as described above , the most common treatment for cataracts is to emulsify the clouded natural lens , aspirate the lens from the eye and replace the lens with an artificial lens . a phacoemulsifying tool achieves a first stage of aspiration and then is removed from the corneal incision . an irrigation - aspiration tool of the type shown in fig1 is inserted . as used herein , the term &# 34 ; aspirator &# 34 ; includes the phacoemulsifier and the separate irrigation - aspiration tool . the conventional aspirator 50 shown in fig1 includes a handle section 60 that is held by the surgeon and a tip section 70 that is inserted through the cornea . the tip section of the aspirator has two passages . an inner axial passage through an inner cannula 76 is used to aspirate the emulsified lens . an outer passage through an outer cannula 72 delivers a stream of saline solution 64 into the eye . the simultaneous injection of saline solution into the eye while the emulsified lens is being aspirated prevents the lens capsule from collapsing . after the emulsified lens has been aspirated , the surgeon removes the aspirator and inserts an artificial lens according to techniques that are well known in the art . fig2 is a more detailed view of the tip section 70 of the conventional aspirator . the tip 70 includes a barrel section 80 that is received within the handle 60 thereby allowing the same handle to be used with multiple interchangeable tips . the tip , surrounding and coaxial with the first , is sealed within the handle by a pair of o - rings 82 , 84 that seat within corresponding races ( not shown ) to isolate the inner and outer passages . as described above , one problem with a conventional aspiration tip of the type shown in fig1 and 2 is that it can damage the cornea when inserted and / or when manipulated to remove the emulsified lens . fig3 and fig4 show how the tip is inserted through a patient &# 39 ; s cornea 92 . saline solution is delivered through a passage or bore 75 that is formed between the inner cannula 76 and the outer cannula 72 , and exits through a port 74 . the emulsified lens is aspirated through a port 78 , into the inner passage or bore 77 of the inner cannula . as best seen in fig4 a conventional outer cannula creates gaps 94 at the ends of the incision that contribute to excess fluid loss from the eye during the irrigation - aspiration procedure . in addition , the rigid outer cannula can stretch the cornea and cause the incision to tear as the tip is inserted or moved within the lens capsule . one prior attempt to solve the problem created by rigid aspirator tips is to make the outer cannula of a readily deformable material . fig5 shows an aspiration tip with an outer cannula 98 of soft silicon rubber material . while the soft silicon rubber cannula helps avoid tearing the incision and seals the incision to prevent fluid loss , the force of the incision on the soft outer cannula can cause it to collapse or pinch , thereby inhibiting the flow of the saline solution , as can be seen in fig6 . to solve the problems associated with the prior art , the present invention utilizes a tip that is only partially deformable . as shown in fig7 the tip 120 of the present invention preferably includes a rigid or flexible inner cannula 122 having an aspiration port 124 at its distal end for aspirating cortical material from the eye . an outer cannula 130 is concentrically disposed over the inner cannula . the outer cannula 130 includes a rigid tip section 132 and a rigid butt section 136 . the tip section has a port 134 at its distal end to inject saline solution into the eye . separating the tip section and the butt section along the length of the inner cannula are reinforcing members comprising a pair of diametrically opposed , relatively rigid ribs 140 . each of the ribs joins the respective tip and butt section at shoulders 142a , 142b having slightly smaller diameters than the tip and butt sections . the outer cannula 130 fits over the inner cannula 122 and is secured in position conventionally , such as by brazing . to complete the tip , an elastomeric sleeve 150 is slid over the outer cannula to seat between the shoulder sections 142a and 142b . when seated , the elastomeric sleeve has an outer diameter substantially equal to the outer diameters of the tip and butt sections , as can be seen in fig8 . fig9 is a cross - sectional view of the aspirator tip 120 . as can be seen , an inner passage or channel 126 is formed within the inner cannula 122 and an outer passage or channel 128 is formed between the inner cannula 122 and the outer elastomeric tube 150 . fig1 shows how the elastomeric sleeve 150 can be radially compressed between the ribs 140 so that the central portion of the outer cannula has an upright dimension less than the upright dimensions of the rigid tip and butt sections . fig1 shows a cross section of the outer cannula in a compressed state . the elastomeric sleeve 150 can be compressed between the ribs up to a point where the sleeve meets the inner cannula 122 . however , the rigid ribs 140 prevent the complete compression of the elastomeric sleeve in order to maintain the outer channel open and prevent blockage . the aspirator tip shown in fig7 - 11 provides the advantage of reducing the likelihood of tearing the cornea during surgery while at the same time not being pinched to block the outer aspiration channel . in addition , the compression of the elastomeric sleeve creates a good seal with the incision to minimize fluid loss . fig1 shows alternative embodiments of the tip according to the present invention . the tip 200 includes an inner cannula 202 having an input port 204 . an outer cannula includes a rigid tip section 210 and a butt section 214 . in this embodiment , the tip and butt sections are independent of each other and are independently secured to the inner cannula . the tip section 210 includes a shoulder 212 and the butt section includes a shoulder 216 that are both directed to the open center section of the outer cannula . a flexible sleeve is slid over the tip section 210 to seat on the shoulders 212 , 216 in order to complete the outer cannula . in this embodiment of the invention , the support members of the outer cannula are embedded in the flexible rubber tubing . a first embodiment of the elastomeric sleeve 220 has a pair of diametrally opposed rigid or substantially rigid ribs 224 , 226 that are embedded in the tube and oriented along the length of the sleeve 220 . when the sleeve 220 is seated , the ribs 224 , 226 within the sleeve prevent the outer cannula from completely collapsing . an alternative embodiment of the elastomeric sleeve is a sleeve 240 having an embedded reinforcing helical spring 242 . the helical spring has a stiffness such that the elastomeric sleeve can be partially compressed in order to make a good seal when inserted through the incision in the cornea . however , the spring provides sufficient support that the outer cannula is not completely pinched closed at the incision . a third embodiment is an elastomeric tube 250 that has multiple flexible reinforcing wires 252 embedded in the tube . the wires 252 are sufficiently stiff that they prevent the tube from collapsing under the force of the incision , yet are supple enough to allow the outer cannula to compress and form a good seal . in this embodiment , preferably several wires are used , spaced uniformly around the circumference of the tube . fig1 shows yet another embodiment of the invention whereby the tip 260 includes an inner cannula 262 and an outer cannula formed by a rigid tip section 261 and a rigid butt section 266 . the tip section includes a shoulder 264 and the butt section includes a shoulder 268 that are directed toward the center section of the outer cannula . secured between the shoulders 264 , 268 is a helical spring 270 . an elastomeric sleeve 280 is slid over the tip section 262 so that the outer periphery of the spring 270 abuts the inner periphery of the elastomeric tube . after surgery , the elastomeric tube 280 can be removed and the tip including the spring 270 can be sterilized . in the embodiment of the invention shown in fig1 , a tip 300 includes an inner cannula 302 and an outer cannula formed of a rigid tip section 304 and a rigid butt section 310 . the tip section includes a shoulder 306 and the butt section includes a shoulder section 312 . secured between the shoulders 306 , 312 are several flexible wires 320 that are equally spaced about the circumference of the outer cannula and extend between the shoulders 306 , 312 . six such wires can be used . an elastomeric sleeve 330 can be slipped over the tip section 304 to seat on the shoulders 306 , 312 . the flexible wires 310 provide sufficient support that the outer cannula is not completely pinched closed by the force of the corneal incision , but do allow some compression to reduce potential damage to the eye and to provide a more effective seal . in the embodiment of the present invention shown in fig1 , a tip 400 includes an inner cannula 402 and a unitary outer cannula 404 . the outer cannula includes a rigid or at least stiff tip section 406 and , preferably a rigid or at least stiff butt section 408 . the central section 410 extending between the tip and butt sections is more resilient , such that it can be partly compressed by the force of the corneal incision . in a unitary outer cannula having a central section integral with the tip and butt sections , this can be achieved by varying the polymer blend , such as during extrusion of the outer cannula . another alternative , shown in fig1 , is to vary the wall thickness lengthwise of the outer cannula , while maintaining a uniform wall thickness for each cross section . the tip 506 and butt 508 of the outer cannula 504 thus are more rigid than the central portion 510 for this embodiment of aspirator 500 . in either event , the stiffness of the tip section aids in precise placement and insertion of the aspirator tip , but the more flexible or resilient central section lessens the chance of tearing the corneal incision and provides a more effective seal as the tip is manipulated for aspiration of an emulsified lens . while the preferred embodiment of the invention has been illustrated and described , it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention .
the outer cannula of an ophthalmic irrigator - aspirator has rigid tip and butt sections and a more flexible central section . the central section can be an elastomeric sleeve that extends between the tip and butt sections . the outer cannula includes reinforcement members that prevent the elastomeric sleeve from becoming completely closed by compression caused by a tight fit in an incision in a patient &# 39 ; s cornea . the reinforcement members may be rigid or somewhat flexible .