US 20070078379 A1
Methods of manipulating pulses of ultrasonic energy for use with an ophthalmic surgical device.
1. A method of generating ultrasonic energy for use with an ophthalmic surgical device, the method comprising:
generating pulses having an on-time, a first off-time, and a first amplitude, the first off-time being greater than the on-time;
reducing the first off-time of the pulses; and
increasing the amplitude of the pulses from the first amplitude to a second amplitude when the first off-time is reduced to a pre-determined second off-time.
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13. A method of generating ultrasonic energy for use with an ophthalmic surgical device, the method comprising:
generating burst mode pulses; and
transforming the burst mode pulses into pulse mode pulses in response to a controller.
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reducing the first off-time of the pulses to a second off-time in response to the controller, and when the second off-time reaches a pre-determined value,
increasing the amplitude of the pulses from the first amplitude to a second amplitude in response to the controller.
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20. A method of generating ultrasonic energy for use with an ophthalmic surgical device, the method comprising
generating pulse mode pulses; and
transforming the pulse mode pulses into burst mode pulses in response to a controller.
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increasing the first off-time to a second off-time in response to the controller.
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The present invention relates generally to the field of ophthalmic surgery and, more particularly, to a method of manipulating the shapes, sequences and durations of pulses of ultrasonic energy generated by an ultrasound handpiece of a phacoemulsification surgical system.
The human eye functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light that can be transmitted to the retina. This deficiency is medically known as a cataract. An accepted treatment for cataracts is to surgically remove the cataract and replace the lens with an artificial intraocular lens (IOL). In the United States, the majority of cataractous lenses are removed using a surgical technique called phacoemulsification. During this procedure, a thin cutting tip or needle is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens, which is aspirated out of the eye. The diseased lens, once removed, is replaced by an IOL.
A typical ultrasonic surgical device suitable for an ophthalmic procedure includes an ultrasonically driven handpiece, an attached cutting tip, an irrigating sleeve or other suitable irrigation device, and an electronic control console. The handpiece assembly is attached to the control console by an electric cable or connector and flexible tubings. A surgeon controls the amount of ultrasonic energy that is delivered to the cutting tip of the handpiece and applied to tissue by pressing a foot pedal to request power up to the maximum amount of power set on the console. Tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.
The operative part of the handpiece is a centrally located, hollow resonating bar or horn that is attached to piezoelectric crystals. The crystals are controlled by the console and supply ultrasonic vibrations that drive both the horn and the attached cutting tip during phacoemulsification. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible 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.
In use, the ends of the cutting tip and the irrigating sleeve are inserted into a small incision in the cornea, sclera, or other location. One known cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying 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. Other suitable cutting tips include piezoelectric elements that produce both longitudinal and torsional oscillations. One example of such a cutting tip is described in U.S. Pat. No. 6,402,769 (Boukhny), the contents of which are incorporated herein by reference.
A reduced pressure or vacuum source in the console draws or aspirates emulsified tissue from the eye through the open end of the cutting tip, the cutting tip and horn bores and the aspiration line, and into a collection device. The aspiration of emulsified tissue is aided by a saline solution or other irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip.
One known technique is to make the incision into the anterior chamber of the eye as small as possible in order to reduce the risk of induced astigmatism. These small incisions result in very tight wounds that squeeze the irrigating sleeve tightly against the vibrating tip. Friction between the irrigating sleeve and the vibrating tip generates heat. The risk of the tip overheating and burning tissue is reduced by the cooling effect of the aspirated fluid flowing inside the tip.
Some known surgical systems use “pulse mode” in which the amplitude of fixed-width pulses can be varied using a controller, such as a foot pedal. Other known surgical systems utilize “burst mode” in which each pulse of a series of periodic, fixed width, constant amplitude pulses is followed by an “off” time. The off time can be varied using a controller. Other known systems use pulses having an initial maximum power level followed by a lower power level. For example, Publication No. PCT/US2004/007318 describes pulses that rise from zero to an initial, maximum power level, and then subsequently decrease to lower levels.
While known surgical systems have been used effectively, they can be improved by allowing greater control over pulses for use with various surgical devices and applications. For example, known systems that use square or rectangular pulses typically have power levels that increase very quickly to a maximum power level. Sharp pulse transitions can reduce the ability to hold and emulsify lens material. More specifically, when lens material is held at a tip of an ultrasound hand piece by vacuum, the very fast (almost immediate) ramping of a pulse to a maximum power level can displace or push the lens material away from the tip too quickly. This, in turn, complicates cutting of the lens material. In other words, rapid power transitions can create an imbalance between vacuum at the ultrasonic tip that holds or positions the lens material and the ability to emulsify lens material.
Other known systems operate at high power levels when less power or no power would suffice. For example, with rectangular pulses, an initial high power level may be needed to provide power to emulsify lens material. However, after the material is pushed away or emulsified, additional power may not be needed. Rectangular pulses that apply the same amount of power after movement or emulsification of lens material can result in excessive heat being applied to tissue, which can harm the patient.
Further, pulse patterns that are used by some known surgical systems do not adequately reduce cavitation effects. Cavitation is the formation of small bubbles resulting from the back and forth movement of an ultrasonic tip. This movement causes pockets of low and high pressure. As the ultrasonic tip moves backwards, it vaporizes liquid due to a low local pressure and generates bubbles. The bubbles are compressed as the tip moves forwards and implode. Imploding bubbles can create unwanted heat and forces and complicate surgical procedures and present dangers to the patient.
Therefore, a need continues to exist for methods that allow pulse shapes and durations to be manipulated for different phacoemulsification applications and procedures.
In accordance with one embodiment of the invention, a method of generating ultrasonic energy for use with an ophthalmic surgical device includes generating pulses having an on-time, a first off-time, and a first amplitude. The first off-time is greater than the on-time. The method includes reducing the first off-time of the pulses and increasing the amplitude of the pulses from the first amplitude to a second amplitude when the first off-time is reduced to a pre-determined second off-time.
The first off-time can be reduced in response to a controller, such as a foot pedal. The first off-time can be reduced until the foot pedal reaches a pre-determined position corresponding to a certain off-time of the pulses, after which the off-time remains constant. The amplitude of the pulses is increased after the pre-determined second off-time is about the same as the on-time in response to the foot pedal. The off-time and the amplitude can be adjusted with continuous movement of a single controller.
In accordance with another embodiment of the invention, a method of generating ultrasonic energy for use with an ophthalmic surgical device includes generating burst mode pulses and transforming burst mode pulses into pulse mode pulses in response to a controller.
In accordance with a further embodiment of the invention, a method of generating ultrasonic energy for use with an ophthalmic surgical device includes generating pulse mode pulses and transforming pulse mode pulses into burst mode pulses in response to a controller.
Transforming between burst and pulse modes can be performed in response to movement of the foot pedal and begins after the foot pedal reaches a pre-determined position. Burst mode pulses are generated by generating pulses having an on-time, a first off-time and a first amplitude. Burst mode pulses are transformed into pulse mode pulses by reducing the first off-time of the pulses to a second off-time in response to the controller. When the second off-time reaches a pre-determined value, the amplitude of the pulses is increased from the first amplitude to a second amplitude in response to the controller. The pre-determined value can be the same as the on-time or another desired value. The on-time remains constant during the transforming step.
Referring now to the drawings, in which like reference numbers represent corresponding parts throughout and in which:
This specification describes embodiments of methods of manipulating pulses of ultrasonic energy to control a surgical system for use in, for example, phacoemulsification surgery. Embodiments can be implemented on commercially available surgical systems or consoles through appropriate hardware and software controls.
The control system 100 is used to operate an ultrasound handpiece 112 and includes a control console 114, which has a control module or CPU 116, an aspiration, vacuum or peristaltic pump 118, a handpiece power supply 120, an irrigation flow or pressure sensor 122 and a valve 124. Various ultrasound handpieces 112 and cutting tips can be utilized including, but not limited to, handpieces and tips described in U.S. Pat. Nos. 3,589,363; 4,223,676; 4,246,902; 4,493,694; 4,515,583; 4,589,415; 4,609,368; 4,869,715; 4,922,902; 4,989,583; 5,154,694 and 5,359,996, the contents of which are incorporated herein by reference. The CPU 116 may be any suitable microprocessor, micro-controller, computer or digital logic controller. The pump 118 may be a peristaltic, a diaphragm, a Venturi or other suitable pump. The power supply 120 may be any suitable ultrasonic driver. The irrigation pressure sensor 122 may be various commercially available sensors. The valve 124 may be any suitable valve such as a solenoid-activated pinch valve. An infusion of an irrigation fluid, such as saline, may be provided by a saline source 126, which may be any commercially available irrigation solution provided in bottles or bags.
In use, the irrigation pressure sensor 122 is connected to the handpiece 112 and the infusion fluid source 126 through irrigation lines 130, 132 and 134. The irrigation pressure sensor 122 measures the flow or pressure of irrigation fluid from the source 126 to the handpiece 112 and supplies this information to the CPU 116 through the cable 136. The irrigation fluid flow data may be used by the CPU 116 to control the operating parameters of the console 114 using software commands. For example, the CPU 116 may, through a cable 140, vary the output is of the power supply 120 being sent to the handpiece 112 and the tip 113 though a power cable 142. The CPU 116 may also use data supplied by the irrigation pressure sensor 122 to vary the operation of the pump 118 and/or valves through a cable 144. The pump 118 aspirates fluid from the handpiece 112 through a line 146 and into a collection container 128 through line 148. The CPU 116 may also use data supplied by the irrigation pressure sensor 122 and the applied output of power supply 120 to provide audible tones to the user. Additional details concerning such surgical systems can be found in U.S. Pat. No. 6,179,808 (Boukbny, et al.) and U.S. Pat. No. 6,261,283 (Morgan, et al.), the entire contents of which are incorporated herein by reference.
The control console 114 can be programmed to control and manipulate pulses that are delivered to the handpiece 112 and, in turn, control the power of the pulses of the handpiece that is used during surgery. Referring to
The following description assumes that a maximum power level of 100% is the maximum attainable power (i.e., maximum stroke or displacement of the ultrasonic tip). In other words, 50% power refers to half of the maximum attainable power. Power levels are represented as a percentage (%) of the maximum attainable power. Embodiments of pulse manipulation that can be used with the exemplary phacoemulsification surgical system described above are illustrated in
Controlling the rise and decay components 310 and 312 and rise and decay times 312 and 322 provides advantageously allows different pulse configurations to be generated for particular surgical applications and systems. For example, pulses having programmed rise components 310 that gradually increase in power allow the lens material to be positioned more accurately. Gradual power transitions, for example, do not prematurely push the lens material away from the tip of the handpiece. In contrast, known systems using pulses having sharp minimum to maximum transitions may inadvertently push lens material away from the tip too quickly, thus complicating the surgical procedure. Accordingly, pulses that include programmed rise components can improve the positioning and cutting of lens material and the effectiveness of surgical procedures. Further, programming decay components and pulse times allows less energy to be delivered to the eye, resulting in less heating of the tissue.
According to one embodiment, the programmed rise and/or decay component is programmed according to a linear function. In the embodiment illustrated in
The linear rise component 310 has a linear rise time 312, the linear decay component 320 has a linear decay time 322, and the maximum amplitude component 330 has a maximum amplitude or active or “on” time 332. Linear rise and linear decay times 312 and 322 can vary depending on the maximum power level of a pulse since more time is typically required to reach higher power levels.
In one embodiment, the linear rise time 312 can be programmed to be about 5 ms to about 500 ms. If a pulse must reach 100% power, the duration of the linear rise time 312 may be longer. However, if the pulse must reach less than 100% power, then the linear rise time 312 can be shorter, e.g. less than or about 5 ms. Linear rise time 312 durations may increase with increasing power levels and can be appropriately programmed using the control console 114. If necessary, the rate at which the linear component increases can be limited to protect power components, such as an amplifier.
According to one embodiment, the linear decay time 322 can be programmed to be about 5 ms to about 500 ms. In one embodiment, the liner decay time 322 is programmed using the control console 114 so that power decays linearly and about 70% of the power dissipates in about 2 ms, and about 98% of the power dissipates in about 4 ms. The linear decay time 322 may be longer than, about the same as, or shorter than the linear rise time 312. For example,
The maximum amplitude or active or “on” time 332 can vary with different applications. The maximum amplitude time can be about 5 ms to about 500 ms. In the illustrated embodiment, the intermediate component 330 has a constant amplitude (at the second amplitude). In an alternative embodiment, the duration of the maximum amplitude time can be less than 5 ms depending on, for example, required power and resulting heat considerations. In further alternative embodiments, the amplitude may vary across the intermediate component 330, e.g., increase or decrease between the first and second components 310 and 320.
In the illustrated embodiment, the rise component 310 begins at a non-zero level. In an alternative embodiment, the rise component 310 can begin at a zero level. The initial power level may depend on the particular surgical procedure and system configuration. Similarly, the decay component 320 can end at a zero or non-zero power level.
In an alternative embodiment, the programmed rise and/or decay component can be a non-linear component. A non-linear component can be programmed according to logarithmic, exponential and other non-linear functions. For purposes of explanation, not limitation,
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In the illustrated embodiment, a first step 2010 has less power than a subsequent step 2020. For example, as shown in
The different pulses and pulse patterns described above are pulses of ultrasonic energy that can be delivered in packets to transducer elements of the handpiece. For example, as shown in
Although references have been made in the foregoing description to various embodiments, persons of skilled in the art will recognize that insubstantial modifications, alterations, and substitutions can be made to the described embodiments without departing from the scope of embodiments.