Abstract:
A shunt for relief of intra-ocular pressure includes a pressure-relief valve and a jacket enclosing the pressure relief valve. When implanted on the sclera of an eye, the jacket protects the valve from interference by a capsule formed on the shunt.

Description:
RELATED APPLICATIONS 
   This application claims priority under 35 U.S.C. §119 from the U.S. Provisional Patent Applications 60/565,009, filed Apr. 23, 2004 and 60/626,190, filed Nov. 9, 2004. 

   FIELD OF INVENTION 
   The invention relates to ocular implants, and in particular, to implants for relieving excess intra-ocular fluid pressure. 
   BACKGROUND 
   The interior of the eye is bathed in a fluid often referred to as “aqueous” or “aqueous humor.” This fluid is constantly being renewed. As additional fluid enters the eye, a corresponding amount of fluid must be drained from the eye to maintain a constant intra-ocular pressure. If the drainage of fluid cannot keep up with the entry of new fluid, the intra-ocular pressure will increase. If that pressure increases too much, the optic nerve will be damaged. This condition is often referred to as “glaucoma.” 
   One way to relieve intra-ocular pressure is to implant a shunt having a one-way pressure-relief valve. When the intra-ocular pressure exceeds a threshold, the valve opens, and excess fluid drains onto a drainage bed. When the pressure drops sufficiently, the valve closes. This relieves the intra-ocular pressure. 
   Conventional shunts are designed to lead the fluid to the surrounding tissue. As a result, a capsule eventually forms over the valve and thereby interferes with its operation. This is particularly troublesome for patients who have an artificial cornea, (i.e., a keratoprosthesis). 
   SUMMARY 
   In one aspect, the invention includes a shunt for relief of intra-ocular pressure. The shunt has a pressure-relief valve having an inlet and an outlet, and an intake duct in fluid communication with the inlet. A jacket encloses the valve and forms a chamber for accumulation of fluid from the outlet. A drainage duct is disposed to direct fluid away from the chamber. 
   In another aspect, the invention includes a shunt for relief of intra-ocular pressure. The shunt includes a pressure-relief valve and a jacket that encloses the pressure relief valve. When implanted on the sclera of an eye, the jacket protects the valve from interference by a capsule formed on the shunt. 
   In one embodiment, the jacket is a silicone rubber jacket. 
   In another embodiment, the shunt includes an intake duct in fluid communications with the pressure-relief valve. 
   Another embodiment includes a drainage duct in fluid communication with the valve. The drainage duct can be configured for drainage into a fornix of a lower lid of an eye, into a nasal sinus cavity, or into a lacrimal sac. 
   In another embodiment, the jacket forms a chamber for accumulation of fluid from the pressure-relief valve. In this case, the drainage duct is in fluid communication with the chamber. 
   In another aspect, the invention includes a method for relieving intra-ocular pressure by enclosing a pressure-relief valve in a jacket; placing the jacket on the sclera; and leading fluid from inside the eye into a chamber defined by the jacket. 
   Practices of the invention include those that also include draining fluid away from the chamber. 
   Additional practices of the invention include those in which leading fluid from inside the eye includes leading fluid from the anterior chamber of the eye. 
   The fluid can be drained into any of a number of locations. For example, practices of the invention includes those in which fluid is drained into a fornix of a lower lid of an eye, a lacrimal sac, a nasal sinus cavity, a maxillary sinus cavity, an ethmoid sinus cavity, and any epithelial cavity. 
   Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
   These and other features and advantages of the invention will be apparent from the following detailed description and the accompanying figures, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a conventional shunt; 
       FIG. 2  is a jacketed shunt with a drainage duct; 
       FIG. 3  is a jacketed shunt with a drainage duct for drainage into a sinus cavity; and 
       FIG. 4  is a jacketed shunt with a drainage duct for drainage into the fornix behind the lower lid of the eye. 
   

   DETAILED DESCRIPTION 
   A conventional glaucoma shunt  10 , shown in  FIG. 1 , includes a valve  12  having a valve inlet  14  and a valve outlet  16 . The valve outlet  16  is in fluid communication with a polypropylene drainage bed  18 . The valve inlet  14  is in fluid communication with a proximal end  20  of an intake duct  22 . 
   The valve  12  is a pressure-regulating valve that opens its outlet  16  whenever the fluid pressure at its inlet  14  is in excess of a pre-determined threshold. An exemplary valve  12  of this type is the Ahmed valve, which is manufactured by New World Medical, Inc. of Rancho Cucamonga, Calif. 
   In operation, the valve  12  and the drainage bed  18  are implanted onto the surface of the sclera of the eye. An open distal end of the intake duct  22  is inserted into the anterior chamber of the eye. Fluid, under pressure, fills the intake duct  22 . When the pressure exceeds the pre-defined threshold, the valve outlet  16  opens. This causes the fluid to pass out of the valve  12  and over the drainage bed  18 . The fluid is eventually absorbed by the surrounding tissue. 
   A difficulty that arises in the conventional shunt, particularly in those patients having a keratoprosthesis, is that a capsule slowly begins to form around the valve  12  and its associated drainage bed  18 . This capsule eventually interferes with the shunt&#39;s ability to drain fluid. 
   A glaucoma shunt  24  incorporating the invention, as shown in  FIG. 2 , omits the drainage bed  18  and encloses the valve  12  in a silicone rubber jacket  26 . In this case, fluid from the outlet  16  collects in a cavity  28  defined by the jacket  26 . 
   Since the fluid is entrapped with the cavity  28 , it can no longer drain into the surrounding tissue. To provide the necessary drainage, the shunt  24  includes a drainage duct  30  having a proximal end  32  and a distal end  34 . The proximal end  32  of the drainage duct  30  is placed in fluid communication with the cavity  28 . The distal end  34  is inserted into a nearby epithelial cavity. This enables fluid that collects in the cavity  28  to be drained into a nearby epithelial cavity, such as the maxillary sinus. 
   A preferred epithelial cavity for receiving the distal end  34  of the drainage duct  30  is the maxillary sinus. However, the distal end  34  of the drainage duct  30  may also be inserted into the fornix of the lower lid, the lacrimal sac, or the ethmoid sinus. 
   Because the valve  12  in  FIG. 2  is enclosed in a jacket  26 , the capsule that would normally interfere with the leaching of fluid into surrounding tissue now forms outside the jacket  26 . As a result, it no longer interferes with fluid flow, as was the case with the shunt  10  in  FIG. 1 . 
   Materials other than silicone rubber can be used to form a jacket  26  around the valve  12 . What is necessary is that the jacket material be biocompatible and that it be impervious to water. 
   The shape of the drainage duct  30  can vary depending on where it is to be inserted. In one embodiment, shown in  FIG. 2 , the drainage duct  30  is intended to extend into the maxillary sinus cavity. However, the drainage duct  30  can also be configured, as shown in  FIG. 3 , for extending into the fornix of the lower eyelid. 
   It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.