Abstract:
Systems and methods stabilize corneal tissue after treatment of the corneal tissue. For example, thermokeratoplasty may be applied to the corneal tissue to address disorders associated with abnormal shaping of the cornea. To stabilize the desired structural changes caused by the treatment, embodiments apply ophthalmic formulations that help to inhibit wound healing. Wound healing may occur in response to the application of the treatment and may produce further structural changes that mitigate or alter the desired effects of the treatment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/256,714, which was filed on Oct. 30, 2009, the contents of which are entirely 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 systems and methods for stabilizing corneal tissue after treatment of the corneal tissue. 
     2. Description of Related Art 
     A variety of eye disorders, such as myopia, hyperopia, astigmatism, and keratoconus 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 excessive. Parallel rays of light are focused in front of the retina, producing a blurred image of objects at a distance. Flattening aspects of the cornea&#39;s shape about the visual axis through keratoplasty decreases the refractive power of an eye with myopia and causes the image to be properly focused at the retina. 
     In another example, with hyperopia, the shape of the cornea causes the refractive power of an eye to be insufficient. Parallel rays of light are focused behind the retina, producing a blurred image of objects proximate to the eye. Steepening or bulging aspects of the cornea&#39;s shape about the visual axis through keratoplasty, such as by removing a ring of tissue from the outer edge of the cornea, increases the refractive power of the eye, and causes the image to be properly focused at the retina. 
     With astigmatism and keratoconus, the surface of the cornea or the lens behind the cornea is not spherically shaped, and is instead shaped irregularly. An astigmatic eye is often shaped like the back of a spoon, causing parallel rays of light to focus at two separate points, creating a distorted image, and can accompany hyperopia or myopia. A keratoconus eye has more of a conical shape than a normal, gradual curve. In order to cause the image to be properly focused at the retina, the cornea can be given an overall more spherical shape using keratoplasty. For example, with respect to keratoconus, the abnormally steep curves in the cornea can be flattened. 
     Invasive surgical procedures, such as laser-assisted in-situ keratomileusis (LASIK), may be employed to reshape the cornea. However, such surgical procedures may typically require an extended healing period after surgery. Furthermore, such surgical procedures may involve complications caused by the cutting of a flap in the cornea to provide access to the stromal layer, such as dry eye syndrome caused by the severing of corneal nerves. 
     Many other serious, risky complications may arise in LASIK due to the cutting of the flap, such as striae, ectasia, buttonhole flap, and free flap. For example, striae, or wrinkles in the corneal flap, can occur following surgery due to the improper replacement of the flap during surgery and/or movement of the flap caused by normal activity post-surgery. Although it does not require correction in some cases, in others surgical correction is necessary to re-lift and smooth the flap. 
     In ectasia, the corneal flap is cut too deep and/or too much tissue is removed, causing the remaining corneal tissue can become too thin. The thinness of corneal tissue can cause it to weaken under normal, everyday pressure, causing it to bulge or deform. Such deformation can itself cause residual myopia and astigmatism that may require contact lenses to be worn despite the LASIK surgery. In severe cases, a corneal transplant may be necessary. 
     Buttonhole flap can also result from corneal flap cutting, which refers to a tear, uneven cut or rip in the flap. This can be caused by a variety of factors, including improper placement of the blade, the use of an excessively worn blade, or the use of an improperly sized blade. In other cases, the flap rips when it is placed back over the eye at the end of surgery. This can result in astigmatism and scarring that can worsen vision beyond its original state, and requires surgical correction once the flap has time to heal, usually around  6  months post-op. 
     Free flap is caused by the complete removal of the corneal flap. In other words, no connecting hinge is maintained between the flap and the eye. This can be caused by a loss of suction at the blade as it is creating the flap or by operator error. In some cases, the surgery can be completed as usual and the flap replaced without the hinge. However, this may increase the risk of other flap complications such as striae or buttonhole flap resulting from the increased handling required to remove and replace the flap without a hinge. In addition, the flap can suffer irreparable harm or be lost entirely, requiring that a corneal transplant be performed on the patient. 
     Thermokeratoplasty, on the other hand, is a noninvasive procedure that eliminates the need to cut a flap in the eye to correct corneal abnormalities. Thermokeratoplasty may be used to correct the vision of persons who have disorders associated with abnormal shaping of the cornea, such as myopia, hyperopia, astigmatism, and keratoconus, as described above. 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 according to particular patterns, including, but not limited to, circular or annular patterns, may cause aspects of the cornea to flatten and improve vision in the eye, without resorting to surgical intervention. 
     SUMMARY OF THE INVENTION 
     Embodiments according to aspects of the present invention provide systems and methods for stabilizing corneal tissue after treatment of the corneal tissue. For example, thermokeratoplasty may be applied to the corneal tissue to address disorders associated with abnormal shaping of the cornea. To stabilize the desired structural changes caused by the treatment, embodiments apply ophthalmic formulations that help to inhibit wound healing. Wound healing may occur in response to the application of the treatment and may produce further structural changes that mitigate or alter the desired effects of the treatment. 
     In some embodiments, the ophthalmic formulation applied to help inhibit wound healing may include Interleukin 10 (IL-10). IL-10, also referred to as human cytokine synthesis inhibitory factor (CSIF), is an anti-inflammatory cytokine that enhances antibody responses within humans. As recognized by one skilled in the art, cytokine consists of small, cell-signaling protein molecules that are produced by cells of the nervous and immune systems. IL-10 is in the four-α-helix bundle family, meaning that it has a three-dimension structure with four bundles of α-helices. 
     In other embodiments, the ophthalmic formulation may include Transforming Growth Factor beta 3 (TGFb3). TGFb3 is a protein produced by platelets, macrophages and fibroblasts that regulates the healing process in humans. TGFb3 often interacts, or binds together, with the Transforming Growth Factor beta receptor 2 (TGFbr2), a single-pass receptor and tumor suppressor gene. In further embodiments, the ophthalmic formulation may include Mannose 6-phosphate (M6P). M6P is a molecule bound by lectin in the immune system, and is expressed by the molecular formula C 6 H 13 O 9 P. 
     It is understood, however, that embodiments of the present invention are not limited to the use of IL-10, TGFb3, or M6P. In general, embodiments of the present invention can apply any drug that inhibits healing pathways to prevent wound healing after treatment of the eye, e.g., thermally induced shape change in the cornea. 
     According to one embodiment of the invention, a method for applying therapy to an eye is described. The method comprises the steps of positioning an electrical energy conducting element in contact with a surface of an eye; applying electrical energy to an area of the eye with the electrical energy conducting element, the electrical energy reshaping the area of the eye to a new shape, the new shape being determined by a pattern of energy application; and applying a wound healing inhibitor to the surface of the eye, the wound healing inhibitor reducing at least one of corneal haze and central islands of the eye. 
     In another embodiment of the invention, a system for applying therapy to an eye is described. The system comprises an electrical energy source; an electrical energy conducting element in contact with the electrical energy source, the electrical energy conducting element having a proximal end configured to receive electrical energy generated by the electrical energy source, and a distal end configured to apply electrical energy; a wound healing inhibitor configured to reduce at least one of corneal haze and central islands of an eye; and a wound healing inhibitor delivery element in contact with the wound healing inhibitor. 
     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 an example system for applying heat to a cornea of an eye to cause reshaping of the cornea. 
         FIG. 2A  illustrates a high resolution image of a cornea after heat has been applied. 
         FIG. 2B  illustrates another high resolution images of the cornea of  FIG. 2A . 
         FIG. 2C  illustrates a histology image of the cornea of  FIG. 2A . 
         FIG. 2D  illustrates another histology image of the cornea of  FIG. 2A . 
         FIG. 3  illustrates an example application of a drug to inhibit wound healing according to aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an example system for applying energy to a cornea  2  of an eye  1  to generate heat and cause reshaping of the cornea. In particular,  FIG. 1  shows an applicator  110  with an electrical energy conducting element  111  that 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 energy to the 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 400 MHz to 3000 MHz, and more specifically at a frequency of around 915 MHz or 2450 MHz. As used herein, the term “microwave” may correspond to a frequency range from about 10 MHz to about 10 GHz. 
     As further illustrated in  FIG. 1 , the electrical energy conducting element  111  may include two microwave conductors, or electrodes,  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 outer conductor  111 A. With the inner passage, the conductor  111 A may have a substantially tubular shape. The outer conductor  111 A and inner conductor  111 B may be formed, for example, of aluminum, stainless steel, brass, copper, other metals, coated 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  110 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 systems, 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 . 
     A controller  140  may be employed to selectively apply the energy any number of times according to any predetermined or calculated sequence. The controller  140  may include a computer device to control the application of energy according to instructions provided via a computer-readable storage medium. In addition, the controller  140  may include a monitor and keyboard, or other user interface devices for receiving instructions from an operator. 
     Depending on the instructions, the energy may be applied for any length of time. Furthermore, the magnitude of energy being applied may also be varied. Adjusting such parameters for the application of energy determines the extent of changes that are brought about within the cornea  2 . 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  FIG. 1 , 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 (epithelium)  2 A and the conductors  111 A and  111 B. In some systems, 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  110 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 fibrils in a 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 deposited to a thickness of about 51 μm (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 . The dielectric material may be elastic, such as polyurethane and silastic, or nonelastic, such as Teflon® and polyimides. The dielectric material may have a fixed dielectric constant or varying dielectric constant by mixing materials or doping the sheet, the variable dielectric being spatially distributed so that it may affect the microwave hearing pattern in a customized way. The thermal conductivity of the material may have fixed thermal properties (thermal conductivity or specific heat), or may also vary spatially, through mixing of materials or doping, and thus provide a means to alter the heating pattern in a prescribed manner. Another approach for spatially changing the heating pattern is to make the dielectric sheet material of variable thickness. The thicker region will heat less than the thinner region and provides a further means of spatial distribution of microwave heating. 
     The system of  FIG. 1  is provided for illustrative purposes only, and other systems may be employed to apply energy to cause reshaping of the cornea. Other systems are described, for example, in U.S. patent application Ser. No. 12/208,963, filed Sep. 11, 2008, which is a continuation-in-part application of U.S. patent application Ser. No. 11/898,189, filed on Sep. 10, 2007, the contents of these applications being entirely incorporated herein by reference. 
     As described in U.S. patent application Ser. No. 12/208,963, a cooling system may be employed in combination with the applicator  110  to apply coolant to the cornea  2  and determine how the energy is applied to the cornea  2 . For example, the applicator  110  may include, internally or externally, at least one coolant delivery element in fluid communication with a coolant supply, or reservoir. The coolant delivery element delivers a coolant, or cryogen, from the coolant supply to the distal end of the applicator. In some embodiments, the coolant may be applied more directly to the dielectric layer  110 D disposed along the distal end  110 B, if the dielectric layer  110 D substantially encloses the distal end  110 B of the applicator  110 . In general, the applicator may be employed to apply coolant to selectively cool the surface  2 A of the cornea  2  positioned at the distal end  110 B. The delivery of coolant from the coolant delivery element 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 . 
     In operation, the distal end  110 B of the applicator  110  as shown in  FIG. 1  is positioned on or near the corneal surface  2 A. Preferably, the applicator  110  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, though a thin interposing dielectric layer  110 D may be disposed 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. 
     Prior to positioning of the applicator  110  in contact with the corneal surface  2 A, the corneal surface  2 A may be scanned to make a topographical map showing the shape and curvature of the surface of the cornea. Then, with the conductors  111 A and  111 B positioned flush with the corneal surface  2 A, the treatment may apply durations of microwave pulses to heat and reshape collagen and coolant pulses to protect the corneal surface. In one aspect, the treatment attempts to shrink the collagen in the cornea  2  and form a precisely controlled annular lesion in approximately the upper 150 μm of the stroma. The microwave treatment raises the temperature of an annulus, just below the surface of the cornea, to a temperature in the range of approximately 60 to 75° C. Using evaporative surface cooling techniques, the system cools the surface of the cornea during treatment to isolate and protect the epithelium and Bowman&#39;s membrane from microwave heating. Thus, the treatment is noninvasive, as there is no cutting or penetration of the eye. In one example application, the applicator  110  predictably flattens the central cornea to achieve mild-to-moderate myopic correction (−0.5 to −3.5 diopters, D) without compromising the biomechanical integrity of the cornea. 
     Accordingly, embodiments according to aspects of the present invention may use microwave energy emitted from the applicator  110 , e.g., in a ring-shaped pattern, around the pupil to shrink stromal collagen and modify the dioptric power of the cornea, while a cooling system acts on the corneal surface to minimize thermal damage to the epithelium. In particular, electric field lines form a fringing pattern that extends into the corneal stroma to a depth determined by the applied power and applicator geometry. This electric field causes the polar water molecules to align themselves with the field; the rapid reversal of the sinusoidally-varying field causes frictional heating by these molecules as they rotate in place. This effect does not require a conduction current to flow through a point of electrical contact between a conductor and tissue; heating is caused by a displacement current. 
       FIGS. 2A-D  illustrate an example of the effect of applying heat to corneal tissue with a system for applying heat, such as the system illustrated in  FIG. 1 . In particular,  FIGS. 2A and 2B  illustrate high resolution images of cornea  2  after heat has been applied. As  FIGS. 2A and 2B  show, a lesion  4  extends from the corneal surface  2 A to a mid-depth region  2 B in the corneal stroma  2 C. The lesion  4  is the result of changes in corneal structure induced by the application of heat as described above. These changes in structure result in an overall reshaping of the cornea  2 . It is noted that the application of heat, however, has not resulted in any heat-related damage to the corneal tissue. 
     As further illustrated in  FIGS. 2A and 2B , the changes in corneal structure are localized and limited to an area and a depth specifically determined by an applicator as described above.  FIGS. 2C and 2D  illustrate histology images in which the tissue shown in  FIGS. 2A and 2B  has been stained to highlight the structural changes induced by the heat. In particular, the difference between the structure of collagen fibrils in the mid-depth region  2 B where heat has penetrated and the structure of collagen fibrils outside the region  2 B is clearly visible. Thus, the collagen fibrils outside the region  2 B remain generally unaffected by the application of heat, while the collagen fibrils inside the region  2 B have been rearranged and formed new bonds to create completely different structures. In other words, unlike processes, such as orthokeratology, which compress areas of the cornea to reshape the cornea via mechanical deformation, the collagen fibrils in the region  2 B are in an entirely new state. 
     In summary, energy is applied to a cornea through an applicator, such as the applicator  110  shown in  FIG. 1 , to generate heat that produces a desired reshaping of the cornea. Although the heat induces structural changes in the collagen fibrils of the cornea, the desired effects of reshaping the cornea may be mitigated or altered if the collagen fibrils continue to change after the desired reshaping has been achieved. In particular, further changes to the corneal structure may be caused by the wound healing response after the application of the energy to the cornea. The wound healing response may affect the final corneal shape and hence the refractive and visual outcome. In addition, the wound healing response may lead to the development of scar tissue having a lack of transparency, in addition to causing corneal haze and central islands. The degree to which the wound healing can be controlled determines whether the treatment actually yields the desired changes to the corneal shape. 
     Therefore, aspects of the present invention provide approaches for stabilizing the desired corneal structure and minimizing the effects of the wound healing that occur in response to the application of heat. Referring to  FIG. 3 , an example embodiment  300  according to aspects of the present invention is illustrated. Specifically, in step  310 , energy is applied to corneal tissue to generate heat-induced structural changes and a desired shape change, as described previously. For example, the applicator  110  of  FIG. 1  may be used to treat the cornea. 
     In step  320 , a wound healing inhibitor comprising an ophthalmic formulation is applied to the cornea to inhibit the wound healing. Inhibited wound healing may be exhibited by, for example, reduced or prevented corneal haze, central islands, and a lack of transparency in the eye, that may otherwise be caused without the application of the inhibitor. The wound healing inhibitor can be applied by, for example, an eye dropper or a drug application device, such as a bandage, that is removably attached to the eye. The ophthalmic formulation includes a drug  322 , which in some embodiments, may include Interleukin 10 (IL-10). In other embodiments, the drug  322  may include Transforming Growth Factor beta 3 (TGFb3), which may be recombinant or genetically engineered. 
     In another embodiment, the drug  322  may include Mannose 6-phosphate (M6P). The effects of M6P on corneal wound healing in rabbits following excimer laser photorefractive keratectomy (PRK) is described in G. Sutton, et al., Mannose 6-phosphate reduces haze following excimer laser photorefractive keratectomy, Lasers and Light, Vol. 7, No. 2/3, pp. 117-119 (1996), the contents of which are incorporated entirely herein by reference. In this study, a group of rabbits were exposed to identical excimer laser photorefractice keratectomy ablations and were treated with either a control drop of an M6P drop. A significant reduction in corneal haze was observed at 4 weeks in the M6P group compared to the control group. In addition, the M6P group had less subepithelial collagen. It is theorized that M6P acts by competing with latent Transforming Growth Factor beta (TGFb) at the Insulin Like Growth Factor II receptor. Although there are a number of growth factors which may affect the healing process, TGFb plays a key role. More specifically, TGFb2 of epithelial origin has been shown to be an inhibitor of stromal collegenase, which implies epithelial modulation of the underlying stromal wound healing. Indeed, neutralizing antibodies to TGFb can be used to modify wound healing. Thus, aspects of the present invention may apply drugs that control wound healing by determining TGFb activity. For example, a processor may be used to determine Transforming Growth Factor beta (TGFb) activity. In addition, the wound inhibitor delivery element can be adjusted based on the Transforming Growth Factor beta (TGFb) activity. 
     It is understood that embodiments of the present invention are not limited to the use of IL-10, TGFb3, or M6P. In general, embodiments of the present invention can apply any drug that inhibits healing pathways to prevent wound healing after treatment of the eye, such as treatment that thermally induces shape change in the cornea. 
     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 the spirit the invention reflected by the claims herein. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive.