Patent Publication Number: US-2007106200-A1

Title: Intraocular shunt device and method

Description:
FIELD OF INVENTION  
      The present invention relates to intraocular treatment devices and methods, and more particularly to controllable shunts and methods for controlling intraocular pressure.  
     BACKGROUND OF THE INVENTION  
      Glaucoma is a pathological condition of the eye often resulting in elevated intraocular pressure. If the intraocular pressure remains elevated for a long enough period of time, total vision loss occurs. The blindness that results from glaucoma involves both central and peripheral vision and has a major impact on an individual&#39;s ability to lead an independent life. Because glaucoma is a major cause of blindness, glaucoma is a significant public health problem.  
      The following explanation of glaucoma is given with reference to the schematic illustration of the eye in  FIG. 1 . High pressure develops in an eye as a result of glaucoma because of an intraocular fluid imbalance. The pertinent fluid, known as aqueous humor, is formed in the posterior chamber  75  of the eye by the ciliary body at a fairly constant rate of about 2.5 microliters per minute. The aqueous fluid passes from the posterior chamber around the lens, through the pupillary opening  65  in the iris  40  and into the anterior chamber  35  of the eye. Once in the anterior chamber, the fluid drains out of the eye through two different routes. In a first route (referred to as the “uveoscleral route”) the fluid percolates between muscle fibers  77  of the ciliary body. This route accounts for approximately ten percent of the aqueous outflow in humans. The primary route for aqueous outflow (referred to as the “canlicular route”) involves the trabecular meshwork  50  and Schlemm&#39;s canal  30 .  
      The trabecular meshwork and Schlemm&#39;s canal are located at the junction between the iris  40  and the sclera  79 . This junction is commonly referred to as “the angle.” The trabecular meshwork is a wedge-shaped structure that runs around the circumference of the eye. It is composed of collagen beams arranged in a three-dimensional sieve-like structure. The beams are lined with a monolayer of cells called trabecular cells. The spaces between the collagen beams are filled with an extracellular substance that is produced by the trabecular cells. These cells also produce enzymes that degrade extracellular material. Schlemm&#39;s canal is adjacent to the trabecular meshwork. The outer wall of the trabecular meshwork coincides with the inner wall of Schlemm&#39;s canal. Schlemm&#39;s canal is a tube-like structure that runs around the circumference of the cornea.  
      The aqueous fluid travels through the spaces between the trabecular beams, across the inner wall of Schlemm&#39;s canal into the canal, through a series of about 25 collecting channels that drain from Schlemm&#39;s canal and into the episcleral venous system  60 . In a normal situation, aqueous fluid production is equal to aqueous fluid outflow and intraocular pressure remains fairly constant in the 15 to 21 mmHg range. In glaucoma, the resistance through the canalicular outflow system is abnormally high, thus causing internal fluid imbalance.  
      In primary open angle glaucoma, which is the most common form of glaucoma, the abnormal resistance is believed to be along the outer aspect of trabecular meshwork and the inner wall of Schlemm&#39;s canal. It is believed that an abnormal metabolism of the trabecular cells leads to an excessive build up of extracellular materials or a build up of abnormally “stiff” materials in this area. Primary open angle glaucoma accounts for approximately eighty-five percent of all glaucoma. Other forms of glaucoma (such as angle closure glaucoma and secondary glaucomas) also involve decreased outflow through the canalicular pathway but the increased resistance is from other causes such as mechanical blockage, inflammatory debris, cellular blockage, etc.  
      With the increased resistance, the aqueous fluid builds up in the anterior chamber because it cannot exit fast enough to maintain the intraocular fluid balance. As mentioned above, as the fluid builds up, the intraocular pressure (IOP) increases. The increased IOP compresses the axons in the optic nerve (which carries visual information from the eye to the brain) and also may compromise the vascular supply to the optic nerve. While research is investigating ways to protect the nerve from an elevated pressure, the only therapeutic approach currently available for glaucoma is to reduce the intraocular pressure.  
      Conventional therapy involves a stepwise procedure. Typically, topical or oral medication is the first step of treatment. The medication has many serious side effects including: heart failure, respiratory distress, hypertension and depression. When the medication fails to adequately control the pressure, laser trabeculoplasty is often performed. If laser trabeculoplasty does not reduce the pressure enough, a trabeculectomy is performed, in which a hole is made in the sclera and angle region to allow aqueous fluid to leave the eye. The trabeculectomy is associated with many problems, including scarring and infection that results from bacteria entering the eye through the hole in the sclera.  
      When trabeculectomy doesn&#39;t successfully lower the eye pressure, the next surgical step may be insertion of an aqueous shunt device. In some conventional shunt devices, a silicone tube is attached at one end to a plastic (polypropylene or other synthetic) plate, which is sewn into the surface of the eye. The tube is inserted into the eye through a hole. The external portion of the tube is covered with either donor sclera or pericardium, and the conjunctiva is replaced and the incision is closed.  
      With such aqueous diversion devices, aqueous drains out of the eye through the silicone tube to the surface of the eye. Most of the problems that have developed with such shunt devices and procedures have occurred because aqueous fluid is drained from inside of the eye to the surface of the eye.  
      In many glaucoma patients, the resistance problem that causes increased intraocular pressure lies between Schlemm&#39;s canal and the anterior chamber. The canal itself, the collecting channels and the episcleral venous system all are functional. As a result, some conventional shunts have been configured to function by directing aqueous flow into Schlemm&#39;s canal rather than outside of the eye. Some such devices have included a pump. However, such devices have not provided suitable flow control.  
     SUMMARY  
      Aspects of the present invention are directed to a shunt device providing improved flow control. In one embodiment the shunt comprises a conduit sized to fit within Schlemm&#39;s canal, the conduit having a proximal end, a distal end, and an inlet intermediate the proximal end and the distal end; and a Venturi feature configured and arranged within the conduit so as to be capable of controlling flow from the inlet into the conduit. The shunt may further comprise a pressure sensor capable of measuring pressure within an eye, coupled to the Venturi feature, the Venturi feature being configured to control flow from the inlet into the conduit in response to a pressure measurement from the sensor. The Venturi feature may be electronically or magnetically actuatable in response to the pressure measurement. The sensor may be adapted to measure pressure continuously or intermittently.  
      The shunt may include an activation device configured to activate the Venturi feature and thereby control flow from the inlet to the conduit. The activation device may be connected to at least one of the conduit and the inlet. The activation device may be adapted to electrically or magnetically actuate the Venturi feature. The activation device may be adapted to control flow from the inlet into the conduit in response to a pressure measurement from a sensor. The Venturi feature may comprise one leaf, two leaves or more. Alternatively, the Venturi feature may be rotationally continuous (e.g., funnel-shaped).  
      The inlet may extend from the conduit or may simply be an opening in the conduit. In embodiments where the inlet extends from the conduit, the inlet is selected to have a length sufficient to extend into the anterior chamber of an eye when the shunt is implanted in Schlemm&#39;s canal.  
      The shunt may comprise a pump configured and arranged to control the flow in the conduit. In such embodiments, the shunt may comprise a pressure sensor capable of measuring pressure in the eye, the pressure sensor being coupled to the pump, and the pump being adapted to control flow from the inlet into the conduit in response to a pressure measurement from the sensor. The pump may be connected to the conduit. The pump may be separate from the conduit. The pump may be a peristaltic pump.  
      Another aspect of the invention is directed to a method of controlling a pressure in an anterior chamber of an eye, comprising providing in a Schlemm&#39;s canal of the eye a conduit having a Venturi feature disposed therein, and controlling flow along the Venturi feature, thereby achieving a pressure proximate an inlet from the anterior chamber into the Schlemm&#39;s canal. The method may further comprise a step of actuating the Venturi feature. The method may further comprise pumping fluid along the Venturi feature.  
      The term “Venturi feature” as used herein includes any suitable structure extending from the conduit and capable of producing a pressure change in response to fluid flow along the feature and thereby altering flow through the inlet. A Venturi feature may be actuatable or non-actuatable as described hereinbelow.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Illustrative, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which the same reference number is used to designate the same or similar components in different figures, and in which:  
       FIG. 1  is a schematic illustration of certain anatomic features of the human eye;  
       FIG. 2A  is a perspective view of an embodiment of a shunt according to aspects of the present invention;  
       FIG. 2B  is a cross sectional side view of the embodiment of the present invention illustrating further aspects of the shunt shown in  FIG. 1A ;  
       FIG. 3  is a cross sectional side view of another embodiment of the present invention; and  
       FIG. 4  is a schematic illustration showing the surgical placement of an exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Aspects of the present invention are directed to a shunt, comprising: a conduit sized to fit within Schlemm&#39;s canal, the conduit having a proximal end, a distal end, and an inlet intermediate the proximal end and the distal end; and a Venturi feature configured and arranged within the conduit so as to be capable of controlling flow from the inlet into the conduit.  
       FIG. 2A  is a schematic, perspective view of an embodiment of a shunt  100  according to aspects of the present invention including a Venturi feature (not shown). Shunt  100  is comprised of two portions, a conduit  25  and an inlet  10 .  FIG. 2B  is a cross sectional view of shunt device  100  illustrating the internal fluid communication path.  FIG. 2B  also illustrates Venturi feature  50  disposed in the shunt to control fluid flow from the anterior chamber of an eye into Schlemm&#39;s canal. During operation of the device, conduit  25  is disposed in a portion of Schlemm&#39;s canal, and inlet  10  is exposed to the anterior chamber to divert fluid from the anterior chamber into Schlemm&#39;s canal as determined by Venturi feature  50 .  
      In the illustrated embodiment, Venturi feature  50  may be configured and arranged in conduit  25  in any suitable manner such that actuation of the Venturi feature affects the amount of flow from the anterior chamber into inlet  10  and then into conduit  25 . In the illustrated embodiment, Venturi feature  50  is disposed at least partially within the flow path  11  from inlet  25  as indicated by dashed lines.  
      It is to be appreciated that, according to the Venturi effect, flow through conduit  25  from proximal end  25   a  toward distal end  25   b  results in a flow on the interior side of Venturi feature  50  (i.e., the radially inward side of Venturi feature  50 ). Such flow results in a relatively low pressure region being formed in proximity to Venturi feature  50 , thereby affecting flow into conduit  25  from the anterior chamber via inlet  10 . As Venturi feature  50  is actuated to achieve more constricted flow through conduit  25 , the pressure in proximity to Venturi feature  50  is reduced and flow from the anterior chamber via inlet  10  is increased. Correspondingly, as Venturi feature  50  is activated to achieve less constricted flow through conduit  25 , the pressure in proximity to Venturi feature  50  is increased and flow into conduit  25  from the anterior chamber via inlet  10  is decreased.  
      For example, the Venturi feature may comprise a first leaf  50   a  and a second leaf  50   b , where first leaf  50   a  is at least partially within flow path  11 . In some embodiments, Venturi feature  50  may comprise only a single leaf  50   a  (i.e., leaf  50   b  may be omitted). In other embodiments, Venturi feature  50  may comprise a rotationally continuous structure, such as a funnel-shaped structure (e.g., a cone) having a channel formed therethrough where flow through conduit  25  may pass. In embodiments including a funnel-shaped structure, the structure may be made of compressible material, or the funnel-shaped structure may comprise flexible regions such that the cone is capable of being activated to constrict flow through conduit  25  and thereby control flow form the anterior chamber in the manner described above. In the present embodiment, control of fluid from the anterior chamber may be achieved using any suitable Venturi feature configuration by actuating Venturi feature  50  to increase and decrease pressure in proximity to Venturi feature  50 .  
      Venturi feature  50  may be actuatable by any suitable technique. For example, an activation device  75  may be disposed proximate Venturi feature  50 . The activation device  75  may, for example, comprise a plate capable of maintaining an electric potential relative Venturi feature  50  so that activation device  75  may attract or repulse Venturi feature  50 . Accordingly, Venturi feature  50  may be controlled to achieve greater or lesser flow through conduit  25 , and thereby control flow from inlet  10  into conduit  25 . It is to be appreciated that, by selecting a suitable material and geometry for the Venturi feature, a selected amount of resilience of the Venturi feature can be attained such that the Venturi feature reaches an equilibrium for a given amount of attractive or repulsive force in response to activation device  75 , thereby controlling the flow along conduit  50 .  
      Alternatively, activation device  75  may provide a variable magnetic field (e.g., the activation device may comprise an electromagnet) and Venturi feature  50  may be made of a material capable of responding to the magnetic field such that the Venturi feature may increase or decrease flow through conduit  25 . It is to be appreciated that activation device  75  may be located inside, outside or within conduit  25 ; and device  75  may extend completely around conduit  25  or may only extend a limited portion of the channel. The activation device may be powered by a suitable power source, such as a battery source or an inductive energy source.  
      In some embodiments, shunt  50  is coupled to a sensor  70  capable of measuring pressure in the anterior chamber of the eye; and activation device  75  is adapted to control Venturi feature  50  in response to the measured pressure. For example, in response to an undesirably high anterior chamber pressure, the Venturi feature may be operated as described above to increase flow from the anterior chamber into Schlemm&#39;s canal; and in response to an undesirably low anterior chamber pressure, the Venturi feature may be operated as described above to decrease flow from the anterior chamber into Schlemm&#39;s canal.  
      Sensor  70  may measure anterior chamber pressure continuously or intermittently. Additionally, activation device  75  may be operated to activate the Venturi feature continuously in response to measured pressure or intermittently. Examples of suitable pressure sensors are given in U.S. Pat. No. 5,431,057, issued Jun. 11, 1995 to Zimmer, et al., the substance of which is hereby incorporated by reference in its entirety, U.S. Pat. No. 5,005,577, issued Apr. 9, 1991 to Frenkel and U.S. Pat. No. 6,443,893, issued Sep. 3, 2002 to Schnakenburg, et al. A processor (not shown) may be included to receive pressure information from sensor  70  and to provide a control signal to activation device  75  to control thereby the Venturi feature.  
      In embodiments where pressure is measured intermittently and/or activation device  75  is operated intermittently, actuation of Venturi feature  50  can provide a constant level of actuation between measurements and/or actuations. In some embodiments, sensor  70  is capable of providing pressure measurements to an instrument outside of (i.e., remote from) a patient&#39;s body such that anterior chamber pressure may be monitored. Additionally, in some embodiments, Venturi feature  50  is actuatable from outside of a patient&#39;s body independently of or based on pressure measurements. Any suitable telemetric devices may be used to achieve such remote measurement and/or control.  
      Conduit  25  may have any suitable length, and external or internal shape. Conduit  25  may be of sufficient length to extend from the junction with inlet  10  through any suitable portion of the entire circumference of Schlemm&#39;s canal. In some embodiments, conduit  25  is selected to have length of about 6 mm. For example, the internal and or external shape of conduit  25  may be round, oval, rectangular or triangular. Typically the external shape will be selected such that conduit  25  fills Schlemm&#39;s canal so that all fluid flowing through Schlemm&#39;s canal will flow through conduit  25 . Further details of a suitable conduit structures are given in U.S. Pat. No. 6,450,984, issued Sep. 17, 2002, to Lynch, the substance of said patent is hereby incorporated by reference in its entirety.  
      In the illustrated embodiment, inlet  10  joins the conduit  25  at an angle sufficient to allow the placement of inlet  10  within the anterior chamber of the eye when conduit  25  is oriented in Schlemm&#39;s canal. Inlet  10  may be selected to have a sufficient length, about 0.1 to 3.0 mm or about 2.0 mm, to extend from its junction with conduit  25  into Schlemm&#39;s canal towards the adjacent space of the anterior chamber. While many geometries can be used for channeling aqueous humor, an internal diameter of between about 0.1 and 0.5 mm, preferably 0.20 mm for a shunt having a round conduit shape. Although inlet  10  was discussed above and illustrated in  FIGS. 2A and 2B  as having a length extending into the anterior chamber, it is to be appreciated that in some embodiments, inlet  10  may simply be an opening in conduit  25  exposed to anterior chamber to permit fluid to enter conduit  25 .  
      Shunt  100  can be fabricated from a material that will be compatible with the tissues and fluids with which it is in contact. It is preferable that the shunt not be absorbed, corroded, or otherwise structurally compromised during its presence in situ. Moreover, it is also preferable that the eye tissues and the aqueous fluid remain non-detrimentally affected by the presence of the implanted device. A number of materials are available to meet the engineering and medical specifications for the shunts. In the exemplary embodiments of the present invention, shunt  100  is constructed of a biologically inert, flexible material such as silicone or similar polymers. Alternate materials might include, but are not limited to, thin-walled Teflon, polypropylene, other polymers or plastics, metals, or some combination of these materials. The material may contain a therapeutic agent deliverable to the adjacent tissues.  
      Because the nature of the iris  40  is such that it tends to comprise a plurality of rather flaccid fimbriae of tissue, it is desirable to avoid said fimbriae from being drawn into the lumen of a shunt, thus occluding the shunt. Therefore, inlet  10  may contain a plurality of fenestrations in a lateral surface of the inlet as well as the end of the end of the inlet to allow fluid ingress, arranged to prevent occlusion by the adjacent iris.  
      Furthermore, inlet  10  may be positioned sufficiently remotely from the iris  40  to prevent interference therewith. Shunt  100  may contain one or more unidirectional valves to prevent backflow into the anterior chamber from Schlemm&#39;s canal.  
      The conduit  25  may have a pre-formed curve to approximate the 6.0 mm radius of Schlemm&#39;s canal in a human eye. Such a pre-formed curvature may not be implemented when a flexible material is used to construct the shunt device  100 .  
       FIG. 3  is a cross sectional view of another embodiment according to aspects of the present invention. Shunt  200  is similar to shunt  100  described above, other than a pump  80  is added which controls flow through conduit  25  in response to a measured anterior chamber pressure measured by sensor  70 . Because many aspects of shunt  200  are the same as those described above with reference to  FIGS. 2A and 2B , only the aspects unique to shunt  200  or aspects that were not discussed above will be described below. It is to be appreciated that in the embodiment of  FIG. 3  Venturi feature  50  need not be actuatable (i.e., it may be non-actuatable). In such embodiments, a pressure change proximate inlet  10  is established by increasing or decreasing the flow rate through conduit  25 .  
      Pump  80  is inserted along Schlemm&#39;s canal in a manner such that fluid from the portion of Schlemm&#39;s canal enters an input  80   a  of pump  80  and flows to an output  80   b  of pump  80  into conduit  25  which is disposed in Schlemm&#39;s canal. Pump  80  is a pump capable of controlling the flow rate of fluid through Schlemm&#39;s canal (i.e., flow rate may be increased or decreased relative to the natural Schlemm&#39;s canal flow rate). Pump  80  may be connected to conduit  25 ; alternatively, pump  80  may be separate from conduit  25 , but fluidly coupled to conduit  25 . Pump  80  may comprise any suitable pump for controlling flow along Schlemm&#39;s canal. For example, the pump may be a peristaltic pump (e.g., a pump as described in U.S. Pat. No. 6,852,500 or U.S. Patent Applic. US2002/0013545, both to Soltanpour, et al; or U.S. Pat. No. 6,408,878 to Unger et al.). Alternatively, the pump may be a pump as described in U.S. Pat. No. 6,699,211 to Savage.  
      As described above, the flow rate that is established in conduit  25  affects the pressure proximate to Venturi feature  50 , and thereby affects the flow rate of fluid flowing into input  10  from the anterior chamber. Accordingly, by controlling flow rate using pump  80 , it is possible to control flow rate from the anterior chamber, and to thereby control the pressure within the anterior chamber.  
       FIG. 4  illustrates the placement of the exemplary embodiment of a shunt in an eye according to aspects of the present invention.  FIG. 4  illustrates the anterior chamber  35 , Schlemm&#39;s canal  30 , the iris  40 , cornea  45 , trabecular meshwork  50 , collecting channels  55 , pupil  65  and lens  70 . It should be noted that the inventive device is designed so that placement of conduit  25  within Schlemm&#39;s canal  30  results in an orientation of the inlet  10  within the anterior chamber  35  between the iris  40  and the inner surface of the cornea  45 .  
      Any suitable surgical procedure may be used to insert shunts as described herein. An exemplary surgical procedure to insert at least some shunt device according to aspects of the present invention includes an approach through a conjunctival flap. A partial thickness scleral flap is then created and dissected half-thickness into clear cornea. The posterior aspect of Schlemm&#39;s canal is identified and the canal is entered posteriorly. The anterior chamber may be deepened with injection of a viscoelastic and a miotic agent. The inlet of the shunt is then inserted through the inner wall of Schlemm&#39;s canal and trabecular meshwork into the anterior chamber within the angle between the iris and the cornea. In some cases, as incision may be needed from Schlemm&#39;s canal through the trabecular meshwork into the anterior chamber to facilitate passage of the proximal portion therethrough. One arm of the conduit (having proximal end  25   a ) is grasped and threaded into Schlemm&#39;s canal. In a similar fashion, the other arm of the conduit (having distal end  25   b ) may be inserted into Schlemm&#39;s canal in the opposing direction from the first arm. The scleral flap and conjunctival wound are closed in a conventional manner.  
      Having thus described the inventive concepts and a number of exemplary embodiments, it will be apparent to those skilled in the art that the invention may be implemented in various ways, and that modifications and improvements will readily occur to such persons. Thus, the embodiments are not intended to be limiting and presented by way of example only. The invention is limited only as required by the following claims and equivalents thereto.