Patent Publication Number: US-10307293-B2

Title: Methods for intraocular shunt placement

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/476,503, filed on Sep. 3, 2014, which is a continuation of U.S. patent application Ser. No. 12/946,572, filed on Nov. 15, 2010, now U.S. Pat. No. 8,852,256, the entirety of each of which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to methods for reducing intraocular pressure by creating a drainage pathway between the anterior chamber of the eye and the intra-Tenon&#39;s space. 
     BACKGROUND 
     Glaucoma is a disease in which the optic nerve is damaged, leading to progressive, irreversible loss of vision. It is typically associated with increased pressure of the fluid (i.e., aqueous humor) in the eye. Untreated glaucoma leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness. Once lost, this damaged visual field cannot be recovered. Glaucoma affects 1 in 200 people aged fifty and younger, and 1 in 10 over the age of eighty for a total of approximately 70 million people worldwide, and glaucoma is the second leading cause of blindness in the world. 
     The importance of lowering intraocular pressure (10P) in delaying glaucomatous progression has been well documented. When drug therapy fails, or is not tolerated, surgical intervention is warranted. Surgical filtration methods for lowering intraocular pressure by creating a fluid flow-path between the anterior chamber and the subconjunctival tissue have been described. One particular ab interno glaucoma filtration method has been described whereby an intraocular shunt is implanted by directing a needle which holds the shunt through the cornea, across the anterior chamber, and through the trabecular meshwork and sclera, and into the subconjunctival space. See, for example, U.S. Pat. No. 6,544,249, U.S. patent application publication number 2008/0108931 and U.S. Pat. No. 6,007,511. 
     Proper positioning of a shunt in the subconjunctival space is critical in determining the success or failure of subconjunctival glaucoma filtration surgery for a number of reasons. In particular, the location of the shunt has been shown to play a role in stimulating the formation of active drainage structures such as veins or lymph vessels. See, for example, U.S. patent application publication number 2008/0108933. In addition, it has been suggested that the conjunctiva itself plays a critical role in glaucoma filtration surgery. A healthy conjunctiva allows drainage channels to form and less opportunity for inflammation and scar tissue formation, which are frequent causes of failure in subconjunctival filtration surgery. See, for example, Yu et al., Progress in Retinal and Eye Research, 28: 303-328 (2009). 
     SUMMARY 
     The present invention generally relates to methods for deploying intraocular shunts into the subconjunctival space the eye while avoiding or minimizing contact with the conjunctiva. In particular, the present invention provides methods for deploying an intraocular shunt into the eye such that the shunt forms a drainage pathway from the anterior chamber of the eye to the region of the eye that is bound between the sclera and Tenon&#39;s capsule, referred to herein as the intra-Tenon&#39;s space. Deployment of an intraocular shunt such that the shunt inlet (i.e., the portion of the shunt that receives fluid from an anterior chamber of the eye) terminates in the anterior chamber and the shunt outlet (i.e., the portion of the shunt that directs fluid to the intra-Tenon&#39;s space) terminates in the intra-Tenon&#39;s space safeguards the integrity of the conjunctiva to allow subconjunctival drainage pathways to successfully form. 
     The methods of the invention involve inserting into the eye a hollow shaft that is configured to hold an intraocular shunt, deploying the shunt from the shaft such that the shunt forms a passage from the anterior chamber to the intra-Tenon&#39;s space, and withdrawing the hollow shaft from the eye. The hollow shaft may hold the shunt within the interior of hollow shaft. Alternatively, the hollow shaft may hold the shunt on an outer surface of the shaft. In certain embodiments, the methods of the invention involve the use of a hollow shaft configured to hold an intraocular shunt, as previously described, wherein a portion of the hollow shaft extends linearly along a longitudinal axis and at least one other portion of the shaft extends off the longitudinal axis, to insert and deploy the intraocular shunt into the eye such that the shunt forms a passage from the anterior chamber to the intra-Tenon&#39;s space. 
     Optionally, an aqueous fluid is injected into the eye simultaneously with or prior to the insertion and deployment steps of the methods of the invention. For example, an aqueous solution may be injected below Tenon&#39;s capsule to balloon the capsule away from the sclera and allow positioning of the intraocular shunt in the intra-Tenon&#39;s space. 
     Methods of the invention are typically conducted using an ab interno approach by inserting the hollow shaft configured to hold the intraocular shunt through the cornea, across the anterior chamber, through the sclera and into the intra-Tenon&#39;s space. Such an approach is contrasted with an ab externo approach, which involves inserting the shaft from the outside of the eye through the conjunctiva and inward through the sclera to reach a drainage structure such Schlemm&#39;s canal. Although, methods of the invention may be conducted using an ab externo approach. 
     Methods of the invention may be performed such that the shaft is inserted above or below the corneal limbus. Methods of the invention may also be performed such that the shaft is inserted into the eye without removing an anatomical feature of the eye, such as the trabecular meshwork, the iris, the cornea, or the aqueous humor. In certain embodiments, methods of the invention may be conducted without inducing substantial ocular inflammation such as, for example, subconjunctival blebbing or endophthalmitis. In other certain embodiments, methods of the invention may be conducted without the use of an optical apparatus, particularly an optical apparatus that directly contacts the eye, such as a goniolens. In yet other certain embodiments, the methods of the invention may be conducted using an optical apparatus that does not directly contact the eye, such as an ophthalmic microscope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  provides a cross-sectional diagram of the general anatomy of the eye. 
         FIG. 2  provides another cross-sectional view the eye, and certain anatomical structures of the eye. 
         FIG. 3  depicts, implantation of an intraocular shunt with a distal end of a deployment device holding a shunt, shown in cross-section. 
         FIG. 4  depicts an example of a hollow shaft configured to hold an intraocular shunt. 
         FIG. 5A  depicts a hollow shaft having a bend in a distal portion of the shaft. 
         FIG. 5B  depicts a hollow shaft having a U-shape.  FIG. 5C  depicts a hollow shaft having a V-shape. 
         FIG. 6A  depicts a simulation of the exit site distance from the limbus and height above the iris after needle entry at the limbus using an ab interno procedure.  FIG. 6B  depicts a simulation of the exit site distance from the limbus and height above the iris after needle entry above the limbus using an ab interno procedure. 
         FIG. 7A  depicts the tip bevel portion of a triple-ground needle tip.  FIG. 7B  depicts the flat bevel portion of a triple-ground needle tip.  FIG. 7C  depicts an intraocular shunt within a triple-ground needle tip.  FIG. 7D  depicts 100% penetration of the flat bevel portion of a triple-ground needle tip through the sclera of an eye. 
         FIG. 8A  depicts an intraocular shunt inserted into the scleral channel using a beveled needle tip to completely penetrate the scleral tissue prior to insertion of the shunt. 
         FIG. 8B  depicts an intraocular shunt inserted into the scleral channel using a beveled needle tip to partially penetrate the scleral tissue prior to insertion of the shunt. 
         FIG. 9  provides a schematic of a shunt having a flexible portion. 
         FIGS. 10A, 10B and 10C  provide schematics of a shunt implanted into an eye for regulation of fluid flow from the anterior chamber of the eye to a drainage structure of the eye. 
         FIGS. 11A-11C  show different embodiments of multi-port shunts.  FIG. 11A  shows an embodiment of a shunt in which the proximal portion of the shunt includes more than one port and the distal portion of the shunt includes a single port.  FIG. 11B  shows another embodiment of a shunt in which the proximal portion includes a single port and the distal portion includes more than one port.  FIG. 11C  shows another embodiment of a shunt in which the proximal portions include more than one port and the distal portions include more than one port. 
         FIGS. 12A and 12B  show different embodiments of multi-port shunts having different diameter ports. 
         FIGS. 13A-13C  provide schematics of shunts having a slit located along a portion of the length of the shunt. 
         FIG. 14  depicts a shunt having multiple slits along a length of the shunt. 
         FIG. 15  depicts a shunt having a slit at a proximal end of the shunt. 
         FIG. 16  provides a schematic of a shunt that has a variable inner diameter. 
         FIG. 17  is a schematic showing an embodiment of a shunt deployment device according to the invention. 
         FIG. 18  shows an exploded view of the device shown in  FIG. 17 . 
         FIGS. 19A-19D  are schematics showing different enlarged views of the deployment mechanism of the deployment device. 
         FIGS. 20A-20C  are schematics showing interaction of the deployment mechanism with a portion of the housing of the deployment device. 
         FIG. 21  shows a cross sectional view of the deployment mechanism of the deployment device. 
         FIGS. 22A and 22B  show schematics of the deployment mechanism in a pre-deployment configuration.  FIG. 22C  shows an enlarged view of the distal portion of the deployment device of  FIG. 22A . This figure shows an intraocular shunt loaded within a hollow shaft of the deployment device. 
         FIGS. 23A and 23B  show schematics of the deployment mechanism at the end of the first stage of deployment of the shunt from the deployment device.  FIG. 23C  shows an enlarged view of the distal portion of the deployment device of  FIG. 23A . This figure shows an intraocular shunt partially deployed from within a hollow shaft of the deployment device. 
         FIG. 24A  shows a schematic of the deployment device after deployment of the shunt from the device.  FIG. 24B  show a schematic of the deployment mechanism at the end of the second stage of deployment of the shunt from the deployment device.  FIG. 24C  shows an enlarged view of the distal portion of the deployment device after retraction of the shaft with the pusher abutting the shunt.  FIG. 24D  shows an enlarged view of the distal portion of the deployment device after deployment of the shunt. 
         FIGS. 25 and 26  show an intraocular shunt deployed within the eye. A proximal portion of the shunt resides in the anterior chamber and a distal portion of the shunt resides within the intra-Tenon&#39;s space. A middle portion of the shunt resides in the sclera. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  provides a schematic diagram of the general anatomy of the eye. An anterior aspect of the anterior chamber  1  of the eye is the cornea  2 , and a posterior aspect of the anterior chamber  1  of the eye is the iris  4 . Beneath the iris  4  is the lens  5 . The anterior chamber  1  is filled with aqueous humor  3 . The aqueous humor  3  drains into a space(s)  6  below the conjunctiva  7  through the trabecular meshwork (not shown in detail) of the sclera  8 . The aqueous humor is drained from the space(s)  6  below the conjunctiva  7  through a venous drainage system (not shown). 
       FIG. 2  provides a cross-sectional view of a portion of the eye, and provides greater detail regarding certain anatomical structures of the eye. In particular,  FIG. 2  shows the relationship of the conjunctiva  12  and Tenon&#39;s capsule  13 . Tenon&#39;s capsule  13  is a fascial layer of connective tissue surrounding the globe and extra-ocular muscles. As shown in  FIG. 2 , it is attached anteriorly to the limbus of the eye and extends posteriorly over the surface of the globe until it fuses with the dura surrounding the optic nerve. In  FIG. 2 , number  9  denotes the limbal fusion of the conjunctiva  12  and Tenon&#39;s capsule  13  to the sclera  11 . The conjunctiva  12  and Tenon&#39;s capsule  13  are separate membranes that start at the limbal fusion  9  and connect to tissue at the posterior of the eye. The space formed below the conjunctiva  12  is referred to as the subconjunctival space, denoted as number  14 . Below Tenon&#39;s capsule  13  there are Tenon&#39;s adhesions that connect the Tenon&#39;s capsule  13  to the sclera  11 . The space between Tenon&#39;s capsule  13  and the sclera  11  where the Tenon&#39;s adhesions connect the Tenon&#39;s capsule  13  to the sclera  11  is referred to as the intra-Tenon&#39;s space, denoted as number  10 . 
     In conditions of glaucoma, the pressure of the aqueous humor in the eye (anterior chamber) increases and this resultant increase of pressure can cause damage to the vascular system at the back of the eye and especially to the optic nerve. The treatment of glaucoma and other diseases that lead to elevated pressure in the anterior chamber involves relieving pressure within the anterior chamber to a normal level. 
     Glaucoma filtration surgery is a surgical procedure typically used to treat glaucoma. The procedure involves placing a shunt in the eye to relieve intraocular pressure by creating a fluid-flow pathway for draining aqueous humor from the anterior chamber of the eye. The shunt is typically positioned in the eye such that it creates a drainage pathway between the anterior chamber of the eye and a region of lower pressure. Various structures and/or regions of the eye having lower pressure that have been targeted for aqueous humor drainage include Schlemm&#39;s canal, the subconjunctival space, the episcleral vein, the suprachoroidal space, or the subarachnoid space. Methods of implanting intraocular shunts are known in the art. Shunts may be implanted using an ab externo approach (entering through the conjunctiva and inwards through the sclera) or an ab interno approach (entering through the cornea, across the anterior chamber, through the trabecular meshwork and sclera). 
     Ab interno approaches for implanting an intraocular shunt in the subconjunctival space are shown for example in Yu et al. (U.S. Pat. No. 6,544,249 and U.S. patent publication number 2008/0108933) and Prywes (U.S. Pat. No. 6,007,511), the contents of each of which are incorporated by reference herein in its entirety. Briefly and with reference to  FIG. 3 , a surgical intervention to implant the shunt involves inserting into the eye a deployment device  15  that holds an intraocular shunt, and deploying the shunt within the eye  16 . A deployment device  15  holding the shunt enters the eye  16  through the cornea  17  (ab interno approach). The deployment device  15  is advanced across the anterior chamber  20  (as depicted by the broken line) in what is referred to as a transpupil implant insertion. The deployment device  15  is advanced through the sclera  21  until a distal portion of the device is in proximity to the subconjunctival space. The shunt is then deployed from the deployment device, producing a conduit between the anterior chamber and the subconjunctival space to allow aqueous humor to drain through the conjunctival lymphatic system. 
     While such ab interno subconjunctival filtration procedures have been successful in relieving intraocular pressure, there is a substantial risk that the intraocular shunt may be deployed too close to the conjunctiva, resulting in irritation and subsequent inflammation and/or scarring of the conjunctiva, which can cause the glaucoma filtration procedure to fail (See Yu et al., Progress in Retinal and Eye Research, 28: 303-328 (2009)). Additionally, commercially available shunts that are currently utilized in such procedures are not ideal for ab interno subconjunctival placement due to the length of the shunt (i.e., too long) and/or the materials used to make the shunt (e.g., gold, polymer, titanium, or stainless steel), and can cause significant irritation to the tissue surrounding the shunt, as well as the conjunctiva, if deployed too close. 
     The present invention provides methods for deploying an intraocular shunt into an eye such that the shunt forms a passage from the anterior chamber of the eye to the intra-Tenon&#39;s space. The present invention further relates to intraocular shunts that are designed to form a drainage pathway between the anterior chamber of the eye and the intra-Tenon&#39;s space and are suitable for use in an ab interno glaucoma filtration procedure. Deployment and/or design of an intraocular shunt such that the inlet terminates in the anterior chamber and the outlet terminates in the intra-Tenon&#39;s space safeguards the integrity of the conjunctiva to allow subconjunctival drainage pathways to successfully form. The conjunctiva is protected from direct contact with the shunt by Tenon&#39;s capsule. Additionally, drainage into the intra-Tenon&#39;s space provides access to more lymphatic channels than just the conjunctival lymphatic system, such as the episcleral lymphatic network. Moreover, deployment and/or design of an intraocular shunt such that the outlet terminates in the intra-Tenon&#39;s space avoids having to pierce Tenon&#39;s capsule which can otherwise cause complications during glaucoma filtration surgery due to its tough and fibrous nature. 
     Methods for Intra-Tenon&#39;s Shunt Placement 
     The methods of the invention involve inserting into the eye a hollow shaft configured to hold an intraocular shunt. In certain embodiments, the hollow shaft is a component of a deployment device that may deploy the intraocular shunt. The shunt is then deployed from the shaft into the eye such that the shunt forms a passage from the anterior chamber to the intra-Tenon&#39;s space. The hollow shaft is then withdrawn from the eye. 
     Referring to  FIGS. 25 and 26 , which show an intraocular shunt placed into the eye such that the shunt forms a passage for fluid drainage from the anterior chamber to the intra-Tenon&#39;s space. To place the shunt within the eye, a surgical intervention to implant the shunt is performed that involves inserting into the eye  202  a deployment device  200  that holds an intraocular shunt  201 , and deploying at least a portion of the shunt  201  within intra-Tenon&#39;s space  208 , within the subconjunctival space  209  beneath the conjunctiva  210 . In certain embodiments, a hollow shaft  206  of a deployment device  200  holding the shunt  201  enters the eye  202  through the cornea  203  (ab interno approach). The shaft  206  is advanced across the anterior chamber  204  (as depicted by the broken line) in what is referred to as a transpupil implant insertion. The shaft  206  is advanced through the sclera  205  until a distal portion of the shaft  206  is in proximity to Tenon&#39;s capsule  207 . After piercing the sclera  205  with the hollow shaft  206  of the deployment device  200 , resistance to advancement of the shaft  206  encountered by an operator of the deployment device  200  informs the operator that the shalt  206  has contacted Tenon&#39;s capsule  207  and is thus in proximity to Tenon&#39;s capsule  207 . 
     Numerous techniques may be employed to ensure that after piercing the sclera  205 , the hollow shaft  206  does not pierce Tenon&#39;s capsule  207 . In certain embodiments, the methods of the invention involve the use of a hollow shaft  206 , in which a portion of the hollow shaft extends linearly along a longitudinal axis and at least one other portion of the shaft extends off the longitudinal axis. For example, the hollow shaft  206  may have a bend in the distal portion of the shaft, a U-shape, or an arcuate or V-shape in at least a portion of the shaft. Examples of such hollow shafts  206  suitable for use with the methods of the invention include but are not limited to the hollow shafts  206  depicted in  FIGS. 5A-5C . In embodiments in which the hollow shaft  206  has a bend at a distal portion of the shaft, intra-Tenon&#39;s shunt placement can be achieved by using the bent distal portion of the shaft  206  to push Tenon&#39;s capsule  207  away from the sclera  205  without penetrating Tenon&#39;s capsule  207 . In these embodiments, the tip of the distal end of the shaft  206  does not contact Tenon&#39;s capsule  207 . 
     In other embodiments, a straight hollow shaft  206  having a beveled tip is employed. The angle of the beveled tip of the hollow shaft is oriented such that after piercing the sclera  205 , the hollow shaft  206  does not pierce Tenon&#39;s capsule  207 . In these embodiments, the shaft  206  is inserted into the eye  202  and through the sclera  205  at an angle such that the bevel of the tip is oriented to be parallel to Tenon&#39;s capsule  207 , thereby pushing Tenon&#39;s capsule  207  away from the sclera  205 , rather than penetrating Tenon&#39;s capsule  207 , and allowing for deployment of a distal portion of the shunt  201  into the intra-Tenon&#39;s space  208 . 
     Once a distal portion of the hollow shaft  206  is within the intra-Tenon&#39;s space  208 , the shunt  201  is then deployed from the shaft  206  of the deployment device  200 , producing a conduit between the anterior chamber  204  and the intra-Tenon&#39;s space  208  to allow aqueous humor to drain from the anterior chamber  204  (See  FIGS. 25 and 26 ). 
       FIG. 4  provides an exemplary schematic of a hollow shaft for use in accordance with the methods of the invention. This figure shows a hollow shaft  22  that is configured to hold an intraocular shunt  23 . The shaft may hold the shunt within the hollow interior  24  of the shaft, as is shown in  FIG. 4 . Alternatively, the hollow shaft may hold the shunt on an outer surface  25  of the shaft. In particular embodiments, the shunt is held within the hollow interior of the shaft  24 , as is shown in  FIG. 4 . Generally, in one embodiment, the intraocular shunts are of a cylindrical shape and have an outside cylindrical wall and a hollow interior. The shunt may have an inside diameter of approximately 10-250 μm, an outside diameter of approximately 190-300 μm, and a length of approximately 0.5 mm to 20 mm. The hollow shaft  22  is configured to at least hold a shunt of such shape and such dimensions. However, the hollow shaft  22  may be configured to hold shunts of different shapes and different dimensions than those described above, and the invention encompasses a shaft  22  that may be configured to hold any shaped of dimensioned intraocular shunt. 
     Preferably, the methods of the invention are conducted by making an incision in the eye prior to insertion of the deployment device. Although in particular embodiments, the methods of the invention may be conducted without making an incision in the eye prior to insertion of the deployment device. In certain embodiments, the shaft that is connected to the deployment device has a sharpened point or tip. In certain embodiments, the hollow shaft is a needle. Exemplary needles that may be used are commercially available from Terumo Medical Corp. (Elkington, Md.). In a particular embodiment, the needle has a hollow interior and a beveled tip, and the intraocular shunt is held within the hollow interior of the needle. In another particular embodiment, the needle has a hollow interior and a triple ground point or tip. 
     The methods of the invention are preferably conducted without needing to remove an anatomical portion or feature of the eye, including but not limited to the trabecular meshwork, the iris, the cornea, or aqueous humor. The methods of the invention are also preferably conducted without inducing substantial ocular inflammation, such as subconjunctival blebbing or endophthalmitis. Such methods can be achieved using an ab interno approach by inserting the hollow shaft through the cornea, across the anterior chamber, through the trabecular meshwork and sclera and into the intra-Tenon&#39;s space. However, the methods of the invention may be conducted using an ab externo approach. 
     In another embodiment, the methods of the invention further involves injecting an aqueous solution into the eye below Tenon&#39;s capsule in order to balloon the capsule away from the sclera. The increase in intra-Tenon&#39;s space caused by the ballooning of Tenon&#39;s capsule is helpful for positioning of the outlet of the shunt in the intra-Tenon&#39;s space. The solution is injected prior to the shaft piercing the sclera and entering the intra-Tenon&#39;s space. Suitable aqueous solutions include but are not limited to Dulbecco&#39;s Phosphate Buffered Saline (DPBS), Hank&#39;s Balanced Salt Solution (HBSS), Phosphate-Buffered Saline (PBS), Earle&#39;s Balanced Salt Solution (EBSS), or other balanced salt solutions known in the art. In some embodiments, the methods of the invention involve injecting a viscoelastic fluid into the eye. Preferably, the methods of the invention are conducted without the use of a viscoelastic fluid. 
     When the methods of the invention are conducted using an ab interno approach, the angle of entry through the cornea affects optimal placement of the shunt in the intra-Tenon&#39;s space. Preferably, the hollow shaft is inserted into the eye at an angle above or below the corneal limbus, in contrast with entering through the corneal limbus. For example, the hollow shaft is inserted approximately 0.25 to 3.0 mm, preferably approximately 0.5 to 2.5 mm, more preferably approximately 1.0 mm to 2.0 mm above the corneal limbus, or any specific value within said ranges, e.g., approximately 1.0 mm, approximately 1.1 mm, approximately 1.2 mm, approximately 1.3 mm, approximately 1.4 mm, approximately 1.5 mm, approximately 1.6 mm, approximately 1.7 mm, approximately 1.8 mm, approximately 1.9 mm or approximately 2.0 mm above the corneal limbus. 
     Without intending to be bound by any theory, placement of the shunt farther from the limbus at the exit site, as provided by an angle of entry above the limbus, is believed to provide access to more lymphatic channels for drainage of aqueous humor, such as the episcleral lymphatic network, in addition to the conjunctival lymphatic system. A higher angle of entry also results in flatter placement in the intra-Tenon&#39;s space so that there is less bending of the shunt, less pressure on Tenon&#39;s capsule, and subsequently less erosion pressure on the conjunctiva via Tenon&#39;s capsule. 
     For example, as shown in  FIG. 6A , shaft entry at the limbus  52  results in exit site distance  53  of approximately 1.6 mm from the limbus, and very close proximity to the iris  4 . Such placement results in a large degree of bending of the shunt, resulting in increased pressure on Tenon&#39;s capsule and subsequently on the conjunctiva. In contrast, a high angle of entry  54  above the limbus  52  (e.g., 2 mm above the limbus  52 ), results in an exit site distance  53  of approximately 2.1 mm from the limbus and a height well above the iris  4 , as shown in  FIG. 6B . Such placement results in flatter placement in the intra-Tenon&#39;s space so that there is less bending of the shunt, less pressure on Tenon&#39;s capsule, and subsequently less erosion pressure on the conjunctiva via Tenon&#39;s capsule. 
     In certain embodiments, to ensure proper positioning and functioning of the intraocular shunt, the depth of penetration through the sclera is important when conducting the methods of the invention. In one embodiment, the distal tip of the hollow shaft pierces the sclera without coring, removing or causing major tissue distortion of the surrounding eye tissue. The shunt is then deployed from the shaft. Preferably, a distal portion of the hollow shaft (as opposed to the distal tip) completely penetrates the sclera before the shunt is deployed from the hollow shaft. In certain embodiments, the hollow shaft is a flat bevel needle, such as a needle having a triple-ground point. The tip bevel first pierces through the sclera making a horizontal slit. In a preferred embodiment of the methods of the invention, the needle is advanced even further such that the entire flat bevel penetrates through the sclera, as shown in  FIG. 7D , to spread and open the tissue to a full circular diameter. The tip bevel portion  56  and flat bevel portion  58  of a triple ground needle point, and the configuration of the shunt  23  disposed in the needle point, are exemplified as the gray shaded areas in  FIGS. 7A-7C . Without intending to be bound by any theory, if the scleral channel is not completely forced open by the flat bevel portion of the needle, the material around the opening may not be sufficiently stretched and a pinching of the implant in that zone will likely occur, causing the shunt to fail. Full penetration of the flat bevel through the sclera causes minor distortion and trauma to the local area. However, this area ultimately surrounds and conforms to the shunt once the shunt is deployed in the eye. 
       FIG. 8A  depicts an example of an intraocular shunt implanted in an eye in accordance with the methods of the invention using a triple ground need point with 100% penetration of the flat bevel in the scleral channel.  FIG. 8B  depicts an example of a shunt implanted in an eye in accordance with the methods of the invention using a triple ground needle point with approximately 50% penetration of the flat bevel in the scleral channel. As shown in  FIG. 8B , the shunt is almost completely pinched off as compared to the open shunt depicted in  FIG. 8A . 
     The methods of the invention may be conducted using any commercially available shunts, such as the Optonol Ex-PRESS mini Glaucoma shunt, and the Solx DeepLight Gold Micro-Shunt. However, the methods of the invention are preferably conducted using the intraocular shunts of the present invention, as described herein. 
     Intraocular Shunts 
     The present invention also provides intraocular shunts that are configured to form a drainage pathway from the anterior chamber of the eye to the intra-Tenon&#39;s space. In particular, the intraocular shunts of the invention have a length that is sufficient to form a drainage pathway from the anterior chamber of the eye to the intra-Tenon&#39;s space. The length of the shunt is important in achieving placement specifically in the intra-Tenon&#39;s space. A shunt that is too long will extend beyond the intra-Tenon&#39;s space and irritate the conjunctiva, which can cause the filtration procedure to fail, as previously described. A shunt that is too short will not provide sufficient access to drainage pathways such as the episcleral lymphatic system or the conjunctival lymphatic system. 
     Shunts of the invention may be any length that allows for drainage of aqueous humor from an anterior chamber of an eye to the intra-Tenon&#39;s space. Exemplary shunts range in length from approximately 0.5 mm to approximately 20 mm or between approximately 4 mm to approximately 16 mm, or any specific value within said ranges. In certain embodiments, the length of the shunt is between approximately 6 to 8 mm, or any specific value within said range, e.g., 6.0 mm, 6.1 mm, 6.2 mm, 6.3 mm, 6.4 mm, 6.5 mm, 6.6 mm, 6.7 mm, 6.8 mm, 6.9 mm, 7 mm, 7.1 mm, 7.2 mm, 7.3 mm, 7.4 mm, 7.5 mm, 7.6 mm, 7.7 mm, 7.8 mm, 7.9 mm, or 8.0 mm. 
     The intraocular shunts of the invention are particularly suitable for use in an ab interno glaucoma filtration procedure. Commercially available shunts that are currently used in ab interno filtration procedures are typically made of a hard, inflexible material such as gold, polymer, titanium, or stainless steel, and cause substantial irritation of the eye tissue, resulting in ocular inflammation such as subconjunctival blebbing or endophthalmitis. In contrast, the intraocular shunts of the invention are flexible, and have an elasticity modulus that is substantially identical to the elasticity modulus of the surrounding tissue in the implant site. As such, the intraocular shunts of the invention are easily bendable, do not erode or cause a tissue reaction, and do not migrate once implanted. Thus, when implanted in the eye using an ab interno procedure, such as the methods described herein, the intraocular shunts of the invention do not induce substantial ocular inflammation such as subconjunctival blebbing or endophthalmitis. Additional exemplary features of the intraocular shunts of the invention are discussed in further detail below. 
     Tissue Compatible Shunts 
     In certain aspects, the invention generally provides shunts composed of a material that has an elasticity modulus that is compatible with an elasticity modulus of tissue surrounding the shunt. In this manner, shunts of the invention are flexibility matched with the surrounding tissue, and thus will remain in place after implantation without the need for any type of anchor that interacts with the surrounding tissue. Consequently, shunts of the invention will maintain fluid flow away for an anterior chamber of the eye after implantation without causing irritation or inflammation to the tissue surrounding the eye. 
     Elastic modulus, or modulus of elasticity, is a mathematical description of an object or substance&#39;s tendency to be deformed elastically when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress-strain curve in the elastic deformation region: 
             λ   ⁢     =   def     ⁢     stress   strain           
where lambda (λ) is the elastic modulus; stress is the force causing the deformation divided by the area to which the force is applied; and strain is the ratio of the change caused by the stress to the original state of the object. The elasticity modulus may also be known as Young&#39;s modulus (E), which describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis. Young&#39;s modulus is defined as the ratio of tensile stress to tensile strain. For further description regarding elasticity modulus and Young&#39;s modulus, see for example Gere (Mechanics of Materials, 6 th  Edition, 2004, Thomson), the content of which is incorporated by reference herein in its entirety.
 
     The elasticity modulus of any tissue can be determined by one of skill in the art. See for example Samani et al. (Phys. Med. Biol. 48:2183, 2003); Erkamp et al. (Measuring The Elastic Modulus Of Small Tissue Samples, Biomedical Engineering Department and Electrical Engineering and Computer Science Department University of Michigan Ann Arbor, Mich. 48109-2125; and Institute of Mathematical Problems in Biology Russian Academy of Sciences, Pushchino, Moscow Region 142292 Russia); Chen et al. (IEEE Trans. Ultrason. Ferroelec. Freq. Control 43:191-194, 1996); Hall, (In 1996 Ultrasonics Symposium Proc., pp. 1193-1196, IEEE Cat. No. 96CH35993, IEEE, New York, 1996); and Parker (Ultrasound Med. Biol. 16:241-246, 1990), each of which provides methods of determining the elasticity modulus of body tissues. The content of each of these is incorporated by reference herein in its entirety. 
     The elasticity modulus of tissues of different organs is known in the art. For example, Pierscionek et al. (Br J Ophthalmol, 91:801-803, 2007) and Friberg (Experimental Eye Research, 473:429-436, 1988) show the elasticity modulus of the cornea and the sclera of the eye. The content of each of these references is incorporated by reference herein in its entirety. Chen, Hall, and Parker show the elasticity modulus of different muscles and the liver. Erkamp shows the elasticity modulus of the kidney. 
     Shunts of the invention are composed of a material that is compatible with an elasticity modulus of tissue surrounding the shunt. In certain embodiments, the material has an elasticity modulus that is substantially identical to the elasticity modulus of the tissue surrounding the shunt. In other embodiments, the material has an elasticity modulus that is greater than the elasticity modulus of the tissue surrounding the shunt. Exemplary materials includes biocompatible polymers, such as polycarbonate, polyethylene, polyethylene terephthalate, polyimide, polystyrene, polypropylene, poly(styrene-b-isobutylene-b-styrene), or silicone rubber. 
     In particular embodiments, shunts of the invention are composed of a material that has an elasticity modulus that is compatible with the elasticity modulus of tissue in the eye, particularly scleral tissue. In certain embodiments, compatible materials are those materials that are softer than scleral tissue or marginally harder than scleral tissue, yet soft enough to prohibit shunt migration. The elasticity modulus for anterior scleral tissue is approximately 2.9±1.4×10 6  N/m 2 , and 1.8±1.1×10 6  N/m 2  for posterior sclera tissue. See Friberg (Experimental Eye Research, 473:429-436, 1988). An exemplary material is cross linked gelatin derived from Bovine or Porcine Collagen. 
     The invention encompasses shunts of different shapes and different dimensions, and the shunts of the invention may be any shape or any dimension that may be accommodated by the eye. In certain embodiments, the intraocular shunt is of a cylindrical shape and has an outside cylindrical wall and a hollow interior. The shunt may have an inside diameter from approximately 10 μm to approximately 250 μm, an outside diameter from approximately 190 μm to approximately 300 μm, and a length from approximately 0.5 mm to approximately 20 mm. 
     Shunts Reactive to Pressure 
     In other aspects, the invention generally provides shunts in which a portion of the shunt is composed of a flexible material that is reactive to pressure, i.e., the diameter of the flexible portion of the shunt fluctuates depending upon the pressures exerted on that portion of the shunt.  FIG. 9  provides a schematic of a shunt  23  having a flexible portion  51 . In this figure, the flexible portion  51  is shown in the middle of the shunt  23 . However, the flexible portion  51  may be located in any portion of the shunt, such as the proximal or distal portion of the shunt. In certain embodiments, the entire shunt is composed of the flexible material, and thus the entire shunt is flexible and reactive to pressure. 
     The flexible portion  51  of the shunt  23  acts as a valve that regulates fluid flow through the shunt. The human eye produces aqueous humor at a rate of about 2 μl/min for approximately 3 ml/day. The entire aqueous volume is about 0.25 ml. When the pressure in the anterior chamber falls after surgery to about 7-8 mmHg, it is assumed the majority of the aqueous humor is exiting the eye through the implant since venous backpressure prevents any significant outflow through normal drainage structures (e.g., the trabecular meshwork). 
     After implantation, intraocular shunts have pressure exerted upon them by tissues surrounding the shunt (e.g., scleral tissue such as the sclera channel and the sclera exit) and pressure exerted upon them by aqueous humor flowing through the shunt. The flow through the shunt, and thus the pressure exerted by the fluid on the shunt, is calculated by the equation: 
             Φ   =       dV   dt     =       υπ   ⁢           ⁢     R   2       =           π   ⁢           ⁢     R   4         8   ⁢   η       ⁢     (         -   Δ     ⁢           ⁢   P       Δ   ⁢           ⁢   x       )       =         π   ⁢           ⁢     R   4         8   ⁢   η       ⁢            Δ   ⁢           ⁢   P          L                   
where Φ is the volumetric flow rate: V is a volume of the liquid poured (cubic meters); t is the time (seconds); υ is mean fluid velocity along the length of the tube (meters/second); x is a distance in direction of flow (meters); R is the internal radius of the tube (meters); ΔP is the pressure difference between the two ends (pascals); η is the dynamic fluid viscosity (pascal-second (Pa·s)); and L is the total length of the tube in the x direction (meters).
 
       FIG. 10A  provides a schematic of a shunt  26  implanted into an eye for regulation of fluid flow from the anterior chamber of the eye to an area of lower pressure (e.g., the intra-Tenon&#39;s space, the subconjunctival space, the episcleral vein, the suprachoroidal space, or Schlemm&#39;s canal). In certain embodiments, the area of lower pressure is the subarachnoid space. The shunt is implanted such that a proximal end  27  of the shunt  26  resides in the anterior chamber  28  of the eye, and a distal end  29  of the shunt  26  resides outside of the anterior chamber to conduct aqueous humor from the anterior chamber to an area of lower pressure. A flexible portion  30  of the shunt  26  spans at least a portion of the sclera of the eye. As shown in  FIG. 10A , the flexible portion spans an entire length of the sclera  21 . 
     When the pressure exerted on the flexible portion  30  of the shunt  26  by sclera  31  (vertical arrows) is greater than the pressure exerted on the flexible portion  30  of the shunt  26  by the fluid flowing through the shunt (horizontal arrow), the flexible portion  30  decreases in diameter, restricting flow through the shunt  26  ( FIG. 10B ). The restricted flow results in aqueous humor leaving the anterior chamber  28  at a reduced rate. 
     When the pressure exerted on the flexible portion  30  of the shunt  26  by the fluid flowing through the shunt (horizontal arrow) is greater than the pressure exerted on the flexible portion  30  of the shunt  26  by the sclera  31  (vertical arrows), the flexible portion  30  increases in diameter, increasing flow through the shunt  26  ( FIG. 10C ). The increased flow results in aqueous humor leaving the anterior chamber  28  at an increased rate. 
     The invention encompasses shunts of different shapes and different dimensions, and the shunts of the invention may be any shape or any dimension that may be accommodated by the eye. In certain embodiments, the intraocular shunt is of a cylindrical shape and has an outside cylindrical wall and a hollow interior. The shunt may have an inside diameter from approximately 10 μm to approximately 250 μm, an outside diameter from approximately 190 μm to approximately 300 μm, and a length from approximately 0.5 mm to approximately 20 mm. 
     In particular embodiments, the shunt has a length of about 6 mm and an inner diameter of about 64 μm. With these dimensions, the pressure difference between the proximal end of the shunt that resides in the anterior chamber and the distal end of the shunt that resides outside the anterior chamber is about 4.3 mmHg. Such dimensions thus allow the implant to act as a controlled valve and protect the integrity of the anterior chamber. 
     It will be appreciated that different dimensioned implants may be used. For example, shunts that range in length from about 0.5 mm to about 20 mm and have a range in inner diameter from about 10 μm to about 100 μm allow for pressure control from approximately 0.5 mmHg to approximately 20 mmHg. 
     The material of the flexible portion and the thickness of the wall of the flexible portion will determine how reactive the flexible portion is to the pressures exerted upon it by the surrounding tissue and the fluid flowing through the shunt. Generally, with a certain material, the thicker the flexible portion, the less responsive the portion will be to pressure. In certain embodiments, the flexible portion is a gelatin or other similar material, and the thickness of the gelatin material forming the wall of the flexible portion ranges from about 10 μm thick to about 100 μm thick. 
     In a certain embodiment, the gelatin used for making the flexible portion is known as gelatin Type B from bovine skin. An exemplary gelatin is PB Leiner gelatin from bovine skin, Type B, 225 Bloom, USP. Another material that may be used in the making of the flexible portion is a gelatin Type A from porcine skin, also available from Sigma Chemical. Such gelatin is available from Sigma Chemical Company of St. Louis, Mo. under Code G-9382. Still other suitable gelatins include bovine bone gelatin, porcine bone gelatin and human-derived gelatins. In addition to gelatins, the flexible portion may be made of hydroxypropyl methylcellulose (HPMC), collagen, polylactic acid, polylglycolic acid, hyaluronic acid and glycosaminoglycans. 
     In certain embodiments, the gelatin is cross-linked. Cross-linking increases the inter- and intramolecular binding of the gelatin substrate. Any method for cross-linking the gelatin may be used. In a particular embodiment, the formed gelatin is treated with a solution of a cross-linking agent such as, but not limited to, glutaraldehyde. Other suitable compounds for cross-linking include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). Cross-linking by radiation, such as gamma or electron beam (e-beam) may be alternatively employed. 
     In one embodiment, the gelatin is contacted with a solution of approximately 25% glutaraldehyde for a selected period of time. One suitable form of glutaraldehyde is a grade 1G5882 glutaraldehyde available from Sigma Aldridge Company of Germany, although other glutaraldehyde solutions may also be used. The pH of the glutaraldehyde solution should be in the range of 7 to 7.8 and, more particularly, 7.35-7.44 and typically approximately 7.4+/−0.01. If necessary, the pH may be adjusted by adding a suitable amount of a base such as sodium hydroxide as needed. 
     Methods for forming the flexible portion of the shunt are shown for example in Yu et al. (U.S. patent application number 2008/0108933), the content of which is incorporated by reference herein in its entirety. In an exemplary protocol, the flexible portion may be made by dipping a core or substrate such as a wire of a suitable diameter in a solution of gelatin. The gelatin solution is typically prepared by dissolving a gelatin powder in de-ionized water or sterile water for injection and placing the dissolved gelatin in a water bath at a temperature of approximately 55° C., with thorough mixing to ensure complete dissolution of the gelatin. In one embodiment, the ratio of solid gelatin to water is approximately 10% to 50% gelatin by weight to 50% to 90% by weight of water. In an embodiment, the gelatin solution includes approximately 40% by weight, gelatin dissolved in water. The resulting gelatin solution should be devoid of air bubbles and has a viscosity that is between approximately 200-500 cp and more particularly between approximately 260 and 410 cp (centipoise). 
     Once the gelatin solution has been prepared, in accordance with the method described above, supporting structures such as wires having a selected diameter are dipped into the solution to form the flexible portion. Stainless steel wires coated with a biocompatible, lubricious material such as polytetrafluoroethylene (Teflon) are preferred. 
     Typically, the wires are gently lowered into a container of the gelatin solution and then slowly withdrawn. The rate of movement is selected to control the thickness of the coat. In addition, it is preferred that the tube be removed at a constant rate in order to provide the desired coating. To ensure that the gelatin is spread evenly over the surface of the wire, in one embodiment, the wires may be rotated in a stream of cool air which helps to set the gelatin solution and affix film onto the wire. Dipping and withdrawing the wire supports may be repeated several times to further ensure even coating of the gelatin. Once the wires have been sufficiently coated with gelatin, the resulting gelatin films on the wire may be dried at room temperature for at least 1 hour, and more preferably, approximately 10 to 24 hours. Apparatus for forming gelatin tubes are described in Yu et al. (U.S. patent application number 2008/0108933). 
     Once dried, the formed flexible portions may be treated with a cross-linking agent. In one embodiment, the formed flexible portion may be cross-linked by dipping the wire (with film thereon) into the 25% glutaraldehyde solution, at pH of approximately 7.0-7.8 and more preferably approximately 7.35-7.44 at room temperature for at least 4 hours and preferably between approximately 10 to 36 hours, depending on the degree of cross-linking desired. In one embodiment, the formed flexible portion is contacted with a cross-linking agent such as gluteraldehyde for at least approximately 16 hours. Cross-linking can also be accelerated when it is performed a high temperatures. It is believed that the degree of cross-linking is proportional to the bioabsorption time of the shunt once implanted. In general, the more cross-linking, the longer the survival of the shunt in the body. 
     The residual glutaraldehyde or other cross-linking agent is removed from the formed flexible portion by soaking the tubes in a volume of sterile water for injection. The water may optionally be replaced at regular intervals, circulated or re-circulated to accelerate diffusion of the unbound glutaraldehyde from the tube. The tubes are washed for a period of a few hours to a period of a few months with the ideal time being 3-14 days. The now cross-linked gelatin tubes may then be dried (cured) at ambient temperature for a selected period of time. It has been observed that a drying period of approximately 48-96 hours and more typically 3 days (i.e., 72 hours) may be preferred for the formation of the cross-linked gelatin tubes. 
     Where a cross-linking agent is used, it may be desirable to include a quenching agent in the method of making the flexible portion. Quenching agents remove unbound molecules of the cross-linking agent from the formed flexible portion. In certain cases, removing the cross-linking agent may reduce the potential toxicity to a patient if too much of the cross-linking agent is released from the flexible portion. In certain embodiments, the formed flexible portion is contacted with the quenching agent after the cross-linking treatment and, may be included with the washing/rinsing solution. Examples of quenching agents include glycine or sodium borohydride. 
     After the requisite drying period, the formed and cross-linked flexible portion is removed from the underlying supports or wires. In one embodiment, wire tubes may be cut at two ends and the formed gelatin flexible portion slowly removed from the wire support. In another embodiment, wires with gelatin film thereon, may be pushed off using a plunger or tube to remove the formed gelatin flexible portion. 
     Multi-Port Shunts 
     Other aspects of the invention generally provide multi-port shunts. Such shunts reduce probability of the shunt clogging after implantation because fluid can enter or exit the shunt even if one or more ports of the shunt become clogged with particulate. In certain embodiments, the shunt includes a hollow body defining a flow path and more than two ports, in which the body is configured such that a proximal portion receives fluid from the anterior chamber of an eye and a distal portion directs the fluid to the intra-Tenon&#39;s space. 
     The shunt may have many different configurations.  FIG. 11A  shows an embodiment of a shunt  32  in which the proximal portion of the shunt (i.e., the portion disposed within the anterior chamber of the eye) includes more than one port (designated as numbers  33   a  to  33   e ) and the distal portion of the shunt (i.e., the portion that is located in the intra-Tenon&#39;s space) includes a single port  34 .  FIG. 11B  shows another embodiment of a shunt  32  in which the proximal portion includes a single port  33  and the distal portion includes more than one port (designated as numbers  34   a  to  34   e ).  FIG. 11C  shows another embodiment of a shunt  32  in which the proximal portions include more than one port (designated as numbers  33   a  to  33   e ) and the distal portions include more than one port (designated as numbers  34   a  to  34   e ). While  FIG. 11A-11C  show shunts have five ports at the proximal portion, distal portion, or both, those shunts are only exemplary embodiments. The ports may be located along any portion of the shunt, and shunts of the invention include all shunts having more than two ports. For example, shunts of the invention may include at least three ports, at least four ports, at least five ports, at least 10 ports, at least 15 ports, or at least 20 ports. 
     The ports may be positioned in various different orientations and along various different portions of the shunt. In certain embodiments, at least one of the ports is oriented at an angle to the length of the body. In certain embodiments, at least one of the ports is oriented 90° to the length of the body. See for example  FIG. 11A , which depicts ports  33   a ,  33   b ,  33   d , and  33   e  as being oriented at a 90° angle to port  33   c.    
     The ports may have the same or different inner diameters. In certain embodiments, at least one of the ports has an inner diameter that is different from the inner diameters of the other ports.  FIGS. 12A and 12B  show an embodiment of a shunt  32  having multiple ports ( 33   a  and  33   b ) at a proximal end and a single port  34  at a distal end.  FIG. 12A  shows that port  33   b  has an inner diameter that is different from the inner diameters of ports  33   a  and  34 . In this figure, the inner diameter of port  33   b  is less than the inner diameter of ports  33   a  and  34 . An exemplary inner diameter of port  33   b  is from about 20 μm to about 40 μm, particularly about 30 μm. In other embodiments, the inner diameter of port  33   b  is greater than the inner diameter of ports  33   a  and  34 . See for example  FIG. 12B . 
     The invention encompasses shunts of different shapes and different dimensions, and the shunts of the invention may be any shape or any dimension that may be accommodated by the eye. In certain embodiments, the intraocular shunt is of a cylindrical shape and has an outside cylindrical wall and a hollow interior. The shunt may have an inside diameter from approximately 10 μm to approximately 250 μm, an outside diameter from approximately 190 μm to approximately 300 μm, and a length from approximately 0.5 mm to approximately 20 mm. Shunts of the invention may be made from any biocompatible material. An exemplary material is gelatin. Methods of making shunts composed of gelatin are described above. 
     Shunts with Overflow Ports 
     Other aspects of the invention generally provide shunts with overflow ports. Those shunts are configured such that the overflow port remains partially or completely closed until there is a pressure build-up within the shunt sufficient to force open the overflow port. Such pressure build-up typically results from particulate partially or fully clogging an entry or an exit port of the shunt. Such shunts reduce probability of the shunt clogging after implantation because fluid can enter or exit the shunt by the overflow port even if one port of the shunt becomes clogged with particulate. 
     In certain embodiments, the shunt includes a hollow body defining an inlet configured to receive fluid from an anterior chamber of an eye and an outlet configured to direct the fluid to the intra-Tenon&#39;s space, the body further including at least one slit. The slit may be located at any place along the body of the shunt.  FIG. 13A  shows a shunt  35  having an inlet  36 , an outlet  37 , and a slit  38  located in proximity to the inlet  36 .  FIG. 13B  shows a shunt  35  having an inlet  36 , an outlet  37 , and a slit  39  located in proximity to the outlet  37 .  FIG. 13C  shows a shunt  35  having an inlet  36 , an outlet  37 , a slit  38  located in proximity to the inlet  36 , and a slit  39  located in proximity to the outlet  37 . 
     While  FIGS. 13A-13C  show shunts have only a single overflow port at the proximal portion, the distal portion, or both the proximal and distal portions, those shunts are only exemplary embodiments. The overflow port(s) may be located along any portion of the shunt, and shunts of the invention include shunts having more than one overflow port. In certain embodiments, shunts of the invention include more than one overflow port at the proximal portion, the distal portion, or both. For example,  FIG. 14  shows a shunt  40  having an inlet  41 , an outlet  42 , and slits  43   a  and  43   b  located in proximity to the inlet  41 . Shunts of the invention may include at least two overflow ports, at least three overflow ports, at least four overflow ports, at least five overflow ports, at least 10 overflow ports, at least 15 overflow ports, or at least 20 overflow ports. In certain embodiments, shunts of the invention include two slits that overlap and are oriented at 90° to each other, thereby forming a cross. 
     In certain embodiments, the slit may be at the proximal or the distal end of the shunt, producing a split in the proximal or the distal end of the implant.  FIG. 15  shows an embodiment of a shunt  44  having an inlet  45 , outlet  46 , and a slit  47  that is located at the proximal end of the shunt, producing a split in the inlet  45  of the shunt. 
     In certain embodiments, the slit has a width that is substantially the same or less than an inner diameter of the inlet. In other embodiments, the slit has a width that is substantially the same or less than an inner diameter of the outlet. In certain embodiments, the slit has a length that ranges from about 0.05 mm to about 2 mm, and a width that ranges from about 10 μm to about 200 μm. Generally, the slit does not direct the fluid unless the outlet is obstructed. However, the shunt may be configured such that the slit does direct at least some of the fluid even if the inlet or outlet is not obstructed. 
     The invention encompasses shunts of different shapes and different dimensions, and the shunts of the invention may be any shape or any dimension that may be accommodated by the eye. In certain embodiments, the intraocular shunt is of a cylindrical shape and has an outside cylindrical wall and a hollow interior. The shunt may have an inside diameter from approximately 10 μm to approximately 250 μm, an outside diameter from approximately 190 μm to approximately 300 μm, and a length from approximately 0.5 mm to approximately 20 mm. Shunts of the invention may be made from any biocompatible material. An exemplary material is gelatin. Methods of making shunts composed of gelatin are described above. 
     Shunts Having a Variable Inner Diameter 
     In other aspects, the invention generally provides a shunt having a variable inner diameter. In particular embodiments, the diameter increases from inlet to outlet of the shunt. By having a variable inner diameter that increases from inlet to outlet, a pressure gradient is produced and particulate that may otherwise clog the inlet of the shunt is forced through the inlet due to the pressure gradient. Further, the particulate will flow out of the shunt because the diameter only increases after the inlet. 
       FIG. 16  shows an embodiment of a shunt  48  having an inlet  49  configured to receive fluid from an anterior chamber of an eye and an outlet  50  configured to direct the fluid to a location of lower pressure with respect to the anterior chamber, in which the body further includes a variable inner diameter that increases along the length of the body from the inlet  49  to the outlet  50 . In certain embodiments, the inner diameter continuously increases along the length of the body, for example as shown in  FIG. 16 . In other embodiments, the inner diameter remains constant along portions of the length of the body. 
     In exemplary embodiments, the inner diameter may range in size from about 10 μm to about 200 μm, and the inner diameter at the outlet may range in size from about 15 μm to about 300 μm. The invention encompasses shunts of different shapes and different dimensions, and the shunts of the invention may be any shape or any dimension that may be accommodated by the eye. In certain embodiments, the intraocular shunt is via cylindrical shape and has an outside cylindrical wall and a hollow interior. The shunt may have an inside diameter from approximately 10 μm to approximately 250 μm, an outside diameter from approximately 190 μm to approximately 300 μm, and a length from approximately 0.5 mm to approximately 20 mm. Shunts of the invention may be made from any biocompatible material. An exemplary material is gelatin. Methods of making shunts composed of gelatin are described above. 
     Pharmaceutical Agents 
     In certain embodiments, shunts of the invention may be coated or impregnated with at least one pharmaceutical and/or biological agent or a combination thereof. The pharmaceutical and/or biological agent may coat or impregnate an entire exterior of the shunt, an entire interior of the shunt, or both. Alternatively, the pharmaceutical or biological agent may coat and/or impregnate a portion of an exterior of the shunt, a portion of an interior of the shunt, or both. Methods of coating and/or impregnating an intraocular shunt with a pharmaceutical and/or biological agent are known in the art. See for example, Darouiche (U.S. Pat. Nos. 7,790,183; 6,719,991; 6,558,686; 6,162,487; 5,902,283; 5,853,745; and 5,624,704) and Yu et al. (U.S. patent application serial number 2008/0108933). The content of each of these references is incorporated by reference herein its entirety. 
     In certain embodiments, the exterior portion of the shunt that resides in the anterior chamber after implantation (e.g., about 1 mm of the proximal end of the shunt) is coated and/or impregnated with the pharmaceutical or biological agent. In other embodiments, the exterior of the shunt that resides in the scleral tissue after implantation of the shunt is coated and/or impregnated with the pharmaceutical or biological agent. In other embodiments, the exterior portion of the shunt that resides in the intra-Tenon&#39;s space or the subconjunctival space after implantation is coated and/or impregnated with the pharmaceutical or biological agent. In embodiments in which the pharmaceutical or biological agent coats and/or impregnates the interior of the shunt, the agent may be flushed through the shunt and into the area of lower pressure (e.g., the intra-Tenon&#39;s space or the subconjunctival space). 
     Any pharmaceutical and/or biological agent or combination thereof may be used with shunts of the invention. The pharmaceutical and/or biological agent may be released over a short period of time (e.g., seconds) or may be released over longer periods of time (e.g., days, weeks, months, or even years). Exemplary agents include anti-mitotic pharmaceuticals such as Mitomycin-C or 5-Fluorouracil, anti-VEGF (such as Lucintes, Macugen, Avastin, VEGF or steroids). 
     Deployment Devices 
     Deployment into the eye of an intraocular shunt, such as the shunts described herein, in accordance with the methods of the invention can be achieved using a hollow shaft configured to hold the shunt, as described herein. The hollow shaft can be coupled to a deployment device or part of the deployment device itself. Deployment devices that are suitable for use with the methods of the invention include but are not limited to the deployment devices described in U.S. Pat. Nos. 6,007,511, 6,544,249, and U.S. Publication No. US2008/0108933, the contents of each of which are hereby incorporated by reference in their entireties. In other embodiments, the deployment devices are devices as described in co-pending and co-owned U.S. nonprovisional patent application Ser. No. 12/946,222 filed on Nov. 15, 2010, the entire content of which is incorporated by reference herein. 
     In still other embodiments, the methods of the invention are conducted using the deployment device  100  depicted in  FIG. 17 . While  FIG. 17  shows a handheld manually operated shunt deployment device, it will be appreciated that devices of the invention may be coupled with robotic systems and may be completely or partially automated. As shown in  FIG. 17 , deployment device  100  includes a generally cylindrical body or housing  101 , however, the body shape of housing  101  could be other than cylindrical. Housing  101  may have an ergonomical shape, allowing for comfortable grasping by an operator. Housing  101  is shown with optional grooves  102  to allow for easier gripping by a surgeon. 
     Housing  101  is shown having a larger proximal portion that tapers to a distal portion. The distal portion includes a hollow sleeve  105 . The hollow sleeve  105  is configured for insertion into an eye and to extend into an anterior chamber of an eye. The hollow sleeve is visible within an anterior chamber of an eye. The sleeve may include an edge at a distal end that provides resistance feedback to an operator upon insertion of the deployment device  100  within an eye of a person. Upon advancement of the device  100  across an anterior chamber of the eye, the hollow sleeve  105  will eventually contact the sclera, providing resistance feedback to an operator that no further advancement of the device  100  is necessary. The edge of the sleeve  105 , prevents the shaft  104  from accidentally being pushed too far through the sclera. A temporary guard  108  is configured to fit around sleeve  105  and extend beyond an end of sleeve  105 . The guard is used during shipping of the device and protects an operator from a distal end of a hollow shaft  104  that extends beyond the end of the sleeve  105 . The guard is removed prior to use of the device. 
     Housing  101  is open at its proximal end, such that a portion of a deployment mechanism  103  may extend from the proximal end of the housing  101 . A distal end of housing  101  is also open such that at least a portion of a hollow shaft  104  may extend through and beyond the distal end of the housing  101 . Housing  101  further includes a slot  106  through which an operator, such as a surgeon, using the device  100  may view an indicator  107  on the deployment mechanism  103 . 
     Housing  101  may be made of any material that is suitable for use in medical devices. For example, housing  101  may be made of a lightweight aluminum or a biocompatible plastic material. Examples of such suitable plastic materials include polycarbonate and other polymeric resins such as DELRIN and ULTEM. In certain embodiments, housing  101  is made of a material that may be autoclaved, and thus allow for housing  101  to be re-usable. Alternatively, device  100  may be sold as a one-time-use device, and thus the material of the housing does not need to be a material that is autoclavable. 
     Housing  101  may be made of multiple components that connect together to form the housing.  FIG. 18  shows an exploded view of deployment device  100 . In this figure, housing  101 , is shown having three components  101   a ,  101   b , and  101   c . The components are designed to screw together to form housing  101 .  FIGS. 19A-19D  also show deployment mechanism  103 . The housing  101  is designed such that deployment mechanism  103  fits within assembled housing  101 . Housing  101  is designed such that components of deployment mechanism  103  are movable within housing  101 . 
       FIGS. 19A-19D  show different enlarged views of the deployment mechanism  103 . Deployment mechanism  103  may be made of any material that is suitable for use in medical devices. For example, deployment mechanism  103  may be made of a lightweight aluminum or a biocompatible plastic material. Examples of such suitable plastic materials include polycarbonate and other polymeric resins such as DELRIN and ULTEM. In certain embodiments, deployment mechanism  103  is made of a material that may be autoclaved, and thus allow for deployment mechanism  103  to be re-usable. Alternatively, device  100  may be sold as a one-time-use device, and thus the material of the deployment mechanism does not need to be a material that is autoclavable. 
     Deployment mechanism  103  includes a distal portion  109  and a proximal portion  110 . The deployment mechanism  103  is configured such that distal portion  109  is movable within proximal portion  110 . More particularly, distal portion  109  is capable of partially retracting to within proximal portion  110 . 
     In this embodiment, the distal portion  109  is shown to taper to a connection with a hollow shaft  104 . This embodiment is illustrated such that the connection between the hollow shaft  104  and the distal portion  109  of the deployment mechanism  103  occurs inside the housing  101 . In other embodiments, the connection between hollow shaft  104  and the distal portion  109  of the deployment mechanism  103  may occur outside of the housing  101 . Hollow shaft  104  may be removable from the distal portion  109  of the deployment mechanism  103 . Alternatively, the hollow shaft  104  may be permanently coupled to the distal portion  109  of the deployment mechanism  103 . 
     Generally, hollow shaft  104  is configured to hold an intraocular shunt, such as the intraocular shunts according to the invention. The shaft  104  may be any length. A usable length of the shaft may be anywhere from about 5 mm to about 40 mm, and is 15 mm in certain embodiments. In certain embodiments, the shaft is straight. In other embodiments, shaft is of a shape other than straight, for example a shaft having a bend along its length or a shaft as depicted in  FIGS. 5A-5C . 
     A proximal portion of the deployment mechanism includes optional grooves  116  to allow for easier gripping by an operator for easier rotation of the deployment mechanism, which will be discussed in more detail below. The proximal portion  110  of the deployment mechanism also includes at least one indicator that provides feedback to an operator as to the state of the deployment mechanism. The indicator may be any type of indicator known in the art, for example a visual indicator, an audio indicator, or a tactile indicator.  FIGS. 19A-19D  show a deployment mechanism having two indicators, a ready indicator  111  and a deployed indicator  119 . Ready indicator  111  provides feedback to an operator that the deployment mechanism is in a configuration for deployment of an intraocular shunt from the deployment device  100 . The ready indicator  111  is shown in this embodiment as a green oval having a triangle within the oval. Deployed indicator  119  provides feedback to the operator that the deployment mechanism has been fully engaged and has deployed the shunt from the deployment device  100 . The deployed indicator  119  is shown in this embodiment as a yellow oval having a black square within the oval. The indicators are located on the deployment mechanism such that when assembled, the indicators  111  and  119  may be seen through slot  106  in housing  101 . 
     The proximal portion  110  includes a stationary portion  110   b  and a rotating portion  110   a . The proximal portion  110  includes a channel  112  that runs part of the length of stationary portion  110   b  and the entire length of rotating portion  110   a . The channel  112  is configured to interact with a protrusion  117  on an interior portion of housing component  101   a  ( FIGS. 20A and 20B ). During assembly, the protrusion  117  on housing component  101   a  is aligned with channel  112  on the stationary portion  110   b  and rotating portion  110   a  of the deployment mechanism  103 . The proximal portion  110  of deployment mechanism  103  is slid within housing component  101   a  until the protrusion  117  sits within stationary portion  110   b  ( FIG. 20C ). Assembled, the protrusion  117  interacts with the stationary portion  110   b  of the deployment mechanism  103  and prevents rotation of stationary portion  110   b . In this configuration, rotating portion  110   a  is free to rotate within housing component  101   a.    
     Referring back to  FIGS. 19A-19D , the rotating portion  110   a  of proximal portion  110  of deployment mechanism  103  also includes channels  113   a ,  113   b , and  113   c . Channel  113   a  includes a first portion  113   a   1  that is straight and runs perpendicular to the length of the rotating portion  110   a , and a second portion  113   a   2  that runs diagonally along the length of rotating portion  110   a , downwardly toward a proximal end of the deployment mechanism  103 . Channel  113   b  includes a first portion  113   b   1  that runs diagonally along the length of the rotating portion  110   a , downwardly toward a distal end of the deployment mechanism  103 , and a second portion that is straight and runs perpendicular to the length of the rotating portion  110   a . The point at which first portion  113   a   1  transitions to second portion  113   a   2  along channel  113   a , is the same as the point at which first portion  113   b   1  transitions to second portion  113   b   2  along channel  113   b . Channel  113   c  is straight and runs perpendicular to the length of the rotating portion  110   a . Within each of channels  113   a ,  113   b , and  113   c , sit members  114   a ,  114   b , and  114   c  respectively. Members  114   a ,  114   b , and  114   c  are movable within channels  113   a ,  113   b , and  113   c . Members  114   a ,  114   b , and  114   c  also act as stoppers that limit movement of rotating portion  110   a , which thereby limits axial movement of the shaft  104 . 
       FIG. 21  shows a cross-sectional view of deployment mechanism  103 . Member  114   a  is connected to the distal portion  109  of the deployment mechanism  103 . Movement of member  114   a  results in retraction of the distal portion  109  of the deployment mechanism  103  to within the proximal portion  110  of the deployment mechanism  103 . Member  114   b  is connected to a pusher component  118 . The pusher component  118  extends through the distal portion  109  of the deployment mechanism  103  and extends into a portion of hollow shaft  104 . The pusher component is involved in deployment of a shunt from the hollow shaft  104 . An exemplary pusher component is a plunger. Movement of member  114   b  engages pusher  118  and results in pusher  118  advancing within hollow shaft  104 . 
     Reference is now made to  FIGS. 22A-24D , which accompany the following discussion regarding deployment of a shunt  115  from deployment device  100 .  FIG. 22A  shows deployment device  100  is a pre-deployment configuration. In this configuration, shunt  115  is loaded within hollow shaft  104  ( FIG. 22C ). As shown in  FIG. 22C , shunt  115  is only partially within shaft  104 , such that a portion of the shunt is exposed. However, the shunt  115  does not extend beyond the end of the shaft  104 . In other embodiments, the shunt  115  is completely disposed within hollow shaft  104 . The shunt  115  is loaded into hollow shaft  104  such that the shunt abuts pusher component  118  within hollow shaft  104 . A distal end of shaft  104  is beveled to assist in piercing tissue of the eye. 
     Additionally, in the pre-deployment configuration, a portion of the shaft  104  extends beyond the sleeve  105  ( FIG. 22C ). The deployment mechanism is configured such that member  114   a  abuts a distal end of the first portion  113   a   1  of channel  113   a , and member  114   b  abut a proximal end of the first portion  113   b   1  of channel  113   b  ( FIG. 22B ). In this configuration, the ready indicator  111  is visible through slot  106  of the housing  101 , providing feedback to an operator that the deployment mechanism is in a configuration for deployment of an intraocular shunt from the deployment device  100  ( FIG. 22A ). In this configuration, the device  100  is ready for insertion into an eye (insertion configuration or pre-deployment configuration). Methods for inserting and implanting shunts are discussed in further detail below. 
     Once the device has been inserted into the eye and advanced to a location to where the shunt will be deployed, the shunt  115  may be deployed from the device  100 . The deployment mechanism  103  is a two-stage system. The first stage is engagement of the pusher component  118  and the second stage is retraction of the distal portion  109  to within the proximal portion  110  of the deployment mechanism  103 . Rotation of the rotating portion  110   a  of the proximal portion  110  of the deployment mechanism  103  sequentially engages the pusher component and then the retraction component. 
     In the first stage of shunt deployment, the pusher component is engaged and the pusher partially deploys the shunt from the deployment device. During the first stage, rotating portion  110   a  of the proximal portion  110  of the deployment mechanism  103  is rotated, resulting in movement of members  114   a  and  114   b  along first portions  113   a   1  and  113   b   1  in channels  113   a  and  113   b . Since the first portion  113   a   1  of channel  113   a  is straight and runs perpendicular to the length of the rotating portion  110   a , rotation of rotating portion  110   a  does not cause axial movement of member  114   a . Without axial movement of member  114   a , there is no retraction of the distal portion  109  to within the proximal portion  110  of the deployment mechanism  103 . Since the first portion  113   b   1  of channel  113   b  runs diagonally along the length of the rotating portion  110   a , upwardly toward a distal end of the deployment mechanism  103 , rotation of rotating portion  110   a  causes axial movement of member  114   b  toward a distal end of the device. Axial movement of member  114   b  toward a distal end of the device results in forward advancement of the pusher component  118  within the hollow shaft  104 . Such movement of pusher component  118  results in partially deployment of the shunt  115  from the shaft  104 . 
       FIGS. 23A-23C  show schematics of the deployment mechanism at the end of the first stage of deployment of the shunt from the deployment device. As is shown  FIG. 23A , members  114   a  and  114   b  have finished traversing along first portions  113   a   1  and  113   b   1  of channels  113   a  and  113   b . Additionally, pusher component  118  has advanced within hollow shaft  104  ( FIG. 23B ), and shunt  115  has been partially deployed from the hollow shaft  104  ( FIG. 23C ). As is shown in these figures, a portion of the shunt  115  extends beyond an end of the shaft  104 . 
     In the second stage of shunt deployment, the retraction component is engaged and the distal portion of the deployment mechanism is retracted to within the proximal portion of the deployment mechanism, thereby completing deployment of the shunt from the deployment device. During the second stage, rotating portion  110   a  of the proximal portion  110  of the deployment mechanism  103  is further rotated, resulting in movement of members  114   a  and  114   b  along second portions  113   a   2  and  113   b   2  in channels  113   a  and  113   b . Since the second portion  113   b   2  of channel  113   b  is straight and runs perpendicular to the length of the rotating portion  110   a , rotation of rotating portion  110   a  does not cause axial movement of member  114   b . Without axial movement of member  114   b , there is no further advancement of pusher  118 . Since the second portion  113   a   2  of channel  113   a  runs diagonally along the length of the rotating portion  110   a , downwardly toward a proximal end of the deployment mechanism  103 , rotation of rotating portion  110   a  causes axial movement of member  114   a  toward a proximal end of the device. Axial movement of member  114   a  toward a proximal end of the device results in retraction of the distal portion  109  to within the proximal portion  110  of the deployment mechanism  103 . Retraction of the distal portion  109 , results in retraction of the hollow shaft  104 . Since the shunt  115  abuts the pusher component  118 , the shunt remains stationary as the hollow shaft  104  retracts from around the shunt  115  ( FIG. 24C ). The shaft  104  retracts almost completely to within the sleeve  105 . During both stages of the deployment process, the sleeve  105  remains stationary and in a fixed position. 
       FIG. 24A  shows a schematic of the device  100  after deployment of the shunt  115  from the device  100 .  FIG. 24B  shows a schematic of the deployment mechanism at the end of the second stage of deployment of the shunt from the deployment device. As is shown in  FIG. 24B , members  114   a  and  114   b  have finished traversing along second portions  113   a   2  and  113   b   2  of channels  113   a  and  113   b . Additionally, distal portion  109  has retracted to within proximal portion  110 , thus resulting in retraction of the hollow shaft  104  to within the sleeve  105 .  FIG. 24D  shows an enlarged view of the distal portion of the deployment device after deployment of the shunt. This figure shows that the hollow shaft  104  is not fully retracted to within the sleeve  105  of the deployment device  100 . However, in certain embodiments, the shaft  104  may completely retract to within the sleeve  105 . 
     INCORPORATION BY REFERENCE 
     References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes. 
     EQUIVALENTS 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.