Patent Application
20110118729
The present invention relates generally to the field of eye surgery and more particularly to methods and apparatus for performing eye surgery using high-intensity pulsed electric fields.
Techniques and apparatus for dissociation and removal of highly hydrated macroscopic volumes of proteinaceous tissue from the human eye have been previously disclosed. In particular, techniques for dissociation and removal of highly hydrated macroscopic volumes of proteinaceous tissue using rapid variable direction energy field flow fractionation have been disclosed by Steven W. Kovalcheck in “System For Dissociation and Removal of Proteinaceous Tissue”, U.S. patent application Ser. No. 11/608,877, filed 11 Dec. 2006 and published 5 Jul. 2007 as U.S. Patent Application Publ. No. 2007/0156129 (hereinafter “the Kovalcheck application”), the entire contents of which are incorporated herein by reference.
The techniques disclosed in the Kovalcheck application were described in detail in terms of vitreoretinal surgery. However, those of ordinary skill in the art will readily understand that those techniques are applicable to medical procedures in other areas in the body of humans or animals. As explained in the Kovalcheck application, prior art procedures for vitreoretinal posterior surgery have relied for decades on mechanical or traction methods such as: 1) tissue removal with shear cutting probes (utilizing either a reciprocating or rotary cutter); 2) membrane transection using scissors, a blade, or vitreous cutters; 3) membrane peeling with forceps and picks; and 4) membrane separation with forceps and viscous fluids. While improvements in mechanisms, materials, quality, manufacturability, system support, and efficacy have progressed, many of the significant advancements in posterior intraocular surgical outcomes have been primarily attributable to the knowledge, fortitude, skill, and dexterity of the operating ophthalmic physicians.
However, the Kovalcheck application disclosed novel apparatus and methods for delivering a variable direction, pulsed high-intensity and ultra-short duration disruptive electric field (low energy) at a pulse duration, repetition rate, pulse pattern, and pulse train length tuned to the properties of the components of the intraocular extracellular matrix (ECM) to create tissue dissociation. In particular, the Kovalcheck application described a probe for delivering the pulsed rapid disruptive energy field to soft proteinaceous tissue surrounded by the probe. Once the adhesive mechanism between tissue constituents are compromised, fluidic techniques may be used to remove the dissociated tissue.
As described more fully below, embodiments of the present invention include a high-intensity pulsed electric field (HIPEF) vitrectomy apparatus that includes a HIPEF probe comprising at least one electrode disposed at a distal end of the HIPEF probe, such that the distal end is configured for insertion into an eye. A load detection circuit is coupled to the HIPEF probe and is configured to compare a measured physical parameter to a corresponding threshold value. A control circuit is electrically coupled to the load detection circuit and configured to selectively disable application of pulsed energy to the at least one electrode of the HIPEF probe, based on the comparison.
In some embodiments, the measured physical parameter is resistivity between first and second electrodes of the HIPEF probe, the load detection circuit is configured to compare measured resistivity to a resistivity threshold value less than an expected resistivity for air but greater than an expected resistivity for vitreous, and the control circuit is configured to disable application of pulsed energy to the first and second electrodes if the measured resistivity is greater than the resistivity threshold value. In some embodiments, the apparatus includes an optical waveguide extending to the distal end of the HIPEF and coupled to an optical sensor in the load detection circuit, and the measured physical parameter is reflected light energy. In these embodiments, the load detection circuit is configured to compare measured reflected light energy to a reflected light threshold value less than an expected reflected light energy for air but greater than an expected reflected light energy for vitreous, and the control circuit is configured to disable application of pulsed energy to the first and second electrodes if the measured reflected light energy is greater than the reflected light threshold value.
In some embodiments, the apparatus includes a pressure sensor coupled to the load detection circuit and configured to measure pressure at or near the distal end of the HIPEF probe, and the measured physical parameter is intraocular pressure. In these embodiments, the load detection circuit is configured to compare measured intraocular pressure to a pressure threshold value greater than an expected pressure value for air but less than an expected pressure value inside the eye, and the control circuit is configured to disable application of pulsed energy to the first and second electrodes if the measured pressure is less than the pressure threshold value. In still other embodiments, the HIPEF vitrectomy apparatus includes a heating element and a temperature sensor disposed at or near the distal end of the HIPEF probe, and the measured physical parameter is temperature. In these embodiments, the load detection circuit is configured to compare a measured temperature to a temperature threshold value less than an expected temperature value for air but greater than an expected temperature value for vitreous, and the control circuit is configured to disable application of pulsed energy to the first and second electrodes if the measured temperature is greater than the temperature threshold value.
In some embodiments, the measured physical parameter is permittivity between first and second electrodes of the HIPEF probe, the load detection circuit is configured to compare measured permittivity to a permittivity threshold value greater than an expected permittivity for air but less than an expected permittivity for vitreous, and the control circuit is configured to disable application of pulsed energy to the first and second electrodes if the measured permittivity is less than the permittivity threshold value.
In some embodiments, the load detection circuit is configured to compare the measured physical parameter to the corresponding threshold value before each application of a burst of pulses to the at least one electrode of the HIPEF probe, and the control circuit is configured to selectively disable the application of each burst of pulses, based on the corresponding comparison. In others, the load detection circuit is instead configured to compare the measured physical parameter to the corresponding threshold value before each application of a single pulse to the at least one electrode of the HIPEF probe, and the control circuit is configured to selectively disable the application of each pulse, based on the corresponding comparison.
Methods for controlling application of high-intensity pulsed electric field (HIPEF) energy during eye surgery are also disclosed. An exemplary method comprises: measuring a physical parameter at or near the distal end of a HIPEF probe, said HIPEF probe comprising at least one electrode disposed at said distal end and configured for delivering pulsed energy to an eye; comparing the measured physical parameter to a corresponding threshold value; and selectively enabling application of pulsed energy to the at least one electrode, based on the comparison. Other methods corresponding to the various load detection circuits summarized above are also disclosed.
Of course, those skilled in the art will appreciate that the present invention is not limited to the above features, advantages, contexts or examples, and will recognize additional features and advantages upon reading the following detailed description and upon viewing the accompanying drawings.
The present disclosure describes an apparatus and method for the dissociation and removal of highly hydrated macroscopic volumes of proteinaceous tissues, such as vitreous and intraocular tissue, during vitreoretinal surgery. More particularly, the techniques disclosed below are directed to methods and apparatus for detecting whether a high-intensity pulsed electric field (HIPEF) probe used for such surgery is actually positioned in an eye, before enabling the application of pulsed energy to the surgical site. Although the techniques disclosed herein are described in detail in terms of instruments and methods for traction-free removal of vitreous and intraocular membranes from the posterior region of the eye without damaging the ultra-fine structure and function of the adjacent or adherent retina, those of ordinary skill in the art will understand the applicability of the disclosed invention for other medical procedures on both humans and animals.
As mentioned above, the Kovalcheck application (U.S. patent application Ser. No. 11/608,877) described a new approach to performing vitreoretinal surgery, using an ultra-short high-intensity directionally changing electrical field rather than classical mechanical means historically used to engage, decompose, and remove vitreous and intraocular tissues. The Kovalcheck application was based on the discovery that a transient change in tissue condition caused by the application of an ultra-short high-intensity directionally changing electrical field is satisfactory for removal of macroscopic volumes of proteinaceous tissue. The technical success of mechanical and liquefying means supports the contention that vitreous material need not be obliterated or disrupted on a molecular level to be removed—rather, an innocuous macroscopic change of state is all that is needed for tissue removal. Accordingly, the removal of intraocular tissue enabled by the techniques described in the Kovalcheck application is traction-free.
The apparatus and method disclosed in the Kovalcheck application cause a local decoupling of the adhesive and structural relations in components of intraocular proteinaceous tissue, through the application of a rapidly changing electrical field. This localized decoupling of the adhesive and structural relations between components of intraocular proteinaceous tissue enables tractionless detachment between intraocular tissue components and the retinal membrane. Fluidic techniques (irrigation and aspiration) may be utilized during the tissue dissociation process to enhance the formation of a high-intensity ultra-short-pulsed electrical field and to remove disrupted tissue at the moment of dissociation. In general, it is intended that only the material within the applied high-intensity ultra-short-pulsed electrical field (also denoted high-intensity pulsed electric field, or HIPEF, herein) is assaulted and removed. Therefore, because only the material assaulted by the applied ultra-short pulses receives the high-intensity ultra-short-pulsed electrical field, there is no far-field effect during the tissue extraction process. This high-intensity ultra-short-pulsed electrical field assault leads to dissociation of the entrained macroscopic volume of intraocular proteinaceous tissue, and then aspiration removes the dissociated entrained macroscopic volume of tissue.
Generally speaking, then, a probe with two or more electrodes is inserted into the target hydrated tissue, vitreous or intraocular tissue. The ends of the electrodes are exposed at the distal end of the probe. An electrical pulse is transmitted down at least one of the electrodes while the other one or more electrodes act as the return conductors. A non-plasma electrical field is created between the electrodes. With each electric pulse, the direction of the created electrical field is changed by reversing polarity of the electric pulse, by electrode switching, or by a combination of both. Pulses may be grouped into bursts, which may be repeated at different frequencies and/or different amplitudes. Such pulse groups may be directed at heterogeneous tissue. The electrical pulse amplitude, duration, duty cycle and repetition rate along with continual changing of field direction, create the disruptive electrical field across the orifice of the aspiration lumen. Tissue is drawn into the orifice of the aspiration lumen by fluidic techniques (aspiration). The tissue is then mixed or diluted with irrigation fluid and disassociated as it traverses the high-intensity ultra-short-pulsed directionally changing electric field. During a given interval, disorder is created in the entrained proteinaceous tissue by changing the direction of the electrical field between one or more of the electrodes at the tip of the probe.
The affected medium between the electrode terminations at the end of the probe consists of a mix of target tissue (e.g. vitreous) and supplemental fluid (irrigation fluid). The electrical impedance of this target medium in which the electrical field is created is maintained by the controlled delivery of supplemental fluid (irrigation fluid). In some embodiments, the supplemental fluid providing the electrical impedance is a conductive saline. The supplemental fluid may be provided by an irrigation source external to the probe, through one or more lumens within the probe or a combination of both. When the supplemental fluid is provided within and constrained to the probe interior, the supplemental fluid may have properties (e.g. pH) and ingredients (e.g. surfactants) that may be conducive to protein dissociation.
The properties of the generated electrical energy field within the target medium are important. In the techniques disclosed in the Kovalcheck application and expanded upon herein, high-intensity, ultra-short pulses (sub-microseconds) of electrical energy are used. Tissue impedance, conductivity and dilution are maintained in the target medium by supplemental fluid irrigation, in some embodiments. The pulse shape, the pulse repetition rate, and the pulse train length may be tuned to the properties of the intraocular tissues, in some embodiments. In some embodiments, multiple pulse patterns may be employed to address the heterogeneity of intraocular tissue.
One application of the system described herein is for the treatment of pathologic retinal conditions. An exemplary apparatus for this treatment is shown in
The shaft tip 112 of probe 110 may be inserted by a surgeon into the posterior region of an eye 100 via a pars plana approach 101, as shown in
The apparatus pictured in
Switching circuit 170 is configured to control pulse duration and repetition rate, and in some embodiments is configured to generate a stepwise continual change in the direction of the electrical field by switching between electrodes, reversing polarity between electrodes or a combination of both in an array of electrodes at the shaft tip 112 of the hollow probe shaft 114. This continual change in the direction of the electrical field creates disorder in the entrained tissue volume without causing dielectric breakdown of the carrier fluid between the electrodes or thermal effects.
In various applications, the apparatus and techniques described herein may be applied to remove all of the posterior vitreous tissue, or specific detachments of vitreous tissue from the retina or other intraocular tissues or. Engagement, disruption and removal of vitreous tissue, vitreoretinal membranes, and fibrovascular membranes from the posterior cavity of the eye and surfaces of the retina are critical processes pursued by vitreoretinal specialists, in order to surgically treat sight-threatening conditions such as diabetic retinopathy, retinal detachment, proliferative vitreoretinopathy, traction of modalities, penetrating trauma, epi-macular membranes, and other retinopathologies. Though generally intended for posterior intraocular surgery involving the vitreous and retina, it can be appreciated that the techniques described herein are applicable to anterior ophthalmic treatments as well, including traction reduction (partial vitrectomy); micelle adhesion reduction; trabecular meshwork disruption, manipulation, reorganization, and/or stimulation; trabeculoplasty to treat chronic glaucoma; Schlemm's Canal manipulation, removal of residual lens epithelium, and removal of tissue trailers. Applicability of the disclosed apparatus and methods to other medical treatments will become obvious to one skilled in the art, after a thorough review of the present disclosure and the attached figures.
The apparatus of
Generally speaking, the function of load detection circuit 190 is to determine whether or not the one or more electrodes 116 of the probe needle tip 112 are placed in an eye 110, by evaluating a measurement of a physical parameter prevailing at or near the tip. More specifically, load detection circuit 190 is configured in several embodiments of the invention to compare a measured physical parameter such as resistivity, refractivity, pressure, heat dissipation, dielectric constant, or the like, to a corresponding threshold value. Given a pre-determined threshold value suitably situated between the expected measurement value for air and the expected measurement value for vitreous (or other intraocular material), this comparison allows the load detection to determine whether the probe tip is placed in an eye, and to generate a control signal for use by the control circuitry in control unit 180 in selectively disabling the application of pulsed energy to the electrodes.
Load detection can be based on the measurement of one or more of several physical parameters for which the properties of air and vitreous (or balanced salt solution) are sufficiently different to be exploited. These physical parameters include the permittivity (e.g., as expressed by a relative dielectric constant), resistivity, refractive index, and specific heat capacity (e.g., as manifested by a material's ability to dissipate applied heat). Another parameter that may be used is ambient pressure, as the intraocular pressure is normally 15 to 18 mmHg but during Vitreoretinal Surgery could be raised by the physician to 30 to 40 mmHg. Of course, some embodiments may measure two or more of these physical parameters, to enhance the reliability of the load detection.
In the circuit of
Of course, the circuit in
Another example of a load detection circuit according to some embodiments of the invention is illustrated in
The index of refraction of air is about 1.0, whereas the index of refraction of water is about 1.3. It can be assumed that the refractive index of vitreous or BSS is similar to that of water. For a typical fiber optic material, the refractive index is greater than 1.3. Accordingly, if a pulse of light is sent down the waveguide, a larger amount of light will be reflected if air is present at the distal interface than if vitreous or BSS is present. Thus, if the amount of reflected light is below a certain threshold, i.e., a threshold that is less than an expected reflected light energy for air but greater than an expected reflected light energy for vitreous, then a pulse or burst of pulses can be applied.
In the circuit illustrated in
As was the case with the circuit in
An exemplary circuit based on measuring pressure at or near the end of the probe tip is illustrated in
Still another exemplary load detection circuit is illustrated in
Of course, those skilled in the art will appreciate that the circuit of
Yet another load detection circuit is illustrated in
One circuit for measuring the capacitance seen by the probe tip and comparing the measured result to a threshold value is shown in
The value of R2 is chosen, given a switching frequency f, so that the time constant formed by R2 and the effective capacitance when the probe is in vitreous is less than one-half of the switching period 1/f. Thus, if the probe tip is in air, the effective capacitance is smaller, and the voltage applied to the probe electrode quickly approaches zero during the discharge half of the cycle. On the other hand, if the probe tip is in vitreous, the observed capacitance is larger and the electrode voltage discharges more slowly during the discharge half of the cycle. Thus, the “average” voltage of the probe electrode will be higher when in vitreous. This average voltage is collected by the integrating circuit formed by R3 and C1 (which has a time constant substantially longer than a single switching cycle), and compared to threshold voltage VREF 850 with comparator 840. With an appropriately selected VREF 850, the output of comparator 840 is thus “HIGH” if the probe tip is in vitreous, and “LOW” if the probe tip is in air.
Like the circuits discussed earlier, of course, the capacitance-testing load detection circuit of
Given the various examples of load detection circuits presented above, those skilled in the art will appreciate that
Accordingly, each cycle of the pictured method “begins,” as shown at block 910, with the measuring of a physical parameter at or near the distal end of a HIPEF probe, where the HIPEF probe comprises at least one electrode disposed at the distal end and is configured for delivering pulsed energy to an yet. As noted above, the measured physical parameter may be resistivity, refractivity (or reflectivity), pressure, heat dissipation ability (or specific heat capacity), or permittivity. Other physical parameters may be used instead of or in addition to one or more of these, provided only that the measured parameter differs enough between air and vitreous so that an appropriate load detection circuit can distinguish between the two.
As shown at block 920, the measured physical parameter is compared to a pre-determined threshold value, where the threshold value is selected so that it is between the expected measurement value for air and the expected measurement value for vitreous. The exact value of the threshold may be selected to account for expected variations in measurements, including those due to noise from various sources, and/or to provide a desired probability of false detection or false no-detection.
As shown at blocks 930 and 940, if the measured value is greater than the threshold, then the application of a pulse or burst of pulses of energy to the probe electrodes is selectively enabled. On the other hand, if the measured value is less than the threshold value, then application of pulsed energy to the electrodes is not allowed. Instead, the measurement cycle is repeated until the threshold test is met.
Of course, the process illustrated in
Thus, for example, resistivity may be the physical parameter measured in some embodiments of the process flow of
On the other hand, if the measured physical parameter is permittivity (i.e., probe tip capacitance), then application of pulsed energy to the probe electrodes is selectively enabled only if the measured temperature is greater than a corresponding permittivity threshold value is measured. Similarly, if the measured physical parameter is pressure, than energizing the probe electrodes is permitted only if the measured pressure approximately equals the preset intraocular pressure value.
As suggested in the process flow of
Those skilled in the art will appreciate that the control signal generated by the process flow of
Indeed, all of the preceding descriptions of various methods and apparatus for controlling the application of high-intensity pulsed electric field energy during eye surgery were given for purposes of illustration and example, and those skilled in the art will appreciate that the present invention may be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are thus to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
