Patent Publication Number: US-8992516-B2

Title: Eye therapy system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/929,946 filed Jul. 19, 2007, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention pertains to the field of keratoplasty and, more particularly, to thermokeratoplasty and the application of coolant to the eye during thermokeratoplasty. 
     2. Description of Related Art 
     A variety of eye disorders, such as myopia, keratoconus, and hyperopia, involve abnormal shaping of the cornea. Keratoplasty reshapes the cornea to correct such disorders. For example, with myopia, the shape of the cornea causes 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&#39;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 keratonomileusis (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 around the pupil may cause aspects of the cornea to flatten and improve vision in the eye. However, devices for thermokeratoplasty generally apply energy through the corneal surface to heat the underlying collagen fibers. Therefore, the maximum temperature can occur at the corneal surface, resulting in possible heat-related injury and damage to the outer layer, known as the epithelium, at the corneal surface. Moreover, devices for thermokeratoplasty may provide inadequate approaches for controlling the depth of heating below the corneal surface and promoting sufficient heating of the targeted collagen fibers while minimizing the application of heat to areas outside the targeted collagen fibers. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, embodiments of the present invention provide a system that selectively applies coolant to the corneal surface to minimize heat-related damage to the corneal surface during thermokeratoplasty and to determine the depth of heating below the corneal surface. 
     Accordingly, an embodiment of the present invention includes an energy source, a conducting element, a coolant supply, and at least one coolant delivery element. The conducting element is operably connected to the energy source and extends from a proximal end to a distal end. The conducting element directs energy from the energy source to the distal end, which is positionable at an eye. The coolant delivery elements are in communication with the coolant supply and are operable to deliver a micro-controlled pulse of coolant to the distal end. 
     Another embodiment includes an electrical energy source, an electrical energy conducting element, a coolant supply, and at least one coolant delivery element. The electrical energy conducting element includes two conductors that are separated by a gap of a selected distance and that extend from a proximal end to a distal end. The electrical conducting element, which is operably connected to the electrical energy source, receives, at the proximal end, electrical energy generated by the electrical energy source and directs the electrical energy to the distal end, which is positionable at an eye. The coolant delivery elements are in communication with the coolant supply and are operable to deliver a micro-controlled pulse of coolant to the distal end. 
     Yet another embodiment includes an optical energy source, an optical energy conducting element, a coolant supply, and at least one coolant delivery element. The optical energy conducting element, which is connected to the optical energy source, extends from a proximal end to a distal end and directs optical energy from the optical energy source to the distal end, which is positionable at an eye. The coolant delivery elements are in communication with the coolant supply and are operable to deliver a micro-controlled pulse of coolant to the distal end. 
     An additional embodiment includes an energy source, a monopole conductor, a coolant supply, and at least one coolant delivery element. The monopole conductor, which is connected to the energy source, extends from a proximal end to a distal end and contacts, at the distal end, an eye of a body, whereby the body acts as a backplane and the conductor delivers energy to the eye. The coolant delivery elements are in communication with the coolant supply and are operable to deliver a micro-controlled pulse of coolant to the distal end. 
     A further embodiment includes an energy source, a conducting element, a coolant supply, and a vacuum source. The conducting element, which is operably connected to the energy source, extends from a proximal end to a distal end and directs energy from the energy source to the distal end, which is positionable at the eye. The vacuum source is operable to draw the coolant in a micro-controlled pulse from the coolant supply to the distal end, whereby the pulse of coolant is applied to the eye. 
     In addition to delivering micro-controlled pulses of coolant, some embodiments may deliver pulses of energy. In particular, the embodiments may employ high power energy to generate heat in a targeted region of the eye in a relatively short amount of time. To minimize unwanted diffusion of heat, the duration of the energy pulse may be shorter than the thermal diffusion time in the targeted region of the eye. In an exemplary application: a first pulse of coolant is delivered to reduce the temperature of the corneal surface; a high power pulse of microwave energy is then applied to generate heat within selected areas of collagen fibers in a mid-depth region; 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. 
     Another embodiment includes an energy conducting element and a vacuum ring. The vacuum ring receives the energy conducting element and creates a vacuum connection with an eye and positions the energy conducting element relative to the eye, whereby the energy conducting element directs the energy to the eye. The energy conducting element may be detachably coupled to the vacuum ring. 
     The embodiments of the present invention may also employ a controller to control the operation of one or more components or sub-systems. In addition, embodiments may employ pressure relief mechanisms to reduce the pressure introduced by the pulses of coolant into a closed environment. Furthermore, embodiments may also employ a readable use indicator, such as a radio frequency identification (RFID) device, that ensures that elements of the system, particularly those that come into contact with the body and bodily fluids, are disposed of after one use. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic of an embodiment of the present invention. 
         FIG. 2  illustrates an embodiment of the present invention employing a microwave energy source. 
         FIG. 3A  illustrates a variation of the embodiment of  FIG. 2 , which employs a pressure relief valve in place of a vacuum sub-system to reduce pressure created by a pulse of coolant. 
         FIG. 3B  illustrates a variation of the embodiment of  FIG. 2 , which employs a vent passage in place of a vacuum sub-system to reduce pressure created by a pulse of coolant. 
         FIG. 4  illustrates an embodiment of the present invention employing an optical energy source. 
         FIG. 5A  illustrates a variation of the embodiment of  FIG. 4 , which employs a pressure relief valve in place of a vacuum sub-system to reduce pressure created by a pulse of coolant. 
         FIG. 5B  illustrates a variation of the embodiment of  FIG. 4 , which employs a vent passage in place of a vacuum sub-system to reduce pressure created by a pulse of coolant. 
         FIG. 6  illustrates an embodiment of the present invention employing a monopole conductor as an energy conducting element. 
         FIG. 7A  illustrates an embodiment of the present invention employing a vacuum ring to position an applicator over an eye surface. 
         FIG. 7B  illustrates the vacuum ring employed in the embodiment of  FIG. 7A . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an embodiment of the present invention is schematically illustrated. In particular,  FIG. 1  shows an applicator  10  operably connected to an energy source  20 . The applicator  10  includes an energy conducting element  11 , which extends from the proximal end  10 A to the distal end  10 B of the applicator  10 . The applicator  10  may be connected to the energy source  20  at the proximal end  10 A. Operation of the energy source  20  causes energy to be conducted through the energy conducting element  20  and heat to be generated at the distal end  10 B. As such, the applicator  10  may be employed to apply heat to a cornea  2  of an eye  1  that is positioned at or near the distal end  10 B. In particular, the heat is applied to selected areas of collagen fibers in a mid-depth region  2 B of the cornea  2  to shrink the collagen fibers according to a predetermined pattern and reshape the cornea  2 , thereby improving vision through the eye  1 . 
     As further illustrated in  FIG. 1 , the applicator  10  includes at least one coolant delivery element  12  in fluid communication with a coolant supply, or reservoir,  13 . The outer surface  10 C of the applicator  10  may define a substantially enclosed assembly, especially when the distal end  10 A is placed in contact with the corneal surface  2 A. As shown in  FIG. 1 , this enclosed assembly may house the energy conducting element  11 , the coolant delivery element  12 , and the coolant supply  13 . Although the coolant supply  13  in  FIG. 1  is positioned within the applicator  10 , the coolant supply  13  may be external to the applicator  10  in other embodiments. Moreover, although  FIG. 1  shows one coolant delivery element  12 , some embodiments may employ more than one coolant delivery element  12  and/or more than one coolant supply  13 . 
     The coolant delivery element  12  delivers a coolant, or cryogen, from the coolant supply  13  to the distal end  10 B of the applicator  10 . As such, the applicator  10  may be employed to apply coolant to selectively cool the surface  2 A of the cornea  2  positioned at the distal end  10 B. The delivery of coolant from the coolant delivery element  12  toward the corneal surface  2 A, in sequence with the application of heat to the cornea  2 , permits the corneal temperature to be increased to cause appropriate shrinkage of the collagen fibers in the targeted mid-depth region  2 B and reshape the cornea  2 , while also minimizing injury to the outer layer  2 A, i.e. the epithelium, of the cornea  2 . 
     A controller  40 , as also shown in  FIG. 1 , may be operably connected to the energy source  20  and/or the coolant delivery element  12 . The controller  40  may be employed to control the delivery of energy from the energy source  20  to the applicator  10 , thereby determining the magnitude and timing of heat delivered to the cornea  2  positioned at the distal end  10 B. In addition, the controller  40  may be employed to determine the amount and timing of coolant delivered from the coolant delivery element  12  toward the corneal surface  2 A at the distal end  10 B. As described further below, the controller  40  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  2 A before and/or after the application of heat to the cornea  2 . 
     In some embodiments, the coolant delivery element  12  may employ a delivery nozzle  12 A and a solenoid valve. The delivery nozzle  12 A has an opening  12 B directed at the distal end  10 B. As is known, a solenoid valve is an electromechanical valve for use with liquid or gas controlled by running or stopping an electrical current through a coil of wire, thus changing the state of the valve. As such, the controller  40  may electronically control the actuation of the solenoid valve to deliver the coolant through the delivery nozzle  12 A to the corneal surface  2 A. However, other embodiments may employ other types of actuators or alternative techniques for delivering coolant through the delivery nozzle  12 A in place of a solenoid valve. 
     During operation of the embodiment of  FIG. 1 , the controller  40  may be used to actuate the application of micro-controlled pulses of coolant to the corneal surface  2 A before the application of heat to the cornea  2 . A pulse, or a spurt, of coolant is applied to the corneal surface  2 A for a predetermined short period of time so that the cooling remains generally localized at the corneal surface  2 A while the temperature of deeper corneal collagen fibers  2 B remains substantially unchanged. Preferably, the pulse is on the order of tens of milliseconds and is less than 100 milliseconds. The delivery of the coolant to the corneal surface is controlled by the controller  40  and may be less than 1 millisecond. Furthermore, the time between the application of the coolant and the application of the heat is also controlled by the controller  40  and may also be less than 1 millisecond. The coolant pulse generally covers an area of the corneal surface  2 A that corresponds with the application of heat to the cornea  2 . The shape, size and disposition of the cooled region may be varied according to the application. 
     Advantageously, localized delivery of coolant to the corneal surface  2 A before the application of heat to the cornea  2  minimizes the resulting temperature at the corneal surface  2 A when the heat is applied, thereby minimizing any heat-induced injury to the corneal surface  2 A. In other words, the coolant reduces the temperature of the corneal surface  2 A, so that the maximum surface temperature achieved at the corneal surface  2 A 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  2 A rises 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  2 A immediately after heat exposure are lowered by the application of coolant before exposure, a delayed thermal wave may arrive at the corneal surface  2 A after exposure as the heat generated in the corneal areas  2 B below the surface  2 A diffuses toward the cooled surface  2 A. The heat transfer from the corneal surface  2 A 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  2 B beneath the corneal surface  2 A builds up near the corneal surface  2 A and produces an elevated surface temperature that may persist after the application of heat. Although the heat that builds up near the corneal surface  2 A 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  2 A. Thus, embodiments of the present invention 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  FIG. 1 , the controller  40  may also be used to apply micro-controlled pulses of coolant after the applicator  10  applies heat to the cornea  2 . This application of coolant rapidly removes heat which diffuses from the mid-depth corneal region  2 B to the corneal surface  2 A. 
     When the coolant delivery element  12  delivers the pulse of coolant to the corneal surface  2 A, the coolant on the corneal surface  2 A draws heat from the surface  2 A, causing the coolant to evaporate. In general, coolant applied to the surface  2 A creates a heat sink at the surface  2 A, 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  2 A. The heat sink can rapidly remove the trapped heat at the surface  2 A without cooling the collagen fibers in the region  2 B. A factor in drawing heat out of the cornea  2  is the temperature gradient that is established near the surface  2 A. 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  2 A provides a heat sink, the amount and duration of coolant applied to the corneal surface  2 A affects the amount of heat that passes into and remains in the region underlying the corneal surface  2 A. 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  2 B while minimizing the application of heat to regions outside the targeted collagen fibers. 
     In general, dynamic cooling of the corneal surface  2 A may be optimized by controlling: (1) the duration of the cooling pulse(s); (2) the quantity of coolant deposited on the corneal surface  2 A so that the effect of evaporative cooling can be maximized; and (3) timing of dynamic cooling relative to heat application. 
     In some embodiments, the coolant may be the cryogen tetrafluoroethane, C 2 H 2 F 4 , 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  12  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  2 A; (2) a high thermal conductivity so the corneal surface  2 A 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  2 A after laser exposure; 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 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 (N 2 ) gas or carbon dioxide (CO 2 ) gas. 
     Referring now to the cross-sectional view illustrated in  FIG. 2 , an embodiment of the present invention employs an applicator  110 . The applicator  110  includes an electrical energy conducting element  111 , a micro-controlled coolant delivery system  112 , as well as a coolant supply  113 . 
     The electrical energy conducting element  111  is operably connected to an electrical energy source  120 , for example, via conventional conducting cables. The electrical energy conducting element  111  extends from a proximal end  110 A to a distal end  110 B of the applicator  110 . The electrical energy conducting element  111  conducts electrical energy from the source  120  to the distal end  110 B to apply heat energy to a cornea  2 , which is positioned at the distal end  110 B. In particular, the electrical energy source  120  may include a microwave oscillator for generating microwave energy. For example, the oscillator may operate at a microwave frequency range of 500 MHz to 3000 MHz, and more specifically at a frequency of around 2450 MHz which has been safely used in other applications. As used herein, the term “microwave” corresponds to a frequency range from about 10 MHz to about 10 GHz. 
     As further illustrated in  FIG. 2 , the electrical energy conducting element  111  may include two microwave conductors  111 A and  111 B, which extend from the proximal end  110 A to the distal end  110 B of the applicator  110 . In particular, the conductor  111 A may be a substantially cylindrical outer conductor, while the conductor  111 B may be a substantially cylindrical inner conductor that extends through an inner passage extending through the conductor  111 A. With the inner passage, the conductor  111 A has a substantially tubular shape. The inner and the outer conductors  111 A and  111 B may be formed, for example, of aluminum, stainless steel, brass, copper, other metals, metal-coated plastic, or any other suitable conductive material. 
     With the concentric arrangement of conductors  111 A and  111 B, a substantially annular gap  111 C of a selected distance is defined between the conductors  111 A and  111 B. The annular gap  111 C extends from the proximal end  110 A to the distal end  110 B. A dielectric material  111 D may be used in portions of the annular gap  111 C to separate the conductors  111 A and  111 B. The distance of the annular gap  111 C between conductors  111 A and  111 B 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  110 A, the electrical energy generated by the electrical energy source  120 , and directs microwave energy to the distal end  111 B, where the cornea  2  is positioned. 
     The outer diameter of the inner conductor  111 B is preferably larger than the pupil. In general, the outer diameter of the inner conductor  111 B 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  111 A may be selected to achieve a desired gap between the conductors  111 A and  111 B. For example, the outer diameter of the inner conductor  111 B ranges from about 2 mm to about 10 mm while the inner diameter of the outer conductor  111 A ranges from about 2.1 mm to about 12 mm. In some embodiments, the annular gap  111 C 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 . 
     As shown in  FIG. 2 , the micro-controlled coolant delivery system  112  as well as the coolant supply  113  may be positioned within the annular gap  111 C. Although  FIG. 2  may illustrate one coolant delivery system  112 , the applicator  110  may include a plurality of coolant delivery systems  112  arranged circumferentially within the annular gap  111 C. The coolant supply  113  may be an annular container that fits within the annular gap  111 C, with the coolant delivery element  112  having a nozzle structure  112 A extending downwardly from the coolant supply  113  and an opening  112 B directed toward the distal end  110 B. 
     The micro-controlled coolant delivery system  112 , which is in fluid communication with the coolant supply  113 , may operate in a manner similar to the coolant delivery system  12  in  FIG. 1 . In other words, pulses of coolant, or cryogen, from the coolant supply  113  are preferably applied to the corneal surface  2 A before and after energy is applied to the cornea  2  with the electrical energy source  120  and the electrical energy conducting element  111 . 
     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 500 W to 3 KW and a pulse duration in the range of about 10 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  2 A; a high power pulse of microwave energy is then applied to generate heat within selected areas of collagen fibers in a mid-depth region  2 B; 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. 
     Referring again to  FIG. 2 , at least a portion of each of the conductors  111 A and  111 B may be covered with an electrical insulator to minimize the concentration of electrical current in the area of contact between the corneal surface  2 A and the conductors  111 A and  111 B. In some embodiments, the conductors  111 A and  111 B, or at least a portion thereof, may be coated with a material that can function both as an electrical insulator as well as a thermal conductor. A dielectric layer  110 D may be employed along the distal end  111 B of the applicator  110  to protect the cornea  2  from electrical conduction current that would otherwise flow into the cornea  2  via conductors  111 A and  111 B. Such current flow may cause unwanted temperature effects in the cornea  2  and interfere with achieving a maximum temperature within the collagen fibers in the mid-depth region  2 B of the cornea  2 . Accordingly, the dielectric layer  110 D is positioned between the conductors  111 A and  111 B and the cornea  2 . The dielectric layer  110 D may be sufficiently thin to minimize interference with microwave emissions and thick enough to prevent superficial deposition of electrical energy by flow of conduction current. For example, the dielectric layer  110 D may be a biocompatible material, such as Teflon, deposited to a thickness of about 0.002 inches. In general, an interposing layer, such as the dielectric layer  110 D, may be employed between the conductors  111 A and  111 B and the cornea  2  as long as the interposing layer does not substantially interfere with the strength and penetration of the microwave radiation field in the cornea  2  and does not prevent sufficient penetration of the microwave field and generation of a desired heating pattern in the cornea  2 . 
     During operation, the distal end  110 B of the applicator  110  as shown in  FIG. 2  is positioned on or near the corneal surface  2 A. Preferably, the applicator  10  makes direct contact with the corneal surface  2 A. In particular, such direct contact positions the conductors  111 A and  111 B at the corneal surface  2 A (or substantially near the corneal surface  2 A if there is a thin interposing layer between the conductors  111 A and  111 B and the corneal surface  2 A). Accordingly, direct contact helps ensure that the pattern of microwave heating in the corneal tissue has substantially the same shape and dimension as the gap  111 C between the two microwave conductors  111 A and  111 B. An annulus is a preferred heating pattern because the inner diameter of the heated annulus can be selected to be sufficiently large so as to avoid heating the central cornea overlying the pupil. 
     The advantages of direct contact between the applicator  10  and the corneal surface  2 A may be reduced by the presence of a layer of fluid coolant which may exist therebetween. Rather than creating an annular heating pattern with dimensions equal to that of the gap between the conductors  111 A and  111 B, the presence of such a fluid layer may cause a less desirable circle-shaped microwave heating pattern in the cornea  2  with a diameter less than that of the inner conductor  111 B. Therefore, embodiments of the present invention do not require a flow of coolant or a cooling layer to exist over the corneal surface  2 A during the application of energy to the cornea  2 . In particular, the short pulses from the coolant delivery element  112  may apply a coolant that evaporates from the corneal surface before the application of the microwave energy and thus does not create a fluid layer that would interfere with the desired microwave pattern. 
     Embodiments may employ a vacuum passageway  114  operably connected to a vacuum source  130 . The vacuum passageway  114  may have an opening  114 A that is positioned near the corneal surface  2 A and opens to the interior of the applicator  110 . The vacuum source  130  may be used to draw any coolant, or unwanted fluid layer, from the corneal surface  2 A before the microwave energy is applied to the cornea  2 . In this case, the vacuum source  130  also draws the fluid to a waste receptacle (not shown). 
     The application of coolant and the subsequent evaporation of coolant may cause the pressure to increase within the applicator  110 . In particular, the applicator  110  may have an outer surface  110 C that may define a substantially enclosed assembly, especially when the distal end  110 B is placed in contact with the corneal surface  2 A. As shown in  FIG. 2 , the substantially enclosed assembly contains the electrical conducting element  111 , the coolant delivery element  112 , the coolant supply  113 , as well as the vacuum passageway  114 . The pressure is more likely to increase within such an enclosed assembly. As the applicator  110  may be in contact with the corneal surface  2 A, the resulting pressure may act against the corneal surface  2 A. Therefore, to minimize the effects of this pressure on the corneal surface  2 A, embodiments may employ a pressure relief mechanism for removing excess pressure that may occur in the applicator  110 . 
     In addition to the functions of the vacuum passageway  114  discussed previously, the vacuum passageway  114  with opening  114 A may also act as a pressure relief mechanism for the applicator  110 . As such, the pressure in the applicator  110  may be lowered by activating the vacuum source  130 . Alternatively, as shown in  FIG. 3A , the applicator  110  may include any type of pressure relief valve  118  that opens up the interior of the applicator  110  to the environment external to the applicator  110  when the pressure in the applicator  110  rises to a certain level. As another alternative shown in  FIG. 3B , the applicator  110  may simply employ a vent passage  119  that places the interior of the applicator  110  in communication with the environment external to the applicator  110 , in which case the pressure interior will generally be in equilibrium with the external area. 
     As  FIG. 2  further illustrates, the vacuum passageway  114  also passes through the dielectric material  110 D and has an opening  114 B at the distal end  110 B. While the opening  114 A opens to the interior of the applicator  110 , the opening  114 B opens to the corneal surface  2 A which is positioned at the distal end  110 B. With the opening  114 B positioned at the corneal surface  2 A, the vacuum passageway  114  with the vacuum source  140  helps the applicator  110  to maintain a fixed position relative to cornea  2  during treatment. The vacuum source  130  may apply a controlled amount of suction to the corneal surface  2 A to ensure that the applicator surface at the distal end  110 B has a firm and even contact with the cornea  2 . 
     Referring now to the cross-sectional view illustrated in  FIG. 4 , another embodiment of the present invention employs an applicator  210 , which includes an optical energy conducting element  211 , a micro-controlled coolant delivery system  212 , as well as a coolant supply  213 . 
     The optical energy conducting element  211  is operably connected to an optical energy source  220 , for example, via conventional optical fiber. The optical energy source  220  may include a laser, a light emitting diode, or the like. The optical energy conducting element  211  extends to the distal end  210 B from the proximal end  210 A, where it is operably connected with the optical source  220 . The optical energy conducting element includes an optical fiber  211 A. Thus, the optical fiber  211 A receives optical energy from the optical energy source  220  at the proximal end  210 A and directs the optical energy to the distal end  210 B, where the cornea  2  of an eye  1  is positioned. A controller  240  may be operably connected to the optical energy source  220  to control the delivery, e.g. timing, of the optical energy to the optical conducting element  211 . The optical energy conducting element  211  irradiates the cornea  2  with the optical energy and generates heat for appropriately shrinking collagen fibers in the mid-depth region  2 B of the cornea  2 . As also illustrated in  FIG. 4 , the optical conducting element may optionally include an optical focus element  212 B, such as a lens, to focus the optical energy and to determine the pattern of irradiation for the cornea  2 . 
     As  FIG. 4  illustrates, the coolant delivery system  212  may be positioned adjacent to the optical energy conducting element  211 . The coolant delivery system  212 , which is in fluid communication with the coolant supply  213 , delivers micro-controlled pulses of coolant, or cryogen, from the coolant supply  213  to the corneal surface  2 A. Such pulses of coolant may be applied before and/or after energy is applied to the cornea  2  with the optical energy source  220  and the optical energy conducting element  211 . 
       FIG. 4  further illustrates another technique for delivering pulses of coolant to the corneal surface  2 A. In particular, the pulse of coolant may be drawn from the coolant delivery element  212  by creating an area of low pressure at or near the distal end  210 B, where the corneal surface  2 A is positioned. As shown in  FIG. 4 , the applicator  210  may have a vacuum passageway  214 , such as a tube structure, which is connected to the vacuum source  230 . The vacuum passageway  214  has an opening  214 A which is positioned at or near the distal end  210 B to create the area of low pressure. To enhance the applicator&#39;s ability to create this low pressure area, the applicator  210 , as illustrated in  FIG. 4 , may include a contact element  215  that defines a small enclosure in which the area of low pressure can be created. 
     In particular,  FIG. 4  shows that the applicator  210  includes a contact element  215  at the distal end  210 B which makes contact with the corneal surface  2 A. The contact element  215  has a housing  215 A with a cavity  215 B. The housing  215 A has an opening  215 C at the distal end  210 B of the applicator  210 , so that the cavity  215 B is exposed to the distal end  210 B. As such, the contact element  215  forms an enclosure over the cornea  2  when it is positioned over the cornea  2 . As shown further in  FIG. 4 , the nozzle structure  212 A of the coolant delivery element  212  is received by the contact element  215  and the opening  212 B opens to the cavity  215 B. In some embodiments, the coolant delivery system  212  simply places the coolant supply in communication with the contact element  215  via structure  212 A. While one coolant delivery element  212  is illustrated in  FIG. 4 , it is understood that more than one coolant delivery element  212  may be employed by the applicator  210 . The vacuum passageway  214  is also received by the contact element, where the opening  214 A opens to the cavity  215 B. Accordingly, when the contact element  215  is positioned over the corneal surface  2 A to form an enclosure, the vacuum source  240  may be operated to create a near vacuum or low pressure in the cavity  215 B, which in turn draws the coolant through the nozzle structure  212 A toward the corneal surface  2 A positioned at the opening  215 C. The controller  240  may be operably connected to control the vacuum source  240  to cause micro-controlled pulses of coolant to be drawn from the coolant delivery element  212 . 
     Of course, it is understood that in other embodiments, the contact element  215  may be employed with a coolant delivery element  212  that employs a solenoid valve, or other actuator, and does not require the vacuum source  230 . As such, the controller  140  may electronically control the solenoid valve, or other actuator, to deliver the coolant to the corneal surface  2 A. 
     The application of coolant to the corneal surface  2 A and the subsequent evaporation of coolant may cause the pressure to increase within the cavity  215 A of the contact element  215 . As the contact element  215  is positioned against the corneal surface  2 A, the resulting pressure may act against the corneal surface  2 A. Therefore, to minimize the effects of this pressure on the corneal surface  2 A, embodiments may employ a pressure relief mechanism for removing excess pressure that may occur in the applicator  210 . 
     In addition to providing a way to initiate micro-controlled pulses of coolant, the vacuum passageway  214  may also act as a pressure relief mechanism for the applicator  210 . As such, the pressure in the applicator  210  may be lowered by activating the vacuum source  230 . Alternatively, as shown in  FIG. 5A , the applicator  210  may include any type of pressure relief valve  218  that opens up the interior of the applicator  210  to the environment external to the applicator  210  when the pressure in the applicator  210  rises to a certain level. As another alternative shown in  FIG. 5B , the applicator  210  may simply employ a vent passage  219  that places the interior of the applicator  210  in communication with the environment external to the applicator  210 , in which case the interior pressure will generally be in equilibrium with the external area. Of course, as there is no vacuum source shown in the embodiments of  FIGS. 5A and 5B , the coolant delivery element  212  requires another element such as a solenoid valve, or other actuator, to deliver the pulses of coolant. 
     As further shown in  FIG. 4 , the contact element  215  also receives the optical conducting element  211 , so that the applicator  210  can deliver the optical energy from the optical energy source  220  to the cornea  2  at the distal end  210 B.  FIG. 4  shows that the optical focus element  211 B is connected to the contact element  215 . 
     Advantageously, the contact element  215  may act as an additional heat sink for drawing heat from the corneal surface  2 A, as the contact element  215  is in direct contact with the corneal surface  2 A. In particular, the contact element may be formed from a heat conducting material, such as a metal. In general, other heat sinks, such as metal applicator walls  410 C, may be employed with embodiments of the present invention to provide further heat transfer from the corneal surface  2 A. 
     As  FIG. 4  further illustrates, the vacuum passageway  214  also has an opening  214 B at the distal end  210 B. While the opening  214 A opens to the cavity  215 B of the contact element  215 , the opening  214 B opens to the corneal surface  2 A which is positioned at the distal end  110 B. With the opening  214 B positioned at the corneal surface  2 A, the vacuum passageway  214  with the vacuum source  240  helps the applicator  210  to maintain a fixed position relative to cornea  2  during treatment. The vacuum source  230  may apply a controlled amount of suction via opening  214 B to the corneal surface  2 A to ensure that applicator surface at the distal end  210 B has a firm and even contact with the cornea  2 . 
     Referring now to the cross-sectional view illustrated in  FIG. 6 , another embodiment of the present invention is illustrated. In particular, the embodiment of  FIG. 6  illustrates an applicator  310  which employs a monopole conducting element  311  for conducting energy to the cornea  2 . 
     The monopole conducting element  311  is operably connected to an electrical energy source  320 , which may provide a radio frequency (RF) electrical energy. The monopole  311  extends to the distal end  310 B from the proximal end  310 A, where it is operably connected with the electrical energy source  320 . The monopole conducting element  311  may have a needle-like shape at the distal end  310 B, which is designed to contact or penetrate the cornea  2 . When the applicator is positioned to place the monopole  311  into contact with the eye  1 , the eye  1 , i.e. the body, acts as a backplane to complete the circuit. Accordingly, the monopole  311  may receive the electrical energy generated at the electrical energy source  320  and conduct electrical energy to the cornea  2  of an eye  1 . As a result, heat is generated within the cornea  2  to shrink selected collagen fibers in the mid-depth region  2 B of the cornea  2  and to reshape the cornea  2 . A controller  340  may be operably connected to the electrical energy source  320  to control the delivery, e.g. timing, of the electrical energy to the monopole  311 . 
     Other aspects of the embodiment of  FIG. 6  are similar to the embodiments described previously. In particular, as  FIG. 6  illustrates, the applicator  310  also employs a micro-controlled coolant delivery system  312  as well as a coolant supply  313 . The micro-controlled coolant delivery system  312  is positioned adjacent to the monopole  311 . The coolant delivery element  312  may employ a nozzle structure  312 A with an opening  312 B directed at the distal end  310 B. A solenoid valve, or other actuator, may be employed to create the pulses of coolant. The controller  340  may electronically control the solenoid valve, or other actuator, to deliver the coolant to the corneal surface  2 A. As such, the micro-controlled coolant delivery system  312 , which is in fluid communication with the coolant supply  313 , operates in a manner similar to the coolant delivery system  12  in  FIG. 1 . In other words, pulses of coolant, or cryogen, from the coolant supply  313  are preferably applied to the corneal surface  2 A before and after the energy is applied to the cornea  2 . 
     As also shown in  FIG. 6 , the applicator  320  may include a vacuum passageway  314  with an opening  314 A positioned at or near the distal end  310 B. The vacuum passageway  314  is operably connected to a vacuum source  330 , which may be controlled by the controller  340 . Similar to other embodiments described previously, the vacuum source  340  and the vacuum passageway  314  may be operated to relieve pressure created by the delivery of coolant from the coolant delivery element  312 . Alternatively, a pressure relief valve or a vent passage may be employed to act as the pressure relief element, in a manner similar to embodiments described previously. 
     In addition, as further shown in  FIG. 6 , the vacuum passageway  314  may also have an opening  314 B that opens to the corneal surface  2 A which is positioned at the distal end  310 B. With the opening  314 B positioned at the corneal surface  2 A, the vacuum passageway  314  with the vacuum source  340  creates suction between the applicator  110  and the corneal surface  2 A to maintain the applicator  310  in a fixed position relative to cornea  2  during treatment. 
     In general, any arrangement of vacuum openings operably connected to a vacuum source may be employed to keep embodiments of the present invention in position over the corneal surface during treatment. For example,  FIG. 7A  shows an applicator  410  which is positioned over the cornea  2  with a vacuum ring  417 . Like the applicators described above, the applicator  410  includes an energy conducting element  411 , such as those discussed previously, which extends from the proximal end  410 A to the distal end  410 B of the applicator  410 . The energy conducting element  411  is operably connected to an energy source  420  at the proximal end  410 A. Operation of the energy source  420  causes energy to be conducted through the energy conducting element  420  and heat to be generated at the distal end  410 B. As such, the vacuum ring  417  positions the distal end  410 B of the applicator  410  over the cornea  2  to enable the energy conducting element  411  to generate heat at the cornea  2 . In particular, the heat is applied to targeted collagen fibers in a mid-depth region  2 B of the cornea  2 , thereby shrinking the collagen fibers and reshaping the cornea  2  to improve vision through the eye  1 . 
     As shown further in  FIGS. 7A and 7B , the vacuum ring  417  has a substantially annular structure and receives the energy conducting element  411  coaxially through a ring passage  417 A. The vacuum ring  417  creates a vacuum connection with the corneal surface  2 A to fix the energy conducting element  411  to the corneal surface  2 A. The vacuum ring  417  may include an interior channel  417 C which is operably connected to the vacuum source  430  via connection port  417 B. The vacuum ring  417  may also include a plurality of openings  417 D which open the interior channel  417 B to the corneal surface  2 A. Therefore, when the openings  417 D are positioned in contact with the corneal surface  2 A and the vacuum source  430  is activated to create a near vacuum or low pressure within the interior channel  417 C, the openings  417 D operate to suction the vacuum ring  417  and the applicator  410  to the corneal surface  2 A. In this case, the vacuum source  430  may be a syringe or similar device. 
     In some embodiments, the energy conducting element  411  and the vacuum ring  417  may be separate components which may be detachably coupled to each other. Thus, as shown in  FIG. 7A , a separate energy conducting element  411  may be slidingly received by the vacuum ring  417  into the coaxial position. Any coupling technique, such as a mechanical attachment, may be employed to keep the energy conducting element  411  stably positioned within the vacuum ring  417 . The vacuum ring  417  may be positioned on the corneal surface  2 A before it receives the energy conducting element  411 , or alternatively, the electrical conducting element  411  may be combined with the vacuum ring  417  before the combination is positioned on the corneal surface  2 A. 
     In alternative embodiments, the energy conducting element  411  and the vacuum ring  417  may be non-detachably fixed to each other. 
     Other aspects of the embodiment of  FIG. 7  are similar to the embodiments described previously. In particular, as  FIG. 7  illustrates, the applicator  410  also employs a micro-controlled coolant delivery system  412  as well as a coolant supply  413 . The coolant delivery element  412  may employ a nozzle structure  412 A with an opening  412 B directed at the distal end  410 B. A solenoid valve, or other actuator, may be employed to create the pulses of coolant. The controller  440  may electronically control the solenoid valve, or other actuator, to deliver the coolant to the corneal surface  2 A. As such, the micro-controlled coolant delivery system  412 , which is in fluid communication with the coolant supply  413 , operates in a manner similar to the coolant delivery system  12  in  FIG. 1 . In other words, pulses of coolant, or cryogen, from the coolant supply  413  are preferably applied to the corneal surface  2 A before and after the energy is applied to the cornea  2 . 
     The embodiments described herein may all employ sensors to measure physical variables of the eye. For example, in one embodiment,  FIG. 1  depicts a plurality of sensors  16  which are discretely positioned at and about the distal end  10 B of the applicator  10 . The sensors may be operably connected to the controller  40  (not shown) to allow the data to be stored and/or communicated to operators. As a further example, the embodiment of  FIGS. 7A and 7B  employs an arrangement of sensors  416  on the vacuum ring  417  as the vacuum ring  417  makes direct contact with the corneal surface  2 A. In other embodiments, sensors may be more broadly incorporated into a surface at the distal end of the applicator, such as the dielectric layer  110 D in  FIG. 2 . Typically, the sensors are placed in contact with the cornea and provide measurements for various areas of the cornea. In general, the sensors may include devices that are formed as parts of the applicator and/or external devices that are separate from the applicator. The sensors may be microelectronic devices, including, but not limited to, infrared detectors that measure temperature, thin film or microelectronic thermal transducers, mechanical transducers such as a piezoresistive or piezoelectric devices, or force-sensitive quartz resonators that quantify corneal elongation or internal pressure. 
     In general, the sensors may provide information that is used to prepare the systems before treatment, provide feedback during treatment to ensure proper application of treatment, and/or measure the results of the treatment. 
     The cornea and eye have one or more variable physical properties that may be affected by the application of energy and the resulting increase in temperature. The sensors may directly or indirectly measure these physical variables and provide a sensor signal to processing circuitry, such as the controllers  40 ,  140 ,  240 , and  340  described above. The controller may analyze the measurements to determine if and when the treatment has achieved the desired effects. Processing circuitry may also generate a stop signal that terminates treatment when a specified physical variable achieves a predetermined value or falls within a predetermined range. In some embodiments, to avoid thermal damage to the corneal epithelium, and the endothelium, program instructions for the controller may include a safety mechanism that generates a stop signal when the application of heat energy exceeds certain parameters, e.g. time limits. 
     The embodiments described herein may also include disposable and replaceable components, or elements, to minimize cross-contamination and to facilitate preparation for procedures. In particular, components that are likely to come into contact with the patient&#39;s tissue and bodily fluids are preferably discarded after a single use on the patient to minimize cross-contamination. Thus, embodiments may employ one or more use indicators which indicate whether a component of the system has been previously used. If it is determined from a use indicator that a component has been previously used, the entire system may be prevented from further operation so that the component cannot be reused and must be replaced. 
     For example, in the embodiment of  FIG. 1 , a use indicator  50  is employed to record usage data which may be read to determine whether the applicator  10  has already been used. In particular, the use indicator  50  may be a radio frequency identification (RFID) device, or similar data storage device, which contains usage data. The controller  40  may read and write usage data to the RFID  50 . For example, if the applicator  10  has not yet been used, an indicator field in the RFID device  50  may contain a null value. Before the controller  40  delivers energy from the energy source  20  to the energy conducting element  11 , it reads the field in the RFID device  50 . If the field contains a null value, this indicates to the controller  40  that the applicator  10  has not been used previously and that further operation of the applicator  10  is permitted. At this point, the controller  40  writes a value to the field in the RFID device  50  to indicate that the applicator  10  has been used. When a controller  40  later reads the field in the RFID device  50 , the non-null value indicates to the controller  40  that the applicator  10  has been used previously, and the controller will not permit further operation of the applicator  10 . Of course, the usage data written to the RFID device  50  may contain any characters or values, or combination thereof, to indicate whether the component has been previously used. 
     In another example, where the applicator  410  and the vacuum ring  417  in the embodiment of  FIG. 7A  are separate components, use indicators  450 A and  450 B may be employed respectively to indicate whether the application  410  or the vacuum ring  417  has been used previously. Similar to the use indicator  50  described previously, the use indicators  450 A and  450 B may be RFID devices which the controller  440  may access remotely to read or write usage data. Before permitting operation of the applicator  410 , the controller  40  reads the use indicators  450 A and  450 B. If the controller  440  determines from the use indicators  450 A and  450 B that the applicator  410  and/or the vacuum ring  417  has already been used, the controller  440  does not proceed and does not permit further operation of the applicator  410 . When the applicator  410  and the vacuum ring  417  are used, the controller  440  writes usage data to both use indicators  450 A and  450 B indicating that the two components have been used. 
     In operation, a physician or other operator manually accesses a device, such as a computer keyboard, that interfaces with a controller, such as the controllers  40 ,  149 ,  240 , and  340 . The interface enables the operator to set up and/or initiate treatment. The system may request input, such as a predetermined amount of diopter correction that is required for a particular patient, baseline measurements of physical variables, astigmatism measurements, parameters for energy conduction to the cornea, timing and sequence information for the application of heat energy and pulses of coolant, and/or target values for physical variables that will be modified by treatment. The controller accepts program instructions that may access user input data or program selections from the interface and causes the system to implement a selected vision correction treatment. 
     In general, the controller may be a programmable processing device that executes software, or stored instructions, and that may be operably connected to the devices described above. In general, physical processors and/or machines employed by embodiments of the present invention for any processing or evaluation may include one or more networked or non-networked general purpose computer systems, microprocessors, field programmable gate arrays (FPGA&#39;s), digital signal processors (DSP&#39;s), micro-controllers, and the like, programmed according to the teachings of the exemplary embodiments of the present invention, as is appreciated by those skilled in the computer and software arts. The physical processors and/or machines may be externally networked with the image capture device, or may be integrated to reside within the image capture device. Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as is appreciated by those skilled in the software art. In addition, the devices and subsystems of the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as is appreciated by those skilled in the electrical art(s). Thus, the exemplary embodiments are not limited to any specific combination of hardware circuitry and/or software. 
     Stored on any one or on a combination of computer readable media, the exemplary embodiments of the present invention may include software for controlling the devices and subsystems of the exemplary embodiments, for driving the devices and subsystems of the exemplary embodiments, for enabling the devices and subsystems of the exemplary embodiments to interact with a human user, and the like. Such software can include, but is not limited to, device drivers, firmware, operating systems, development tools, applications software, and the like. Such computer readable media further can include the computer program product of an embodiment of the present inventions for performing all or a portion (if processing is distributed) of the processing performed in implementing the inventions. Computer code devices of the exemplary embodiments of the present inventions can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes and applets, complete executable programs, and the like. Moreover, parts of the processing of the exemplary embodiments of the present inventions can be distributed for better performance, reliability, cost, and the like. 
     Common forms of computer-readable media may include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other suitable magnetic medium, a CD-ROM, CDRW, DVD, any other suitable optical medium, punch cards, paper tape, optical mark sheets, any other suitable physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other suitable memory chip or cartridge, a carrier wave or any other suitable medium from which a computer can read. 
     While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto. The present invention may be changed, modified and further applied by those skilled in the art. Therefore, this invention is not limited to the detail shown and described previously, but also includes all such changes and modifications.