Abstract:
A pressurized infusion device has a flexible band with first and second ends, a curved base, and a bag containing fluid. The bag is located between the flexible band and the curved base. The second end of the flexible band is coupled to a shaft. A motor is also coupled to the shaft. The motor is actuated to turn the shaft and produce tension in the band thereby changing the fluid pressure in the bag.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to phacoemulsification surgery and more particularly to a device that better regulates infusion pressure. 
     The human eye functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL). 
     In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. A typical surgical hand piece suitable for phacoemulsification procedures consists of an ultrasonically driven phacoemulsification hand piece, an attached hollow cutting needle surrounded by an irrigating sleeve, and an electronic control console. The hand piece assembly is attached to the control console by an electric cable and flexible tubing. Through the electric cable, the console varies the power level transmitted by the hand piece to the attached cutting needle. The flexible tubing supplies irrigation fluid to the surgical site and draws aspiration fluid from the eye through the hand piece assembly. 
     The operative part in a typical hand piece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting needle during phacoemulsification, and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the hand piece by flexible mountings. The hand piece body terminates in a reduced diameter portion or nosecone at the body&#39;s distal end. Typically, the nosecone is externally threaded to accept the hollow irrigation sleeve, which surrounds most of the length of the cutting needle. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting needle is adjusted so that its tip projects only a predetermined amount past the open end of the irrigating sleeve. 
     During the phacoemulsification procedure, the tip of the cutting needle and the end of the irrigation sleeve are inserted into the anterior capsule of the eye through a small incision in the outer tissue of the eye. The surgeon brings the tip of the cutting needle into contact with the lens of the eye, so that the vibrating tip fragments the lens. The resulting fragments are aspirated out of the eye through the interior bore of the cutting needle, along with irrigation solution provided to the eye during the procedure, and into a waste reservoir. 
     Throughout the procedure, irrigating fluid is pumped into the eye, passing between the irrigation sleeve and the cutting needle and exiting into the eye at the tip of the irrigation sleeve and/or from one or more ports, or openings, cut into the irrigation sleeve near its end. This irrigating fluid is critical, as it prevents the collapse of the eye during the removal of the emulsified lens. The irrigating fluid also protects the eye tissues from the heat generated by the vibrating of the ultrasonic cutting needle. Furthermore, the irrigating fluid suspends the fragments of the emulsified lens for aspiration from the eye. 
     A common phenomena during a phacoemulsification procedure arises from the varying flow rates that occur throughout the surgical procedure. Varying flow rates result in varying pressure losses in the irrigation fluid path from the irrigation fluid supply to the eye, thus causing changes in pressure in the anterior chamber (also referred to as Intra-Ocular Pressure or IOP.) Higher flow rates result in greater pressure losses and lower IOP. As IOP lowers, the operating space within the eye diminishes. 
     Another common complication during the phacoemulsification process arises from a blockage, or occlusion, of the aspirating needle. As the irrigation fluid and emulsified tissue is aspirated away from the interior of the eye through the hollow cutting needle, pieces of tissue that are larger than the diameter of the needle&#39;s bore may become clogged in the needle&#39;s tip. While the tip is clogged, vacuum pressure builds up within the tip. The resulting drop in pressure in the anterior chamber in the eye when the clog is removed is known as post-occlusion surge. This post-occlusion surge can, in some cases, cause a relatively large quantity of fluid and tissue to be aspirated out of the eye too quickly, potentially causing the eye to collapse and/or causing the lens capsule to be torn. 
     Various techniques have been attempted to reduce this surge, such as by venting the aspiration line or otherwise limiting the buildup of negative pressure in the aspiration system. However, there remains a need for improved phacoemulsification devices, including irrigation systems that reduce post-occlusion surge as well as maintain a stable IOP throughout varying flow conditions. 
     SUMMARY OF THE INVENTION 
     In one embodiment consistent with the principles of the present invention, the present invention is a pressurized infusion device comprising a flexible band having first and second ends, a curved base, and a bag containing fluid. The bag is located between the flexible band and curved base. The second end of the flexible band is coupled to a shaft. A motor is also coupled to the shaft. The motor is actuated to turn the shaft and produce tension in the band thereby changing the fluid pressure in the bag. 
     In another embodiment consistent with the principles of the present invention, the present invention is a pressurized infusion system for an ophthalmic surgical machine. The pressurized infusion system comprises a flexible band having first and second ends; a curved base; a bag containing irrigating fluid, the bag located between the flexible band and curved base; an irrigation line coupled to the bag; a pressure sensor for reading pressure in the irrigation line; a motor coupled to a shaft, the second end of the band coupled to the shaft; and a controller, the controller receiving an input from the irrigation pressure sensor to control the motor. When the motor is actuated to turn the shaft, tension is produced in the band to change pressure in the bag. 
     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 diagram of the components in the fluid path of a phacoemulsification system including a pressurized irrigation squeeze band according to the principles of the present invention. 
         FIG. 2  is an end view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. 
         FIG. 3  is a side view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. 
         FIG. 4  is a block diagram of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. 
         FIG. 5  is a block diagram of control system for a pressurized irrigation squeeze band apparatus according to the principles of the present invention. 
         FIG. 6  is a perspective view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. 
         FIG. 7  is a side view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. 
     
    
    
     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. 1  is a diagram of the components in the fluid path of a phacoemulsification system including a pressurized irrigation squeeze band according to the principles of the present invention.  FIG. 1  depicts the fluid path through the eye  145  during cataract surgery. The components include a motor  105 , a band  110 , a bag  115 , a curved base  120 , a frame  125 , an irrigation pressure sensor  130 , an irrigation valve  135 , an irrigation line  140 , a hand piece  150 , an aspiration line  155 , an aspiration pressure sensor  160 , a vent valve  165 , a pump  170 , a reservoir  175  and a drain bag  180 . The irrigation line  140  provides irrigation fluid to the eye  145  during cataract surgery. The aspiration line  155  removes fluid and emulsified lens particles from the eye during cataract surgery. 
     In one embodiment of the present invention, a bag  115  contains irrigation fluid for use during cataract surgery. The bag  115  is located between band  110  and curved base  120 . Curved base  120  is mounted to frame  125 . A motor  105  has a shaft (not shown) that is attached to one end of band  110 . The other end of band  110  is fixed to the curved base  120  or the frame  125 . In this manner, the bag  115  can be squeezed between band  110  and curved base  120 . When motor  105  is actuated so that the shaft (not shown) to which motor  105  is coupled turns, the band  110  is wound around the shaft (not shown) thereby squeezing bag  110  against curved base  120 . This acts to squeeze irrigation fluid out of bag  110 . This is shown more clearly in subsequent drawings. 
     When irrigation fluid is squeezed out of bag  110 , it travels through irrigation line  140  and into the eye  145 . An irrigation pressure sensor  130  measures the pressure of the irrigation fluid in irrigation line  140 . An optional irrigation valve  135  is also provided for on/off control of irrigation. Irrigation pressure sensor  130  is implemented by any of a number of commercially available fluid pressure sensors. Irrigation pressure sensor  130  provides pressure information to a controller (not shown) that operates motor  105 . The operation of motor  105  (and attached band  110 ) controls the pressure of the irrigation fluid exiting bag  115 . 
     Motor  105  can be a DC motor, stepper motor, or other type of motor which can be precisely controlled. In other embodiments of the present invention, motor  105  can be any type of mechanism that is capable of exerting a force on band  110 . 
     A hand piece  150  is placed in the eye  145  during a phacoemulsification procedure. The hand piece  150  has a hollow needle (not shown) that is ultrasonically vibrated in the eye to break up the diseased lens. A sleeve located around the needle provides irrigation fluid from irrigation line  140 . The irrigation fluid passes through the space between the outside of the needle and the inside of the sleeve. Fluid and lens particles are aspirated through the hollow needle. In this manner, the interior passage of the hollow needle is fluidly coupled to aspiration line  155 . Pump  170  draws the aspirated fluid from the eye  145 . An aspiration pressure sensor  160  measures the pressure in the aspiration line. An optional vent valve can be used to vent the vacuum created by pump  170 . The aspirated fluid passes through reservoir  175  and into drain bag  180 . 
     During a phacoemulsification procedure, the tip of the needle can become occluded with a lens particle. This creates a condition that is called an occlusion. During an occlusion, less fluid is generally aspirated from the eye. The vacuum pressure in aspiration line  155  builds up as a result of the occlusion. Accordingly, during an occlusion, aspiration pressure sensor  160  reads the increased vacuum that builds up in aspiration line  155 . When the occlusion breaks (that is when the lens particle that causes the occlusion is broken up by the ultrasonic needle), a surge occurs. The built up vacuum in aspiration line  155  creates a sudden demand for fluid from the eye resulting in a rapid lowering of IOP and shallowing of the operating space within the eye. This can lead to a dangerous situation in which various structures of the eye can be damaged. 
     The squeeze band device of the present invention is capable of responding to this surge effect by increasing the irrigation pressure in irrigation line  140 . When an occlusion breaks and a surge occurs, band  110  is tightened in response to the decrease in irrigation pressure sensed by irrigation pressure sensor  130 . In this manner, the pressure and resulting operating space in eye  145  can be maintained at a relatively constant value. 
     Likewise, when an occlusion occurs, irrigation pressure may increase as the fluid aspirated from the eye decreases. An increase in irrigation fluid pressure detected by irrigation pressure sensor  130  can be used to control motor  105  (and attached band  110 ) to regulate the pressure in eye  145 —that is to keep the pressure in eye  145  within acceptable bounds. 
       FIG. 2  is an end view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. In  FIG. 2 , bag  115  is held between band  110  and curved base  120 . Shaft  210  is attached to motor  105  (not shown). Motor  105  turns shaft  210  to tighten (or loosen, as the case may be) band  110 . When motor  105  is a DC motor or stepper motor, shaft  210  can be turned precisely to apply a known amount of force on bag  115 . The force placed on bag  115  by band  110  is proportional to the pressure of the irrigation fluid in the irrigation line to which bag  115  is connected. The tension of band  110  forces the bag  115  to conform to the convex curve shape of the curved base  120 . There is a linear relationship between pressure in bag  115  and the tension in band  110  approximated by the hoop stress formula:
 σ h   =Pr/t    
     where σ h =hoop stress (in this case, band stress from tension on the band  110 ) 
     P=internal pressure (in this case, pressure in the bag  115 ) 
     t=thickness of the hoop (in this case, the thickness of band  110 ) 
     r=the inside radius of the circle (in this case, the radius of curved base  120 ) 
     Band  110  can be made of a flexible but non-stretching material such as a thin flexible metal or plastic sheet, woven material, or other suitable material. In one embodiment, band  110  is made of a 0.010 inch thick UHMW polyethylene sheet. 
       FIG. 3  is a side view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. In  FIG. 3 , bag  115  is held between band  110  and curved base  120 . Curved base  120  is mounted to frame  125 . Shaft  210  is coupled to motor  105 . As motor  105  turns shaft  210 , band  110  is tightened (or loosened depending on the direction that shaft  210  is turned). By controlling the operation of motor  105 , the pressure in the eye  145  can be maintained within acceptable bounds. 
       FIG. 4  is a block diagram of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. In  FIG. 4 , a controller  410  receives an input from irrigation pressure sensor  130  and controls the operation of motor  105 . In this manner, controller  410  controls motor  105  to adjust irrigation pressure. Controller  410  is typically an integrated circuit with power, input, and output pins capable of performing logic functions. In various embodiments, controller  410  is a targeted device controller. In such a case, controller  410  performs specific control functions targeted to a specific device or component, such as a motor. For example, motor controller has the basic functionality to control motor. In other embodiments, controller  410  is a microprocessor. In such a case, controller  410  is programmable so that it can function to control more than one component of the device. In other cases, controller  410  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  410  may be implemented by many different components or integrated circuits. 
       FIG. 5  is a block diagram of control system for a pressurized irrigation squeeze band apparatus according to the principles of the present invention. In  FIG. 5 , an input  350  represents the desired pressure. In this example, controller  410  is a PID controller that controls the operation of motor  105 . The irrigation pressure sensor  130  provides an input to controller  410 . Controller  410  tracks the desired pressure (input  350 ) by controlling motor  105 . For example, if the irrigation pressure is too low (lower than the desired pressure), controller  410  directs motor  105  to tighten band  110  thereby increasing the pressure in bag  115  (and the irrigation line to which bag  115  is coupled). If the irrigation pressure is too high (higher than the desired pressure), controller  410  directs motor  105  to loosen band  110  thereby decreasing the pressure in bag  115  (and the irrigation line to which bag  115  is coupled). 
       FIG. 6  is a perspective view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. In  FIG. 6 , bag  115  is held between band  110  and curved base  120 . Curved base  120  is mounted to frame  125 . Shaft  210  is coupled to motor  105 . 
       FIG. 7  is a side view of a pressurized irrigation squeeze band apparatus according to the principles of the present invention. In  FIG. 7 , motor  105  and curved base  120  are as described above. Clutch  710  is coupled to motor  105 . Spring  720  is coupled to shaft  210 . Clutch  710  engages or disengages the motor  105  and shaft  210 . In this manner, clutch  710  provides a safety feature allowing for the shaft  210  to be disengaged from motor  105  if necessary. Spring  720  provides a constant torque on shaft  210  if motor  105  disengages from shaft  210 . In this manner, if clutch  710  disengages motor  105  from shaft  210 , then spring  720  provides a constant torque on shaft  210  to maintain a constant minimum pressure in the irrigation line (and the eye). 
     The irrigation squeeze band device of the present invention provides for precise control of irrigation pressure (and pressure in the eye) during cataract surgery. Prior attempts at a squeeze bag type device included using two opposing plates between which the bag is placed. The plates are moved together to increase pressure in the bag. It was discovered, however, that the bag was susceptible to movement while located in between the plates. This movement caused the control of the pressure to be slower than in the squeeze band device of the present invention. In the present invention, band  110  holds bag  115  securely against curved base  120 . This allows for quicker and more precise control of pressure. 
     In addition, the surface contact area of the bag and rigid plates would vary significantly at different bag fill levels. As a result, at different bag fill levels, significantly different forces would be required to produce the same pressure, thus making consistent device control more challenging. The present invention provides significant benefit in minimizing contact surface area variation throughout bag volume depletion. The band conforms to the bag surface on one side, keeping the area nearly constant. While the base to bag contact area somewhat varies, the variations are not as significant as in case of the flat plates. 
     From the above, it may be appreciated that the present invention provides a pressurized infusion system for phacoemulsification surgery. The present invention provides an irrigation squeeze band device that more precisely controls fluid pressure. The present invention is illustrated herein by example, and various modifications may be made by a person of ordinary skill in the art. 
     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.