Patent Grant
8882757
1. Field of the Invention
The invention pertains to the field of keratoplasty and, more particularly, to the application of a device configured to treat one or more eye disorders by causing corrective reshaping of an eye feature.
2. Description of Related Art
A variety of eye disorders, such as myopia, keratoconus, and hyperopia, involve abnormal shaping of the cornea or the eye itself. Keratoplasty reshapes the cornea to correct such disorders. For example, with myopia, the cornea may be too steep or the eyeball too long, causing the refractive power of an eye to be too great and images to be focused in front of the retina. Flattening aspects of the cornea's shape through keratoplasty decreases the refractive power of an eye with myopia and causes the image to be properly focused at the retina.
Invasive surgical procedures, such as laser-assisted in-situ keratomileusis (LASIK), may be employed to reshape the cornea. However, such surgical procedures typically require a healing period after surgery. Furthermore, such surgical procedures may involve complications, such as dry eye syndrome caused by the severing of corneal nerves.
Thermokeratoplasty, on the other hand, is a noninvasive procedure that may be used to correct the vision of persons who have disorders associated with abnormal shaping of the cornea, such as myopia, keratoconus, and hyperopia. Thermokeratoplasty may be performed by applying electrical energy in the microwave or radio frequency (RF) band. In particular, microwave thermokeratoplasty may employ a near field microwave applicator to apply energy to the cornea and raise the corneal temperature. At about 60° C., the collagen fibers in the cornea shrink. The onset of shrinkage is rapid, and stresses resulting from this shrinkage reshape the corneal surface. Thus, application of heat energy in circular or ring-shaped patterns may cause aspects of the cornea to flatten and improve vision in the eye.
Embodiments according to aspects of the present invention provide systems and methods that improve operation of an applicator that delivers heat-generating energy to an eye as a part of an eye therapy. An example method comprises positioning a distal end of an applicator at or proximate to a surface of an eye, supplying an amount of energy from an energy source to the applicator to apply therapy to the eye, a first portion of the energy supplied to the applicator being transmitted through the distal end to the eye and a second portion of the energy supplied to the applicator being reflected from the distal end of the applicator, detecting a signal corresponding to the reflected energy, and determining an amount of contact based on the signal. A corresponding example system comprises an energy source, an applicator, and a dual directional coupler, one or more of the components of the system being configured to carry out one or more steps of the method.
The example method may further include one or more of the steps of: ceasing supply of energy to the applicator based on the amount of contact; after ceasing supply of energy, moving the applicator towards the surface of the eye, and resuming supply of energy to the applicator; and moving the applicator towards the eye until a desired amount of contact is determined based on the signal corresponding to the reflected energy.
The example method may further include one or more of the following characteristics: the amount of contact includes no contact; the signal corresponding to the reflected energy has a power and the method further comprises detecting a decrease in the power; the signal corresponding to the reflected energy has a power and the method further comprises detecting an increase in the power; the signal corresponding to the reflected energy has a power that decreases as the amount of contact increases; the signal corresponding to the reflected energy has a power and the method further comprises determining whether the power is less than a threshold value; the signal corresponding to the reflected energy has a power that increases as the amount of contact increases; the signal corresponding to the reflected energy has a power and the method further comprises determining whether the power is greater than a threshold value; the applicator comprises a conducting element, the conducting element being configured to conduct energy from the energy source to apply therapy to an eye, and a covering configured to be removably attached to the conducting element, the covering having an interface surface positionable at the eye, at least a portion of the interface surface including one or more dielectric materials, the energy from the conducting element being deliverable to the eye through the interface surface; the covering forms an enclosure over a portion of the conducting element and the applicator further comprises a coolant delivery system, the coolant delivery system being operable to deliver coolant within the enclosure to cool the interface surface of the covering and the eye, and the enclosure preventing the coolant from directly contacting the eye; the detecting is performed by a dual directional coupler; and the energy supplied to the applicator is a microwave energy.
Another example method comprises positioning a distal end of an applicator at or proximate to an eye, supplying an amount of energy to the applicator from an energy source to apply therapy to the eye, a first portion of the energy supplied to the applicator being transmitted through the distal end to the eye and a second portion of the energy supplied to the applicator being reflected from the distal end, supplying a coolant pulse to the eye, and detecting a signal corresponding to at least one of the energy supplied to the applicator and the energy reflected from the distal end, the signal further corresponding to the coolant pulse. A corresponding example system comprises an energy source, an applicator, a coolant delivery system operable to deliver coolant to cool the eye, and a dual directional coupler, one or more of the components of the system being configured to carry out one or more steps of the method.
The example method may further include one or more of the following characteristics: the applicator comprises a conducting element, the conducting element being configured to conduct energy from the energy source to apply therapy to an eye, a covering configured to be removably attached to the conducting element, the covering having an interface surface positionable at the eye, at least a portion of the interface surface including one or more dielectric materials, the energy from the conducting element being deliverable to the eye through the interface surface, the covering forming an enclosure over a portion of the conducting element, and a coolant delivery system, the coolant delivery system being operable to deliver coolant within the enclosure to cool the interface surface of the covering and the eye, and the enclosure preventing the coolant from directly contacting the eye; the signal corresponds to the energy supplied to the applicator, the signal having a power, the power decreasing when coolant is delivered to the interface surface; the signal corresponds to the energy reflected from the distal end of the applicator, the signal having a power, the power increasing when coolant is delivered to the interface surface; the detecting is performed by a dual directional coupler; and the energy supplied to the applicator is a microwave energy.
Yet another method comprises supplying an amount of energy from an energy source to a distal end of an applicator to apply therapy to an eye, a first portion of the energy supplied to the applicator being transmitted through the distal end to the eye and a second portion of the energy supplied to the applicator being reflected from the distal end, detecting a forward signal corresponding to the energy supplied to the applicator, detecting a reflected signal corresponding to the reflected energy, determining an efficiency of energy transfer based on the forward signal and the reflected signal, and based on the efficiency of energy transfer, modifying at least one adjustable parameter of a tuning element corresponding to the applicator. A corresponding example system comprises an energy source, an applicator, a dual directional coupler, a tuning element, and one or more controllers, one or more of the components of the system being configured to carry out one or more steps of the method.
The method may further include one or more of the following characteristics: the determining the efficiency of energy transfer comprises measuring at least one of a magnitude change and a phase change of the forward signal and the reflected signal; the at least one adjustable parameter is an inductance; the at least one adjustable parameter is a capacitance; the at least one adjustable parameter is not modified when the efficiency of energy transfer is determined to be greater than a first threshold value; the tuning element is electrically connected to the applicator in parallel; the tuning element is integral with the applicator; the tuning element comprises an inner conductor, an outer conductor and a short connector, the inner conductor and the outer conductor being concentric cylinders having a gap therebetween, the short connector electrically connecting the inner conductor to the outer conductor, the short connector being axially moveable within the gap; the tuning element further comprises a controller configured to provide signals to a motor, the motor being configured to mechanically move the short connector within the gap; the applicator comprises a conducting element, the conducting element being configured to conduct energy from the energy source to apply therapy to an eye, and a covering configured to be removably attached to the conducting element, the covering having an interface surface positionable at the eye, at least a portion of the interface surface including one or more dielectric materials, the energy from the energy conducting element being deliverable to the eye through the interface surface; a dual directional coupler detects the forward signal and the reflected signal; and the energy supplied to the applicator is a microwave energy.
A further method comprises supplying an amount of energy from an energy source to a distal end of an applicator to apply therapy to an eye, a first portion of the energy supplied to the applicator being transmitted through the distal end to the eye and a second portion of the energy supplied to the applicator being reflected from the distal end, detecting a forward signal corresponding to the energy supplied to the applicator, detecting a reflected signal corresponding to the reflected energy, determining an impedance mismatch between the eye and the applicator based on the forward signal and the reflected signal, and based on the impedance mismatch, modifying at least one adjustable parameter of a tuning element corresponding to the applicator. A corresponding example system comprises an energy source, a dual directional coupler, a tuning element, and one or more controllers, one or more of the components of the system being configured to carry out one or more steps of the method.
The example method may further include one or more of the following characteristics: the determining the impedance mismatch comprises measuring at least one of a magnitude change and a phase change of the forward signal and the reflected signal; the at least one adjustable parameter is an inductance; the at least one adjustable parameter is a capacitance; the at least one adjustable parameter is not modified when the impedance mismatch is determined to be less than a threshold value; the tuning element is electrically connected to the applicator in parallel; the tuning element is integral with the applicator; the tuning element comprises an inner conductor, an outer conductor and a short connector, the inner conductor and the outer conductor being concentric cylinders having a gap therebetween, the short connector electrically connecting the inner conductor to the outer conductor, the short connector being axially moveable within the gap; the applicator comprises a conducting element, the conducting element being configured to conduct energy from the energy source to apply therapy to an eye, and a covering configured to be removably attached to the conducting element, the covering having an interface surface positionable at the eye, at least a portion of the interface surface including one or more dielectric materials, the energy from the energy conducting element being deliverable to the eye through the interface surface; a dual directional coupler detects the forward signal and the reflected signal; and the energy supplied to the applicator is a microwave energy.
These and other aspects of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention when viewed in conjunction with the accompanying drawings.
The embodiments described herein relate to a system and method for improving operation of an applicator that delivers heat-generating energy to an eye as a part of an eye therapy. For example, reflected power is measured to determine whether sufficient contact has been established between the applicator and the eye for accurate and precise delivery of energy to the eye. In addition, at least one of forward and reflected power is measured to monitor the application of coolant pulses that control the generation of heat in the eye when the applicator delivers energy to the eye.
Referring now to the drawings, wherein like reference characters denote similar elements throughout the several views,
As further illustrated in
With the concentric arrangement of conductors 111A and 111B, a substantially annular gap 111C of a selected distance is defined between the conductors 111A and 111B. The annular gap 111C extends from the proximal end 110A to the distal end 110B. A dielectric material 111D may be used in portions of the annular gap 111C to separate the conductors 111A and 111B. The distance of the annular gap 111C between conductors 111A and 111B determines the penetration depth of microwave energy into the cornea 2 according to established microwave field theory. Thus, the microwave conducting element 111 receives, at the proximal end 110A, the electrical energy generated by the electrical energy source 120, and directs microwave energy to the distal end 111B, where the cornea 2 is positioned.
The outer diameter of the inner conductor 111B is preferably larger than the pupil. In general, the outer diameter of the inner conductor 111B may be selected to achieve an appropriate change in corneal shape, i.e. keratometry, induced by the exposure to microwave energy. Meanwhile, the inner diameter of the outer conductor 111A may be selected to achieve a desired gap between the conductors 111A and 111B. For example, the outer diameter of the inner conductor 111B ranges from about 2 mm to about 10 mm while the inner diameter of the outer conductor 111A ranges from about 2.1 mm to about 12 mm. In some systems, the annular gap 111C may be sufficiently small, e.g., in a range of about 0.1 mm to about 2.0 mm, to minimize exposure of the endothelial layer of the cornea (posterior surface) to elevated temperatures during the application of heat by the applicator 110.
A controller 140 may be employed to selectively apply the energy any number of times according to any predetermined or calculated sequence. In addition, the heat may be applied for any length of time. Furthermore, the magnitude of heat being applied may also be varied. Adjusting such parameters for the application of heat determines the extent of changes that are brought about within the cornea 2. Of course, the system attempts to limit the changes in the cornea 2 to an appropriate amount of shrinkage of collagen fibrils in a selected region. When employing microwave energy to generate heat in the cornea 2, for example with the applicator 110, the microwave energy may be applied with low power (of the order of 40 W) and in long pulse lengths (of the order of one second). However, other systems may apply the microwave energy in short pulses. In particular, it may be advantageous to apply the microwave energy with durations that are shorter than the thermal diffusion time in the cornea. For example, the microwave energy may be applied in pulses having a higher power in the range of 500 W to 3 KW and a pulse duration in the range of about 10 milliseconds to about one second.
Referring again to
During operation, the distal end 110B of the applicator 110 as shown in
As shown in
In general, the application of energy to the cornea 2 depends in part on the position of the contact surface 111G relative to the corneal surface 2A. As a result, to provide reliable application of energy to the cornea 2, embodiments ensure that the contact surface 111G, or portions thereof, are positioned to make contact with the corneal surface 2A. In this way, the relationship between the energy conducting element 111 and the cornea 2 is more definite and the resulting delivery of energy is more predictable and accurate. Furthermore, safety is enhanced when the applicator 111 is in direct contact with the corneal surface 2A and energy is transferred primarily to the system with good contact. Accordingly, it is preferable not to deliver energy via the energy conducting element 111 unless there is sufficient contact.
In some embodiments, sufficient contact is determined by causing an observable amount of flattening, or applanation, of the cornea. The applanation provides a constant and uniform pressure against the corneal surface 2A. For example, as illustrated in
Other systems and methods for improving electrical and thermal contact between an energy conducting element and the corneal surface are described in U.S. patent application Ser. No. 12/209,123, filed Sep. 11, 2008, which is a continuation-in-part application of U.S. patent application Ser. No. 12/018,457, filed on Jan. 23, 2008, the contents of these applications being entirely incorporated herein by reference. For example, an adjustment system can be employed to improve electrical and thermal contact between the energy conducting element and the corneal surface, as described in further detail below with respect to
As
The coolant delivery element 112 may have a nozzle structure 112A with an opening 112B directed toward the distal end 110B. Although
Furthermore, the applicator 110 may define a substantially enclosed assembly at the distal end 110B, which is placed in contact with the corneal surface 2A. As shown in
The controller 140 may also be operably connected to the coolant delivery element 112 as well as the energy source 120. As such, the controller 140 may be employed to determine the amount and timing of coolant delivered from the coolant delivery element 112 toward the corneal surface 2A at the distal end 110B. The controller 140 may be employed to selectively apply the heat and the coolant any number of times according to a predetermined or calculated sequence. For instance, the coolant may be applied to the corneal surface 2A before, during, or after the application of heat to the cornea 2, or any combination thereof.
In some embodiments, the coolant delivery element 112 may employ a solenoid valve in combination with the delivery nozzle 112A. As is known, a solenoid valve is an electromechanical valve for use with liquid or gas controlled by applying or stopping an electrical current through a coil of wire, thus changing the state of the valve. As such, the controller 140 may electronically control the actuation of the solenoid valve to deliver the coolant through the delivery nozzle 112A to the corneal surface 2A. However, other embodiments may employ other types of actuators or alternative techniques for delivering coolant through the delivery nozzle 112A in place of a solenoid valve.
During operation of the embodiment of
Advantageously, localized delivery of coolant to the corneal surface 2A before the application of heat to the cornea 2 minimizes the resulting temperature at the corneal surface 2A when the heat is applied, thereby minimizing any heat-induced injury to the corneal surface 2A. In other words, the coolant reduces the temperature of the corneal surface 2A, so that the maximum surface temperature achieved at the corneal surface 2A during or immediately after heat exposure is also reduced by a similar magnitude when compared to a case where no coolant is applied prior to heat exposure. Without the application of coolant, the temperature at the corneal surface 2A rises during or immediately after heat exposure with persistent surface heating resulting from a slow dissipation of heat trapped near the surface-air interface.
Although temperatures observed at the corneal surface 2A immediately after heat exposure are lowered by the application of coolant before exposure, a delayed thermal wave may arrive at the corneal surface 2A after exposure as the heat generated in the corneal areas 2B below the surface 2A diffuses toward the cooled surface 2A. The heat transfer from the corneal surface 2A to the surrounding air is likely to be insignificant, because air is an excellent thermal insulator. With no cooling after the application of heat, heat diffusing away from the areas 2B beneath the corneal surface 2A builds up near the corneal surface 2A and produces an elevated surface temperature that may persist after the application of heat. Although the heat that builds up near the corneal surface 2A may eventually dissipate through thermal diffusion and cooling via blood perfusion, such dissipation may take several seconds. More immediate removal of this heat by additional application of coolant minimizes the chances for heat-related injury to the corneal surface 2A. Thus, embodiments of may employ not only a pulse of coolant immediately prior to heat exposure, but also one or more pulses of coolant thereafter. Accordingly, in further operation of the embodiment of
When the coolant delivery element 12 delivers the pulse of coolant to the corneal surface 2A, the coolant on the corneal surface 2A draws heat from the surface 2A, causing the coolant to evaporate. In general, coolant applied to the surface 2A creates a heat sink at the surface 2A, resulting in the removal of heat before, during, and after the application of heat to the cornea 2. The heat sink persists for as long as the liquid cryogen remains on the surface 2A. The heat sink can rapidly remove the trapped heat at the surface 2A without cooling the collagen fibers in the region 2B. A factor in drawing heat out of the cornea 2 is the temperature gradient that is established near the surface 2A. The steeper the gradient, the faster a given quantity of heat is withdrawn. Thus, the application of the coolant attempts to produce a large surface temperature drop as quickly as possible.
Because the cooled surface 2A provides a heat sink, the amount and duration of coolant applied to the corneal surface 2A affects the amount of heat that passes into and remains in the region underlying the corneal surface 2A. Thus, controlling the amount and duration of the cooling provides a way to control the depth of corneal heating, promoting sufficient heating of targeted collagen fibers in the mid-depth region 2B while minimizing the application of heat to regions outside the targeted collagen fibers.
In general, dynamic cooling of the corneal surface 2A may be optimized by controlling: (1) the duration of the cooling pulse(s); (2) the duty cycle of multiple pulses; (3) the quantity of coolant deposited on the corneal surface 2A so that the effect of evaporative cooling can be maximized; and (4) timing of dynamic cooling relative to heat application. For example, a single pulse timing may include applying a 80 ms heat pulse and a 40 ms cooling pulse at the beginning, middle, or end of the heating pulse. In another example, multiple cooling pulses may be applied according to a pattern of 10 ms ON and 10 ms OFF, with four of these pulses giving a total of 40 ms of cooling, but timed differently.
In some embodiments, the coolant may be the cryogen tetrafluoroethane, C2H2F4, which has a boiling point of about −26.5° C. and which is an environmentally compatible, nontoxic, nonflammable freon substitute. The cryogenic pulse released from the coolant delivery element 112 may include droplets of the cryogen cooled by evaporation as well as mist formed by adiabatic expansion of vapor.
In general, the coolant may be selected so that it provides one or more of the following: (1) sufficient adhesion to maintain good surface contact with the corneal surface 2A; (2) a high thermal conductivity so the corneal surface 2A may be cooled very rapidly prior to heat application; (3) a low boiling point to establish a large temperature gradient at the surface; (4) a high latent heat of vaporization to sustain evaporative cooling of the corneal surface 2A; and (5) no adverse health or environmental effects. Although the use of tetrafluoroethane may satisfy the criteria above, it is understood that embodiments of the present invention are not limited to a particular cryogen and that other coolants, such as liquid nitrogen, argon, or the like, may be employed to achieve similar results. For instance, in some embodiments, other liquid coolants with a boiling temperature of below approximately body temperature, 37° C., may be employed. Furthermore, the coolant does not have to be a liquid, but in some embodiments, may have a gas form. As such, the pulse of coolant may be a pulse of cooling gas. For example, the coolant may be nitrogen (N2) gas or carbon dioxide (CO2) gas.
As described previously, the controller 140 may be employed to selectively apply the heat and the coolant pulses any number of times according to any predetermined or calculated sequence. In addition, the heat and the pulses of coolant may be applied for any length of time. Furthermore, the magnitude of heat being applied may also be varied. Adjusting such parameters for the application of heat and pulses of coolant determines the extent of changes that are brought about within the cornea 2. Of course, as discussed, embodiments of the present invention attempt to limit the changes in the cornea 2 to an appropriate amount of shrinkage of selected collagen fibers. When employing microwave energy to generate heat in the cornea 2, for example with the applicator 110, the microwave energy may be applied with low power (of the order of 40 W) and in long pulse lengths (of the order of one second). However, other embodiments may apply the microwave energy in short pulses. In particular, it may be advantageous to apply the microwave energy with durations that are shorter than the thermal diffusion time in the cornea. For example, the microwave energy may be applied in pulses having a higher power in the range of 300 W to 3 kW and a pulse duration in the range of about 2 milliseconds to about one second. Thus, when applying the coolant pulses before and after the application of heat as discussed previously: a first pulse of coolant is delivered to reduce the temperature of the corneal surface 2A; a high power pulse of microwave energy is then applied to generate heat within selected areas of collagen fibers in a mid-depth region 2B; and a second pulse of coolant is delivered in sequence to end further heating effect and “set” the corneal changes that are caused by the energy pulse. The application of energy pulses and coolant pulses in this manner advantageously reduces the amount to heat diffusion that occurs and minimizes the unwanted impact of heating and resulting healing processes on other eye structures, such as the corneal endothelium. Moreover, this technique promotes more permanent and stable change of the shape of the cornea 2 produced by the heat. Although the application of high powered energy in short pulses has been described with respect to the delivery of microwave energy, a similar technique may be applied with other types of energy, such as optical energy or electrical energy with radio frequency (RF) wavelengths described further below.
The system of
As further illustrated in
As shown in
The system 200 of
The approach of system 200 may be particularly advantageous, because when the applicator 110 is positioned over the eye 1 during operation, the clinician's view of the contact between the energy conducting element 111 and the eye 1 may be obstructed by the applicator 110 itself. Thus, the system 200 allows the clinician to determine whether sufficient contact has been established without requiring visual confirmation. During operation, the clinician monitors the change in reflected power as the applicator 110 is positioned. The change in reflected power indicates the change in contact and applanation and thus allows the clinician to accurately determine the position of the energy conducting element 111.
The system of
To demonstrate the sensitivity of the system to tissue contact, experiments were conducted with the system 200 to yield the graph of
Although the embodiments described above involve systems in which the reflected power decreases as the amount of contact increases, the reflected power in other embodiments increases as the amount of contact increases. It is to be understood that the tuning or calibration of the system determines whether the reflected power decreases or increases as the amount of contact increases. In general, a change in the amount of contact between the applicator and the eye is indicated by a change in the reflected power.
As described previously, coolant pulses may also be applied to the eye to preserve the epithelium or surface of the eye during thermal treatment with microwaves. For example, a pulse train with 5 ms ON and 5 ms OFF may be utilized and repeated 3-20 times. Monitoring the effect of the coolant pulses is important, because the coolant application helps to protect the surface of the eye as described previously. Ordinary flow meters, however, may not be sufficiently able to detect and monitor short pulses of coolant on the order of approximately 5 ms to 50 ms as such pulses generally deliver small volumes of coolant, e.g., on the order of microliters. To solve this problem, further aspects of the present invention are able to detect coolant pulses by measuring their effect on the measured forward and reflected power as delivered to the eye. For example, the system 200 shown in
Detecting coolant pulses according to power measurements is sufficiently precise to identify a pulse train, even if, for example, it includes short 10 ms pulses.
Correspondingly,
Referring to
Long cooling pulses may also be detected by monitoring the forward and/or reflected power. For example, if a 50-100 ms pulse of microwaves is applied, the system may detect a cooling pulse is applied for the whole microwave pulse duration or any part thereof.
The tuning element 150 may include an inner conductor 150B and an outer conductor 150A electrically connected to a short connector 150E. In an embodiment, the adjustable aspect may be embodied as a short connector 150E that may be adjustably electrically connected between the inner conductor 150B and the outer conductor 150A. The short connector 150E may be mechanically manipulated so as to move along a path substantially between the outer conductor 150A and the inner conductor 150B. While the short connector 150E moves along the path between the outer conductor 150A and the inner conductor 150B it may maintain a continuous electrical connection between the outer conductor 150A and the inner conductor 150B or it may establish only an intermittent electrical connection between the outer conductor 150A and the inner conductor 150B. Alternatively, the short connector 150E may establish no electrical connection at all between the outer conductor 150A and the inner conductor 150B while moving along a path enclosed by the outer conductor 150A and the inner conductor 150B only to effect an electrical connection between the outer conductor 150A and the inner conductor 150B once mechanical manipulation of the short connector 150E is halted. In an alternative embodiment, the short connector 150E may be embodied as an elastic or deformable conductive material which has an electrical connection on the outer conductor 150A that is fixed in position, and which is connected to the inner conductor 150B with a connection that may be adjusted in position. Alternatively, open stubs of varying lengths may be used in the place of or in addition to shorted stubs.
In general, any circuit with adjustable parameters that change the inductance and/or capacitance of the system may be used for tuning purposes in lieu of or in addition to the fixed single or double tuning stub herein described. An example of such a circuit is shown in
The short connector 150E, the inner conductor 150B, and the outer conductor 150A are each composed, at least in part, of suitable electrically conducting materials. The inner conductor 150B, the outer conductor 150A, and the short connector 150E may be formed, for example, of aluminum, stainless steel, brass, copper, silver, other metals, metal-coated plastic, or any other suitable conductive material. The materials used to construct the inner conductor 150B and the outer conductor 150A may be chosen, for example, in order to effect a characteristic impedance value for an electrical circuit connected to the outer conductor 150A and the inner conductor 150B. The dimensions of the outer conductor 150A and the inner conductor 150B may also be chosen in order to effect a characteristic impedance value for an electrical circuit connected to the outer conductor 150A and the inner conductor 150B. For example, when the tuning element 150 is embodied as having substantial cylindrical symmetry such that both the outer conductor 150A and the inner conductor 150B are embodied as cylinders about a common axis of symmetry, adjustments to the diameters of the inner conductor 150B and the outer conductor 150A may be used to adjust the impedance of the tuning element 150. In an example embodiment the impedance of the tuning element 150 may be adjusted to be 50 Ohms (50Ω).
The tuning element 150 further includes an electric motor 150F which is mechanically engaged to the short connector 150E via a mechanical connection 150G. The mechanical connection 150G may incorporate belts, cogs, wheels, pulleys, screws, levers, devices applying torque, or any other conventional means of achieving movement of the short connector 150G. In an embodiment, the operation of the electric motor 150F is mediated by automated computer control, which may be achieved using the controller 140.
In operation of an embodiment of the tuning element 150 the controller 140 may send a command to the electric motor 150F to move the short connector. The command may be sent and received via an electrical connection or via a wireless signal or any other conventional method of sending digital or analog information across distances. The electric motor 150F may then engage the mechanical connection 150G to move the short connector 150E along a path substantially enclosed by the outer conductor 150A and the inner conductor 150B.
Further illustrated in
The example embodiments of the tuning element 150 shown in
Furthermore, although the tuning element 150 is shown and described in one embodiment in
The tuning elements 152 and 153 may each include conductive components incorporating at least one adjustable aspect such that a modification of the adjustable aspect results in a change in either the inductance, or the capacitance, or both of an electrical circuit in connection with the tuning elements 152 and 153. By modifying either the inductance, or capacitance, or both of the electrical circuit according to adjustments to the at least one adjustable aspect, the tuning elements 152 and 153 enables the circuit to be tuned to a particular impedance value by making changes to the at least one adjustable aspect of the tuning elements 152 and 153. The tuning elements 152 and 153 may substantially incorporate many of the features of the tuning element 150 described above and illustrated in
An embodiment of the system 500 for measuring an electrical characteristic of an eye 1 may incorporate an energy source 120, which may include an oscillator for generating energy at microwave frequencies and an output which is electrically connected to an input of the DDC 122. An output of the DDC 122 may then be connected to an applicator 110. The applicator 110 may include a conducting element 111 for application of energy at its proximal end 110B to an eye 1 at a contact surface 111G. Aspects of the applicator 110 may incorporate features of the applicator 110 shown in
In operation of the system 500 for measuring an electrical characteristic of an eye 1, energy may be generated in the energy source 120 at a microwave frequency. The microwaves may then be conducted to an applicator 110 after passing through a measurement system 127, which incorporates a DDC 122 and a phase sensor 128 or a magnitude sensor 129 or both. Upon conduction of the microwave energy to the eye 1 through the contact surface 111G, some microwave energy is transmitted into the eye 1, while some additional microwave energy is reflected at the junction to travel back through the conducting element 111 toward the measurement system 127. The sum of the microwave energy reflected, the microwave energy transmitted, and all the microwave energy lost due to line losses and radiation leaks will substantially equal the amount of microwave energy generated in the energy source 120. When the microwave energy passes through the DDC 122 from the energy source 120, a signal indicative of the amount of forward power is provided to the forward signal output 125. When the reflected microwave energy passes back through the DDC 122 upon reflection from the applicator 110, a signal indicative of the reflected signal is provided to the reflected signal output 126. The forward signal output 125 may then be passed through an attenuator 125A, which may reduce the amplitude of the forward microwave signal by a predetermined amount. Similarly, the reflected signal output 126 may then be passed through an attenuator 126A, which may reduce the amplitude of the reflected microwave signal by a predetermined amount. The reflected and forward microwave signals may then each be provided to either a phase sensor 128, or a magnitude sensor 129, or both in order to determine the amount of microwave energy reflected compared to the amount of microwave energy generated. As is conventionally understood, this information may also allow for the calculation of the impedance value of the eye 1 when the impedance value of the system 500 is known. Although, in an example embodiment it is not necessary to know the impedance of the system 500 in order to achieve a desired difference in impedance between the eye 1 and the system 500.
In an example embodiment, adjusting the impedance of the applicator 110 may be advantageous, for example, in order to achieve a desired efficiency of energy absorption to the eye 1 by the applicator 110. As is conventionally known, when energy is conducted or transmitted across a surface boundary, i.e. across a junction wherein a first portion of the junction has a first impedance value and a second portion of the junction has a different impedance value, some energy is transmitted through the junction and some is reflected. Energy is most efficiently transmitted when the two impedances are as near as possible to identical. Thus an applicator 110 which includes a tunable aspect 151 in the conducting element 111 so as to adjust the impedance value of the applicator 110 may allow for adjustment of the impedance of value of the applicator 110 so as to correspond in a desirable manner with the impedance value of the eye 1.
In an alternative embodiment, the tunable aspect 151 and/or the first tuning element 152 and/or the second tuning element 153 may not include an adjustable conducting element between the outer conductor 110A and the inner conductor 110B, but may be embodied as a conducting element providing an electrical connection between the outer conductor 110A and the inner conductor 110B which may be fixed in place in a removable or permanent manner so as to allow for the placement of the tunable aspect 151 and/or the first tuning element 152 and/or the second tuning element 153 to be determined according to an electrical characteristic of the system 500.
In operation, the operation of the first step 602 enables the measurement activity accomplished in the second step 604. Upon completion of the second step 604, the third step 608 is undertaken, which is followed by steps four 606 and five 610, which are accomplished in a manner substantially similar to the completion of steps one 602 and two 604. Following step five 610, step six 612 is undertaken and depending on the determination made in step six 612, steps three through six, 608, 606, 610, and 612 may be completed in a loop until a determination is made in step six 612 that an acceptable efficiency has been attained so as to end the method 600.
In an example embodiment, the determination in step six 612 may be based on achieving a predetermined minimal impedance mismatch, which may be determined after sampling a range of values until a local or global minimum is identified in a value of a reflection coefficient as measured in the measurement system 127, as shown, for example, in
In another example embodiment of the method 600, the determination in step six 612 may be based on achieving an acceptable impedance mismatch. That is, the efficiency may be deemed acceptably efficient so as to end the method 600 when the measurement system 127 measures an effective impedance mismatch below some predetermined threshold value. In another example embodiment of the method 600, the determination in step six 612 may be deemed acceptably efficient so as to end the method 600 when the measurement system 127 measures an effective impedance within a certain threshold of upper and lower boundaries. Alternatively, an embodiment of the method 600 may incorporate a determination in step six 612 that is some combination of each of these.
In operation, the operation of the first step 702 enables the measurement activity accomplished in the second step 704. Upon completion of the second step 704, the third step 708 is undertaken, which is followed by steps four 706 and five 710, which are accomplished in a manner substantially similar to the completion of steps one 702 and two 704. Following step five 710, step six 712 is undertaken and depending on the determination made in step six 712, steps three through six, 708, 706, 710, and 712 may be completed in a loop until a determination is made in step six 712 that an acceptable impedance mismatch has been attained so as to end the method 700.
In another example embodiment of the method 700, the determination in step six 712 may be based on achieving an acceptable impedance mismatch. That is, the efficiency may be deemed acceptably efficient so as to end the method 700 when the measurement system 127 measures an effective impedance mismatch below some predetermined threshold value. When the determination in step six 712 is based on achieving an impedance mismatch of some threshold value, step five 710 may not retain subsequent values for future reference. In another example embodiment of the method 700, the determination in step six 712 may be deemed acceptably efficient so as to end the method 700 when the measurement system 127 measures an effective impedance within a certain threshold of upper and lower boundaries. Alternatively, an embodiment of the method 700 may incorporate a determination in step six 712 that is some combination of each of these.
The amount of impedance of the cornea may be determined according to patient characteristics, including, but not limited to, age, gender, corneal thickness, and other similar factors that affect how corneal changes may be induced. Data relating to such factors and corresponding impedances may be compiled from a sample of past patients and reduced to a nomogram, look-up table, or the like. This compiled data may then serve as a guide for determining the impedance in future treatments.
The adjustment system 1300 may be further connected to a user interface system 1305 that accepts input from a user and correspondingly operates the adjustment system 1300. The user interface system 1305, for example, may be a device with a keypad to receive input from a user. The keypad may be part of a processing system, such as a conventional personal computer, with software to control the adjustment system 1300. Alternatively, the user interface system 1305 may be a device, such as a joystick, that receives instructions from the user through more mechanically oriented input.
In embodiments where the outer conductor 1111A and the inner conductor 1111B are fixedly coupled to each other, the adjustment system 1300 moves the outer conductor 1111A and the inner conductor 1111B as a single element relative to a housing 1110. However, in other embodiments, the outer conductor 1111A and the inner conductor 1111B may be decoupled so that they can be moved relative to each other. Accordingly, with the housing 1110 fixed relative to the eye 2 (e.g., with a positioning system 1200), the contact between the outer conductor 1111A and the corneal surface 2A may be controlled separately from the contact between the inner conductor 1111B and the corneal surface 2A.
While the present invention has been described in connection with a number of exemplary embodiments, and implementations, the present inventions are not so limited, but rather cover various modifications, and equivalent arrangements. Other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
This application claims priority to U.S. Provisional Application No. 61/113,395, filed Nov. 11, 2008, the contents of which are incorporated entirely herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20100185192 A1 | Jul 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61113395 | Nov 2008 | US |
