Patent Publication Number: US-2016235298-A1

Title: Systems and methods for priming an intraocular pressure sensor chamber

Description:
This application is a continuation of U.S. application Ser. No. 13/972,608 filed Aug. 21, 2013. 
    
    
     BACKGROUND 
     The present disclosure relates generally to systems and methods for priming chambers within implantable devices that provide ophthalmic treatments. In some instances, embodiments of the present disclosure are configured to be part of an intraocular implant comprising at least a part of an intraocular pressure control system. 
     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. 
     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 humor drainage system. The delicate balance between the production and drainage of aqueous humor determines the eye&#39;s IOP. 
       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 edges of the sclera  170  are pictured. Anatomically, the anterior segment of the eye includes the structures that cause elevated IOP which may lead to glaucoma. Aqueous humor fluid is produced by the ciliary body  140  that lies beneath the iris  130  and adjacent to the lens  110  in 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  180 . The edge of the anterior chamber, 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. The sclera  170 , the white of the eye, connects to the cornea  120 , forming the outer, structural layer of the eye. 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 out its collector channels. 
     As part of a method for treating glaucoma, a doctor may implant a device in a patient&#39;s eye. The device may monitor the pressure in a patient&#39;s eye and facilitate control of that pressure by allowing excess aqueous humor to flow from the anterior chamber of the eye to a drainage site, relieving pressure in the eye and thus lowering IOP. To exert appropriate control, an accurate measurement of the pressure about the patient&#39;s eye may be made. However, accurately monitoring the pressure in the eye or pressure around the eye poses a number of difficulties. For example, bubbles may form inside chambers used to measure the pressure at a remote location. These bubbles may degrade the accuracy of such measurements, in such a way that treatment is suboptimal. 
     The system and methods disclosed herein overcome one or more of the deficiencies of the prior art. 
     SUMMARY 
     In one exemplary aspect, the present disclosure is directed to an intraocular pressure (IOP) sensing device for implantation in an eye of a patient. The IOP sensing device includes a pressure sensor, a substrate having the pressure sensor disposed thereon, and a pressure sensor cap disposed on the substrate over the pressure sensor. The pressure sensor cap includes a wall structure and a cap top. The wall structure extends from the top surface and laterally surrounds the pressure sensor. The cap top is situated above the pressure sensor, with the cap top and wall structure together forming an interior chamber. In the IOP sensing device, at least one of the cap top and the wall structure comprises a semi-permeable material. The IOP sensing device further includes a chamber inlet in the pressure sensor cap that provides fluid access to the interior chamber. 
     In yet another exemplary aspect, the present disclosure is directed to a method for priming a chamber in an IOP sensing device suitable for implantation next to an eye of a patient. The method includes steps of coupling a liquid source to the inlet of a pressure sensor cap and of beginning an injection of a liquid from the liquid source through the inlet and into an interior chamber of the pressure sensor cap. The interior chamber contains a gas that is displaced through a semi-permeable portion of the pressure sensor cap as the liquid is injected. The method further includes steps of detecting the displacement of all of the gas from the interior chamber and of stopping the injection of the liquid. 
     In yet another exemplary aspect, the present disclosure is directed to a method of fabricating a semi-permeable chamber in an IOP sensing device suitable for implantation next to an eye of a patient. The method includes steps of providing a substrate having a plurality of contacts thereon, of coupling a pressure sensor to the plurality of contacts, and of fixing a pressure sensor cap to the substrate. The pressure sensor cap forms an interior chamber that encloses the pressure sensor and that includes at least one semi-permeable surface. The method further includes a step of coupling a tube to an inlet of the pressure sensor cap. 
     It is to be understood that both the foregoing general description and the following drawings and 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is a cross-sectional diagram of the front portion of an eye. 
         FIG. 2  is a perspective view of an ocular implant device that carries an IOP sensing system according to exemplary aspects of the present disclosure. 
         FIG. 3  is a perspective view of an eye and an ocular implant device that includes an IOP sensing system according to exemplary aspects of the present disclosure. 
         FIG. 4A  is a top view of an exemplary pressure sensor cap such as may be used in an IOP sensing system according to additional exemplary aspects of the present disclosure. 
         FIG. 4B  is a cross-sectional view of the exemplary pressure sensor cap of  FIG. 4A  as seen along a line A-A according to exemplary aspects of the present disclosure. 
         FIG. 4C  is a cross-sectional view of an alternative exemplary embodiment of an IOP sensing system according to exemplary aspects of the present disclosure. 
         FIGS. 5A, 5B, 5C, and 5D  are cross-sectional views of the exemplary pressure sensor cap of  FIGS. 4A and 4B  undergoing a priming process according to exemplary aspects of the present disclosure. 
         FIG. 6A  is a top view of an exemplary pressure sensor cap such as may be used in an IOP sensing system according to additional exemplary aspects of the present disclosure. 
         FIG. 6B  is a cross-sectional view of the exemplary pressure sensor cap as seen along a line B-B of  FIG. 6A  according to exemplary aspects of the present disclosure. 
         FIG. 7A  is a top view of an exemplary pressure sensor cap such as may be used in an IOP sensing system according to additional exemplary aspects of the present disclosure. 
         FIG. 7B  is a cross-sectional view of the exemplary pressure sensor cap as seen along the line C-C of  FIG. 7A  according to exemplary aspects of the present disclosure. 
         FIG. 8  is a flowchart showing a method of priming a chamber in an intraocular pressure sensing device according to exemplary aspects of the present disclosure. 
         FIG. 9  is a flowchart showing a method of fabricating a semi-permeable chamber in an intraocular pressure sensing device according to exemplary aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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 simplicity, in some instances the same reference numbers are used throughout the drawings to refer to the same or like parts. 
     The present disclosure relates generally to methods and systems for priming a chamber containing a pressure sensor for use in an intraocular pressure (IOP) monitoring device, such as a glaucoma drainage device (GDD). GDDs are used to alleviate excess pressure caused by aqueous humor accumulation in a patient&#39;s eye. The disclosed methods and systems may facilitate accurate pressure monitoring at a site removed from the pressure sensor by effectively purging air or another gas from a chamber containing the pressure sensor. Thus, the pressure measurement taken inside the chamber by the pressure sensor may more accurately correspond to the pressure at the site where the tube opening is placed. The systems and methods disclosed herein may thereby enable more accurate IOP determinations resulting in better information for determining treatment, potentially providing more effective treatment and greater customer satisfaction. 
       FIG. 2  is a schematic diagram of an intraocular implant or device  200  such as may be used in the monitoring and treatment of a patient&#39;s eye. As depicted, the intraocular device  200  is a GDD. The intraocular device  200  includes a body referred to herein as a plate  210  with a drainage tube  220  that extends from the plate  210 . The drainage tube  220  includes a proximal end portion  222  that couples the tube to one or more structures internal to the plate  210 . A distal end portion  224  of the drainage tube  220  may be coupled to the eye of a patient to allow for the monitoring of pressure and/or the drainage of fluid. As depicted, the intraocular device  200  includes an additional tube  230 . The additional tube  230  may be used to provide atmospheric or ambient pressure measurements taken at a site close to the eye. It may provide access to a chamber that forms part of a IOP sensing system. This chamber will be discussed in greater detail below. 
     The plate  210  is configured to fit at least partially within the subconjunctival space and is sized within a range between about 15 mm×12 mm to about 30 mm×15 mm and has a thickness less than about 2 mm thick, preferably less than about 1 mm thick. The plate  210  may be formed to the radius of the eye globe (about 0.5 inches). It may be rigid and preformed with a curvature suitable to substantially conform to the globe or it may be flexible and can flex to conform to the globe. Some embodiments are small enough that conforming to the globe provides little benefit in comfort or implantation technique. The above dimensions are exemplary only, and other sizes and arrangements are contemplated herein. The plate  210  may include or be arranged to carry various components of an IOP control system. In some embodiments, such components include a power source, a processor, a memory, a data transmission module, and a flow control mechanism (i.e. valve system). It may also carry one or more pressure sensor systems. 
       FIG. 3  is a schematic diagram of an eye of a patient whose IOP is being monitored and/or who is receiving treatment with the intraocular device  200 . In some embodiments, the drainage tube  220  extends from an anterior side of the plate  210  and is sized and arranged to extend into the anterior chamber of the eye through a surgically formed opening  312  in the sclera. The drainage tube  220  may be used to measure pressure in addition to facilitating drainage. In other embodiments, the drainage tube  220  and the additional tube  230  extend to other locations about the eye or body where multiple pressure measurements may be desired. The drainage tube  220  includes a first open end  224  that may be disposed at a location where pressure measurements may be desired, and at least one lumen that extends to a second open end  222  that may be disposed within or connected to the plate  210 . 
     In some embodiments, the additional tube  230  may also extend from an anterior side of the plate  210  of the intraocular device  200 . In such embodiments, the additional tube  230  may provide fluid access to a pressure sensor that measures pressure at an end of the tube. In one example, it measures the atmospheric pressure. An atmospheric reference pressure may be measured at a “dry” subconjunctival location. A “dry” location, as used herein, is a location spaced apart from an aqueous humor drainage site such that it is not influenced by the wetter tissue at the drainage site. This location may be covered and protected by a biocompatible patch material formed of, for example, donor sclera, pericardium, or others. Since atmospheric pressure is a factor used to determine IOP, the accuracy of the IOP measurement corresponds to the accuracy of the atmospheric pressure reading. 
     Prior to placement around a patient&#39;s eye as depicted in  FIG. 3 , one or more chambers within the plate  210  may be primed by the injection of liquid that displaces a gas from the chamber containing a pressure sensor. Liquid may be injected through the drainage tube  220  and/or the additional tube  230 . Thus, in some embodiments, one or more chambers within plate  210  may be primed prior to positioning in or around a patient&#39;s eye. 
       FIG. 4A  illustrates a top view of an IOP sensing device  400 . The IOP sensing device  400  includes a substrate  402  that may be formed from a printed circuit board material or other suitable material. While some features of the substrate  402  are depicted in  FIG. 4A , many features are not explicitly depicted. For example, the substrate  402  may include a number of circuits, processors, power sources, and/or sensors with electrical leads both on a top surface of the substrate  402  and within it. In one embodiment, the substrate  402  is a flex circuit. 
     On top of the substrate  402  is a pressure sensor cap  404  that may be fixed on to the top surface of the substrate  402 . The pressure sensor cap  404  cooperates with and is fixed to the substrate  402  to form an interior chamber  406 . As depicted, the interior chamber  406  contains a pressure sensor  408 . In other embodiments, additional sensors are positioned within the interior chamber  406  as well. For example, in some embodiments, the interior chamber  406  may also contain a temperature sensor and/or other sensors. The pressure sensor  408  may be electrically coupled to a plurality of leads within the chamber  406 . In some embodiments, the pressure sensor  408  may have a ball grid array coupled to a plurality of contacts associated with the plurality of leads. In some other embodiments, the pressure sensor  408  may be wire bonded to a plurality of contacts within the chamber  406 . 
     In order to allow access to the interior chamber  406  after the pressure sensor cap  404  is fixed to the substrate  402 , an inlet  410  is provided in the pressure sensor cap  404 . As depicted, the inlet  410  includes a protruding attachment member  412  having a lumen  413  extending therethrough. The lumen  413  further extends through the pressure sensor cap  404  such that gases, liquids, or other fluids may enter into the interior chamber  406 . The attachment member  412  may facilitate the attachment and positioning of a flexible tube, such as a silicone tube. This flexible tube may be the drainage tube  220  or the additional tube  230  shown in  FIGS. 2 and 3 . Some embodiments of the IOP sensing device  400  may not include the attachment member  412 . In such embodiments, a flexible tube may be abuttingly connected or insertably connected to the pressure sensor cap  404  using an adhesive and/or a press-fit connection. 
       FIG. 4B  illustrates a cross-sectional view of the pressure sensor cap  404  as seen along line A-A of  FIG. 4A .  FIG. 4B  thus provides additional perspective on the substrate  402 , the interior chamber  406 , the pressure sensor  408 , and the inlet  410 . Additionally,  FIG. 4B  shows that in some embodiments, the pressure sensor cap  404  may be formed from multiple subcomponents. As depicted, the pressure sensor cap  404  may include a wall structure  414 A that extends up from the top surface of the substrate  402 . Coupled to the wall structure  414 A is a pressure sensor cap top  414 B. The cap top  414 B is positioned such that it is above the pressure sensor  408 . In some embodiments, the wall structure  414 A and the cap top  414 B are formed separately and then joined together. In such embodiments, the wall structure  414 A and the cap top  414 B may be formed from different materials or from the same material. In other embodiments, the wall structure  414 A and the pressure sensor cap top  414 B are formed from a monolithic piece of material to provide the pressure sensor cap  404 . The pressure sensor cap  404  may have an external area ranging from around 1 mm 2  to around 4 mm 2 , with each side ranging in length from about 1 mm to about 2 mm. 
     Regardless of whether the wall structure  414 A and the cap top  414 B are formed from a single material or from different materials, the pressure sensor cap  404  includes a semi-permeable material. Thus, some embodiments of the pressure sensor cap  404  include a semi-permeable cap top  414 B, other embodiments include a semi-permeable wall structure  414 A, while in other embodiments both the cap top  414 B and the wall structure  414 A are semi-permeable. In yet other embodiments, only a portion of the wall structure  414 A and/or the cap top  414 B may be semi-permeable. While many different combinations of materials may be used to provide the pressure sensor cap  404 , an exemplary embodiment may include a wall structure  414 A formed from polyetheretherketone (PEEK) and a cap top  414 B formed from polytetrafluoroethylene (PTFE), the PTFE acting as the semi-permeable material. 
     Other materials that may be used to create a semi-permeable pressure sensor cap  404  include high-density polyethylene, such as Tyvek® made by the E.I. du Pont de Nemours and Company of Wilmington, Del., polypropylene, and other materials. The permeability of material may be affected by pore size, hydrophobicity, and thickness. Some embodiments of the sensor cap  404  may range in thickness from about 0.1 millimeters to about 1 millimeter thick. Whether semi-permeable or not, the wall structure  414 A and the cap top  414 B may provide an adequate rigidity such that a pressure inside the interior chamber  406  and a pressure outside the chamber may be isolated from each other. Thus, it may be undesirable for the wall structure  414 A or the cap top  414 B to bend or flex significantly after positioning. The operation of the semi-permeable pressure sensor cap  404  may be better understood by reference to  FIGS. 5A-D , discussed below. 
       FIG. 4C  illustrates an alternate embodiment of the exemplary IOP device  400 . Rather than include a pressure sensor  408  as depicted in  FIGS. 4A and 4B ,  FIG. 4C  includes a differential pressure sensor  409 . As illustrated, the differential pressure sensor  409  is a mechanical differential pressure sensor. The differential pressure sensor  409  may be formed from a flexible member or membrane situated below the pressure sensor cap  404  and above the substrate  402 . As depicted in  FIG. 4C , the substrate is patterned to include a chamber  416 , which has an inlet  418  and an outlet  420 . The substrate  402  is patterned so that portions of the substrate  402  contact the membrane of pressure sensor  409  to create a seal under specific conditions. When the pressure within the chamber  406  is greater than a pressure within the chamber  416 , the membrane of pressure sensor  409  and the portions of substrate  402  form and maintain a seal, such that a liquid is prevented from flowing from the inlet  418  to the outlet  420 . 
     For example, the chamber  406  may be pressurized by the atmosphere, such that an atmospheric pressure is present within the chamber  406 , and thus exerted on the membrane of  409  from above as viewed in  FIG. 4C . The inlet  418  may be coupled to the anterior chamber  180  of an eye so that the pressure within the anterior chamber  180  is present within the chamber  416 . When the atmospheric pressure is greater than the anterior chamber pressure, aqueous humor may be prevented from flowing out through the outlet  420 . However, when the pressure present in the anterior chamber  180  is greater than the atmospheric pressure, or greater than the cumulative effects of the atmospheric pressure and an offset proportional to the mechanical and geometric characteristics of the substrate  402 , the membrane  409 , and/or other components, the membrane of the pressure sensor  409  may be displaced toward the cap top  414 B, allowing aqueous humor to drain out through the outlet  420 . In this manner, the pressure sensor  409  may measure and respond to differences in the pressures in chambers  406  and  416 . The mechanical and geometric characteristics of the substrate  402  and the membrane of pressure sensor  409  may be selected so that the offset is a known, desired offset. 
       FIGS. 5A, 5B, 5C, and 5D  illustrate cross-sectional views, as seen in  FIG. 4B , of the exemplary IOP device  400  of  FIG. 4A , undergoing a priming process. In order to prime the interior chamber  406  prior to implantation, a doctor or technician may couple one end of a tube to the attachment member  412  and the other end of the tube to a liquid source, such as a syringe, filled with saline or other such appropriate solution. As the doctor or technician manually exerts pressure on the syringe, the liquid from the syringe flows through the tube and into the inlet  410 , as depicted in  FIG. 5A . As the liquid  500  passes through the tube and into the inlet  410 , the air that previously filled the tube is forced into the interior chamber  406 . As the pressure inside the chamber  406  increases, the air may exit through the semi-permeable material of the pressure sensor cap  404 . As depicted by an arrow  502 A, if the wall structure  414 A is semi-permeable, the air may escape through it. As depicted by an arrow  502 B, if the cap top  414 B is semi-permeable, the air may escape through it. 
     As depicted in  FIG. 5B , as more liquid  500  is injected into the anterior chamber  406 , more air is expelled through the semi-permeable material of pressure sensor cap  404 . As in  FIG. 5A , the air may exit the interior chamber  406  through the wall structure  414 A and or the cap top  414 B. This process may continue as seen in  FIGS. 5C and 5D . As more liquid  500  is injected into the interior chamber  406  the gas that previously occupied the chamber may be forced through the semi-permeable material of the pressure sensor cap  404 . The doctor who injects the liquid  500  may manually detect when the gas has been fully purged from the interior chamber  406 , as depicted in  FIG. 5D . This condition may be detected as the force required to depress the syringe tactilely increases, or as the syringe stops moving under a constant force. However, if excessive pressure is applied in injecting the fluid into the chamber  406 , the liquid  500  may be forced through the semi-permeable material in some portion or portions of the sensor cap  404 . This may damage the sensor cap  404 . 
     In some embodiments, the pressure sensor  408  may be used during the priming process. In such embodiments, a completely primed state, such as depicted in  FIG. 5D , may be detected by the pressure sensor  408  as a significant increase in pressure. In yet other embodiments, the priming may be performed in an automated process, in which a computer-controlled system injects the fluid until the significant increase in pressure occurs, at which point the computer-controlled system may stop the injection of liquid. 
       FIG. 6A  is a top view of an exemplary IOP sensing device  600 . The IOP sensing device  600  shares many similarities with the IOP sensing device  400  as described above and as depicted in  FIGS. 4A, 4B, and 5A -D. The IOP sensing device  600  includes a substrate  402  with a pressure sensor cap  604  thereon. The pressure sensor cap  604  and the substrate  402  form an interior chamber  606 , which may contain a pressure sensor  408 . Some embodiments of IOP sensing device  600  may include a differential pressure sensor, such as pressure sensor  409  of  FIG. 4C . Unlike the interior chamber  406  of  FIGS. 4A-B  and  5 A-D, which as depicted has a rectangular cross-section as viewed from above, the interior chamber  606  as seen in  FIG. 6A  has a curved cross-section. As depicted, the interior chamber  606  has a circular shape, while other embodiments may have other elliptical shapes, or an ovoid shape. The elliptical shape of the interior chamber  606  may further inhibit the formation of trapped bubbles within the chamber. Also depicted in  FIG. 6A , the IOP sensing device  600  includes an inlet  610  providing fluid access to the interior chamber  606 , and an attachment member  612  having a lumen  613  extending therethrough. The attachment member  612  may not be present in some embodiments. 
       FIG. 6B  is a cross-sectional view of the exemplary pressure sensor cap  604  as seen along line B-B depicted in  FIG. 6A .  FIG. 6B  provides additional perspective on the substrate  402 , the interior chamber  606 , the pressure sensor  408 , and the inlet  610 . Additionally,  FIG. 6B  shows that in some embodiments, the pressure sensor cap  604  may be formed from multiple subcomponents. As depicted, the pressure sensor cap  604  may include a wall structure  614 A that extends up from the top surface of the substrate  402 . Coupled to the wall structure  614 A is a pressure sensor cap top  614 B. The cap top  414 B is positioned such that it is above the pressure sensor  408 . In some embodiments, the wall structure  614 A and the cap top  614 B may be formed separately and then joined together. In such embodiments, both the wall structure  614 A and the cap top  614 B may be formed from different materials or from the same material. Additionally, the wall structure  614 A and the cap top  614 B may be formed from a single piece of material, which may obviate a need to join two separate pieces of material. The pressure sensor cap  604  may have an internal surface area ranging from around 0.6 millimeters 2  to around 25 millimeters 2 , with the diameter ranging in length from about 0.25 millimeters to about 5 millimeters. The IOP device  600  may be primed in a manner similar to that depicted in  FIGS. 5A-5D  and described above. 
       FIG. 7A  is a top view of an exemplary pressure sensor cap  704  such as may be used in an IOP sensing device  700 . The IOP sensing device  700  may share many features discussed above in connection with the IOP sensing devices  400  and  600 . For instance, the IOP sensing device  700  includes a substrate  402 , upon which the sensor cap  704  is fixed, forming an interior chamber  706  therebetween. The chamber  706  contains a pressure sensor  408 . Some embodiments of IOP sensing device  700  may include a differential pressure sensor, such as pressure sensor  409  of  FIG. 4C . As viewed from above, the pressure sensor cap  704  is approximately circular in shape; however other embodiments of the sensor cap  704  may have different shapes, such as rectangular, elliptical, etc. In order to provide access to the interior chamber  706 , the sensor cap  704  includes an inlet  710  and an attachment member  712  having a lumen  713  extending therethrough. Although the attachment member  712  may facilitate the coupling of a tube to the pressure sensor cap  704 , some embodiments of the IOP device  700  may not include the attachment member  712 . 
       FIG. 7B  is a cross-sectional view of the IOP sensing device  700  as seen alone the line C-C, depicted in  FIG. 7A .  FIG. 7B  provides additional perspective on the features disclosed above. As depicted, the sensor cap  704  is approximately hemispherical in shape. This may further inhibit the formation of bubbles within the chamber during a priming process, such as that depicted in  FIGS. 5A-5D . Embodiments of the pressure sensor cap  704  may have a diameter ranging from about 1 mm to about 5 mm. In the depicted embodiment, the pressure sensor cap  704  is formed from a monolithic piece of semi-permeable material. However, in other embodiments, more than one material may be used to form the cap  704 . In such embodiments, only a portion of the pressure sensor cap  704  may be semi-permeable. 
       FIG. 8  shows a method  800  of priming a chamber in an intraocular device suitable for implantation next to an eye of a patient. As depicted, the method  800  includes a number of enumerated steps. However, embodiments of the method  800  may include additional steps before, in between, and after the enumerated steps. Method  800  begins at a step  802 , when a liquid source is coupled to an inlet of a pressure sensor cap, the pressure sensor cap being included in the IOP sensing device. In step  804 , a doctor or technician begins injecting a liquid from the coupled liquid source into an interior chamber, such that the liquid displaces a gas, which exits the chamber through a semi-permeable material of the pressure sensor cap. In some embodiments, a computer-controlled machine performs the injection. In step  806 , the displacement of all the gas from the interior chamber is detected. And the injection of the liquid is stopped at step  808 . 
     To better describe the method  800 , reference is made herein to the IOP sensing device of  FIGS. 4A-4B and 5A-5D . The method  800  may also be performed with other embodiments, including those depicted in  FIGS. 6A-B  and  7 A-B. As depicted in  FIGS. 4A and 4B , the IOP sensing device  400  includes an inlet  410 , with an attachment member  412 . The step  802  may be performed when a flexible tube (not shown) is coupled to the attachment member  412  on one end of the tube and to a liquid source, such as a syringe containing a liquid, on the other end of the tube. At step  804 , the doctor or technician may begin injecting the liquid by manually actuating the syringe. In the computer-controlled embodiments, the machine may begin the injection using a pump or other flow driving system. As the liquid flows through the tube, through the inlet  410 , and into the interior chamber  406 , air that was present in the tube (not shown) and in the interior chamber  406  may be forced through the semi-permeable material or surface of the pressure sensor cap  404 . Depending on the particular embodiment of the pressure sensor cap  404 , the air may exit the interior chamber  406  through the wall structure  414 A, the cap top  414 B, or both. 
     As the liquid fills the interior chamber  406 , the flow of liquid into the interior chamber  406  may be roughly consistent until the chamber is filled as seen in  FIG. 5D . At step  806 , when the chamber is filled, a change in flow may be observed by the doctor or technician, or by a machine, and the observation may be interpreted as an indication that all the gas is removed from the chamber. Additionally, a doctor or technician may determine that the gas has been removed when the force required to compress the syringe tactically increases. In some embodiments, the pressure sensor  408  may indicate an increase in pressure associated with the gas being completely purged from the interior chamber  406 . At step  808 , after the displacement of all the gas from the interior chamber  406 , the doctor or technician, or controller in automated or semi-automated embodiments, may stop the injection and detach the liquid source from the flexible tube. 
       FIG. 9  shows a method  900  of fabricating a semi-permeable chamber in an IOP sensing device. As depicted, the method  900  includes a number of enumerated steps. However, embodiments of the method  900  may include additional steps before, in between, and after the enumerated steps. Method  900  begins at step  902  in which a substrate is provided. The substrate may include a plurality of electrical traces (not depicted) on a top surface thereof and/or contacts on the top surface that are in connection with electrical traces below the top surface. At step  904 , a sensor is coupled to at least one electrical trace on the top surface of the substrate. At step  906 , a chamber having at least one semi-permeable surface is formed over the sensor. The semi-permeable surface may allow passage of a gas therethrough, while blocking a liquid. At step  908 , a tube (not depicted) is coupled to an inlet of the chamber. 
     In order to better describe method  900 , reference is made herein to the IOP sensing device  400  of  FIGS. 4A-B  and  5 A-D. A performance of method  900  may result in a device such as the IOP sensing device  400 , though embodiments of method  900  may also result in IOP sensing devices  600  and  700  as depicted in  FIGS. 6A-B  and  7 A-B, and other embodiments of such IOP sensing devices. At step  902 , in order to fabricate an IOP sensing device  400 , a substrate  402  is provided. The substrate  402  may be a printed circuit board, fabricated with layers of insulating plastic with electrical leads between and/or on the layers. The leads printed in between insulating layers may have electrical contacts disposed on the top most layer by which electrical connections may be made. The substrate  402  may be manufactured using semiconductor fabrication processes to create and insulate the electrical leads. 
     In some embodiments, the substrate  402  may include a chamber, and an inlet, and outlet, such as are depicted in  FIG. 4C . These features may be manufactured using micromachining and/or semiconductor processing techniques. In some related embodiments, the membrane of the pressure sensor  409  may include piezoelectric elements by which pressure may be quantified for reference. 
     At step  904 , a sensor, such as pressure sensor  408 , may be coupled to the contacts so that power and signal lines may be provided between the sensor and a controller or processor. This may be accomplished by wire-bonding, through the inclusion of a ball grid array on the pressure sensor package, or any other suitable mechanism or structure. This may also be accomplished by fabricating the pressure sensor  408  into the substrate using microelectromechanical system (MEMS) fabrication techniques. At step  906 , a pressure sensor cap  404  may be fixed or fabricated onto a top surface of the substrate  402  with an adhesive to form an interior chamber  406 . As depicted, the pressure sensor cap  404  includes a wall structure  414 A and a cap top  414 B. In some embodiments the wall structure  414 A is made from a semi-permeable material, such that gas may pass through the wall structure  414 A while liquid may not. In other embodiments, the cap top  414 B may provide the semi-permeable surface. Or in yet other embodiments, both the wall structure  414 A and the cap top  414 B may be made from a semi-permeable material or materials. At step  908 , a flexible tube (not depicted), made of silicone or another suitable material, may be coupled to the inlet  410  of the chamber  406 . The tube may be press fit around an attachment member  412 , press fit into the inlet  410 , adhesively fixed to the wall structure  414 A, or otherwise attached to the pressure sensor cap  404 . After the pressure sensor cap  404  is coupled to the substrate  402  and the tube, the IOP sensing device assembly may be encapsulated in a biocompatible material, such as PEEK or another biocompatible material such as, but not limited to, plastic, metal, glass, or silicon. 
     The systems and methods disclosed herein enable surgeons to more effectively remove all air from the pressure chambers by forcing the air through a semi-permeable surface that restricts passage of fluid. In particular, the semi-permeable chambers may facilitate the removal of gas bubbles that may adversely affect the accuracy of the pressure readings. This may result in more effective treatment and more accurate data, thereby improving the overall clinical result. 
     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.