Abstract:
A system for removing the lens from an eye of a mammal, including a lens-removal device having a probe for penetrating the lens capsule. The probe includes a sheath that shields a rotating impeller at all times, with the impeller being pneumatically actuated to advance to a lens removal position within the sheath. The impeller is pneumatically rotated using a turbine mechanism within a handle for the probe. Irrigation and aspiration are provided to facilitate removal of the lens tissue. The turbine is driven with pulsed air to prevent stiction. A purge/protection cap helps remove air bubbles from the system prior to use and protects the delicate impeller during transport. An operating system is also provided with a foot pedal actuator.

Description:
RELATED APPLICATION 
     This patent application claims priority to U.S. Provisional Patent Application Serial No. 60/120,538 filed on Feb. 17, 1999, entitled Method, Apparatus and System for Removing Cataract-Affected Lenses From Mammalian Eyes. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to medical methods and devices, and more particularly to methods and devices for removing the lenses from the eyes of mammalian patients. 
     BACKGROUND OF THE INVENTION 
     A. Pathological and Age Related Changes of the Ophthalmic Lens 
     The lens of a human eye is a crystalline, transparent biconvex structure that serves to focus rays of light on the retina of the eye. The lens consists of a central portion or “nucleus” and a peripheral portion or “cortex” and is enclosed within a lens capsule. The lens capsule is a bag-like anatomical structure that surrounds the lens and is suspended by fine ligaments that are attached to the ciliary muscles. The ciliary muscles radially stretch and relax the capsule thereby flexing the lens in a manner that varies the optical characteristics of the lens to provide the desired focus for an image. This is commonly referred to as accommodation. 
     The lens cortex is a jelly-like portion of the lens and is located between the denser inner nucleus and the elastic outer capsule. The lens nucleus is an optically defined-zone which is denser in the central position of the lens. The lens nucleus becomes even denser with age, and can eventually harden and fill increasing portions of the total lens space. Age-related hardening of the lens typically results in a condition known as presbyopia or farsightedness. Additionally the lens may become opacified and/or cloudy. This opacity or cloudiness of the lens is commonly referred to as a cataract. 
     B. The Pathogenesis and Treatment of Cataracts 
     Cataracts can be present at birth or can be caused by trauma, toxins, radiation, or certain diseases (e.g., diabetes mellitus). Approximately ninety percent of all cataracts form as a result of the aging of the lens, which can occur as early as age 40. Although cataracts can develop in people at any age, it is a virtual certainty that people who live long lives will eventually develop some degree of cataracts. 
     The cataractous lens obstructs the passage of light and tends to prevent the formation of a clear image on the retina. Once a cataract develops, it typically becomes more severe over a period of years, though some develop more rapidly. As a cataract “matures,” the initial change is a yellowing in the lens, which becomes cloudy or opacified. 
     There is one stage in the development of some cataracts when “near” vision actually improves while “distance” vision worsens. This condition is known as “second sight,” when some people can read without their glasses. However, the cataract will continue to progress so that even “near” vision becomes blurred. 
     Surgery (i.e., surgical removal of the cataractous lens) is currently the only method of restoring vision in a patient who suffers from cataracts. Generally, four types of surgical procedures are known to be useable for removing cataract-affected lenses. These four types of surgical procedures are, as follows: 
     Extracapsular Cataract Extraction (ECCE): An incision about 10 mm long is made in the lens capsule and the surgeon extracts the harder nucleus of the lens usually in one piece. The softer peripheral portions of the lens are then suctioned out. The typical ECCE procedure results in disruption or removal of a substantial portion of the anterior aspect of the lens capsule. 
     Intracapsular Cataract Extraction (ICCE): An incision about 15 mm long is made in the lens capsule and the surgeon extracts the whole lens, usually in one piece. The ICCE procedure results in disruption of the zonules so as to detach the lens with its capsule from the surrounding ciliary muscles. At least in the United States, ICCE is no longer a widely used method. 
     Phacoemulsification (PE): For the phacoemulsification procedure, a limbal or corneal incision of about 3 mm is made allowing insertion of the instrument&#39;s tip into the anterior chamber in a direction almost parallel to the iris. Once the incision has been made, the central part of the anterior lens capsule is typically opened widely to facilitate emulsification of the lens nucleus and cortical clean-up, as well as to provide for an ideal intraocular lens placement into the capsule. 
     When compared to conventional extracapsular cataract removal procedures, the phacoemulsification technique provides the advantages of a smaller incision, a stronger post-operative globe which reduces astigmatism, better wound closure, lower trauma and quicker improvement in vision. However, this phacoemulsification procedure is contraindicated, except with respect to the most highly skilled surgeon, in patients having a dislocated cataract lens, a shallow anterior chamber, miotic pupils, or low cornea-endothelial cell counts. 
     Inadvertent perforation of the posterior aspect of the lens capsule during the phacoemulsification procedure can result in vitreous prolapse into the lens capsule. Also, stray ultrasound energy from the phacoemulsification procedure can be destructive to the endothelial cells of the cornea, and can ultimately result in complete degeneration of the cornea. 
      i. Endocapsular Phacoemulsification 
     In a rarely performed procedure, the cataractous lens is removed by an endocapsular phacoemulsification. The cataractous lens must be carved away while not only the posterior side of the lens capsule but also most of the anterior side are left intact. A significant amount of operator skill and training is required to perform endocapsular phacoemulsification. The operator must repeatedly move the ultrasound probe back and forth, while altering its angle, to effect complete emulsification of the lens without causing trauma to or inadvertently perforating the lens capsule. 
      ii. Extracapsular Phacoemulsification 
     Extracapsular phacoemulsification can be performed in the anterior chamber or posterior chamber of the eye. In the case of anterior chamber phacoemulsification, the cataract lens is maneuvered into the anterior chamber where it is carved and removed from the chamber. Anterior chamber phacoemulsification is more traumatic to the endothelial layer of the cornea than posterior chamber phacoemulsification, but it is often an easier procedure for the surgeon to perform. Posterior chamber phacoemulsification consists of carving or shaving the central part of the lens while the lens is still in the lens capsule. This method is more difficult to perform than ECCE due to the possibility of rupturing the posterior lens capsule and exposing the vitreous which fills the volume of the posterior eyeball. 
     EndocapsularVortex Emulsification (EVE): The procedure is described in applicants&#39; prior U.S. Pat. No. 5,437,678 (Sorensen), U.S. Pat. No. 5,690,641. (Sorensen et al.) and U.S. Pat. No. 5,871,492 (Sorensen). In the procedure, an EVE probe having a rotating lens-reducing head is inserted into the lens capsule through a small opening of approximately 1-3 mm that is formed in the periphery of the lens capsule. The 1-3 mm opening in the lens capsule may be formed by an electrosurgical capsulotomy device of the type described in U.S. patent application Ser. No. 08/744,404 (Mirhashemi, et al.) The EVE probe is held in a substantially stationary position while the lens-reducing head is rotated. Concurrently with the rotation of the lens-reducing head, an irrigation solution (e.g., balanced salt solution) is gently infused through the probe and excess irrigation solution and debris are aspirated out of the lens capsule causing the nucleus to rotate and thereby coming into contact with the lens reducing head. The flow causes the entire lens (including the relatively hard nucleus) to be repeatedly brought into contact with the rotating lens reducing head and fully emulsified, without the need for substantial movement or manipulation of the position of the probe. In this manner, the entire lens is removed through the small 1-3 mm opening and the anterior aspect of the lens capsule remains essentially intact. 
     In addition to the ECCE, PE and EVE devices and procedures described hereabove, several other devices and procedures have also been purported to be useable for removing cataract-affected lenses. These other devices and procedures include those described in U.S. Pat. No. 3,732,858 (Banko), U.S. Pat. No. 4,167,944 (Banko), U.S. Pat. No. 4,363,743 (Banko), and U.S. Pat. No. 4,646,736 (Auth). 
     C. The Pathogenesis of and Treatments for Presbyopia 
     As pointed out hereabove, the ability of the human eye to change focus depends upon the inherent elasticity of the lens. However, the human lens typically undergoes a gradual loss of elasticity and/or swells with the aging process, thereby causing a gradual decrease in the eye&#39;s ability to focus on objects that are close up. Clinically, this condition is known as presbyopia. Presbyopia occurs to some degree in almost everyone, during the aging process. 
     Presbyopia has heretofore been treated with prescription glasses or contact lenses. In most cases, a reading correction is required, such as the use of bifocals. However, many patients find bifocals to be difficult to become accustomed to or uncomfortable. 
     The EVE procedure and apparatus summarized hereabove and described in applicants&#39; prior U.S. Pat. No. 5,437,678 (Sorensen), U.S. Pat. No. 5,690,641 (Sorensen et al.) and U.S. Pat. No. 5,871,492 (Sorensen) is unique in that it may be useable to treat presbyopia as well as cataracts. This is so because the EVE procedure leaves the main part of the anterior aspect of the lens capsule as well as the ligamentous attachments between the lens capsule and the ciliary muscles, intact. Also, with the EVE procedure no trauma to the endothelium (inner lining of the cornea) is expected because the entire procedure is performed inside the lens capsule. Because the lens capsule remains substantially intact and capable of accommodation, an elastic lens prosthesis can be introduced into the intact lens capsule through the same 1-3 mm opening through which the native lens had been removed by the probe. Thereafter, the normal contractions and relaxations of the ciliary muscles may cause flexing or movement of the lens capsule and resultant changes in the shape of the elastic prosthetic lens, in the same manner as did the crystalline lens before it underwent its age-related stiffening. In this manner, the procedure, in conjunction with a flexible prosthetic lens, may be used as a treatment for presbyopia. This aspect of the procedure, including the introduction of a flexible lens replacement such as a flowable/injectable lens material, are claimed in applicants&#39; U.S. Pat. No. 5,437,678 (Sorensen), U.S. Pat. No. 5,690,641 (Sorensen et al.) and 5,871,492 (Sorensen). 
     Currently, there remains a need for further improvement and refinement of the devices and procedures used in for surgical removal of the ophthalmic lens so as to further advance the state of the art and the use of such devices to treat disorders of the eye such as cataracts and presbyopia. 
     SUMMARY OF THE INVENTION 
     The present invention provides a device for reducing an ophthalmic lens within the lens capsule in a mammalian eye. In accordance with one aspect of the invention, the device includes an elongate probe insertable into the lens capsule. The probe is defined by an outer tubular sheet comprising a hollow bore extending therethrough, and defining a longitudinal axis. An impeller shaft is disposed in the outer tubular sheath and has an impeller on a distal end thereof, wherein an axis of rotation of the impeller is generally coincident with longitudinal axis. The outer tubular sheath is configured and positioned, during operation of the device, such that a distal portion of the sheath will shield a portion of the impeller while allowing a remainder of the impeller to contact and reduce the lens. 
     In another aspect, the invention provides a device for reducing an ophthalmic lens within the lens capsule in a mammalian eye. The device has an elongate probe insertable into the lens capsule and defining a longitudinal axis. The probe includes an impeller shaft at least partially disposed in a sheath, the impeller shaft having an impeller disposed at a distal end thereof. An axis of rotation of the impeller shaft is generally co-incident with the longitudinal axis of the probe. The device further includes a handpiece having an interior space into which a proximal portion of the elongate probe extends. A drive assembly within the handpiece interior space is functionally connected to a proximal portion of the impeller shaft such that the impeller shaft rotates upon operation of the drive assembly. The drive assembly is adapted to receive non-rotational energy and transmit rotational energy to the impeller shaft. 
     In a further aspect of the invention, a device for reducing an ophthalmic lens within the lens capsule in a mammalian eye comprises an elongate probe insertable into the lens capsule and defining a longitudinal axis. The probe comprises an impeller shaft having a lens-reducing head disposed at a distal end thereof, wherein an axis of rotation of the impeller shaft is generally co-incident with the longitudinal axis of the probe. A handpiece having an interior space, a front end, and a back end, receives a proximal portion of the elongate probe. Additionally, a pneumatic drive assembly disposed in handpiece interior space includes a turbine, wherein a direct drive connection transfers rotational energy from the turbine to the impeller shaft. 
     A device for reducing an ophthalmic lens within the lens capsule of mammalian eye accordance with the present invention includes an elongate probe insertable into the lens capsule and defining a longitudinal axis. The probe comprises an impeller shaft having a lens-reducing head disposed at a distal end thereof, wherein an axis of rotation of the impeller shaft is generally co-incident with the longitudinal axis of the probe. A handpiece having an interior space, a front end, and a back end, receives a proximal portion of the elongate probe. A drive assembly is disposed in the handpiece interior space and functionally connects to a proximal portion of the impeller shaft such that the impeller shaft rotates upon operation of the drive assembly. Finally, a translation apparatus at least partially disposed in the handpiece interior space connects to longitudinally displace the drive assembly. 
     In another aspect, the present invention provides a device for reducing an ophthalmic lens within the lens capsule of mammalian eye including an elongate probe insertable into the lens capsule. The probe comprises an outer tubular sheath having a hollow bore extending therethrough, a hollow impeller shaft having a lumen disposed in the outer tubular sheath and having an impeller disposed at a distal end thereof, an irrigation tube position within and rotationally fixed with respect to the tubular sheath, and a bearing disposed between the impeller shaft and the irrigation tube. The device further includes a handpiece having an interior space into which a proximal portion of the elongate probe extends. A drive assembly is provided for rotating the impeller shaft. An irrigation channel formed within the handpiece interior space is in fluid communication with an annular space formed in the elongate probe between the irrigation tube and impeller shaft. Finally, an aspiration channel formed in the handpiece interior space is in fluid communication with the lumen of the impeller shaft. 
     In a still further aspect, present invention provides a medical device having an elongate probe insertable into a body and defining a longitudinal axis. The probe has a hollow shaft defining a lumen therein and has a tool disposed at a distal end thereof. An axis of rotation of the tool is generally coincident with the elongate probe axis. A handpiece having an interior space and a front end receives a proximal portion of the elongate probe. A drive assembly disposed in the handpiece interior space is connected to a proximal portion of the impeller shaft such that the shaft rotates upon operation of the drive assembly. An irrigation channel within the handpiece interior space is in fluid communication with an irrigation conduit formed in the elongate probe. An aspiration channel disposed in the handpiece interior space is in fluid communication with the lumen of the impeller shaft. In addition, a fluid block about the impeller shaft between the drive assembly and the handpiece front end provides a barrier between the irrigation channel and the aspiration channel. 
     In a further aspect of the invention, a variable speed pneumatic turbine system is provided, comprising a turbine in a housing, and a pneumatic system. The pneumatic system includes a pneumatic energy source and a pneumatic delivery line functionally connecting the pneumatic energy source to a orifice in the turbine housing. The orifice is designed to impinge a gas stream from the pneumatic energy source onto the turbine. The turbine system further includes a pneumatic energy controller functionally connected the pneumatic system and capable of controlling delivery of first, second, and third zones of pneumatic energy to the turbine. The first zone comprises pulses of pneumatic energy capable of overcoming stiction of the turbine. The second zone comprises a second zone level of pneumatic energy that is sufficient to sustain rotation of the turbine combined with pulses of pneumatic energy that would overcome stiction if the turbine were to stop rotating. Finally, the third zone comprises a variable level of pneumatic energy that is at least as high as the second zone level of pneumatic energy. 
     Still further objects and advantages attaching to the device and to its use and operation will be apparent to those skilled in the art from the following particular description. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Further objects of this invention, together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of a preferred embodiment of the present invention which is shown in the accompanying drawings with like reference numerals indicating corresponding parts throughout and which is to be read in conjunction with the following drawings, wherein: 
     FIG. 1 schematically shows of a lens removal system of the present invention operatively positioned in relation to a human eye. 
     FIG. 1 a  is a perspective view of the head of a human patient showing a lens reducing probe of a lens-removing device of the present invention inserted for removal of the lens from the patient&#39;s left eye. 
     FIG. 1 b  is a schematic view of a lens removal system of the present invention incorporating the lens-removing device of FIG.  1  and including desirable accessories. 
     FIG. 2 is an enlarged perspective view of the lens-removing device of the system shown in FIG.  1 . 
     FIGS. 3 a  and  3   b  (slightly enlarged) are longitudinal cross-sectional views of the lens-removing device of FIG. 2, with its drive assembly and lens-reducing impeller in their retracted positions. 
     FIG. 3 c  is an enlarged partially cut-away perspective view of the distal tip of the lens-removing device showing a lens-reducing head in its retracted position, corresponding to the configuration of the device in FIGS. 3 a / 3   b.    
     FIGS. 4 a  and  4   b  (slightly enlarged) are longitudinal cross-sectional views of the lens-removing device of FIG. 2, with its drive assembly and lens-reducing head in their advanced positions. 
     FIG. 4 c  is an enlarged cross-sectional view of the distal tip of the lens-removing device showing the lens-reducing head in its advanced position, and taken within circle  4   c - 4   c  of FIG. 4 a.    
     FIG. 5 is a cross-sectional view through line  5 — 5  of FIG.  3 . 
     FIG. 6 is a cross-sectional view through line  6 — 6  of FIG.  3 . 
     FIG. 7 is a cross-sectional view through line  7 — 7  of FIG.  3 . 
     FIG. 8 is a side elevational view of the lens-reducing head of the device of FIG.  3 . 
     FIG. 9 is a distal end view of the lens reducing head of FIG.  8 . 
     FIG. 10 is a sectional view through the lens capsule and cornea of a mammalian eye, wherein a lens-reducing probe of the present invention has been operatively inserted thereinto to effect endocapsular rotary emulsification of the lens. 
     FIG. 11 is a schematic diagram of a pressure waveform for pulsed, anti-stiction acceleration of the turbine to drive the lens reducing head. 
     FIG. 12 is an elevational view of a purging chamber and protection cap for use with the lens-removal device of the present invention. 
    
    
     These and additional embodiments of the invention may now be better understood by turning to the following detailed description wherein an illustrated embodiment is described. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following sets forth a description of the invention with reference to a presently preferred embodiment of the invention shown in FIGS. 1-12. The description of the preferred embodiment is intended to serve as an example of the invention, and is not intended to limit the scope of the invention in any way. 
     FIGS. 1 and 1 a  illustrate a system  20  that can be operated by a surgeon to remove a lens from a lens capsule  22  in an eye  24  of a patient  26 . An elongate lens-reducing probe  28  of a lens-removing device  30  is inserted at an angle into the eye  24 . More specifically, the elongate probe  28  is inserted at an angle through the cornea  32  and through the lens capsule  22  of the eye  24 . A preferred angle is 9:00 as seen from the front into the right eye as shown, or 3:00 into the left eye. An impeller morcellates the lens within the lens capsule and the lens particles are aspirated, as discussed in more detail below. 
     The lens removing device  30  is connected to a control station  40  that is also part of the system  20 . The control station  40  comprises a gravity irrigation feed  42  and control modules  44 ,  46 , and  48 . The gravity irrigation feed  42  is an elevated bag filled with a sterile balanced salt solution (BSS) that is delivered to the device  30  through an irrigation fluid tube  50   a . Other embodiments of the invention may use a pump to feed the irrigation fluid to the device  30 . 
     The modules  44 , 46 , and  48  of the system control station  40  control the operation of the lens-removing device  30  and the aspiration of the eye  24 . The module  44  supplies actuation fluid (i.e., a gas or liquid), preferably a gas such as filtered air, to the device  30  through the tube  50   b . The introduction of actuation fluid into the device  30  translates the device from a shielded position to a non-shielded position, as is discussed below. The module  46  controls the aspiration of fluid and particles from the eye  24  through tube  50   c . The aspiration module  46  comprises a pump to perform the aspiration. In a preferred embodiment of the invention, the device  30  is powered by a pneumatic turbine located in the device (see FIGS.  4  and  5 ). A module  48  controls a turbine drive fluid (i.e., a gas or liquid and preferably a gas such as filtered air) being delivered to the device  30 . The details of the delivery of the turbine drive fluid are discussed below. 
     An operator controls the modules  44 , 46 , and  48  via a foot pedal  52  of the system control station  40 . If the operator depresses the foot pedal  52  down, the module  48  increases the speed of an impeller in the elongate probe  28  (see FIGS.  3  and  4 ). Likewise, if the operator releases the foot pedal  52  and permits it to rise, the module  48  decreases the speed of the impeller. The speed of the impeller is displayed on a screen  54  of the control station  40 . The device  30  can be made to transition between shielded and non-shielded positions by laterally moving the foot pedal  52 . In one embodiment of the invention, the device  30  is placed in the non-shielded position when a predetermined impeller speed is achieved. 
     With reference now to FIG. 1 b , a lens-removal system  60  including accessories is schematically shown. The system  60  incorporates a control station  40 ′, that is a slightly modified version from the control station  40  shown in FIG.  1 . The control station  40 ′ includes an electro-pneumatic module  62  seen on the left side in FIG. 1 b , and an aspiration pump module  64  seen on the right side. 
     The aspiration pump module  64  is a combination of modules  42  and  46  of FIG. 1, and incorporates flow passages and controls for both irrigation and aspiration. More particularly, the aspiration pump module  64  receives a sterile balanced salt solution (BSS) from a bottle  66  suspended thereabove for gravity drainage. The BSS passes through a combination bottle spike/vent/filter device  68  and a tube  70  having a roller shut-off clamp (not shown) before reaching the module  64 . The module  64  delivers the BSS to the irrigation tube  50   a  in communication with a proximal end of the lens-removing device  30 . The aforementioned aspiration tube  50   c  returns aspirated fluid and particles from the device  30  to the aspiration pump module  64 . The aspirated matter is then deposited in a collection bag  72 . 
     The electro-pneumatic module  62  includes a compressor and associated controls, an electrosurgical generator, and respective power supplies, module interfaces, and associated hardware. The compressor supplies gas to both an actuation gas tube  50   b  and a turbine drive gas delivery tube  50   d . The tubes  50   b  and  50   d  are in communication with the proximal end of the lens-removal device  30 , and supply pneumatic power to mechanisms therein which will be described in more detail below. An electrosurgical handpiece  74  having a probe  76  is electrically connected with the module  62  via cable  78 . In addition, an electrosurgical antenna plate  80  is electrically connected with the module  62  via cable  82 . 
     The system  60  further includes a number of accessories to facilitate removal of a patient&#39;s lens. A purge chamber  84  is shown exploded from the distal end of device probe  28 . The purge chamber will be described in more detail below with respect to FIG.  12 . Various hand-held instruments are also provided for the system  60 , including a viscoelastic  86 , a slit knife  88 , a capsulotomy sizing probe  90 , and a hydrodissection needle  92 . 
     The lens-removing device  30  is seen in FIG.  2  and comprises a handpiece  100  having a distally located front end  102  (to the left) and a proximally located rear cap  104  (to the right). The handpiece  100  has an approximately cylindrical body  106  extending from the rear cap  104  and terminating in a frustoconical portion  108  The front end  102 . As is clear from drawings, the exterior of the handpiece  100  includes a plurality of longitudinally extending facets  110  for ease of manipulation by a surgeon. 
     The elongate probe  28  extends centrally from the front end  102  of the handpiece  100 . More specifically, the elongate probe  28  extends through an apex hole  112  at the apex of the frustoconical portion  108 . The general appearance of one embodiment of this handpiece  100  is disclosed in co-pending United States design patent application Ser. No. 09/100,749, filed on Feb. 17, 1999 entitled Cataract Removal Device. 
     The four tubes  50   a - 50   d  extended proximally from the rear cap  104  of the handpiece  100 . In particular, the irrigation fluid tube  50   a  for delivering irrigation fluid to the device  30  is seen at the top. Below tube  50   a  is shown tube  50   b  that delivers actuation gas to the device  30 . Aspirated fluid and debris are removed from the device  30  through aspirated tube  50   c . Finally, partly seen below and behind tube  50   c  is the tube  50   d  for delivering turbine drive gas to the device  30 . 
     FIGS. 3 a / 3   b  and  4   a / 4   b  are longitudinal sections through the device  30  shown in, respectively, a retracted, insertion position and an advanced, operative position. In addition, details of the distal end of the elongated probe  28  are shown enlarged in FIGS. 3 c  and  4   c , corresponding to the retracted and advanced positions. For the purpose of this discussion, the proximal orientation is to the right, and the distal orientation is to the left for the components of the device  30 . 
     With reference first to FIGS. 3 c  and  4   c , the elongate probe  28  of the device  30  comprises an outer sheath  120  and an impeller shaft  122  (both preferably tubular) concentrically nested therein. In the illustrated embodiment, the hollow sheath  120  and shaft  122  are generally cylindrical in shape, whereas other embodiments of the invention may have a sheath or a shaft of a different shape. For example, it will be appreciated that in some embodiments of the invention, a solid impeller shaft may be used in place of the hollow impeller shaft  122 . 
     As seen in FIG. 3 a , the elongate probe  28  has a fixed distal length  124  that extends distally from the apex hole  112  (FIG. 2) of the handpiece body  106 . The impeller shaft  122  has a distal end on which an impeller  128  (lens-reducing head) is integrally formed from the side wall of the hollow impeller shaft (see FIG.  8 ). Other embodiments of the invention may have an impeller that is not integrally formed on the impeller shaft. The impeller shaft  122  is desirably formed from a relatively rigid biocompatible metal, although alternative embodiments may have an impeller tube or shaft that is not metal, or is flexible to permit a curved elongate probe  28 . 
     As best seen in FIG. 3 c , the sheath  120  has a distal portion terminating at a distal end in an angled, generally oval-shaped mouth  130 . The mouth  130  includes an apex  132  that defines the distal most extent of the sheath  120 . The mouth  130  is desirably planar and forms angle of between 30-60 degrees with a longitudinal axis through the probe  28 . Other embodiments of the mouth  130  may be concavely or convexly curved. 
     FIG. 3 c  shows that when the device  30  is in the retracted position, the impeller  128  is fully shielded by the sheath  120 . That is, the impeller  128  is disposed fully within the sheath  120 , proximal with respect to an imaginary surface extending across the mouth  130 . FIG. 4 c  shows the impeller in the advanced position, only partially shielded by the sheath  120 . More specifically, at least a portion of the impeller  128  projects beyond the imaginary surface extending across the mouth  130 . Desirably, however, the distal most portion of the impeller  128  remains proximal to the apex  132 . Of course, FIG. 4 c  is a sectional view in which the apex  132  is shown behind the impeller  128 , and the opposite side of the mouth  130  is not shown at all, so that the projection of the impeller  128  beyond the mouth  130  is not explicitly illustrated. In general, it will be understood that at least a portion of the impeller  128  projects beyond the distal mouth  130  of the sheath  120  in the advanced, operable position of the device  30 . 
     The partial shielding of the impeller  128  during operation directs the flow of fluid entrained by the impeller, as described below. The described configuration and arrangement of the sheath distal portion  130  and the position of the impeller  128  is also disclosed in U.S. Pat. No. 5,871,492 to Sorensen, entitled “Rotary Device for Removing Ophthalmic Lens,” which is incorporated herein by reference in its entirety. 
     The elongate probe  28  provides both irrigation and aspiration during operation of the device  30 . In this regard, and as best seen in FIG. 4 c , the probe  28  also includes an irrigation tube  134  that extends concentrically within and in close proximity to the outer sheath  120 . The irrigation tube  134  is adapted to slide within the sheath  120 , and a tubular irrigation channel  136  in the probe  28  is defined between the impeller shaft  122  and the irrigation tube  134 . Furthermore, the hollow impeller shaft  122  defines a lumen  138  (see FIG. 3 c ) therein that is used as an aspiration channel, as will be described below. 
     Details of the handpiece  100  will now be explained with reference to FIGS. 3 a - 3   c  and  4   a  - 4   c . The sheath  120  has a proximal portion that extends into the handpiece  100  is fixedly connected to an interior surface  154  of the apex hole  112  using adhesive, or similar expedient. The irrigation tube  134  continues through the apex hole  112  and an O-ring  156  disposed in the interior of the handpiece  100  provides a sliding seal therearound. A proximal end of the irrigation tube  134  extends into a turbine drive assembly  170  disposed in the handpiece  100 . More specifically, as best seen in FIGS. 3 b  and  4   b , the irrigation tube  134  proximal end extends through an axial bore in a turbine housing  172  of the turbine drive assembly  170 . The turbine housing  172  is held from rotation within the handpiece  100  but can translate axially therewithin. 
     With specific reference to FIGS. 3 b  and  4   b , a proximal portion of the impeller shaft  122  extends into the turbine drive assembly  170 , and rotates about a pin bearing (not numbered) in the center of a backing disk  174 . In the illustrated, and preferred, embodiment of the invention, the impeller shaft  122  fits tightly in a central bore of a drive sleeve  176 , thus providing a direct drive connection between the shaft and the turbine. As will be explained, the turbine drive assembly  170  receives non-rotational energy and transmits rotational energy to the impeller shaft  122 , as disclosed below. The direct drive connection has the advantage of reducing the parts and the size of the turbine drive assembly  170 . Other embodiments of the invention may have gear boxes or other devices to transmit the rotational energy to the impeller shaft  122 . 
     As mentioned above, the elongate probe  28  provides irrigation and aspiration during operation of the device  30 . Irrigation fluid enters the device  30  through an irrigation port  178 , shown at the upper side of the rear handpiece cap  104 . Extending distally from the irrigation port  178  is an irrigation channel  180  in communication with the tubular space  136  in the elongate probe  28  between the irrigation tube  134  and the impeller shaft  122  (see FIG. 4 c ). 
     In the preferred embodiment of the invention, as illustrated in FIGS. 3 c ,  4   c  and  10 , irrigation fluid flows distally in the tubular space  136  and out of the elongate probe  28  through holes  182  extending through the sheath  120 . The two holes  182  extend through the sheath  120  proximate to the mouth  130 , and are longitudinally positioned adjacent each other. At least in the advanced, operable position of the shaft  122 , the irrigation fluid does not flow out of the distal mouth  130  of the sheath  120  due to a fluid block bearing  184 . The bearing  184  provides a seal between the shaft  122  and the irrigation tube  134 , and is positioned axially between the holes  182  and the mouth  130  in the advanced position of the device  30 , as in FIG. 4 c . The fluid block bearing  184  is generally tubular and supports the shaft  122  in the irrigation tube  134 . Other embodiments of the invention may have impeller shaft bearings that permit the irrigation fluid to flow out of the sheath distal end or not have impeller shaft bearings. 
     In the shown and preferred embodiment of the invention, aspiration fluid is drawn by the impeller  128  into the lumen  138  of the impeller shaft  122 . The impeller shaft distal end has a strainer  320  (See FIG. 9) in the lumen  138  that prevents particles from traveling into the handpiece  100  but permits fluid to pass therethrough. Fluid from the procedure is also aspirated into the impeller shaft lumen  138  through holes  324  proximate the impeller shaft distal end. A preferred embodiment of the strainer  320  and holes  324  is discussed in connection with FIG.  9 . Other embodiments of the invention may have the impeller shaft distal end plugged (not shown) using any suitable means. In a preferred embodiment of the invention, the plug is a liquid that has hardened. 
     The aspirated fluid exits the impeller shaft lumen  138  through one or more holes  186  (FIG. 3 a ) extending through the wall of the tubular shaft  122 . The hole  186  is located within the turbine drive assembly  170  and the lumen  138  is sealed proximate to the hole. The hole  186  is in fluidic communication with an outer aspiration channel  188  that extends axially to an aspiration port  190  (shown in FIG. 3 a  at the lower portion of the rear handpiece cap  104 ). As a consequence, aspiration fluid traveling through shaft  122  flows through the hole  186  to the aspiration channel  188 , and then to port  190 . 
     Referring now to FIG. 4 b  in conjunction with FIG. 5, the turbine housing  172  of the turbine drive assembly  170  surrounds a fluid block comprising three identical fluid block bearings  194   a ,  194   b ,  194   c . The distal bearing  194   a  is adjacent the distal end of the turbine housing  172  with the bearings  194   a-c  serially arranged in a proximal direction. Although not shown, each of the bearings  194   a-c  is clocked in position by a proximally extending post  198  (see FIG. 5) that extends into a complementary hole in a distal face of the adjacent component. The fluid block bearings  194   a-c  are secured in place with respect to the turbine housing  172  as will be described. The fluid block functions to support the impeller shaft  122  during operation, to seal the operation of the turbine from the operational, distal end of the elongate shaft  122 , and to provide a portion of the irrigation and aspiration channels  180  and  188 . 
     Referring to FIGS. 3 a ,  3   b , and  5 , the aspiration channel  188  is made up of a number of portions. One portion is a channel  189  formed within a front housing cap  173  that is disposed between the frustoconical portion  108  and the turbine housing  172 . Another portion is an aspiration hole  210  that extends through the turbine housing  172  and is in fluidic communication with channel  189 . An additional portion of the aspiration channel  188  is a U-shaped gap  212  in the fluid block bearing  194   b . The U-shaped gap  212  opens outward into the aspiration port  210  and continues into the fluid block bearing  194   b  such that the gap is in fluidic communication with an axial hole (not illustrated) in the fluid block bearing and the impeller shaft hole  186 . During operation, the aspiration fluid moves from the lumen  138 , and outward through the impeller shaft hole  186 , the U-shaped gap  212 , and the aspiration hole  210 , into the channel  189 . 
     The irrigation channel  180  is made up of a number of portions analogous to the aspiration channel  188 . Referring now to FIG. 4 a , the front housing cap  173  forms a channel  183  that is in fluidic communication with a U-shaped gap  213  in the fluid block bearing  194   a . The U-shaped gap  213  is in fluidic communication with the annular space  136  in the elongate probe  28 . Irrigation fluid is delivered to the elongate probe  28  through the channel  183  and the U-shaped gap  213 . 
     As seen in FIG. 4 a , U-shaped gap  220  in the fluid block bearing  194   c  forms a first fluid block between the turbine and the operative end of the elongate probe  28 . The U-shaped gap  220  is in fluidic communication with the channel  183  of the irrigation channel  180 . The fluid block bearing  194   c  is designed to proximally leak a small percentage of irrigation fluid along the impeller shaft  122  and into a gap formed in the distal turbine bearing  222   a . The leaked aspiration fluid exits the gap through a channel (not shown) in the housing  172 . 
     Once irrigation or aspiration fluid enters the U-shaped gaps  212 ,  213 , and  220 , beneficial fluidic blocks are formed between the turbine and the operative end of the elongate probe  28 . In the shown and preferred embodiment of the invention, the turbine operates pneumatically. 
     Now referring to FIGS. 4 b , and  6 , the turbine comprises a pneumatically-driven star wheel  224  with the drive sleeve  176  extending therethrough in an interference fit. The star wheel  224  is concentrically disposed in the turbine housing  172  and held in place by opposing, axially positioned turbine bearings  222   a ,  222   b . The impeller shaft  122  extends axially through the drive sleeve  176  and rotates within both bearings  222   a,b . A distal flange  228  of the distal bearing  222   a  contacts the fluid block and axially retains the fluid block bearings  194   a ,  194   b ,  194   c  in place. Other embodiments of the invention may have pneumatic turbines of other designs, or utilize other types of turbines, such as electrical. Still other embodiments of the invention may have drive systems for delivering rotational energy to the device  30 , such as is disclosed in U.S. Pat. No. 5,871,492 to Sorensen entitled “Rotary Device for Removing Ophthalmic Lens,” which is incorporated herein by reference in its entirety. 
     Referring specifically to FIG. 6, a compressed gas injector  230  for directing compressed gas onto the star wheel  224  is shown extending through the lower left portion of the turbine housing  172 . The injector  230  is arranged to direct a compressed gas stream to perpendicularly strike surfaces  232  of teeth  234  of the star wheel  224 . In a preferred embodiment of the invention, a single compressed gas orifice  230  directs a compressed gas stream onto the middle of the surfaces  232 . Other embodiments of the invention may have multiple compressed gas orifices either laterally and/or axially spaced apart. A turbine gas exhaust port  236  is shown extending through the turbine housing  172  to the left of the star wheel  224 . Preferably, in the embodiment shown, the injector  230  has a progressively decreasing cross-section or lumen diameter, such that the gas or other turbine drive fluid will accelerate as it passes through and out of the injector  230 , thereby increasing the velocity with which the gas or other drive fluid impacts the blade surfaces  232 . 
     FIG. 11 illustrates a preferred pressure waveform exerted on the star wheel  224  to overcome the problem of stiction. Stiction, in this sense, is the common phenomenon affecting rotating machinery whereby the static coefficient of friction exceeds the dynamic coefficient of friction. The preferred waveform shown in FIG. 11 helps initiate rotation of the star wheel  224  from a standstill, but in addition helps prevent premature stalling at low speeds. In small pneumatic motors, such as the turbine illustrated, the rotating element may stall at speeds as high as 10,000 rpm if the pressure wave is constant. The preferred waveform utilizes pulsed air which enables smoother start-ups and rotation at speeds lower than 10,000 rpm. 
     More specifically, the graph in FIG. 11 shows the pressure applied to the star wheel  224  on the Y-axis, and time along the X-axis. The X-axis is shown divided into three zones; Zone  1  from time t 0  to time t 1 , Zone  2  from time t 1  to time t 2 , and Zone  3  beyond time t 2 . The pressure wave is seen as a square wave between time t 0  and time t 2 , and then constantly increasing after time t 2 . 
     In Zone  1 , the pressure wave has a maximum amplitude P max,1  that gradually increases from zero to amplitude P 2 . Also in zone  1 , the pressure wave has a minimum or residual amplitude that stays constant at zero. Approaching t 1 , therefore, the pressure swings increase. After time t 1 , in zone  2 , the pressure wave has a maximum amplitude which stays constant at P 2 . The minimum or residual amplitude P min,2  in zone  2  gradually increases from zero to P 2 . Approaching t 2 , therefore, the pressure swings decrease. At time t 2  and beyond, in Zone  3 , the pressure increases at a constant rate P 3 ′. 
     The gradually increasing pressure swings in Zone  1  promote even acceleration of the star wheel  224 . That is, each burst of pressure is sufficient to impart a small rotational component to star wheel  224  without inducing excessive torsional stresses in the star wheel and connected components which might cause failure. That is, if a pressure P 2  was suddenly applied for extended duration to the star wheel  224 , the severe change in rotational energy from zero to 35,000 rpm, for example, might be detrimental to the star wheel and/or support bearings. More importantly, a sudden startup of the star wheel  224  may cause failure of the relatively delicate impeller  128 . By maintaining the minimum pressure at zero, these excessive startup torques are avoided. 
     During Zone  2 , the minimum pressure P min,2  begins to increase while the maximum pressure remains constant at P 2 . This ramp up gradually increases the average speed of the star wheel  224  to avoid excess torque on the bearings and impeller  128 . Ultimately, the inertia of the system reaches a particular magnitude at time t 2  so that the input pressure can be increased linearly at rate P 3 ′ during Zone  3 . 
     There are a number of possible waveforms which can be used to pulse the air pressure and produce the even acceleration just described. A preferred waveform is seen in FIG. 11, which is approximately trapezoidal accounting for the slight delay in the pressure delivery system. One example of a waveform is  10  pulses per second. The duration of the pulses can be varied depending on the current rotational speed of star wheel  224 . That is, the “duty cycle” of the square waves can be varied depending on the speed of the turbine. The “duty cycle” in this regard pertains to the proportion of time that the star wheel  224  is pressurized. At low levels, the duty cycle might be 80%, while at high levels of rotation the duty cycle might be 20%, reflecting the reduced torque needed to impart a change in speed. 
     Referring back to FIGS. 3 b  and  4   b , a bladder  240  is used to longitudinally translate the turbine drive assembly  170  between non-shielded and shielded positions. The bladder  240  is disposed between a  242  at the turbine housing back end and the rear handpiece cap  104 . The bladder  240  comprises a proximally opening cup-shaped structure having a closed distal end that contacts and acts upon the cap  242 . The bladder open end has a inwardly extending radial lip  250  that is sealed in a complementary groove  252  of the rear handpiece cap  104 . 
     Referring to FIGS. 3 b  and  7 , the irrigation port  178  and the aspiration port  190  are located at the top and the bottom of the device rear cap  104  (FIG.  3 ), respectively. In the center of the rear cap  104  is an actuator gas port  256 . Three vents  258  are located in three quadrants of the rear cap  104  and are of a curved, oblong shape. The vents  258  extend through the rear cap  104  and enable spent turbine gas and liquid from the aforementioned gap in the distal turbine bearing  222   a  to exit the handpiece  100 . In the remaining quadrant is a vent  260  of the same general shape as the vents  258  except for a circular region  261 . The circular region permits access of the turbine drive gas tube  24   d  (not shown) to the turbine star wheel  224 . 
     The actuator gas port  256  axially and centrally extends through the rear handpiece cap  104 , and is in fluidic communication with an interior  262  of the cup-shaped bladder  240  (see FIG. 4 b ) facing the rear handpiece cap  104 . The actuator gas port  256  is adapted to be connected to the actuator gas tube  24   b  (see FIG.  1 ). The tube  24   b  provides compressed gas to expand the bladder  240  and, thereby, longitudinally translating the turbine drive assembly  170  and the attached impeller shaft  122 . 
     With reference to FIG. 3 b , the bladder  240  is shown un-inflated and the device  30  is in the retracted, shielded position. The turbine drive assembly  170  is proximally located in the handpiece  100 . The impeller  128  is substantially shielded by the sheath  120 , as seen in FIG. 3 c . 
     Linear actuation of the turbine assembly  170  within the handpiece  100  will be described with reference to FIGS. 3 b  and  4   b . Initially, it will be noted that the handpiece rear cap  104  is fixed at the proximal end of the body  106 . The irrigation port  178  and aspiration port  190  are each located at the proximal end of an irrigation tube  270  and an aspiration tube  272 , respectively. The tubes  270 ,  272  extend proximally to the turbine housing cap  173 , and are fixed to translate with the turbine assembly  170 . In this regard, the tubes  270 ,  272  slide through apertures formed in the rear cap  104 . 
     An irrigation fitting  274  and an aspiration fitting  276  are provided on the proximal ends of the creation tube  270  and aspiration tube  272 , respectively, to provide couplings for flexible tubes attached to the handpiece  100 . Each of the fittings  274 ,  276  is sized to fit within counterbores  270 ,  280  provided in the rear cap  104 . The fittings  274 ,  276  are biased out of the counterbores  270 ,  280  by coil springs  282 ,  284  surrounding the tubes  270 ,  272 , respectively. Because of the rigid connection between the fittings  274 ,  276  and tubes  270 ,  272 , and between the tubes and the rest of the turbine assembly  170 , the turbine assembly is biased in a proximal direction by the springs  282 ,  284 . This biased position is indicated in FIG. 3 b  by a gap  286  between the fitting  276  and a step formed in the recess  280  of the cap  104 . Again, the position shown in FIG. 3 b  is the retracted, non-operable position of the device  30 . 
     FIG. 4 b  illustrates the device  30  in its advanced, operable position, wherein the  286 ′ and has been significantly reduced. The proximal bias of the springs  282 ,  284  has been overcome by introduction of gas through port  256  to the interior  262  of the cup-shaped bladder  240 . Consequently, the bladder  240  has expanded, pushing in a distal direction on the turbine housing cap  242  and displacing the turbine assembly  170  to its operable position. Various physical limit stops can be provided to halt displacement of the turbine assembly  170 , or the bladder  240  can be designed to be fully expanded prior to physical contact between such stops. Again, the advanced position of the device  30  urges the impeller  128  to its partially shielded position, as seen in FIG. 4 c . 
     Referring now to FIGS. 8 and 9, the impeller or lens-reducing head  128  in the preferred embodiment of the invention is comprised of three blades  300  integrally formed from the hollow impeller shaft  122 . The blades  300  extend from flat portions  301  of the impeller shaft  122 , making the impeller shaft distal end approximately triangular in shape with the remainder of the impeller shaft being tubular. Other embodiments of the invention may have impeller tubes or shafts of any shape. Still other embodiments of the invention may have an impeller of more or less blades or an impeller that is attached to the impeller tube or shaft distal end instead of integrally formed therefrom. 
     The impeller blades  300  are arranged about the impeller shaft distal end, and are identical in size and shape. In the presently preferred embodiment shown, each blade  300  comprises a first portion  302  and a second portion  304 . The blade first portion  302  extends approximately radially from the impeller shaft distal end and is pitched. The first blade portion  302  is connected to the impeller shaft  122  via two connector portions  306 . The blade second portion  304  extends axially and distally from an outward edge  308  of the blade first portion  302 . The blade second portion  304  has a leading edge  310  that is generally parallel to a longitudinal axis  312  of the impeller shaft  122 . The impeller  128  is configured to draw a flow of fluid toward the impeller during rotation. Other embodiments of the invention may have blades of other configurations and/or size or impellers that are not configured to draw a flow of fluid. For example, in some embodiments, the second blade portion  304  may be eliminated or modified in shape, on one or more of the blades  300 . Also, in some embodiments, the number of blades  300  my vary and/or the tangential spacing, symmetry and/or lack of symmetry of the blades  300  my be varied. Also, in some embodiments, the blades may not all be of the same shape and/or size, but rather may vary in shape and/or size. 
     The preferred embodiment of the strainer  320  is also shown in FIGS. 8 and 9. The strainer  320  is proximate to the impeller shaft distal end. The strainer  320  is comprised of three symmetrically positioned tabs  322  that extend inward from the three generally flat portions  301  of the impeller shaft  122  and create the aforementioned shaft holes  324 . The tabs  322  are integrally formed from the shaft  122  and are bent radially inwardly so as to be disposed in a radial plane. The tabs  322  are sized and shaped to restrict particles from being aspirated through the impeller shaft  122 . In the preferred embodiment, the tabs  322  and shaft holes  324  are polygonal, and the tabs have angled points that fit closely together in the shaft lumen  138 , as seen in FIG. 9, to help improve the straining effect. A strainer in other embodiments of the invention may have more or less tabs, be of a different configuration, or may not be integral with the impeller shaft  122 . 
     The tabs  322  of the strainer  320  are also sized and shaped to support a drop of liquid through the liquid&#39;s surface tension such that the liquid may solidify and form a plug (not shown) in embodiments where it is desired to plug the lumen of the impeller shaft  122  distal to the tabs  322 , thereby causing fluid to flow into/out of the shaft  122  only through the side holes created in the shaft by the infolding of the tabs  322 . Any suitable liquid that hardens to a plug and resists extraction or mechanical breakdown may be used for this purpose, such as epoxy, resin, or caulk. 
     The side holes created by the infolding of the tabs  322  will not likely become blocked or clogged because such side holes are located in a shear field as the impeller shaft  122  rotates. 
     Referring now to FIG. 10, an elongate EVE probe  28  is shown in a position to remove a lens (not shown) from an eye  24 . The elongate probe  28  is inserted at an angle through the cornea  32  of the eye  24  and into the lens capsule  34 . The impeller  128  is in a non-shielded position and projects beyond the surface defined by the angled mouth  130 . Again, however, the impeller  128  remains proximally disposed with respect to the apex  132  of the sheath  120 . This partial shielding of the impeller  128  permits the operator of the device  30  to direct the flow of liquid and particles in the lens capsule  22 . The flow created by the impeller  128  also helps keep the lens capsule  22  expanded during operation. Additionally, the lens is drawn to the impeller  128  because the impeller draws the flow towards it, resulting in reduced movement of the elongated probe  28  to reach and morcellate the lens. These advantages of the preferred embodiment of the invention reduce the chance that the lens capsule  22  will come into contact with the impeller  128  or the distal end of the sheath  120  and become damaged. 
     Typically, some gravity feed or positive pressure will be applied to irrigation fluid being infused through the EVE probe  28 . However, in the event that the feed or flow of irrigation fluid is momentarily interrupted, the dynamic force of the fluid circulating within the lens capsule  22  will maintain the lens capsule in a fully expanded or non-collapsed state, thereby minimizing the likelihood of iatrogenic laceration or puncture of the lens capsule wall by the rotating lens reducing impeller  128 . Additionally, in some embodiments, a flow meter, bubble detector or pressure sensor may be positioned so as to monitor the flow of irrigation fluid and/or the return of aspiration fluid/particles and may be connected to the controller and adapted to automatically stop the rotation of the impeller in the event of any disruption in the flow of irrigation fluid and/or the return of aspiration fluid/particles. 
     In the embodiment shown, the EVE Probe  28  may include an optional apparatus for protecting the fragile probe  28  and impeller  122  therein, and for facilitating the purging of air from the infusion system just prior to use. In this regard, FIG. 12 shows an optional purge cap  330  that closely receives the probe  28 . The purge cap  330  comprises a tubular body  332 , an integrally formed collapsible nipple  334 , and a rigid insert  336 . The aforementioned purge chamber  84  is defined partly within the collapsible nipple  334 , and partly within a relief chamber  338  of the rigid insert  336 . The rigid insert  336  is tightly received within a through bore  340  of the tubular body  332  and further includes a tapered bore  342  extending proximally from the relief chamber  338 . The tapered bore  342  narrows in diameter until it is approximately the same diameter as the probe  28  at a seal portion  344 . 
     The purge cap  330 , comprising the tubular body  332  and collapsible nipple  334 , is desirably formed of an elastomeric material, such as silicone. The rigid insert  336 , on the other hand, is desirably formed of a rigid material, such as polycarbonate or other high-density polymer. The assembly of the purge cap  330  and rigid insert  336  is formed by press fitting the insert into the bore  340  until the distalmost end  346  of the insert is approximately aligned with the distalmost end  348  of the tubular body  332 . The assembly is then secured around a probe  28  by an interference fit between the bore  340  and an annular, triangular rib  350  formed at the end of the frustoconical portion  108  of the handpiece  100 . The probe  28  is guided through the tapered bore  342  until the distal end resides in a relief chamber  338 . A fluid-tight fit between the rigid insert  336  and probe  28  is created at the narrow seal portion  344 . 
     In use, irrigation fluid is circulated through the handpiece  100  and probe  28  to exit into the purge chamber  84 . At the same time, the aspiration system is operated to remove the irrigation fluid from within the purge chamber  84 . At a predetermined time, the irrigation fluid flow is halted and a high vacuum is drawn within the purge chamber  84 . The nipple  334  collapses to indicate to the operator that the vacuum is in effect. The high vacuum tends to expand any bubbles remaining in the device  30 , which loosens them and encourages them to migrate through the aspiration channels. This procedure may be repeated more than once for precautionary reasons. Ultimately, the purge cap  330  with the rigid insert  336  is removed from the probe  28  just prior to use of the lens-removal device  30 . 
     It is to be appreciated that the invention has been described hereabove with reference to certain presently preferred embodiments or examples only, and no attempt has been made to exhaustively describe all possible embodiments and examples in which the invention may be practiced. It is to be appreciated that various additions, deletions and modifications may be made to the above-described embodiments or examples without departing from the intended spirit and scope of the invention, and it is intended that all such additions, deletions and modifications be included within the scope of the following claims.