RELATED APPLICATIONS 
     This Application is a continuation-in-part of U.S. patent application Ser. No. 11/581,629 filed Oct. 16, 2006 and U.S. patent application Ser. No. 11/435,906 filed May 17, 2006 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a medical device and more particularly to an ophthalmic drug delivery device containing piezoelectric array. 
     Several diseases and conditions of the posterior segment of the eye threaten vision. Age related macular degeneration (ARMD), choroidal neovascularization (CNV), retinopathies (e.g., diabetic retinopathy, vitreoretinopathy), retinitis (e.g., cytomegalovirus (CMV) retinitis), uveitis, macular edema, glaucoma, and neuropathies are several examples. 
     These, and other diseases, can be treated by injecting a drug into the eye. Such injections are typically manually made using a conventional syringe and needle.  FIG. 1  is a perspective view of a prior art syringe used to inject drugs into the eye. In  FIG. 1 , the syringe includes a needle  105 , a luer hub  110 , a chamber  115 , a plunger  120 , a plunger shaft  125 , and a thumb rest  130 . As is commonly known, the drug to be injected is located in chamber  115 . Pushing on the thumb rest  130  causes the plunger  120  to expel the drug through needle  105 . 
     In using such a syringe, the surgeon is required to puncture the eye tissue with the needle, hold the syringe steady, and actuate the syringe plunger (with or without the help of a nurse) to inject the fluid into the eye. The volume injected is typically not controlled in an accurate manner because the vernier on the syringe is not precise relative to the small injection volume. Fluid flow rates are uncontrolled. Reading the vernier is also subject to parallax error. Tissue damage may occur due to an “unsteady” injection. Reflux of the drug may also occur when the needle is removed from the eye. 
     An effort has been made to control the delivery of small amounts of liquids. A commercially available fluid dispenser is the ULTRA™ positive displacement dispenser available from EFD Inc. of Providence, R.I. The ULTRA dispenser is typically used in the dispensing of small volumes of industrial adhesives. It utilizes a conventional syringe and a custom dispensing tip. The syringe plunger is actuated using an electrical stepper motor and an actuating fluid. Parker Hannifin Corporation of Cleveland, Ohio distributes a small volume liquid dispenser for drug discovery applications made by Aurora Instruments LLC of San Diego, Calif. The Parker/Aurora dispenser utilizes a piezo-electric dispensing mechanism. Ypsomed, Inc. of Switzerland produces a line of injection pens and automated injectors primarily for the self-injection of insulin or hormones by a patient. This product line includes simple disposable pens and electronically-controlled motorized injectors. 
     U.S. Pat. No. 6,290,690 discloses an ophthalmic system for injecting a viscous fluid (e.g. silicone oil) into the eye while simultaneously aspirating a second viscous fluid (e.g. perflourocarbon liquid) from the eye in a fluid/fluid exchange during surgery to repair a retinal detachment or tear. The system includes a conventional syringe with a plunger. One end of the syringe is fluidly coupled to a source of pneumatic pressure that provides a constant pneumatic pressure to actuate the plunger. The other end of the syringe is fluidly coupled to an infusion cannula via tubing to deliver the viscous fluid to be injected. 
     It would be desirable to have a portable hand piece for injecting a drug into the eye that includes reliable, low-cost technology. Piezoelectric actuators provide a technology that can be adapted for such use. It would be desirable to utilize piezoelectric actuators to dispense a drug. Such a system provides numerous benefits over prior art injectors. 
     SUMMARY OF THE INVENTION 
     In one embodiment consistent with the principles of the present invention, the present invention is an ophthalmic injection system having a tip segment attachable to and removable from limited reuse assembly. The tip segment includes a dispensing chamber, a storage chamber, a piezoelectric array, a needle fluidly coupled to the dispensing chamber, and a first housing at least partially enclosing the dispensing chamber housing, the storage chamber, and the piezoelectric array. A dispensing chamber housing has an inner surface and an outer surface. The inner surface defines a dispensing chamber for receiving a quantity of a substance. The storage chamber is located near the dispensing chamber housing. The piezoelectric array is located between the storage chamber and the dispensing chamber housing. The limited reuse assembly includes a power source for providing power to the piezoelectric array, a controller for controlling the power source, and a second housing at least partially enclosing the power source and the controller. The piezoelectric array is activated to pump the substance from the storage chamber to the dispensing chamber. 
     In another embodiment consistent with the principles of the present invention, the present invention is an ophthalmic injection device having a dispensing chamber, a storage chamber, a piezoelectric array, a needle fluidly coupled to the dispensing chamber, a power source for providing power to the piezoelectric array, and a controller for controlling the power source. A dispensing chamber housing has an inner surface and an outer surface. The inner surface defines a dispensing chamber for receiving a quantity of a substance. The storage chamber is located near the dispensing chamber housing. The piezoelectric array is located between the storage chamber and the dispensing chamber housing. A housing at least partially encloses the dispensing chamber housing, the storage chamber, the piezoelectric array, the power source, and the controller. The piezoelectric array is activated to pump the substance from the storage chamber to the dispensing chamber. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed. The following description, as well as the practice of the invention, set forth and suggest additional advantages and purposes of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a perspective view of a prior art syringe. 
         FIG. 2  is one view of an ophthalmic medical device including a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention. 
         FIG. 3  is another embodiment of a limited reuse assembly according to the principles of the present invention. 
         FIG. 4  is cross section view of a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention. 
         FIGS. 5A and 5B  are exploded cross section views of disposable tip segments for an ophthalmic medical device according to an embodiment of the present invention. 
         FIGS. 6A and 6B  are exploded cross section views of disposable tip segments for an ophthalmic medical device according to an embodiment of the present invention. 
         FIG. 7  is a cross section view of an ophthalmic injection device according to the principles of the present invention. 
         FIG. 8  is a cross section view of an ophthalmic injection device according to the principles of the present invention. 
         FIG. 9  is a flow chart of one method of delivering a substance into an eye using a shape memory alloy. 
         FIG. 10  is a flow chart of one method of delivering a substance into an eye using a shape memory alloy. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is now made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like parts. 
       FIG. 2  is one view of an ophthalmic medical device including a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention. In  FIG. 2 , the medical device includes a tip segment  205  and a limited reuse assembly  250 . The tip segment  205  includes a needle  210 , a housing  215 , and an optional light  275 . The limited reuse assembly  250  includes a housing  255 , a switch  270 , a lock mechanism  265 , and a threaded portion  260 . 
     Tip segment  205  is capable of being connected to and removed from limited reuse assembly  250 . In this embodiment, tip segment  205  has a threaded portion on an interior surface of housing  215  that screws onto the threaded portion  260  of limited reuse assembly  250 . In addition, lock mechanism  265  secures tip segment  215  to limited reuse assembly  250 . Lock mechanism  265  may be in the form of a button, a sliding switch, or a cantilevered mechanism. Other mechanisms for connecting tip segment  205  to limited reuse assembly  250 , such as those involving structural features that mate with each other, are commonly known in the art and are within the scope of the present invention. 
     Needle  210  is adapted to deliver a substance, such as a drug, into an eye. Needle  210  may be of any commonly known configuration. Preferably, needle  210  is designed such that its thermal characteristics are conducive to the particular drug delivery application. For example, when a heated drug is to be delivered, needle  210  may be relatively short (several millimeters) in length to facilitate proper delivery of the drug. 
     Switch  270  is adapted to provide an input to the system. For example, switch  270  may be used to activate the system or to turn on a heater. Other switches, buttons, or user-directed control inputs are commonly known and may be employed with limited reuse assembly  250  and/or tip segment  205 . 
     Optional light  275  is illuminated when tip segment  205  is ready to be used. Optional light  275  may protrude from housing  215 , or it may be contained within housing  215 , in which case, optional light  275  may be seen through a clear portion of housing  215 . In other embodiments, optional light  275  may be replaced by an indicator, such as a liquid crystal display, segmented display, or other device that indicates a status or condition of disposable tip segment  205 . For example, optional light  275  may also pulse on and off to indicate other states, such as, but not limited to a system error, fully charged battery, insufficiently charged battery or faulty connection between the tip segment  205  and limited use assembly  250 . While shown on tip segment  205 , optional light  275  or other indicator may be located on limited reuse assembly  250 . 
       FIG. 3  is another embodiment of a limited reuse assembly according to the principles of the present invention. Limited reuse assembly  250  includes a button  308 , a display  320 , and a housing  330 . Disposable tip segment  205  attaches to end  340  of limited reuse assembly  250 . Button  308  is actuated to provide an input to the system. As with switch  270 , button  308  may activate a heater or other temperature control device or initiate actuation of a plunger. Display  320  is a liquid crystal display, segmented display, or other device that indicates a status or condition of disposable tip segment  205  or limited reuse assembly  250 . 
       FIG. 4  is cross section view of a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention.  FIG. 4  shows how tip segment  205  interfaces with limited reuse assembly  250 . In the embodiment of  FIG. 4 , tip segment  205  includes dispensing chamber housing  425 , dispensing chamber  405 , storage chamber  445 , optional heater  450 , piezoelectric array  415 , tip segment housing  215 , thermal sensor  460 , needle  210 , interface  530 , and tip interface connector  453 . Limited reuse assembly  250  includes power source  505 , controller  305 , limited reuse assembly housing  255 , interface  535 , and limited reuse assembly interface connector  553 . 
     In  FIG. 4 , dispensing chamber  405  is fluidly coupled to storage chamber  445  by piezoelectric array  415 . When activated, piezoelectric array can pump a substance from storage chamber  445  to dispensing chamber  405 . As such, dispensing chamber housing  425  has openings that interface with piezoelectric array  415 . Optional heater  405  is located adjacent to or surrounds storage chamber  445 . Thermal sensor  460  is located adjacent to heater  450  or storage chamber  445 . 
     Piezoelectric array  415  is an array of piezoelectric actuators. The active element is basically a piece of polarized material (i.e. some parts of the molecule are positively charged, while other parts of the molecule are negatively charged) with electrodes attached to two of its opposite faces. When an electric field is applied across the material, the polarized molecules will align themselves with the electric field, resulting in induced dipoles within the molecular or crystal structure of the material. This alignment of molecules will cause the material to change dimensions. This phenomenon is known as electrostriction. In addition, a permanently-polarized material such as quartz (SiO2) or barium titanate (BaTiO3) will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. This phenomenon is known as the piezoelectric effect. 
     Piezoelectric array  415  is configured so that its elements act to pump a substance from storage chamber  445  to dispensing chamber  405  in a manner similar to that used in inkjet printers. While shown as a single array, piezoelectric array  415  may be comprised of multiple arrays or elements. Typically, piezoelectric arrays are made using high volume silicon chip technology. As such, a commercially available chip may be employed as piezoelectric array  415 . 
     In  FIG. 4 , dispensing chamber housing  425  is tubular or cylindrical in shape thus making dispensing chamber  405  a similar shape. Dispensing chamber housing has perforations or openings that interface with piezoelectric array  415 . Dispensing chamber housing  425  may be heated by an optional heater (not shown). In one embodiment according to the principles of the present invention, heater  450  heats both dispensing chamber  405  and storage chamber  445 . 
     Storage chamber  405  holds a substance, typically a drug, that is to be delivered into an eye. Storage chamber  445  may be of any suitable configuration. Optional heater  450  heats the substance in storage chamber  445 . 
     Optional thermal sensor  460  provides temperature information to assist in controlling the operation of tip segment  205 . Thermal sensor  460  may be located near or in thermal contact with storage chamber  445  or dispensing chamber housing  425  and measure a temperature near them. Thermal sensor  460  may be any of a number of different devices that can provide temperature information. For example, thermal sensor  460  may be a thermocouple or a resistive device whose resistance varies with temperature. Thermal sensor is also electrically coupled to interface  530  or other similar interface. 
     Needle  210  is fluidly coupled to dispensing chamber  405 . As such, a substance contained in dispensing chamber  405  can pass through needle  210  and into an eye. Interface  530  connects piezoelectric array  415 , optional heater  450 , and optional thermal sensor  460  with tip interface connector  453 . 
     In limited reuse assembly  250 , power source  505  is typically a rechargeable battery, such as a lithium ion battery, although other types of batteries may be employed. In addition, any other type of power cell is appropriate for power source  505 . Power source  505  provides current to dispensing chamber housing  425  to heat it and change its shape. Optionally, power source  505  can be removed from housing  255  through a door or other similar feature (not shown). 
     Controller  305  is typically an integrated circuit with power, input, and output pins capable of performing logic functions. In various embodiments, controller  305  is a targeted device controller. In such a case, controller  305  performs specific control functions targeted to a specific device or component, such as a temperature control device or a power supply. For example, a temperature control device controller has the basic functionality to control heater  450 . In other embodiments, controller  305  is a microprocessor. In such a case, controller  305  is programmable so that it can function to control more than one component of the device. In other cases, controller  305  is not a programmable microprocessor, but instead is a special purpose controller configured to control different components that perform different functions. While depicted as one component in  FIG. 4 , controller  305  may be made of many different components or integrated circuits. 
     Controller  305  is connected via interface  535  to limited reuse assembly interface connecter  553 . Limited reuse assembly interface connecter  553  is located on a top surface of limited reuse assembly housing  255 . In this manner, limited reuse assembly interface connector  553  is adapted to be connected with tip interface connector  453  to provide an electrical connection between tip segment  205  and limited reuse assembly  250 . 
     An interface between power source  505  and controller  305  allows controller  305  to control operation of power source  505 . In such a case, controller  305  may control the charging and the discharging of power source  505  when power source  505  is a rechargeable battery. 
     In operation, when tip segment  205  is connected to limited reuse assembly  250 , controller  305  controls the operation of piezoelectric array  415  and optional heater  450 . Controller  305  directs power to actuate piezoelectric array  415  and heater  450 . In one embodiment, a first current is directed to heater  450  to heat the substance in storage chamber  445 . Once the substance has reached the proper temperature, the piezoelectric array is actuated so that the substance in storage chamber  445  is pumped into dispensing chamber  405  where it exits needle  210  and is injected into an eye. 
     A substance to be delivered into an eye, typically a drug suspended in a phase transition compound, is located in dispensing chamber  405 . In this manner, the drug and phase transition compound are contained in storage chamber  445 . The phase transition compound is in a solid or semi-solid state at lower temperatures and in a more liquid state at higher temperatures. Heater  450  can be activated to heat the compound to a more liquid state, piezoelectric array can be activated to inject the compound into the eye where it forms a bolus that erodes over time. 
     In one embodiment of the present invention, the substance located in storage chamber  445  is a drug that is preloaded into the dispensing chamber. In such a case, tip segment  205  is appropriate as a single use consumable product. Such a disposable product can be assembled at a factory with a dosage of a drug installed. 
       FIGS. 5A and 5B  are exploded cross section views of disposable tip segments for an ophthalmic medical device according to an embodiment of the present invention. In  FIG. 5A , piezoelectric array  415  has not been activated. In  FIG. 5B , piezoelectric array  415  has been activated. In  FIGS. 5A and 5B , an optional luer is also picture to secure needle  210 . 
     In  FIG. 5A , a current is applied to heater  450  to heat the substance in storage chamber  445 . The current applied to the heater  450  can be regulated to control the temperature of the substance contained in storage chamber  445 . For example, the amount of current (typically DC current) can be controlled to precisely control the temperature of heater  450 . The more current applied to heater  450 , the greater its temperature. Thermal sensor  460  provides temperature information to controller  305 , so that it can control the amount of current sent to heater  450 . Controller  305  may employ any of a number of different control algorithms, such as, for example, a PID algorithm. 
     After the substance has reached the proper temperature, piezoelectric array  415  can be activated to pump the substance from storage chamber  445  to dispensing chamber  405  as depicted in  FIG. 5B . Piezoelectric array may be controlled to deliver a certain dosage and to deliver that dosage at a certain rate. The power applied to piezoelectric array  415  can be regulated to control a dosage and rate of delivery of the substance in dispensing chamber  405 . As is known, a piezoelectric actuator, such as those in piezoelectric array  415 , can be controlled very precisely and can make very precise movements. Such precise control can be applied to piezoelectric array  415  to precisely control the amount of substance transferred from storage chamber  445  to dispensing chamber  405  as well as the rate of that transfer. 
       FIGS. 6A and 6B  are exploded cross section views of disposable tip segments for an ophthalmic medical device according to an embodiment of the present invention. In  FIG. 6A , piezoelectric array  415  has not been activated. In  FIG. 6B , piezoelectric array  415  has been activated. In  FIGS. 6A and 6B , a flexible chamber  435  is positioned between two piezoelectric arrays  415  as shown. In other embodiments, any number of piezoelectric arrays  415  may be positioned about flexible chamber  435 . Needle  210  is fluidly coupled to flexible chamber  435 . Thermal sensor  460  is located near flexible chamber  435 . An optional luer is also picture to secure needle  210 . 
     In  FIGS. 6A and 6B , the piezoelectric arrays  415  are actuated to compress flexible chamber  435  and dispense a substance contained therein. Since the application of a voltage across a piezoelectric element causes that element to change shape (and expand when crystals align), piezoelectric arrays  415  can be activated to compress flexible chamber  435 , decreasing its volume and expelling a substance from needle  210 . This is shown in  FIG. 6B  in which the piezoelectric arrays  415  have been activated to compress flexible chamber  435  and expel substance  559 . As with  FIG. 5 , piezoelectric array  415  can be precisely controlled to precisely control the amount of substance delivered and the rate at which that substance is delivered. 
     Flexible chamber  435  may also have a heater (not shown) disposed around it or in proximity to it. This heater (not shown) can function like the heater  450  of  FIG. 5 . 
       FIGS. 7 and 8  are cross section views of ophthalmic injection devices according to the principles of the present invention. In  FIGS. 7 and 8 , the injection device is integrated into a single unit. The single piece device of  FIGS. 7 and 8  operates in the same manner as the two piece device previously described. In  FIGS. 7 and 8 , a single interface  536  is used instead of two separate interfaces ( 530  and  535 ) and two separate connectors ( 453  and  553 ). Housing  216  encloses the components pictured. 
       FIG. 9  is a method of delivering a substance into an eye using a piezoelectric array. In  710 , a first input indicating that a substance is to be heated is received. In  720 , the substance is heated. In  730 , a second input is received indicating that the substance is to be delivered. In  740 , after the substance is heated, a piezoelectric array is activated to dispense the substance. 
       FIG. 10  is a method of delivering a substance into an eye using a piezoelectric array. In  805 , a connection between a tip segment and a limited reuse assembly is recognized. In  810 , a first input indicating that a substance is to be heated is received. In  815 , the substance is heated. In  820 , a determination is made as to whether the substance has reached the proper temperature. If the substance has not reached the proper temperature, then in  825  the heater is controlled to properly heat the substance. If the substance has reached the proper temperature, then in  830 , a piezoelectric array is activated to deliver the substance. In  835 , a determination is made as to whether the proper dosage has been delivered. If the proper dosage has been delivered, then in  840  an indication that the substance has been delivered is provided. If the proper dosage has not been delivered, then in  845  a failure indication is provided. 
     From the above, it may be appreciated that the present invention provides an improved system and methods for delivering precise volumes of a substance into an eye. The present invention provides a piezoelectric array that can dispense a substance. In one embodiment, a disposable tip segment that interfaces with a limited reuse assembly is employed. In another embodiment, a single unit is employed. The present invention is illustrated herein by example, and various modifications may be made by a person of ordinary skill in the art. 
     While the present invention is described in the context of a single-use drug delivery device, the present invention encompasses any injection device. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
An ophthalmic injection device has a dispensing chamber, a storage chamber, a piezoelectric array, a needle fluidly coupled to the dispensing chamber, a power source for providing power to the piezoelectric array, and a controller for controlling the power source. A dispensing chamber housing has an inner surface and an outer surface. The inner surface defines a dispensing chamber for receiving a quantity of a substance. The storage chamber is located near the dispensing chamber housing. The piezoelectric array is located between the storage chamber and the dispensing chamber housing. A housing at least partially encloses the dispensing chamber housing, the storage chamber, the piezoelectric array, the power source, and the controller. The piezoelectric array is activated to pump the substance from the storage chamber to the dispensing chamber.