Patent Application
20080172076
This invention relates to ultrasonic devices and more particularly to torsional ultrasound ophthalmic phacoemulsification handpieces.
A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece, an attached hollow cutting tip, an 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.
Although some prior art handpiece are of the magnetostrictive type, the operative part of most commercially available handpieces is a centrally located, and 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/hom assembly is suspended within the hollow body or shell of the handpiece at its nodal points by relatively inflexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body'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.
When used to perform phacoemulsification, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the comea, sclera, or other location in the eye tissue in order to gain access to the anterior chamber of the eye. The cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic hom, thereby emulsifying upon contact 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 bore of the cutting tip, the horn bore, 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 outside surface of the cutting tip.
There have been prior attempts to combine ultrasonic longitudinal motion of the cutting tip with rotational motion of the tip, see U.S. Pat. No. 5,222,959 (Anis), U.S. Pat. No. 5,722,945 (Anis, et al.) and U.S. Pat. No. 4,504,264 (Kelman), the entire contents of which are incorporated herein by reference. These prior attempts have used electric motors to provide the rotation of the tip which require O-ring or other seals that can fail in addition to the added complexity and possible failure of the motors.
There have also been prior attempts to generate both longitudinal and torsional motion without the use of electric motors. For example, in U.S. Pat. Nos. 6,028,387, 6,077,285 and 6,402,769 (Boukhny), one of the inventors of the current invention, describes a handpiece having two pairs of piezoelectric crystals are used. One pair is polarized to product longitudinal motion. The other pair is polarized to produce torsional motion. Two separate drive signals are used to drive the two pairs of crystals. In actual practice, making a handpiece using two pairs of crystals resonate in both longitudinal and torsional directions is difficult to achieve. One possible solution, also described by one of the current inventors, is described in U.S. Patent Publication No. US 2001/0011176 A1 (Boukhny) and U.S. Patent Publication No. US 2006/0041200 A1 (Boukhny, et al.). These references disclose a handpiece have a single set of piezoelectric crystals that produces longitudinal motion, and a series of diagonal slits on the handpiece horn or tip that produce torsional motion when the horn or tip is driven at the resonate frequency of the piezoelectric crystals.
Accordingly, a need continues to exist for a reliable ultrasonic handpiece that will vibrate both longitudinally and torsionally, either simultaneously or separately, without the use of piezoelectric crystals.
The present invention improves upon prior art ultrasonic handpieces by providing a magnetostrictive ultrasonic handpiece capable of providing both longitudinal and torsional or twisting motion.
Accordingly, one objective of the present invention to provide an ultrasound handpiece having both longitudinal and torsional motion.
Another objective of the present invention to provide a magnetostrictive ultrasound handpiece having both longitudinal and torsional motion.
Other objects, features and advantages of the present invention will become apparent with reference to the drawings, and the following description of the drawings and claims.
Magnetostriction (or the Joule effect) is a property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field. The effect was first identified in 1842 by James Joule when observing a sample of nickel. Internally, ferromagnetic materials have a crystal structure that is divided into domains, each of which is a region of uniform magnetic polarisation. When a magnetic field is applied, the boundaries between the domains shift and the domains rotate, both these effects causing a change in the material's dimensions.
An important characteristic of a wire made of a magnetostrictive material is the Wiedemann effect. When an axial magnetic field is applied to a magnetostrictive element, and a current is passed through the element, a twisting occurs at the location of the axial magnetic field. The twisting is caused by interaction of the axial magnetic field with the magnetic field along the magnetostrictive element, which is present due to the current in the element. The current is applied as a short-duration pulse, −1 or 2 μs; the minimum current density is along the center of the element and the maximum at the element surface. The magnetic field intensity is also greatest at the element surface. This aids in developing the waveguide twist, as the current is applied as a pulse, the mechanical twisting travels in the element as an ultrasonic wave. The magnetostrictive element is therefore called the waveguide. The wave travels at the speed of sound in the waveguide material, ˜3000 m/s.
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One skilled in the art will recognize that vibrating horn 120 in a continuous fashion or alternating between longitudinal and torsional motions may be desirable depending upon the desired surgical technique. This is accomplished by continuously passing a drive signal though coil 150 while continuously and/or episodically passing a drive signal through stack 110.
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One skilled in the art will recognize that core 200 may also be operated in a manner described above with respect to Core 100.
While certain embodiments of the present invention have been described above, these descriptions are given for purposes of illustration and explanation. Variations, changes, modifications and departures from the systems and methods disclosed above may be adopted without departure from the scope or spirit of the present invention.
