Abstract:
An automated method of forming a viscoelastic-free surgical pocket in the anterior chamber. The method constantly compares the unobstructed flow vacuum level with the current vacuum level and sounds an alert or automatically proceeds to the next step in the surgical procedure when the vacuum level approaches the unobstructed vacuum level and remains at that level for a certain duration.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to the field of cataract surgery and more particularly to an infusion control system for a phacoemulsification handpiece.  
           [0002]    The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the 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 lens.  
           [0003]    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).  
           [0004]    In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.  
           [0005]    A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece, an attached cutting tip, and irrigating sleeve and an electronic control console. The handpiece assembly is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.  
           [0006]    The operative part of the handpiece 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 tip during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body&#39;s distal end. The nosecone is externally threaded to accept the irrigation sleeve. 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 tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve. Ultrasonic handpieces and cutting tips are more fully described in U.S. Pat. Nos. 3,589,363; 4,223,676; 4,246,902; 4,493,694; 4,515,583; 4,589,415; 4,609,368; 4,869,715; 4,922,902; 4,989,583; 5,154,694 and 5,359,996, the entire contents of which are incorporated herein by reference.  
           [0007]    In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the cornea, sclera, or other location. The cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the eye through the open end of the cutting tip, the cutting tip and horn bores and the aspiration line and into a collection device. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip.  
           [0008]    The preferred surgical technique is to make the incision into the anterior chamber of the eye as small as possible in order to reduce the risk of induced astigmatism. These small incisions result in very tight wounds that squeeze the irrigating sleeve tightly against the vibrating tip. Friction between the irrigating sleeve and the vibrating tip generates heat, but the risk of the tip overheating and causing a burn to the tissue is reduces by the cooling effect of the aspirated fluid flowing inside the tip. When the tip becomes occluded with tissue or viscoelastic, this aspiration flow can be reduced or eliminated, allowing the tip to heat up.  
           [0009]    Many surgeons prefer to use a viscoelastic agent in the anterior chamber during phacoemulsification. The viscoelastic helps to protect the endothelium during surgery. As discussed above, the viscoelastic agent can block the aspiration channel and reduce the flow of cooling irrigating solution during surgery. Therefore, many surgeons recommend removing the viscoelastic agent from a pocket adjacent to the anterior capsular membrane. Prior to the present invention, this procedure was performed manually by the surgeon, who had very little indication when the pocket was formed sufficiently to continue with the surgical procedure.  
           [0010]    Therefore, a need continues to exist for an automated method of forming a viscoelastic-free surgical pocket in the anterior chamber.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention improves upon the prior art by providing an automated method of forming a viscoelastic-free surgical pocket in the anterior chamber. The method constantly compares the unobstructed flow vacuum level with the current vacuum level and sounds an alert or automatically proceeds to the next step in the surgical procedure when the vacuum level approaches the unobstructed vacuum level and remains at that level for a certain duration.  
           [0012]    Accordingly, one objective of the present invention is to provide a surgical console control system.  
           [0013]    Another objective of the present invention is to provide a method of operating a surgical console control system having aspiration fluid pressure sensing capability.  
           [0014]    Another objective of the present invention is to provide a method of operating a surgical console control system that provides more accurate removal of the viscoelastic agent prior to initiation of phacoemulsification.  
           [0015]    These and other advantages and objectives of the present invention will become apparent from the detailed description and claims that follow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a schematic illustration of an ophthalmic surgical system suitable for practicing the method of the present invention.  
         [0017]    [0017]FIG. 2 is a block diagram of the method of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    As best seen in FIG. 1, surgical system  10 , suitable for practicing the method of the present invention generally contains control console  12 , infusion fluid source  14 , collection container  24  and handpiece  16 . Control console  12  generally includes CPU  18 , aspiration pump  20 , handpiece power supply  22 , infusion fluid valve  26 , aspiration valve  28 , infusion flow sensor  32  and aspiration pressure sensor  30 . Information supplied to CPU  18  from sensor  30  is used to control aspiration valve  28 , pump  20  and infusion fluid valve  26 . CPU  18  also controls the power supplied to handpiece  16  by power supply  22 . Surgical systems similar to system  10  are well-know in the art and commercially available from Alcon Laboratories, Inc., Fort Worth, Tex. under the ACCURUS® and LEGACY® trademarks. Sensor  32  may be any commercially available flow sensor, such as Models Nos. T101D or T201D available from Transonic Systems, Inc., Ithaca, N.Y.  
         [0019]    As best seen in FIG. 2, upon initialization of system  10 , pump  20  is run at a preset aspiration fluid flow rate (F check ), and the aspiration fluid pressure (vacuum) (P aspcheck ) is measured by sensor  30 . P aspcheck  is compared by CPU  18  to a predetermined expected vacuum for unobstructed flow in handpiece  16  at the preset rate for pump  20 . If P aspcheck  is within the allowed range, system  10  continues to the next stage of the procedure. If P aspcheck  is outside the allowable range, system  10  signals an error and will not proceed to the next stage of the procedure. During this initialization step, the pressure of infusion fluid flowing from source  14  to handpiece  16  (P irrcheck ) is monitored by sensor  32 .  
         [0020]    The overall fluidics resistance (R) in system  10  can be approximated using the following equation: 
           R= ( P   irrcheck   −P   aspcheck )/ F   check   
         [0021]    Once R is known, the expected aspiration pressure (P asp ) for any other aspiration fluid flow rate (F) and infusion fluid pressure (P irr ) may be calculated in linear approximation using the following equation: 
           P   asp   =P   irr   −F *(( P   irrcheck   −P   aspcheck )/ F   check ) 
         [0022]    CPU  18  may continuously calculate an expected value of P asp (P threshold ) or may be provided a set of look-up tables so as to know continuously P threshold  for the instantaneous aspiration fluid flow and infusion fluid pressure conditions.  
         [0023]    During an occluded or partially occluded condition P asp  will be greater than P threshold  for the instantaneous aspiration fluid flow and infusion fluid pressure conditions (indicating a higher vacuum level). As the occlusion or partial occlusion subsides, P asp  will decrease and approach P threshold . CPU  18  uses this information to provide an alert to the system user that the occlusion has been removed or has subsided. Alternatively, CPU  18  may use this information to proceed automatically to the next stage of the procedure. CPU  18  may also contain a timer that can vary when the alert is sounded or when the next stage of the procedure is started.  
         [0024]    This method is particularly useful in indicating the presence or absence of a viscoelastic agent. When handpiece  16  begins to aspirate the viscoelastic agent, the increased viscosity of the agent versus the infusion fluid causes P asp  to increase and F to decrease, thereby reducing the amount of cooling infusion fluid entering handpiece  16 . These variations in P asp  can be monitored by CPU  18  in the manner described above to indicate to system  10  or to the user the presence or absence of viscoelastic agent or other obstruction at handpiece  16 .  
         [0025]    This description is given for purposes of illustration and explanation. It will be apparent to those skilled in the relevant art that changes and modifications may be made to the invention described above without departing from its scope or spirit.