Tapered structure in a phacoemulsification device for node placement
Disclosed is a surgical instrument directed to phacoemulsification for cataract eye surgery. The instrument generally includes a hollow titanium needle extending from a vibration generating handpiece. Together, the hollow needle and handpiece form an aspiration pathway to suck cataractous debris from an eye. A piezoelectric transducer in the handpiece generates both high and low ultrasonic frequency vibrations that rings the needle. The low frequency produces a node-free standing wave along the needle and the high frequency produces a standing wave along the needle with a node of minimum amplitude along the needle. Both frequencies produce a high anti-node at the needle's tip. The low frequency causes higher cavitation for emulsifying the cataract and the high frequency facilitates fragmentation of the cataract with a low heat portion of the needle at the eye incision point. The placement of the node along the needle can be tailored by way of a tapered section in a step horn region of the handpiece.
1. A surgical instrument for a phacoemulsification procedure, the surgical instrument comprising:
a handpiece that includes a piezoelectric transducer and a step horn;
a hollow titanium needle having a free distal tip and a supported end structure that is attached to the handpiece, the supported end structure includes external threads that mate with internal threads in the handpiece, the hollow titanium needle having a substantially cylindrical portion extending from the free distal tip towards the step horn;
a tapered section in the step horn, the step horn is between the piezoelectric transducer and the hollow titanium needle; and
the piezoelectric transducer configured to periodically vibrate the hollow titanium needle at either a low mode or a high mode, the substantially cylindrical portion devoid of a node of minimum amplitude at the low mode and the substantially cylindrical portion possessing a single node of minimum amplitude at the high mode.
2. The surgical instrument of claim 1 wherein the low mode is below 60 kHz and the high mode is equal or above 60 kHz.
3. The surgical instrument of claim 1 wherein the tapered section is selected from a group consisting of a geometry that is conical, elliptical, Gaussian, exponential, or Fourier.
4. The surgical instrument of claim 1 wherein the piezoelectric transducer is configured to switch between the high mode and the low mode by a surgeon command.
5. The surgical instrument of claim 1 wherein the tapered section extends approximately to the supported end structure.
6. The surgical instrument of claim 1 wherein the piezoelectric transducer is configured to switch automatically between the high mode and the low mode by a command received from the phaco machine controller.
7. The surgical instrument of claim 1 wherein there is a single taper node of minimum amplitude at the high mode along the tapered substantially cylindrical section of the needle and at the low mode along the tapered section.
8. The surgical instrument of claim 1 wherein the free distal tip is configured to periodically vibrate at a high amplitude in both the low mode and the high mode.
9. The surgical instrument of claim 1 wherein the tapered section is integral with the headpiece.
10. The surgical instrument of claim 1 wherein the piezoelectric transducer is adapted to switch between the high mode and the low mode after a predetermined time interval.
11. A method to drive oscillations in a surgical instrument during phacoemulsification, the method comprising:
providing a handpiece that includes a piezoelectric transducer and a step horn, the step horn possessing a tapered section that tapers towards a distal handpiece end, a hollow titanium needle having a free distal tip and a supported end structure that is attached to the distal handpiece end, the hollow titanium needle possessing a length being defined along a longitudinal axis of the hollow titanium needle;
energizing the piezoelectric transducer to periodically longitudinally expand and contract in a high ultrasonic driving frequency that rings the hollow titanium needle with a high ultrasonic standing wave or a low ultrasonic frequency that rings the hollow titanium needle with a low ultrasonic standing wave;
inserting the hollow titanium needle in an eye;
after the inserting step, energizing the piezoelectric transducer to drive the hollow titanium needle at either the high ultrasonic standing wave or the low ultrasonic standing wave, only the high ultrasonic standing possessing a node of minimum amplitude along the length of the hollow titanium needle.
12. The method of claim 11 wherein the high and the low standing waves have a proximal node of minimum amplitude along the tapered section.
13. The method of claim 11 wherein the high and the low standing waves have a distal anti-node of maximum amplitude at the free distal tip.
14. The method of claim 11 further comprising switching from the high ultrasonic frequency to the low ultrasonic frequency after a predetermined amount of time.
15. The method of claim 11 further comprising switching from the low ultrasonic standing wave to the high ultrasonic standing wave when the hollow titanium needle becomes at least partially occluded and switching from the high ultrasonic standing wave to the low ultrasonic standing wave when the hollow titanium needle is no longer partially occluded.
16. The method of claim 11 wherein the low ultrasonic frequency is below 60 kHz and the high ultrasonic frequency above 60 kHz.
17. The method of claim 11 wherein the tapered section is defined by a profile that is selected from a group consisting of a geometry that is conical, elliptical, Gaussian, exponential, or Fourier.
18. A surgical instrument comprising:
a phacoemulsification device possessing a handpiece, a hollow titanium needle attached to the handpiece, the hollow titanium needle having a substantially cylindrical portion that extends from approximately the handpiece to a free distal tip; and
a transducer configured to drive the hollow titanium needle with at least two simultaneous driving frequencies that define a standing wave with a single semi-node of low amplitude along the hollow titanium needle and an anti-node of high amplitude at the free distal tip.
19. The surgical instrument of claim 18 wherein the transducer is configured to increase power to the high frequency mode while inversely decreasing the power to the low frequency mode, or decrease the power to the high frequency mode while inversely increasing the power to the low frequency mode.
20. The surgical instrument of claim 18 wherein at least two simultaneous driving frequencies comprise a high ultrasonic frequency of more than 60 kHz and a low ultrasonic frequency of less than 60 kHz.