, while most circulates in the anterior segment of the eye to nourish avascular structures such as the lens  110  and the cornea  120  before outflowing by two major routes: the conventional outflow pathway route  205  and the uveoscleral outflow route  210 . The angle of the anterior chamber  170 , which extends circumferentially around the eye, contains structures that allow the aqueous humor to drain. The conventional outflow pathway (or trabecular meshwork) route is the main mechanism of outflow, accounting for a large percentage of aqueous egress. The route extends from the anterior chamber angle (formed by the iris  130  and the cornea  120 ), through the trabecular meshwork  150 , into Schlemm&#39;s canal  160 . The trabecular meshwork  150 , which extends circumferentially around the anterior chamber  170 , is commonly implicated in glaucoma. The trabecular meshwork  150  seems to act as a filter, limiting the outflow of aqueous humor and providing a back pressure that directly relates to IOP. Schlemm&#39;s canal  160  is located just peripheral to the trabecular meshwork  150 . Schlemm&#39;s canal  160  is fluidically coupled to collector channels (not shown) allowing aqueous humor to flow out of the anterior chamber  170 . The arrows  205  show the flow of aqueous humor from the ciliary bodies  140 , over the lens  110 , over the iris  130 , through the trabecular meshwork  150 , and into Schlemm&#39;s canal  160  and its collector channels (to eventually reunite with the bloodstream in the episcleral vessels (not shown)). 
         [0006]    The uveosceral route  210  accounts for the major remainder of aqueous egress in a normal eye, and also begins in the anterior chamber angle. Though the anatomy of the uveoscleral route  210  is less clear, aqueous is likely absorbed by portions of the peripheral iris  130 , and the ciliary body  140 , after which it passes into the suprachoroidal space  200 . The suprachoroidal space  200  is a potential space of loose connective tissue between the sclera  180  and the choroid  185  that provides a pathway for uveoscleral outflow. Aqueous exits the eye along the length of the suprachoroidal space to eventually reunite with the bloodstream in the episcleral vessels. 
         [0007]    One method of treating glaucoma includes implanting a drainage device in a patient&#39;s eye. The drainage device allows fluid to flow from the interior of the eye (e.g., from the posterior segment to a drainage site, relieving pressure in the eye and thus lowering IOP). The system and methods disclosed herein overcome one or more of the deficiencies of the prior art. 
       SUMMARY 
       [0008]    According to an exemplary aspect, the present disclosure is directed to a system for treating an ocular condition including a heating chamber comprising a material expandable when heated and comprising a flow passage having an inlet and an outlet. A heating element is arranged and disposed to introduce heat in the heating chamber. A flexible diaphragm separates the heating chamber from the flow passage, and is moveable between a first position and a second position to change a volume of one of the pump chamber and flow passages in response to a temperature change in the heating chamber. 
         [0009]    In an aspect, the heating element is a resistive heating element configured to increase in temperature when a current is passed therethrough. In an aspect, the heating element is disposed within the pump chamber. In an aspect, the heating element is a resistive heating element disposed along a wall of the heating chamber opposite the flexible diaphragm. In an aspect, the system includes a power source and a feed wire extending on opposing sides of the heating element, the feed wire being in electrical communication with the power source. In an aspect, the system includes at least one sensor arranged to detect a pressure indicative of intraocular pressure. In an aspect, the system includes a processor configured to operate the heating element based on information detected by the at least one sensor. In an aspect, the system includes a first one-way valve and a second one-way valve operable as the flexible diaphragm moves from the first position to the second position and back to the first position to promote the passage of drainage fluid through the flow passage in one direction. In an aspect, the first and second check valves are reed valves or flapper valves. 
         [0010]    According to another exemplary aspect, the present disclosure is directed to a system implantable in an eye for treating an ocular condition. The system includes a housing sized for implantation in an eye of a patient, comprising: a sealed heating chamber; and a fluid flow passage having an inlet and an outlet. The system also includes a flexible diaphragm carried by the housing and disposed between and separating the heating chamber from the fluid flow passage and includes a heating element arranged and disposed to induce heat in the heating chamber to change pressure in the chamber. A power source may be in electrical communication with the heating element and configured to induce electrical current in the heating element. 
         [0011]    In another exemplary aspect, the present disclosure is directed to a method for treating an ocular condition comprising: inducing flow of a liquid through a flow pump having a flexible diaphragm separating a flow passage from a heating chamber; moving the flexible diaphragm from a first position to a second position by increasing a temperature of a fluid in the heating chamber; forcing fluid from the flow passage as the flexible diaphragm moves the first position to the second position; and drawing fluid into the flow passage by moving the flexible diaphragm from the second position to the first position. 
         [0012]    In an aspect, moving the flexible diaphragm by increasing a temperature of a fluid in the heating chamber comprises applying voltage to a heating element disposed in a closed chamber. In an aspect, the method includes drawing fluid into the flow passage through a first one-way valve and pushing fluid out of the flow passage through a second one-way valve. In an aspect, the method includes implanting the flow pump in an eye of a patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings illustrate embodiments of the devices and methods disclosed herein and together with the description, serve to explain the principles of the present disclosure. 
           [0014]      FIG. 1  is a diagram of the front portion of an eye. 
           [0015]      FIG. 2  is a schematic diagram of an exemplary drainage device disposed on an eye according to the principles of the present disclosure. 
           [0016]      FIG. 3  is a block diagram illustrating elements of an exemplary flow controller according to one embodiment of the present disclosure. 
           [0017]      FIG. 4A  illustrates a cross-sectional, schematic side view of an exemplary drainage implant with a flexible diaphragm in a position according to one embodiment of the present disclosure. 
           [0018]      FIG. 4B  illustrates a cross-sectional, schematic side view of an exemplary drainage implant with a flexible diaphragm in a position different than in  FIG. 4A  according to one embodiment of the present disclosure. 
           [0019]      FIG. 5  illustrates a cross-sectional view of an exemplary drainage implant taken along lines  5 - 5  in  FIG. 4A  according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications to the described devices, instruments, methods, and any further application of the principles of the present disclosure are fully contemplated as would normally occur to one skilled in the art to which the disclosure relates. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure. For the sake of brevity, however, the numerous iterations of these combinations will not be described separately. For simplicity, in some instances the same reference numbers are used throughout the drawings to refer to the same or like parts. 
         [0021]    The present disclosure is directed to a flow control system for treating a medical condition, such as glaucoma, by using a heat generating resistive element within an intraocular implant to create a pumping action usable to transfer or pump fluid. In one aspect, the system may use this pumping action to adjust IOP by regulating fluid drainage through the intraocular implant, such as a glaucoma drainage device (GDD). Since the system employs a diaphragm that flexes in cycles and cooperates with check valves to generate pumping action, the system may be actuated and may recover more quickly than other types of pump systems, such as those using electrolysis to create air bubbles. Thus, the flow control systems and methods disclosed herein allow the flow control system to pump aqueous solutions to control IOP while maintaining responsiveness unachieved in traditional GDDs. 
         [0022]      FIG. 2  is a schematic diagram of an exemplary drainage device or implant  300  positioned within an eye of a patient. The drainage implant  300  is designed to regulate IOP by utilizing an adjustable smart valve or active element (e.g., without limitation, a pump) to throttle or pump fluid out of a posterior segment  178  into a drainage site. 
         [0023]    In the embodiment pictured in  FIG. 2 , the implant  300  is arranged in the eye such that three areas of pressure interact with the implant: P 1 , P 2 , and P 3 . Pressure area P 1  reflects the pressure of the posterior segment  178 , pressure area P 2  reflects the pressure of a drainage site  320 , and pressure area P 3  reflects a pressure located remotely from P 1  and P 2  (effectively reflecting atmospheric pressure). In some embodiments, pressure area P 1  reflects the pressure located in a lumen or tube that is in fluidic communication with the posterior segment  178 . 
         [0024]    In  FIG. 2 , the implant  300  includes a drainage tube  305  and a divider  310  associated with a flow controller  315 . The drainage tube  305  drains fluid from the posterior segment  178  of the eye to the drainage location  320 , which may be the suprachoroidal space  200  shown in  FIG. 1 . Other examples of a drainage location  320  include, but are not limited to: a subconjunctival space, a subscleral space, a supraciliary space, an episcleral vein, and other uveoscleral pathways. The drainage tube  305  includes an inlet tube or inlet tube portion  325 , which extends from the posterior segment  178  to the flow controller  315 , and an outlet tube or outlet tube portion  330 , which extends from the flow controller  315  to the drainage site  320 . The inlet tube  325  includes a proximal end  332  coupled to the flow controller  315  and a distal end  334  positioned within the posterior segment  178 . The outlet tube  330  includes a proximal end  335  coupled to the flow controller  315  and a distal end  340  positioned within the drainage site  320 . 
         [0025]    The flow controller  315  regulates IOP by controlling, such as by throttling or inducing the flow of fluid, through the tube  305 , from the inlet tube  325  to the outlet tube  330 . In some instances, the flow controller  315  throttles the flow of fluid through the tube  305  as a function of a pressure differential. The flow controller  315  may include components or elements, such as valves, pumps or others, described further below with reference to  FIG. 3 , that control pressure by regulating the amount of drainage flow through the implant  300 . The flow controller  315  may include any number of valves and any number of pumps, or may not include a pump or may not include a valve. In some embodiments, the flow controller  315  is an active system that is responsive to signals from a processor to increase flow, decrease flow, or to maintain a steady flow as a function of pressure differentials at pressure areas P 1 , P 2 , and P 3 . In one embodiment, it does this by actuating a pump to increase or decrease the fluid flow passage through the flow controller  315 . 
         [0026]    In addition, the flow controller  315  may incorporate pressure sensors to monitor and utilize the pressures P 1 , P 2 , and P 3  to achieve a desired IOP. In some embodiments, the implant  300  responds to the pressure differentials between the pressures sensed at P 1 , P 2 , and P 3  by sensors S 1 , S 2 , and S 3 , respectively, to control the flow controller  315  and thereby throttle the flow rate of fluid through the drainage tube  305  to control IOP. In some embodiments, the various pressure differentials across the pressure areas sensed at P 1 , P 2 , and P 3  (P 1 -P 2 , P 1 -P 3 , P 2 -P 3 ) drive the flow controller  315  and dictate the valve position or pump state to throttle the flow rate of fluid through the drainage tube  305  to control IOP. In some embodiments, the implant may include only a pressure sensor S 1 , and may be coupled with a separate drainage device that includes the remaining sensors S 2  and S 3 . Such a separate drainage device may lack a drainage tube  305  and/or a flow controller  315 . 
         [0027]    In the embodiment shown, a pressure sensor S 1  measures the pressure in the tube  305  upstream from the flow controller  315  and downstream from the posterior segment  178 . In this manner, the pressure sensor S 1  measures the pressure in the posterior segment  178 . The expected measurement discrepancy between the true posterior segment pressure and that measured by S 1  when located in a tube downstream of the posterior segment (even when located between the sclera and the conjunctiva) may be negligible. 
         [0028]    A pressure sensor S 2  is located at the drainage site  320  or in fluid communication with the drainage site  320  via the outlet tube  320 . As such, the pressure sensor S 2  may be located in the subconjunctival space, suprachoroidal space  200 , a subscleral space, a supraciliary space, an episcleral vein, or another uveoscleral pathway, for example. 
         [0029]    In some embodiments, the divider  310  acts as a barrier that separates the pressure region measured by the pressure sensor S 3  from the pressure region measured by the pressure sensor S 2 . In some embodiments, the system includes other barriers that separate the sensors S 1 , S 2 , and S 3 . These barriers may be elements of the flow controller  315  itself. In  FIG. 2 , the pressure region measured by the pressure sensor S 3  is physically separated from the pressure region measured by the pressure sensor S 2  by the divider  310 . The divider  310  is a physical structure that separates the drainage area  306  from the isolated location of pressure region measured by the pressure sensor S 3 . The divider  310  may be sutured and/or healed tissue. 
         [0030]    Generally, IOP is a gauge pressure reading—the difference between the absolute pressure in the eye (as measured by sensor S 1 ) and atmospheric pressure (as measured by sensor S 3 ). Atmospheric pressure, typically about 760 mmHg, often varies in magnitude by 10 mmHg or more depending on weather conditions or indoor climate control systems or elevation changes. In addition, the effective atmospheric pressure can vary significantly—in excess of 300 mmHg—if a patient goes swimming, hiking, riding in an airplane, etc. Such a variation in atmospheric pressure is significant since IOP is typically in the range of about 15 mmHg. Thus, for accurate monitoring of IOP, it is desirable to have pressure readings for the interior chamber of the eye (as measured by sensor S 1 ) and atmospheric pressure in the vicinity of the eye (as measured by sensor S 3 ). 
         [0031]    In one embodiment of the present invention, pressure readings are taken by the pressure sensors S 1  and S 3  simultaneously or nearly simultaneously over time so that the actual IOP can be calculated (as S 1 -S 3  or S 1 - f (S 3 ), where f(S 3 ) indicates a function of S 3 ). In another embodiment of the present invention, pressure readings taken by the pressure sensors S 1 , S 2 , and S 3  can be used to control a device that drains aqueous from the posterior segment  178 . For example, in some instances, the implant  300  reacts to the pressure differential across S 1  and S 3  continuously or nearly continuously so that the actual IOP (as S 1 -S 3  or S 1 - f (S 3 )) can be responded to accordingly. 
         [0032]    The drainage implant  300  may be shaped and configured to be implanted within the subconjunctival space, between the conjunctiva  202  and the sclera  180 . In some embodiments, the bulk of the implant  300  may be positioned within the eye in a subconjunctival space between the conjunctiva  202  and the sclera  180  with the flow controller  315  positioned such that the implant does not come into contact with the optic nerve. For example, in one embodiment, depending upon the size and shape of the implant, the implant  300  may be positioned approximately 8 to 10 mm posterior to the limbus  190  (the border between the cornea and the sclera). The drainage implant  300  may be held in place within the eye via anchoring sutures, the angle of implantation and surrounding anatomy, or by a spring force or other mechanisms that stabilize the implant  300  relative to the patient&#39;s eye. In some embodiments, the inlet tube  325  and the outlet tube  330  are coupled to the flow controller  315  at the location of the subconjunctival space, and extend from the subconjunctival space into the posterior segment  178  and the delivery site, respectively. 
         [0033]      FIG. 3  is a block diagram of an exemplary flow controller  315  forming a part of an implant implantable in an eye of a patient for the treatment of glaucoma or other conditions. The flow controller  315  is configured in a manner that provides IOP pressure control, but may also regulate and control bleb pressures, reducing complications arising from surgical implant glaucoma treatments. In  FIG. 3 , the flow controller  315  includes a power source  350 , a processor  355 , a memory  360 , a data transmission module  365 , and a flow system  370 . 
         [0034]    The power source  350  is typically a rechargeable battery, such as a lithium ion or lithium polymer battery, although other types of batteries may be employed. In addition, any other type of power cell is appropriate for power source  350 . Power source  350  provides power to the flow controller  315 , and more particularly to processor  355 . Power source can be recharged via an RFID link or other type of magnetic coupling. 
         [0035]    Processor  355  is typically an integrated circuit with power, input, and output pins capable of performing logic functions. In various embodiments, processor  355  is a targeted device controller. In such a case, processor  355  performs specific control functions targeted to a specific device or component, such as a data transmission module  365 , power source  350 , flow system  370 , or memory  360 . In other embodiments, processor  355  is a microprocessor. In such a case, processor  355  is programmable so that it can function to control more than one component of the device. In other cases, processor  355  is not a programmable microprocessor, but instead is a special purpose controller configured to control different components that perform different functions. 
         [0036]    Memory  360  is typically a semiconductor memory such as NAND flash memory. As the size of semiconductor memory is very small, and the memory needs of the implant  300  are small, memory  360  occupies a very small footprint of the flow controller  315 . Memory  360  interfaces with processor  355 . As such, processor  355  can write to and read from memory  360 . For example, processor  355  can be configured to receive data as signals from the sensors S 1 , S 2 , and S 3  ( FIG. 2 ) and write data to memory  360 . In this manner, a series of measurements that may be indicative of IOP readings can be stored in memory  360 . Processor  355  is also capable of performing other basic memory functions, such as erasing or overwriting memory  360 , detecting when memory  360  is full, and other common functions associated with managing semiconductor memory. 
         [0037]    Data transmission module  365  may employ any of a number of different types of data transmission. For example, data transmission module  365  may be an active device such as a radio. Data transmission module  365  may also be a passive device such as the antenna on an RFID tag. In this case, an RFID tag includes memory  360  and data transmission module  365  in the form of an antenna. An RFID reader can then be placed near the implant  300  to write data to or read data from memory  360 . Since the amount of data typically stored in memory  360  is likely to be small (consisting of IOP readings over a period of time), the speed with which data is transferred is not crucial. Other types of data that can be stored in memory  360  and transmitted by data transmission module  365  include, but are not limited to, power source data (e.g. low battery, battery defect), speaker data (warning tones, voices), IOP sensor data (IOP readings, problem conditions), and the like. 
         [0038]    Alternatively, data transmission module  365  may be activated to communicate an elevated IOP condition to a secondary device such as a PDA, cell phone, computer, wrist watch, custom device exclusively for this purpose, remote accessible data storage site (e.g. an internet server, email server, text message server), or other electronic device. In one embodiment, a personal electronic device uploads the data to the remote accessible data storage site (e.g. an internet server, email server, text message server). Information may be uploaded to a remote accessible data storage site so that it can be viewed in real time, for example, by medical personnel. For example, in a hospital setting, after a patient has undergone glaucoma surgery and had implant  300  implanted, a secondary device may be located next to the patient&#39;s hospital bed. Since IOP fluctuations are common after glaucoma surgery (both on the high side and on the low side which is also a dangerous condition), processor  355  can read IOP measurements made by the sensors S 1 , S 2 , and S 3 . If processor  355  determines that an unsafe IOP condition exists, data transmission module  365  can alert the patient and medical staff directly or by transmitting the unsafe readings to a secondary device. 
         [0039]    The flow system  370  is the physical structure used to control the flow of fluid through the flow controller  315 . It may include, for example, one or more pump mechanisms, valves, or other elements that help regulate the flow of fluid through the implant. 
         [0040]      FIGS. 4A and 4B  show an exemplary flow system  370  that may be used in the implant  300 , connected to the inlet tube  325  and the outlet tube  330 . The flow system  370  includes a flexible diaphragm  588  shown in  FIG. 4A  biased inward and shown in  FIG. 4B  biased outward. The flexible diaphragm  588  may be, for example, a Parylene or glass membrane, and may have a thickness ranging from 1 to 15 μm, although thicker and thinner diaphragms are contemplated. In the exemplary embodiment shown, the flow system  370  includes an upper housing  570  forming a part of a heating chamber  580 , a lower housing  571  forming a part of a flow passage  590 , an entrance port  572  in communication with the flow passage  590 , and an exit port  574  in communication with the flow passage  590 . The flexible diaphragm  588  is disposed between and separates the heating chamber  580  from the flow passage  590 . Here, the entrance port  572  is in fluid communication with the inlet tube  325 , and the exit port  574  is in fluid communication with the outlet tube  330 . In some embodiments the outlet tube  330  is not present in the flow system  370 , and the exit port  574  exits directly to the drainage site, which may include a bleb. 
         [0041]    The upper and lower housings  570 ,  571 , along with other aspects of the implant  300  and flow system  370  may be formed using MEMS (Micro-Electro-Mechanical Systems) technology. 
         [0042]    In this embodiment, the flow system  370  is a pump  576  formed by the flexible diaphragm  188 , a one-way check valve  592  adjacent the exit port  574 , and a one-way check valve  594  adjacent the entrance port  572 . Here, the check valves  592 ,  594  are formed of deformable cantilevers that prevent backflow. This ensures that drainage fluid travels one direction from the posterior segment of the eye toward the drainage site. It also ensures that fluid at the bleb does not reenter the flow system  370 . Other embodiments include other types of check valves, such as ball valves, spring valves, reed valves, and others. Some embodiments include tapered openings at the flow passage entrance that decreases in cross-sectional area (according to flow direction) and the check valve  592  at the flow passage exit may include a narrow opening that increases in cross-sectional area. Accordingly, because of the shape of the openings, fluid flow will tend to flow easier out the exit port than out the entrance port—even in the absence of any movable parts such as flapper or reed valves. 
         [0043]    Within the heating chamber  580 , the flow system  315  includes an actuator fluid  582  that may be a liquid or gas, and a heating element  584 . In some embodiments, the heating element  584  may be disposed adjacent the flexible diaphragm  588 , and in some embodiments, may be in contact with the flexible diaphragm  588  to provide heat to the flow system  315 . In the embodiment shown, the heating element is disposed adjacent the housing permitting the flexible diaphragm to flex without being inhibited by the possibly more rigid heating element. The heating element  584  can be powered by the power source under the control of the processor  355 . 
         [0044]      FIG. 5  shows a bottom view of the flexible diaphragm  588  and the heating element  584  on the upper housing  570 , taken along lines  5 - 5  in  FIG. 4A . With reference to  FIGS. 4A, 4B, and 5 , the flexible diaphragm  588  is disposed over the upper housing  570 , which has a circular void that forms the heating chamber  580 . The diaphragm  588  may deflect into or out of the heating chamber  580 , as is apparent in  FIGS. 4A and 4B . The resistive heating element  584  extends across the heating chamber  580 , and is in electrical connection with feed wires  596  that extend beyond the heating chamber  580  and diaphragm  588  to connect to the power source  350 . 
         [0045]    The fluid in the chamber may be a gas, such as air, or may be a fluid or gel. The fluid is selected to expand when subjected to heat to force the diaphragm to displace from a first position to a second position, such as from the position in  FIG. 4B  to the position shown in  FIG. 4A . For example, as the temperature of the fluid in the heating chamber  580  expands, the volume of the flow passage  590  decreases. This forces fluid in the flow passage  590  to exit the flow passage  590  though the one-way check valve  592  toward the drainage site  320 . As the temperature of the heating element  584  decreases, the temperature of the fluid in the heating chamber  580  decreases, and the volume correspondingly decreases. This causes the diaphragm  588  to move from its position in the flow passage  590 , as is shown in  FIG. 4A  toward the heating chamber  580 , increasing the volume of the flow passage as is shown in  FIG. 4B . Accordingly, fluid may be drawn though the one way check valve  594  from the inlet tube  325 . 
         [0046]    The heating element may be a resistive heating element that converts electrical current to heat, and may be operated to gradually increase the volume of the pump chamber  429  as the fluid expands or to rapidly increase the volume of the pump chamber  429 . When operated to slowly heat the fluid in the heating chamber, fluid flow from the flow passage can be gradual. When operated to rapidly increase the volume of the flow passage, fluid flow from the flow passage can be relatively rapid. This rapid movement of fluid can serve to clear blockages in the tubes or the drainage location. When the drainage site is a bleb, the rate at which fluid is expelled to the bleb can be controlled to maintain the bleb at a desirable size and/or pressure. In other words, by controlling fluid flow rates to the drainage site, the drainage site can be maintained in an optimal fashion. 
         [0047]    In some embodiments, the heating element is simply turned off or not powered to permit the fluid to cool and gradually decrease in volume in order to reduce the volume of the heating chamber  580 . When the heating element operates to gradually decrease the volume of the heating chamber  580 , fluid flow from the inlet tube  325  into the flow passage  590  can be gradual. Both the speed of the deflection and the overall cycle frequency can be important in driving the flow. 
         [0048]    In some embodiments, activation of the flow system  370  is based on the flow controller  315  comprising one or more electronic pressure sensors that may be located in pressure areas P 1 , P 2 , and/or P 3  (shown in  FIG. 2 ). If IOP is high, the flow controller  315  may determine that pumping action is desired in order to lower the IOP. To do this, electrical current is passed through the resistive heating element  584  to change the temperature of the fluid in the heating chamber  580 . This in turn increases the volume of fluid in the heating chamber  580 . To accommodate the increase in volume, the flexible diaphragm  588  expands into the flow passage  590 , displacing the drainage fluid to force fluid out of the exit port  574 . The current may then be stopped and the heating element may be allowed to cool to an ambient temperature, causing the flexible diaphragm to return to its original position. The cycle may then be repeated if additional pumping is determined to be desired. Accordingly, the pump  514  may be cycled or actuated a plurality of times to force the drainage fluid past the pump into the drainage site. 
         [0049]    Persons of ordinary skill in the art will appreciate that the embodiments encompassed by the present disclosure are not limited to the particular exemplary embodiments described above. In that regard, although illustrative embodiments have been shown and described, a wide range of modification, change, and substitution is contemplated in the foregoing disclosure. It is understood that such variations may be made to the foregoing without departing from the scope of the present disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the present disclosure.