Abstract:
An apparatus is provided for decreasing or eliminating flow of fluid between a probe and an incision during surgical procedures. The apparatus may comprise a deformable layer on the probe. The deformable layer may be comprised of a polymer foam, which may be covered with a surface layer. In another embodiment, baffles on a base layer are provided. The deformable layer or baffles may be on a slidable base surrounding the probe.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     This invention pertains to decreasing flow around a probe, cannula, needle or trocar, such as during aspiration and irrigation of fluids within a closed volume for medical purposes. More particularly, apparatus and method are provided for minimizing or eliminating fluid flow around a phacoemulsification probe or other instrument during irrigation and aspiration of the eye or human organs or cavities. 
     2. Description of Related Art 
     Traditional small incision cataract surgery uses a coaxial irrigation-aspiration system and ultrasound to fragment the cataract material. Recently, Micro-Incision Cataract Surgery (MICS) has evolved, which uses two very small incisions and divides the irrigation mode from the ultrasound-aspiration mode of the phacoemulsification technique, thus introducing “bimanual” phacoemulsification. The advantage of MICS is smaller incisions in the eye, which are less invasive, allow quicker healing and typically leave less astigmatism. In the bi-manual technique the surgeon uses both hands during the phacoemulsification procedure, with separate irrigation and aspiration instruments. 
     New ultrasound and other fragmenting machines have also increased the appeal of MICS and allowed smaller, tighter incisions with less chance of “wound burn” by reducing the amount of energy employed inside the eye, using techniques such as described in US 2004/0068300, for example. Similarly, vitreous resection has also progressed by the utilization of smaller incisions and bi-manual removal of vitreous. The small vitrectomy tip normally involves use of a hollow shaft enclosing a rotating or isolating blade to which an aspiration line is affixed. 
     In both instances, cataract lens or vitreous removal, the infusion needle and the mechanically active aspirator needle used in the bi-manual technique are preferably “water tight” in the incision of the eye, so as to form a closed fluid system. Working in a closed environment provides a significant improvement from routine cataract surgery, where the closed chamber concept is not available. There is a need to optimize the probes to allow the balance between outflow and inflow in this new environment. The goal is to have a pressurized volume of fluid in the anterior chamber, posterior chamber or vitreous body of an eye and to minimize the outflow and inflow volumes. The decrease in flow rate into and out of the eye can reduce the circulation inside the eye and lead to greater safety and control of the surgery. 
     New micro instruments have been designed to be incorporated into the system used by the surgeon in MICS. The new probes may be of smaller size and are designed to be used without an irrigation sleeve. They should be designed to be manipulated efficiently through the micro-incisions without creating enough tension in the corneal tissue to tear the incision or damage the tissue. Friction between the probe and the corneal tissue should preferably be minimized. 
     It is important to avoid thermal burn when using MICS. Some prior methods depended on cooling the phaco tip and incision tissue by leaking solution through the incision. Newer methods reduce tip temperature by operating in a pulse mode or computer-controlled mode as described in US 2004/0068300, which minimizes the amount of energy input to the ultrasound probe and lowers its temperature, which may decrease the need for leaking through the incision. A Teflon coated tip has also been used in the past, which provides lower friction between the probe and the tissue and adds a thermal insulation layer to the probe. 
     What is needed is apparatus and method to increase resistance to fluid flow or to provide a limited seal around a phacoemulsification probe or other needle, cannula or trocar through an incision to minimize or prevent fluid leakage or to afford a closed system at normal pressures for performing surgery. The apparatus should also assist in avoiding thermal damage to tissue. 
     SUMMARY OF THE INVENTION 
     A device is provided for increasing flow resistance around a probe during surgical procedures. In one embodiment, the device includes a deformable polymer foam layer around the probe. The foam layer may have a low friction layer on top and be shaped for easy insertion into an incision. In another embodiment, the device includes baffles on a base layer. The baffles are selected to deform as a probe moves through an incision. In yet another embodiment, the deformable layer is attached to a slidable base. A method for selecting a deformable layer is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric drawing of a prior art phacoemulsification probe designed for use with an infusion sleeve to provide coaxial irrigation and evacuation. 
         FIG. 2  is an isometric drawing of one embodiment of the apparatus disclosed herein with a deformable cover on a phacoemulsification probe. 
         FIG. 3  is a cross-section view of one embodiment of the apparatus disclosed herein. 
         FIG. 4  is a drawing of a closed-cell elastomeric foam. 
         FIG. 5  is a drawing of an open-cell elastomeric foam. 
         FIGS. 6A ,  6 B and  6 C are plots of force vs compression for various materials. 
         FIG. 7  is a drawing of a film on the surface of a closed-cell elastomeric foam. 
         FIG. 8  is an isometric drawing of one embodiment of the apparatus disclosed herein with a baffle structure to decrease flow around a phacoemulsification probe. 
         FIG. 9  is an isometric drawing of one embodiment of the apparatus disclosed herein with a deformable cover on a slidable base disposed between stops on a phacoemulsification probe. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , prior art phacoemulsification probe  10  is shown. The probe includes needle  12 , shoulder section  14  and ultrasonic source  16 . Phacoemulsification needle  12  is used to emulsify the nucleus of a cataract in the natural lens of the eye. A sleeve (not shown) may be placed over section  14  to carry water between the sleeve and needle  12 . Water serves to act as a coolant of the needle to decrease danger of burning of the cornea. Lumen  18  through needle  12  allows suction to be placed in the opening to aspirate fluids from the eye along with fragments of cataract to be removed. The sleeve (not shown) over needle  12  serves to prevent corneal burn. The diameter of the sleeve over needle  12  is selected by the surgeon to fit inside an incision in the cornea and to allow, in some instances, leakage through the incision to assist in cooling of the needle. 
     When the newer bi-manual phacoemulsification method is used, two incisions are made and irrigation and aspiration are separately carried out through separate incisions. No sleeve on the phacoemulsification probes for both infusion and aspiration is necessary in such instances. Infusion fluid may pass through lumen  18  in a needle such as shown in  FIG. 1  and ultrasonic source  16  may not be present. 
     Referring to  FIG. 2 , probe or cannula  12 , containing lumen  18 , is covered with deformable material  20 . Cannula  12  and deformable material  20  have been placed through incision  22  in cornea  25  and into anterior chamber  30  of an eye. The outside diameters of probe  12  and deformable material  20  are selected in view of the size of incision  22  so as to cause material  20  to be deformed to fit inside incision  22  as it passes through the incision without placing excess stress on cornea  25  around incision  22 . Preferably, deformable material  20  will exert enough force against incision  22  to allow only very low flow rate between material  20  and incision  22  when pressure inside an eye is within the normal range of eye pressure, which is up to about 30 mm Hg, or about 0.6 psi. Tests may be performed in simulated incisions using different material properties and thicknesses of deformable material  20  to select the material and thickness on probe  12  so as to allow material  20  to substantially seal against incision  22  or at least greatly increase resistance to fluid flow through incision  22  when pressure in chamber  30  is within the normal range. Material  20  may also be selected to allow flow through incision  22  at a higher rate should pressure in chamber  30  increase to a value that could cause damage to an eye. 
     Deformable material  20  is preferably a foamed polymeric material having a selected compression modulus. The foamed material may be an open-cell foam or a closed-cell foam. If material  20  is a closed-cell foam, deformable material  20  may form a hydraulic seal between needle  12  and cornea  25  because flow does not occur through the body of the foam. If material  20  is an open-cell material, it may allow some fluid flow between needle  12  and cornea  25 , but it may greatly increase the resistance to flow through incision  22  in cornea  25 . The thickness of the layer of deformable material  20  and the compression modulus of the material may be selected to allow material  20  to seal against incision  22  as probe  12  is moved through incision  22 . 
     A cross-sectional view of needle, cannula or probe  12  with lumen  18  and deformable material  20  is shown in  FIG. 3 . Preferably, deformable material  20  has lesser thickness on the distal end of needle  12  such that it will more easily enter an incision. Material  20  is preferably a polymeric material selected for its inertness, its deformability, its permeability to fluid and its thermal conductivity. A suitable material is a silicone rubber product. Other rubber-like or elastic materials may be used. A particular suitable material is silicone elastic material available from Saint-Gobain Performance Plastics of Grandville, N.Y. The material is available in either closed-cell foam, open-cell foam or solid. A closed-cell foam is illustrated in  FIG. 4  and an open-cell (or partially open-cell) foam is illustrated in  FIG. 5 . 
     The compression modulus of the Saint-Gobain materials is illustrated in  FIGS. 6A ,  6 B and  6 C. In  FIG. 6A , the force required to cause compression is shown for firm, medium and soft silicone sponge rubber materials. In  FIG. 6C  similar data are shown for a silicone foam rubber material, which is the most deformable material illustrated.  FIG. 6B  shows compression data for five different compositions of solid silicone rubber, which illustrates the much higher force required to obtain compression of solid material and demonstrates that a more deformable material must be used to avoid excessive physical force to corneal tissue. Data for the most deformable material, shown in  FIG. 6C , shows that a force of 1.5 lbs. per square inch (psi) results in a compression of the material of about 20 percent, which translates into an effective compression modulus of 13.3 percent compression per psi at this pressure. In contrast, the most deformable material illustrated in  FIG. 6B  shows a compression modulus of 20/47=0.42 percent compression per psi. 
     Saint-Gobain Performance Plastics also supplies a variety of tapes made of foamed materials. The tapes may be supplied with coatings or adhesives on the surfaces. Such foamed polymer having a smooth surface layer may be manufactured and used as deformable material  20 . Such a configuration is illustrated in  FIG. 7 , for a closed cell material. Closed-cell foam  70   a  is covered with layer  70   b , which is preferably made of a material, such as TEFLON, having low frictional resistance as the coated deformable material on a needle is moved through an incision in a cornea of an eye. If the foam is open cell, the coating may be perforated to allow fluid to flow through the coating as the deformable material deforms by moving through an incision. 
       FIG. 8  illustrates an alternate method of obtaining a deformable covering on needle  12 . Deformable coating  80  is made up of base  82  and circumferential baffles  84 . Base  82  and baffles  84  are preferably constructed of a deformable elastomeric material and are sized such that deformable coating  80  may pass through incision  22  in cornea or sclera  25 . Baffles  84  may be made convex toward anterior chamber  30  or concave toward anterior chamber  30  or perpendicular to base  82 . Baffles  84  are designed so as to increase resistance to flow from chamber  30 .  FIG. 8  shows one baffle  84  confined by incision  22  to lie against base  82 , but base  82  may be smaller in size than incision  22 , such that baffle  84  may be extended to contact cornea  25  or to extend in incision  22  toward cornea  25 . A suitable elastomeric material for base  82  and baffles  84  is a silicone rubber. The modulus of the rubber may be varied in base  82  and baffles  84  to provide a selected low leakage rate at a selected pressure in anterior chamber  30 . 
       FIG. 9  illustrates deformable sleeve  90  that consists of deformable material  90   a  that is attached to rigid base  90   b . Base  90   b  is sized to slide along needle  92  containing lumen  98 . Stops  94  and  96  at selected locations on needle  92  keep sleeve  90  constrained along a segment of needle  92  and allow manipulation of needle  92  for phacoemulsification procedures or other surgical procedures while sealing or increasing resistance to flow between needle or probe  92  and an incision (not shown). The same materials may be used for material  90   a  as discussed above referring to  FIG. 2 . Base  90   b  may be formed from TEFLON or other plastic material. 
     Other benefits of deformable material  20  in  FIGS. 2 and 3  and material  90   a  in  FIG. 9  are as a barrier to heat flow from probe  12  and to isolate vibration of probe  12  from an incision. This can be of particular benefit when probe  12  is vibrated for phacoemulsification purposes. 
     Although bi-manual phacoemulsification has been used to illustrate application of a phacoemulsification probe having a deformable coating, it should be understood that the deformable material and methods described herein may be used to create a tamponade to prevent or minimize leakage of fluid around a needle, trocar or cannula used in other medical procedures. 
     To use the apparatus disclosed herein in eye surgery, the surgeon forms an incision of small size through the wall of the eye (cornea or sclera). Multiple incisions may also be used, in the event of removing tissue, such as lens material or vitreous, as well as portions of the iris, trabecular meshwork or other structures. Additionally the instruments may be modified to implant into the eye, including medication, lenses, retinal and sub-retinal implants. 
     Although the present disclosure has been described in certain details, it should be understood that various changes, substitutions and alterations can be made thereto without departing from the scope and spirit of the invention, which is defined by the appended claims.