Abstract:
Disclosed herein are an apparatus, a system, and a method to monitor drainage from a first region of a patient to a second region. The apparatus comprises pressure sensors configured to measure the pressures of the first and second regions, a flow system to regulate drainage of fluid from the first region to the second region, a memory having a stored pressure drop across the flow system; and a processor associated with the memory and configured to compare the first pressure, the second pressure, and the stored pressure drop threshold and selectively generate control signals based on the comparisons. In some instances, the apparatus further comprises an alarm, and the processor is configured to generate the control signals that trip the alarm when a pressure drop exceeds the stored pressure drop threshold.

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. Most forms of glaucoma result when the intraocular pressure (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. 
         [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 trabecular meshwork and the uveoscleral pathways, both of which contribute to the aqueous drainage system. The delicate balance between the production and drainage of aqueous humor determines the eye&#39;s IOP. 
         [0004]      FIG. 1  is a diagram of the front portion of an eye 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 , and the anterior chamber  170  are pictured. Anatomically, the anterior segment of the eye includes the structures that cause elevated IOP which may lead to glaucoma. Aqueous fluid is produced by the ciliary body  140  that lies beneath the iris  130  and adjacent to the lens  110  in the anterior chamber  170  of the anterior segment of the eye. 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 angle of the anterior chamber  170 , which extends circumferentially around the eye, contains structures that allow the aqueous humor to drain. The trabecular meshwork  150  is commonly implicated in glaucoma. The trabecular meshwork  150  extends circumferentially around the anterior chamber. 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 beyond 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 two arrows in the anterior segment of  FIG. 1  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. 
         [0005]    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 chamber of the eye to a drainage site, relieving pressure in the eye and thus lowering IOP. These devices are generally passive devices and do not provide a smart, interactive control of the amount of flow through the drainage tube. 
         [0006]    The system and methods disclosed herein overcome one or more of the deficiencies of the prior art. 
       SUMMARY 
       [0007]    In one exemplary aspect, the present disclosure is directed to an apparatus for treatment of a medical condition of a patient to monitor drainage from a first region of a patient to a second region. The apparatus comprises a first pressure sensor, a second pressure sensor, a flow system, a memory, and a processor. The first pressure sensor is configured to measure a first pressure of the first region. The second pressure sensor is configured to measure a second pressure of the second region. The flow system regulates drainage of fluid from the first region to the second region. The memory has a stored pressure drop threshold across the flow system, and the processor is associated with the memory. The processor is configured to compare the first pressure, the second pressure, and the stored pressure drop threshold and selectively generate control signals based on the comparisons. 
         [0008]    In one aspect, the processor is configured to calculate a pressure differential between the first pressure and the second pressure and compare the pressure differential with the stored pressure drop threshold to determine whether the pressure differential is within an acceptable range. 
         [0009]    In another aspect, the apparatus further comprises an alarm, wherein the control signals trip the alarm, the processor being configured to generate the control signals when the processor determines that the pressure differential is not within an acceptable range. 
         [0010]    In another aspect, the apparatus further comprises an accessory device apart from the flow system, wherein the alarm is carried on the accessory device. 
         [0011]    In another aspect, the stored pressure drop threshold comprises an upper pressure drop threshold and a lower pressure drop threshold. 
         [0012]    In another exemplary aspect, the present disclosure is directed to a control system for treatment of an ocular condition of a patient to ensure drainage from an anterior chamber of the eye to a drainage location. The control system comprises a first pressure sensor, a second pressure sensor, a flow system, a memory, and a processor. The first pressure sensor is configured to detect a pressure representative of an anterior chamber of the eye. The second pressure sensor is configured to detect a pressure representative of the drainage location. The flow system regulates drainage of fluid from the anterior chamber to the drainage location. The memory has a stored pressure drop threshold across the flow system, the stored pressure drop threshold comprising an upper pressure drop threshold and a lower pressure drop threshold, and the processor is associated with the memory. The processor is configured to compare the first pressure, the second pressure, and the stored pressure drop threshold and selectively generate control signals based on the comparisons. In one aspect, the control system further comprises an alarm, wherein the control signals trip the alarm, and the processor is configured to generate the control signals when a pressure drop across the flow system is not within an acceptable range defined by the upper pressure drop threshold and the lower pressure drop threshold. 
         [0013]    In another aspect, the control system further comprises an accessory device apart from the flow system, wherein the alarm is carried on the accessory device. 
         [0014]    In another exemplary aspect, the present disclosure is directed to a method comprising: storing a pressure drop threshold in a memory, the pressure drop threshold comprising an upper pressure drop threshold and a lower pressure drop threshold, measuring a first pressure representative of the a region of an eye, measuring a second pressure representative of a second region of an eye, communicating the first and second pressures to a processor, calculating a pressure differential between the first and second pressures with the processor, comparing the pressure differential and the stored pressure drop threshold, and activating an alarm when the pressure differential exceeds the upper pressure drop threshold or when the pressure differential is less than the lower pressure drop threshold. 
         [0015]    In one aspect, the method comprises storing a predetermined time interval in the memory, and evaluating if the pressure differential exceeds the upper pressure drop threshold or is less than the lower pressure drop threshold over the predetermined time interval. 
         [0016]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    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. 
           [0018]      FIG. 1  is a diagram of the front portion of an eye. 
           [0019]      FIG. 2  is a block diagram of an exemplary IOP control system according to the principles of the present disclosure. 
           [0020]      FIG. 3  is a schematic diagram of an exemplary implant including the IOP control system of  FIG. 2  disposed on an eye according to the principles of the present disclosure. 
           [0021]      FIG. 4  is a schematic diagram of the exemplary implant shown in  FIG. 3  including various clogs in the IOP control system. 
           [0022]      FIG. 5  is a flow chart of an exemplary method of indicating a problem with the IOP control system, such as a clog, according to one embodiment consistent with the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    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. 
         [0024]    The present disclosure is directed to clog detection within a flow control system for treating a medical condition, such as glaucoma. In one aspect, the system adjusts IOP by regulating fluid drainage through an implant such as a glaucoma drainage device (GDD). The system directs fluid drainage from the anterior chamber of an eye to a drainage site through a drainage tube. In one aspect, the system includes stored pressure drop thresholds across the flow control system that are generally predetermined based on the structure of the flow control system. The system monitors the actual pressure difference between the anterior chamber and the drainage site to ensure that it lies within the stored pressure drop thresholds when the flow control system is in an open condition. If not, the system alerts the user and/or the health care provider to a possible problem in the system preventing the drainage of fluid from the anterior chamber to the drainage site. Possible problems include, by way of non-limiting example, a clog within the system or a ruptured drainage site. If a problem is detected, the flow control system may power down to conserve energy. Prompt awareness on the part of the user and/or the health care provider to an ineffective and/or clogged flow control system may result in better treatment, less complications, a more consistent recovery, and ultimately a better patient outcome. 
         [0025]      FIG. 2  is a block diagram of an exemplary IOP monitoring system  190 . The IOP monitoring system  190  includes an IOP control system  200  that is usable as a part of an implant  300  (shown in  FIG. 3 ) in an eye of a patient for the treatment of glaucoma or other conditions and includes an accessory device  214 . In  FIG. 2 , the IOP control system  200  includes a power source  202 , an IOP sensor system  204 , a processor  206 , a memory  208 , a data transmission module  210 , and a flow system  212 . 
         [0026]    The power source  202  is typically a rechargeable battery, such as a lithium ion or lithium polymer battery, although other types of power sources may be employed, such as a capacitive bank. In addition, any other type of power cell is appropriate for power source  202 . Power source  202  provides power to the system  200 , and more particularly to processor  206 . In one embodiment, the power source can be recharged via inductive coupling such as an RFID link or other type of electromagnetic coupling. 
         [0027]    The IOP sensor system  204  includes pressure sensors P 1 , P 2 , and P 3 , which are distributed to detect pressures at different locations about the IOP control system  200 . The IOP sensor system  204  will be described in further detail below. 
         [0028]    The processor  206  is typically an integrated circuit with power, input, and output pins capable of performing logic functions. In various embodiments, the processor  206  is a targeted device controller. In such a case, the processor  206  performs specific control functions targeted to a specific device or component, such as the data transmission module  210 , the power source  202 , the sensor system  204 , the flow system  212 , or the memory  208 . In other embodiments, the processor  206  is a microprocessor. In such a case, the processor  206  is programmable so that it can function to control more than one component of the device and/or perform calculations to evaluate the status or functionality of various components of the device. For example, in one embodiment, the processor  206  is able to read data from the IOP sensor system  204  and perform calculations using the data to ensure that the flow system  212  is performing properly. In other cases, the processor  206  is not a programmable microprocessor, but instead is a special purpose controller configured to control different components that perform different functions. 
         [0029]    The memory  208  is typically a semiconductor memory such as RAM, FRAM, or flash memory. The memory  208  interfaces with the processor  206 . As such, the processor  206  can write to and read from the memory  208 . For example, the processor  206  can be configured to read data from the IOP sensor system  204  and write that data to the memory  208 . In the embodiments shown, stored pressure drop thresholds  209  across the flow system  212  are stored in the memory  208  for access, calculation, and comparison by the processor  206 . The processor  206  is also capable of performing other basic memory functions, such as erasing or overwriting the memory  208 , detecting when memory  208  is full, and other common functions associated with managing memory. 
         [0030]    The data transmission module  210  may employ any of a number of different types of data transmission. For example, the data transmission module  210  may be an active device such as a radio. The data transmission module  210  may also be a passive device such as the antenna on an RFID tag. In one embodiment, an RFID tag includes the memory  208  and the data transmission module  210  in the form of an antenna. An RFID reader can then be placed near the system  200  to write data to or read data from the memory  208 . Therefore, data such as the stored pressure drop thresholds  209  across the flow system  212  may be transmitted to the memory via the data transmission module, along with any selection of or adjustment to the stored pressure difference. Other types of data that can be stored in the memory  208  and transmitted by the data transmission module  210  include, but are not limited to, IOP measurement data, power source data (e.g. low battery, battery defect), speaker data (warning tones, voices), pressure sensor data (IOP readings, calculations), time stamp data, IOP regulation setpoint (or predetermined IOP setpoint or IOP target value), and the like. In some embodiments, the data transmission module  210  may be activated to communicate data to the accessory device  214 . 
         [0031]    The accessory device  214  is an external device such as, by way of non-limiting example, 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. For example, after a patient has undergone glaucoma surgery and had the flow control system  200  implanted, the accessory device  214  may be carried by the patient or periodically positioned near the patient. The processor  206  can read and compare pressure measurements made by the implanted sensor system  204 . If the processor  206  reads data indicative of an undesirable and/or unsafe condition while the flow control system is open, such as, by way of non-limiting example, a clog or blockage in the IOP control system  200 , the data transmission module  225  can transmit the relevant data to the accessory device  214 , which utilizes an electronic notification or alarm  215  to alert the patient to the undesirable and/or unsafe condition. In other embodiments, the data transmission module  225  may regularly transmit data from the IOP sensor system  204  to the accessory device  214 , which is able to perform calculations using the data to ensure that the IOP control system  200  is performing properly. In such embodiments, if the accessory device  214  determines that the presence of an undesirable and/or unsafe condition, the alarm  215  is activated to alert the patient to the condition. 
         [0032]    The alarm  215  may comprise a visual, tactile, and/or audible signal that alerts the patient to a potential problem with the IOP control system  200  and/or the flow system  212 . By way of non-limiting example, in some instances, the problem may comprise a clog or blockage in their implant. In other instances, the problem may comprise a ruptured drainage site, such as a ruptured bleb. In other instances, the alarm  215  may signal a correction of the patient&#39;s underlying IOP elevation, and an end to the need for operation of the IOP control system  200 . The alarm  215  may spur the patient to seek immediate medical attention to correct the problem, thereby limiting the potential complications of prolonged exposure to a malfunctioning IOP control system. For example, an alarm alerting a patient to a clogged GDD may prompt the patient to seek immediate medical attention, thereby limiting the exposure of the optic nerve to elevated IOP pressures and increasing the probability of limiting further progression of their glaucoma. 
         [0033]    In one embodiment, the accessory device  214  comprises a personal electronic device that uploads relevant data to a remote accessible data storage site (e.g., an internet server, email server, text message server) via wired or wireless communication. Information may be uploaded to a remote accessible data storage site so that it can be viewed in real time, for example, by healthcare professionals that are not present at the patient&#39;s side. Thus, both the patient and his or her healthcare professionals may be alerted to a problem with the IOP control system, such as a potential blockage or clog within the IOP control system or a ruptured drainage site, prior to the patient&#39;s next scheduled examination. 
         [0034]    In one embodiment, the accessory device  214  comprises a personal electronic device used for both recharging of the power source  202  and data collection from the sensor system  204 . Such an embodiment allows the step of checking the functionality of the implantable control system  200  to be integrated with the patient&#39;s routine steps of recharging the implant  300  and collecting data from the implant  300 . Therefore, when the patient routinely recharges their implant  300  or collects data from the implant  300 , the patient can also check the functional status of the implantable control system  200  by observing whether the alarm  215  has been activated or not. For example, in instances where the patient routinely recharges and collects data from the implant  300  every day, the accessory device  214  will also provide the patient with a specific daily reminder of the functional state of their implant, i.e., depending upon whether the alarm  215  is activated (indicating a potential problem) or not. If the alarm  215  has been activated, the patient will be alerted to a potential problem within the IOP control system  200 , thereby prompting the patient to seek immediate medical attention, which may reduce the complications arising from prolonged exposure to an undesirably elevated IOP. 
         [0035]    The pressure/flow system  212  may include components or elements that control pressure by regulating the amount of drainage flow. In the example shown, the flow system  212  includes a valve and a pump. The flow system 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 system  212  is an active system that is responsive to signals from the processor  206  to increase flow, decrease flow, or to maintain a steady flow as a function of pressure differentials across the valve system. In one embodiment, it does this by maintaining a valve setting at a consistent setting, or increasing or decreasing the amount that the valve is open. In such embodiments, as described further below is relation to  FIG. 5 , an activated alarm  215  may indicate a resolution of the patient&#39;s elevated IOP, which may necessitate removal or deactivation of the IOP control system. The IOP sensor system  204  is described below with reference to  FIG. 3 . 
         [0036]      FIG. 3  is a diagram of the exemplary IOP control system  200  as a part of the implant  300  implanted within an eye of a patient. In this example, the implant  300  includes a drainage tube  302  and a divider  305  associated with components of the control system  200 . For example, the flow system  212  and the pressure sensors of the IOP sensor system  204  are identified in  FIG. 3 . In particular, the exemplary IOP sensor system  204  includes three pressure sensors, P 1 , P 2 , and P 3  (also shown in  FIG. 2 ). Pressure sensor P 1  is located in or is in fluidic communication with the anterior chamber (labeled  170 ), pressure sensor P 2  is located at a drainage site (e.g.,  306  in  FIG. 3 ) that may be in the subconjunctival space, and pressure sensor P 3  is located remotely from P 1  and P 2  in manner to measure atmospheric pressure. In some embodiments, pressure sensor P 1  is located in a lumen or tube that is in fluid communication with the anterior chamber. 
         [0037]    Pressure sensors P 1 , P 2 , and P 3  can be any type of pressure sensors suitable for implantation in the eye. They each may be the same type of pressure sensor, or they may be different types of pressure sensors. For example, pressure sensors P 1  and P 2  may be the same type of pressure sensor (implanted in the eye), and pressure sensor P 3  may be a different type of pressure sensor (in the vicinity of the eye). 
         [0038]    The IOP control system  200  responds to the pressure differentials between the pressures sensed by sensors P 1 , P 2 , and P 3  to control the flow system  212  and thereby throttle the flow rate of aqueous humor through the drainage tube  302  to control IOP. In some embodiments, the various pressure differentials across the pressure areas sensed by P 1 , P 2 , and P 3  (P 1 -P 2 , P 1 -P 3 , P 2 -P 3 ) drive the flow system  212  and dictate the valve position or pump state to throttle the flow rate of aqueous humor through the drainage tube  302  without requiring external power at the flow system  212  to control IOP. 
         [0039]    The drainage tube  302  drains aqueous humor from the anterior chamber  170  of the eye to the drainage location  306 , which may be placed at any of numerous locations within the eye. For example, some tubes are arranged to shunt aqueous from the anterior chamber  170  to the subconjunctival space thus forming a bleb under the conjunctiva or alternatively, to the subscleral space thus forming a bleb under the sclera. Other tube designs shunt aqueous humor from the anterior chamber to the suprachoroidal space, the supraciliary space, the juxta-uveal space, or to the choroid, forming blebs in those respective locations. In other applications, the drainage tube shunts aqueous humor from the anterior chamber to Schlemm&#39;s canal, a collector channel in Schlemm&#39;s canal, or any of a number of different blood vessels like an episcleral vein. In some examples, the drainage tube even shunts aqueous humor from the anterior chamber to outside the conjunctiva. Each of these different anatomical locations to which aqueous is shunted is an example of a drainage location  306 . Other examples of a drainage location  306  include, but are not limited to: a subconjunctival space, a suprachoroidal space, a subscleral space, a supraciliary space, Schlemm&#39;s canal, a collector channel, an episcleral vein, and an uveo-scleral pathway. 
         [0040]    The flow system  212  throttles the flow of aqueous humor through the tube  302 , from a drainage tube inlet  303  to a drainage tube outlet  304 . In some instances, the flow system  212  throttles the flow of aqueous humor through the tube  302  as a function of a pressure differential. In the embodiment shown, the pressure sensor P 1  measures the pressure in the tube  302  upstream from the flow system  212  and downstream from the anterior chamber  170 . In this manner, pressure sensor P 1  measures the pressure in the anterior chamber  170 . The expected measurement discrepancy between the true anterior chamber pressure and that measured by P 1  when located in a tube downstream of the anterior chamber (even when located between the sclera and the conjunctiva) is very minimal. For example, Poiseuille&#39;s law for pipe flow predicts a pressure drop of 0.01 mmHg across a 5-millimeter long tube with a 0.300 millimeter inner diameter for a flow rate of 3 microliters per minute of water. Therefore, because there is almost no pressure difference between the anterior chamber  170  and the interior of the tube  302  that is in fluid contact with the anterior chamber  170 , the pressure sensor P 1  effectively measures the pressure of the anterior chamber  170 . 
         [0041]    Pressure sensor P 2  is located at the drainage site  306 . As such, pressure sensor P 2  may be located in a pocket, such as a bleb, that generally contains aqueous or in communication with such a pocket, via a tube for example, and is in a wet location  306 . The drainage site  306  may be, for example, in a subconjunctival space, a suprachoroidal space, a subscleral space, a supraciliary space, Schlemm&#39;s canal, a collector channel, an episcleral vein, and an uveo-scleral pathway, among other locations in the eye. 
         [0042]    In some embodiments, the divider  305  acts as a barrier that separates the pressure sensor P 3  from the pressure sensor P 2 . In some embodiments, the system includes other barriers that separate the sensors P 1 , P 2 , and P 3 . These barriers may be elements of the system itself. In  FIG. 3 , the pressure sensor P 3  is physically separated from the pressure sensor P 2  by the divider  305 . The divider  305  is a physical structure that separates the drainage area  306  from the isolated location of P 3 . In some embodiments, the divider  305  separating anterior chamber pressure sensor P 1  and the drainage site pressure sensor P 2  includes physical components of the flow system  212 , such as parts of a housing. Note that the divider  305  may take many forms, such as, but not limited to, a tube connected to the sensor P 3  that is routed to a site representative of atmospheric pressure (and away from and fluidly independent of the drainage site). The drainage site sensor P 2  may then reside on the IOP control system  200  in direct contact with the drainage site. 
         [0043]    Generally, IOP is a gauge pressure reading—the difference between the absolute pressure in the eye (as measured by sensor P 1 ) and atmospheric pressure (as measured by sensor P 3 ). Atmospheric pressure, typically about 760 mm Hg, often varies in magnitude by 10 mmHg or more depending on weather conditions or indoor climate control systems. 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 mm Hg. Thus, for accurate monitoring of IOP, it is desirable to have pressure readings for the anterior chamber (as measured by sensor P 1 ) and atmospheric pressure in the vicinity of the eye (as measured by sensor P 3 ). 
         [0044]    In one embodiment of the present invention, pressure readings are taken by pressure sensors P 1  and P 3  simultaneously or nearly simultaneously over time so that the actual IOP can be calculated (as P 1 -P 3  or P 1 - f (P 3 ), where f(P 3 ) indicates a function of P 3 ). The pressure readings of P 1  and P 3  (as well as P 2 ) can be stored in the memory  208  by the processor  206 . They can later be read from memory so that actual IOP over time can be interpreted by a healthcare professional. 
         [0045]    In another embodiment of the present invention, pressure readings taken by the pressure sensors P 1 , P 2 , and P 3  can be used to control a device that drains aqueous from the anterior chamber  170 . For example, in some instances, the IOP control system  200  reacts to the pressure differential across P 1  and P 3  continuously or nearly continuously so that the actual IOP (as P 1 -P 3  or P 1 - f (P 3 )) can be responded to accordingly. 
         [0046]    In one exemplary aspect, the present disclosure is directed to a system that utilizes the pressure measurements from the sensors P 1  and P 2  and the stored pressure drop thresholds  209  to evaluate the functionality of the IOP control system  200  and alert the patient to potential problems with the flow control system  200 . For example, a potential problem that can arise is the clogging of the implant  300 , as indicated in  FIG. 4 . Clogs or blockages within the IOP control system  200  may arise from a variety of medical conditions, especially in the early postoperative period. For example, clogs within the drainage tube  302  or the flow system  212  may arise from blood, vitreous, fibrin, iris incarceration, or buildup of other cellular debris. 
         [0047]    As described above, the IOP control system  200  includes the predetermined pressure drop thresholds  209  across the flow system  212 . The pressure drop represents the difference in pressure between the pressures measured by P 1  and P 2 , caused by the resistance to flow through the drainage tube  302  and the flow system  212 . The stored pressure drop thresholds  209  are generally predetermined by the structural characteristics of the flow system  212  and the flow demands on the system. In particular, the pressure drop across the flow control system  212  is determined as a function of the flow rate through the drainage tube  302  and the geometry of the flow control system  212 . For example, as the flow rate increases, the pressure drop across the flow control system  212  increases proportionately, and as the flow rate decreases, the pressure drop across the flow control system  212  decreases proportionately. 
         [0048]    Thus, in a passive flow control system where the base IOP setpoint does not change, the stored pressure drop thresholds  209  define the bounds of a predetermined range of acceptable values for the pressure drop across the flow control system. In active flow control systems, however, where the base IOP setpoint may be intentionally manipulated, the pressure drop thresholds  209  across the flow system  212  may be adjusted to a degree. In some embodiments, the pressure drop threshold  209  may comprise a discrete pressure value instead of a list of values. In some instances, the stored pressure drop thresholds  209  may be selected by a health care provider for utilization by the processor  208 . For example, in some embodiments, the healthcare provider may adjust the stored pressure drop thresholds  209  while activating the flow control system. In some embodiments, the stored pressure drop thresholds  209  may be modified by the healthcare provider throughout the use of the implanted system. 
         [0049]      FIG. 4  illustrates a situation where the implant  300  contains one or more blockages or clogs  310  along the drainage path of the aqueous humor. As shown, the clogs  310  may be located anywhere along the drainage path of the aqueous humor extending from the inlet  303  to the outlet  304 . For example, by way of non-limiting example, the clog  310   a  is located near the drainage tube inlet  303 , the clog  310   b  is located within the drainage tube  302  and proximal to the flow system  212 , the clog  310   c  is located within the flow system  212 , the clog  310   d  is located within the drainage tube  302  and distal to the flow system  212 , and clog  310   e  is located at the drainage tube outlet  304 . Clogs within the drainage tube  302  and the flow system  212  increase the resistance to flow from the inlet  303  to the outlet  304 , thereby increasing the pressure proximal to the clog (as measured by the sensor P 1 ) and decreasing the pressure distal to the clog (as measured by the sensor P 2 ). 
         [0050]    In an exemplary embodiment, the IOP control system  200  disclosed herein can detect such clogs within the system by comparing the measured pressures from sensors P 1  and P 2  with each other and with the stored pressure drop threshold  209 . A flow chart  400  shown in  FIG. 5  represents an exemplary clog detection algorithm employed by the IOP control system  200 . For ease of description, the pressure measured by sensor P 1  will be referred to as pressure p 1  and the pressure measured by sensor P 2  will be referred to as pressure p 2 . 
         [0051]    The relationship between pressures p 1  and p 2  while the valve system  212  is in an open condition is generally described by the following equation: the pressure drop across the valve system  212 , ΔP V , equals the difference between pressures p 1  and p 2  (i.e., ΔP V =p 1 −p 2 ). The stored pressure drops  209  comprise a lower pressure drop threshold  209   a  and an upper pressure threshold  209   b . In other words, the acceptable range of pressure drop values is bounded by the lower pressure drop threshold  209   a , ΔP L , and the upper pressure drop threshold  209   b,  ΔP U . Therefore, by utilizing the pressure sensors P 1  and P 2 , and comparing the pressure drop ΔP V  with the stored pressure drop thresholds  209   a  and  209   b  (i.e., ΔP L  and ΔP U ), the IOP control system  200  may determine if a clog or blockage exists within the implant  300 . For example, if the valve system  212  of the implant  300  is in an open condition and ΔP V &gt;ΔP U  or ΔP V &lt;ΔP L , there may be a clog within the implant  300 , either in the drainage tube  302  or in the flow system  212 , that is preventing the flow of aqueous humor from the anterior chamber  170  to the drainage site  306 , or the bleb has been breached and aqueous humor is draining freely from the bleb. In another situation where the pressure drop ΔP V  may lie outside of the range defined by ΔP L  and ΔP U , p 2  may be approaching p 1  because the bleb is severely scarred or fibrosed. In some embodiments, the flow control system may track the length of time required for p 1  to meet a target IOP value, and if the length of time exceeds a certain predetermined time, the system may be alerted to either failed valve actuation or a forming or formed blockage within the flow control system. 
         [0052]      FIG. 5  shows a flow chart representing an exemplary method of detecting an abnormal pressure drop and alerting a patient and/or healthcare provider of the condition. The method may be carried out by the IOP monitoring system  190  shown in  FIG. 2 . The method begins at a step  410 , where the IOP control system  200  is activated and begins to regulate flow of aqueous humor through the drainage tube  302  from the anterior chamber  170  toward the drainage site  306 . At step  412 , the pressure sensors P 1  and P 2  acquire pressure measurements p 1  and p 2  from their respective positions within the IOP control system  200 . In particular, as shown in  FIG. 3 , the sensor P 1  measures the pressure p 1  representing the pressure of the anterior chamber  170  and the sensor P 2  measures the pressure p 2  of the drainage site  306 . At step  414 , the detected pressures p 1  and p 2  are transmitted or otherwise communicated from the sensors P 1  and P 2  to the processor  206 . 
         [0053]    At step  416 , the processor  206  accesses the stored pressure drop thresholds  209  from the memory  208  for comparison with the measured pressures p 1  and p 2 . As described above in relation to  FIG. 2 , the stored pressure drop thresholds  209  (i.e., pressure drop thresholds  209   a,  or ΔP L , and  209   b,  or ΔP U ) are stored in the memory  208  for use in the exemplary clog detection algorithm or pressure comparison method depicted in the flow chart  400 . The IOP control system  200  may include a selected set of stored pressure drop thresholds  209  preloaded into the memory  208 . This pre-selected or predetermined set can be established during manufacturing of the IOP control system  200  or programmed into the memory  208  by the user (e.g., a healthcare professional), and represents a set of pressure drop thresholds corresponding to typical known operating conditions for the system  200 . 
         [0054]    In the pictured embodiment, the processor  206  performs the steps  418 - 438 . In some embodiments, the pressure measurements from sensors P 1  and P 2  and the stored pressure drop threshold  209  are transmitted to the accessory device  214 , which performs the steps  418 - 438 . 
         [0055]    The processor  206  is configured to calculate a pressure differential between the pressures p 1  and p 2  and to compare the pressure differential with the stored pressure drop thresholds  209   a  and  209   b  to determine whether the pressure differential is within an acceptable range. The acceptable range of pressure differentials may vary between different IOP control systems. In one example, the acceptable range of pressure differentials (ΔP V ) may range from 2 mmHg to 5 mmHg. Such a range is merely exemplary in nature, and it not intended to be limiting. In particular, the processor  206  may be configured to determine that the pressure differential is not within an acceptable range if the pressure differential ΔP V  between the pressures p 1  and p 2  is greater than the stored pressure drop threshold  209   b,  ΔP U . For example, in some embodiments, the ΔP U =20 mmHg. In one example where the valve has been actuated open for a significant amount of time, the stored pressure drop threshold ΔP U =20 mmHg, the IOP setpoint=10 mmHg, p 1 =780 mmHg, p 2 =752 mmHg and p 3 =750 mmHg. In this example, the processor  206  would determine that the IOP (p 1 -p 3 )=30 mmHg, and p 1 -p 2  (ΔP V )=28 mmHg. The high ΔP V  value (ΔP V &gt;ΔP U ) indicates that a possible blockage has occurred. 
         [0056]    The processor  206  may be configured to determine that the pressure differential ΔP V  is not within an acceptable range if the pressure differential ΔP V  between the pressures p 1  and p 2  is less than the stored pressure drop threshold  209 , ΔP L . In another example, the stored threshold pressure drop ΔP L =1 mmHg, the IOP setpoint=10 mmHg, p 1 =755 mmHg, p 2 =754.5 mmHg, and p 3 =750 mmHg. In this example, the processor  206  would determine that the IOP (p 1 -p 3 )=5 mmHg, and p 1 -p 2  (ΔP V )=0.5 mmHg. The low ΔP V  value (ΔP V &lt;ΔP L ) indicates that a problem has occurred, and the very low IOP value of 5 mmHg (IOP&lt;&lt;IOP setpoint) indicates that the eye is in a state of hypotony. Such pressure differentials and pressures are merely exemplary in nature, and are not intended to be limiting. 
         [0057]    In the pictured embodiment, at step  418 , the processor  206  calculates the pressure differential ΔP V  between pressures p 1  and p 2 , i.e., p 1  minus p 2 , when the flow system  212  is in an open condition. At step  420 , the actual pressure differential ΔP V  between pressures p 1  and p 2  is compared to the stored pressure drop thresholds  209   a  and  209   b  (i.e., ΔP L  and ΔP U , respectively). The comparisons may be made by the IOP control system  200  (e.g., by the processor  206  or the accessory device  214 ) according to the stored pressure drop thresholds  209  installed into the memory  208  at manufacture or entered by the user. Theoretically, the user would be able to input any stored pressure drop thresholds  209   a  and  209   b  that fall within the capabilities of the system. 
         [0058]    If the pressure differential ΔP V  between pressures p 1  and p 2  is within the acceptable range of pressure differentials defined by the stored pressure drop thresholds  209 , then the implant  300  is likely draining aqueous fluid from the anterior chamber  170  (shown in  FIG. 3 ) to the drainage site  306  as intended. Thus, if, at step  422 , the pressure differential ΔP V  is within the acceptable range defined by the stored pressure drop thresholds  209 , then the process returns to step  412 . If, however, the pressure differential ΔP V  between pressures p 1  and p 2  is outside of the acceptable range of pressure differentials defined by the stored pressure drop thresholds  209  while the valve system  212  is in an open condition, the implant  300  may not be operating correctly, and in particular the drainage tube  302  and/or the valve system  212  may be clogged (as shown in  FIG. 4 ). Thus, if, at step  424 , the pressure differential ΔP V  between pressures p 1  and p 2  is outside the range of acceptable pressure differentials defined by the stored pressure drop thresholds  209 , then the processor  206  progresses to step  426 . 
         [0059]    At step  426 , the processor  206  queries whether this state (i.e., where ΔP V &lt;ΔP L  or ΔP V &gt;ΔP U ) continues for a predetermined amount of time, T. The predetermined time T may be installed into the memory  208  at manufacture or entered by the user. The determination at step  432  may be made by comparing a second set of measured pressures p 1  and p 2  after passage of the time T. 
         [0060]    At step  426 , the processor  206  essentially queries whether the disruption in flow through the implant  300  is a transient condition such as a transient, swiftly-resolved occlusion or an on-going condition such as a stationary clog within the drainage tube  302 . If, at step  428 , the processor  206  determines that this state of disrupted flow (i.e., where the pressure differential ΔP V  is outside of an acceptable range of pressure differentials as defined by the stored pressure differential thresholds  209 ) does not continue for the predetermined amount of time T while the flow system  212  is in an open condition, then the process returns to step  412 . If, however, at step  430 , the processor  206  determines that this state continues for the predetermined amount of time T while the flow system  212  is in an open condition, the processor  206  at step  432  generates control signals to activate the alarm  215 , which alerts the user and/or healthcare professional to a potential problem with the IOP control system  200 . 
         [0061]    In some embodiments, the processor generates the control signals to activate the alarm if the pressure p 1  does not change while the flow system is in an open condition for a time equal to or greater than the predetermined amount of time T. In some embodiments, the processor generates the control signals to activate the alarm if neither the pressure p 1  nor the pressure differential ΔP V  between pressures p 1  and p 2  changes while the flow system is in an open condition for a time equal to or greater than the predetermined amount of time T. 
         [0062]    In some embodiments, the flow control system  212  powers down when the alarm  215  is activated to conserve energy. In some embodiments, the processor  206  may be configured to stop supplying power to the flow control system  212  when the alarm  215  is activated, thereby powering OFF the system. 
         [0063]    As described above, the problem may comprise a clog or blockage in the implant  300 . In other instances, the problem may comprise a ruptured drainage site  306 , such as a ruptured bleb. In other instances, the alarm  215  may signal a correction of the patient&#39;s underlying IOP elevation, and an end to the need for operation of the IOP control system  200 . In some embodiments, the alarm  215  comprises a range of signal intensities that vary depending upon the severity of the problem (e.g., the severity of the pressure drop). By way of non-limiting example, in some embodiments, the alarm may comprise a series of visual signals such as lights where the number of lit lights reflects the severity of the problem. In other embodiments, the alarm may comprise an audible tone which increases in frequency or pitch with increasing severity of the problem. In other embodiments, the alarm may comprise a digital readout on the accessory device  214 . 
         [0064]    As described above, the alarm  215  may spur the patient to seek immediate medical attention to correct the problem, thereby limiting the potential complications of prolonged exposure to a malfunctioning IOP control system. In one embodiment, the accessory device  214  uploads the relevant data to a remote accessible data storage site (e.g., an internet server, email server, text message server) that activates an alarm at the remote site. The relevant data may be uploaded to a remote accessible data storage site and the remote alarm may be activated so that it can be observed in real time, for example, by healthcare professionals that are not present at the patient&#39;s side. Thus, both the patient and his or her healthcare professionals may be alerted to a problem with the IOP control system, such as a potential blockage or clog within the IOP control system or a ruptured drainage site, prior to the patient&#39;s next scheduled examination. 
         [0065]    Embodiments in accordance with the present disclosure provide users with a convenient and continuous clog detection system for their IOP control device that enables users to seek immediate medical attention for problematic flow control implants. Prompt awareness on the part of the user and/or the health care provider to an ineffective and/or clogged flow control system may result in better treatment, less complications, a more consistent recovery, and ultimately a better patient outcome. 
         [0066]    Embodiments in accordance with the present disclosure may be used in a variety of applications to regulate flow and/or pressure. For example, but not by way of limitation, embodiments of the present disclosure may be utilized to detect abnormalities such as clogs in a flow control system as part of a microanalytical system, a dialysis system, a process control system, a drug delivery system, a solar thermal system, a cooling system, and/or a heating system. Some embodiments of the present disclosure may be utilized to detect abnormalities such as clogs in a variety of fluidic systems such as, but not by way of limitation, the urinary tract, the brain (e.g., to regulate intracranial pressure), and the circulatory/renal system (e.g., as part of a dialysis system). Moreover, some embodiments are shaped and configured for implantation in a patient, while others are not. 
         [0067]    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