Patent Publication Number: US-2019183677-A1

Title: Apparatus For Phototherapy Of The Eye

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/873,163, filed Jan. 17, 2018, which is a continuation of U.S. patent application Ser. No. 14/314,518, filed Jun. 25, 2014, which application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/839,016 filed Jun. 25, 2013, the disclosures of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present application relates generally to devices for applying light such as ultraviolet (“UV”) light to the cornea of the eye; to methods of manufacturing such devices; and to methods of applying phototherapy to the eye. 
     In humans and other mammals, the eye includes a clear, dome-shaped element referred to as the cornea disposed at the front of the eye. Light passes into the eye through the cornea and, after passing through other structures such as the iris and the lens of the eye, ultimately impinging on the retina. The light impinging on the retina is converted to neural impulses that are processed to form the visual images. The cornea and the lens refract the light passing through them. In a healthy eye, the refraction imparted by the cornea and the lens focuses the light on the retina. 
     Most of the light refraction required for the primary focusing on the retina is done by the cornea, with the lens making the accommodative changes to move focus from close to distant objects. Mismatches between the corneal curvature and the axial length of the eye, imperfections in the shape of the cornea, malpositions of the lens, and error in the vitreous of the eye can all lead to vision errors. For example, an eye that has a cornea that focuses the light in front of the retina (an eye with too much curvature relative to the axial length of the eye) suffers from myopia (also referred to as near-sightedness). Conversely, a cornea that is not curved enough for the axial length results in hyperopia (also referred to as far-sightedness), where the focal point is behind the retina. Astigmatism is an uneven curvature of the cornea with respect to the shape of the retina. All three conditions result in an out of focus image formed on the retina. Beyond these errors in curvature that affect healthy eyes, pathological conditions such as keratoconus and corneal ectasia result in unstable corneas and impaired vision. 
     Eyeglasses and contact lenses can correct conditions such as myopia, hyperopia and astigmatism by adding an artificial refractive element to the system. However, these devices impose some inconvenience on the patient. Accordingly, refractive surgical therapies such as radial keratotomy and laser ablation of the cornea have been developed. These procedures correct vision by reshaping the cornea so as to alter its refractive properties. However, these procedures have certain drawbacks and can have undesirable side effects. 
     In a technique known as orthokeratolgy, the cornea is mechanically reshaped by applying a rigid contact lens having a shape different from the existing shape of the cornea. The lenses are worn overnight. However, changes in shape induced by orthokeratology are temporary. They typically last only 24-48 hours, after which the cornea reverts to its original shape. 
     In yet another technique, the cornea can be reshaped by crosslinking fibers of collagen which form part of the cornea. The crosslinking can be performed by applying UV light to the cornea in conjunction with a chemical agent such as riboflavin. Typically, the UV light is applied by directing UV light from one or more light emitting diodes (“LEDs”) m into the patient&#39;s eye, substantially perpendicular to the surface of the cornea. The crosslinking strengthens the cornea and can also cause reshaping of the cornea Procedures of this type require that the patient keep the treated eye open for a prolonged period without blinking. This creates discomfort for the patient and also requires close monitoring by trained personnel to assure that the cornea remains hydrated. 
     It has also been proposed to apply crosslinking in conjunction with orthokeratology. In this approach, the crosslinking is performed after mechanical reshaping or while the cornea is held mechanically in the desired shape. The crosslinking acts to set the cornea and prevent reversion of the cornea to its original shape. For example, Mrochen et al., U.S. Published Patent Application No. 2008/0208177, proposes a thick, rigid mold equipped with an array of light emitting diodes or “LED&#39;s.” While the mold is applied to the cornea, the LED&#39;s emit UV light in the direction toward the surface of the cornea. The mold may include a diffuser plate interposed between the LED&#39;s and the cornea to make the light impinging on the cornea more uniform. In another variant, the array of LED&#39;s and the diffuser plate is replaced by a branching array of “optical light guides” extending to numerous points on the surface of the cornea. Structures of this type still require that the patient keep his or her eye open during the treatment, without blinking. 
     Chuck et al., U.S. Published Patent Application No. 2013/0211389, discloses a treatment device which incorporates radiation-emitting elements such as LEDs, along with the circuitry required to drive these elements, into a device having size and shape resembling a conventional contact lens. Using this device, the patient can blink or keep his or her eye shut while receiving crosslinking therapy. This provides a more comfortable patient experience, greatly reduces the risk of corneal dehydration during the therapy, and also reduces the need for constant monitoring of hydration by medical personnel. However, LEDs and circuitry incorporated into the device evolve heat during operation. Therefore, the power which can be applied by the device must be restricted. 
     BRIEF SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a device for applying light to the eye of a human or other mammalian subject. A device according to this aspect of the present invention desirably includes a contact lens structure having a first inner surface generally corresponding to the shape of the cornea. Optionally, the device may have a second interior surface corresponding to the shape of the sclera. The contact lens structure desirably includes an optically dispersive element. The optically dispersive element desirably is constructed and arranged so that light passing into the optically dispersive element in a direction generally parallel to the inner surface will be dispersed and at least some of the dispersed light will pass through the inner surface of the contact lens structure into the cornea. 
     The optically dispersive element may include an optically dispersive fiber. The optically dispersive fiber may be arranged in one or more loops encircling a central axis of the contact lens structure. Alternatively or additionally, the optically dispersive element may include an optically dispersive mass, and the mass may have an inner surface having a shape generally conforming to the shape of the cornea. In certain embodiments, the structure includes both an optically dispersive fiber and an optically dispersive mass. The optically dispersive fiber may be in optical communication with the optically dispersive mass, so that light dispersed by the fiber will pass into the mass, and will be further dispersed by the mass and pass into the cornea. Desirably, the structure includes a reflector that defines a cavity encompassing the dispersive mass. In one arrangement, a transmission optical fiber has a distal end disposed within the cavity, and the light is dispersed by the dispersive mass and passes out through an aperture in the reflector. 
     The entire contact lens structure may be formed as a shell generally conforming to the shape of the eye. The thickness of the shell may be similar to that of a conventional contact lens as, for example, less than about 1 mm thick. 
     A further aspect of the present invention provides methods of applying phototherapy to the eye of human or other mammalian subject. A method according to this aspect of the invention desirably includes directing light into a structure generally in the form of a shell similar in form and size to a contact lens, desirably less than 3 mm thick, overlying the eye and dispersing the light within the structure so that the dispersed light passes out of the structure and into the cornea of the eye. For example, the step of directing light into the contact lens structure may include directing light into the structure through a transmission fiber connected to the contact lens structure. The light may be UV light, and the method may further include the step of applying a photoactivated cross-linking agent to the eye so that the cross-linking agent is present when the light passes into the eye. The method desirably further includes the step of allowing the subject to close his or her eyelids over the contact lens structure while the light is being applied. 
     Methods and apparatus according to certain embodiments of the invention can provide effective phototherapy, such as effective cross-linking, without requiring the patient to keep his or her eye open during the procedure, or to lie down facing a light source. This greatly enhances the comfort and practicality of the procedure. Moreover, the methods and apparatus according to these embodiments of the invention do not require the complex and expensive apparatus used to direct light into the eye heretofore. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic perspective view depicting a component of a device in accordance with one embodiment of the invention. 
         FIG. 2  is a further diagrammatic perspective view depicting the component of  FIG. 1  in conjunction with another component. 
         FIG. 3  is a diagrammatic partially sectional perspective view depicting the components of  FIGS. 1 and 2  in conjunction with still further components of the device. 
         FIG. 4  is a fragmentary, diagrammatic sectional view depicting the components of  FIGS. 1-3  in conjunction with still further components of the device. 
         FIG. 5  is a diagrammatic sectional view depicting the device incorporating the components of  FIGS. 1-4 . 
         FIG. 6  is a diagrammatic plan view depicting the device of  FIG. 5 . 
         FIG. 7  is a diagrammatic sectional view depicting the device of  FIGS. 1-5  in conjunction with a human eye. 
         FIG. 8  is a diagrammatic plan view depicting a device in accordance with a further embodiment of the invention. 
         FIG. 9  is a view similar to  FIG. 7 , but depicting yet another embodiment of the invention. 
         FIG. 10  is a diagrammatic plan view depicting a device according to yet another embodiment of the invention. 
         FIG. 11  is a diagrammatic plan view of a device in accordance with yet another embodiment of the invention. 
         FIGS. 12 and 13  are diagrammatic, partially schematic block-diagram depictions of devices in accordance with still further embodiments of the invention. 
         FIG. 14  is a schematic diagram of a component used in the device of  FIG. 13 . 
         FIG. 15  is a schematic depiction of a device according to a further embodiment of the invention. 
         FIG. 16  is a circuit diagram of an element used in the device of  FIG. 15 . 
         FIGS. 17 and 18  are diagrammatic plan views of elements used in further embodiments of the invention. 
         FIG. 19  is a diagrammatic, partially sectional view of a device according to a further embodiment of the invention. 
         FIGS. 20 and 21  are fragmentary sectional views of the device shown in  FIG. 19 . 
         FIG. 22  is a view similar to  FIG. 20 , but depicting a device according to yet another embodiment of the invention. 
         FIG. 23  is a fragmentary, diagrammatic sectional view depicting a portion of a device according to a further embodiment of the invention. 
         FIG. 24  is a diagrammatic sectional view depicting a device according to a still further embodiment of the invention. 
         FIG. 25  is a diagrammatic sectional view depicting a device according to yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A device according to one embodiment of the invention incorporates a first optically dispersive element in the form of a radially dispersive optical fiber  20  ( FIG. 1 ). As used in this disclosure, the term “optically dispersive element” refers to an element that is adapted to scatter light propagating in a direction of propagation so that an appreciable portion of such light is redirected in directions transverse to the direction of propagation. The term “dispersive” is used herein interchangeably with the term “scattering”, and has the same meaning as discussed in the foregoing sentence. The term “radially dispersive optical fiber” refers to a fiber, such as fiber  20 , which is adapted to allow propagation of light along the length of the fiber while also scattering an appreciable portion of the light propagating along the fiber in directions transverse to the length of the fiber. 
     The degree of dispersion in an optical fiber can be stated in terms of its “extinction length.” With respect to a fiber, the extinction length as referred to in this disclosure is the length along the direction of propagation in which light transmitted from a starting point along the length of the fiber loses 90% its power. Stated another way, the extinction length of a fiber is the length of fiber over which 90% of the incoming light is dispersed and thus emitted out of the fiber in directions transverse to the length of the fiber. Radially dispersive optical fibers having essentially any desired extinction length are available from sources including Corning Glass Works of Corning, New York, USA. As further discussed below, the desired extinction length depends in part on the length of radially dispersive fiber incorporated into the device. However, typical designs incorporate optical fibers having extinction lengths on the order of 0.5-4 meters. 
     Fiber  20  is arranged in one or more loops extending around a central axis  22 . In the particular embodiment depicted, fiber  20  is arranged in a spiral of approximately two full turns constituting the loops. The inner turn  21   a  has an average diameter slightly larger than the diameter of an area of the cornea to be treated. Thus, the total length of fiber incorporated in the turns is about 25 mm Most typically, the ratio of the length of radially dispersive optical fiber incorporated in the one or more loops to the extinction length of the optical fiber is 0.05:1 to 0.3:1, most typically about 0.2:1 to 0.3:1. As further explained below, the ratio is selected in conjunction with other design features to enhance the uniformity of light distribution achieved by the system. 
     The end  23  of the inner turn  21   a  is referred to herein as the termination end of the dispersive fiber. Termination end  23  is covered by a coating  25  adapted to absorb UV light. The outer end of the outer turn  21   b  constitutes the input end of the fiber in the loops. The radially dispersive optical fiber includes a short stub  24  extending out from the outer end of the outer turn  21   b.  Stub  24 , and hence fiber  20 , is connected to the distal end of a conventional, substantially non-dispersive transmission optical fiber  26  by a splice  28 . For example, splice  28  may be a fusion splice made by fusing the ends of fibers  20  and  26  to one another or a mechanical coupling holding polished ends of the fibers in precise alignment with one another. Stub  24 , splice  28  and transmission fiber  26  are referred to collectively as the input fiber system. The input fiber system may be covered with a conventional jacket or other protective element (not shown), so as to protect it from physical damage. However, the distal portion of the input fiber system adjacent the loops, including any jacket covering this portion of the fiber system, desirably is of relatively small diameter as, for example, 0.6 mm or less and more preferably 0.25 mm or less. As explained below, this helps to minimize irritation to the patient&#39;s eyelids in use of the device. 
     The proximal end of transmission fiber  26  is releasably connected to a UV light source  30 , as by a conventional connector (not shown). Source  30  may be a conventional device such as a UV laser arranged to emit light at the desired wavelength for the therapy to be performed. Where the device is to be used in cross-linking of the cornea using riboflavin as a cross-linking agent, the light may be near UV light of 360 nm to 380 nm wavelength or blue light of about 425 nm to 475 nm wavelength. 
     The device further includes a fiber carrier  34  ( FIGS. 2, 3 ) formed from a transparent material, preferably a polymer such as an acrylic. The fiber carrier is shown as opaque in  FIG. 2  for illustrative purposes only. The transparent material of the fiber carrier will transmit UV light substantially without dispersion. 
     Fiber carrier  34  is generally in the form of a shallow dome with a concave interior surface  36 , a convex exterior surface  38 , and a hole  40  extending between the interior and exterior surfaces at the center of the dome. The fiber carrier  34  also defines a generally cylindrical edge surface  42  extending between the interior and exterior surfaces. As best seen in  FIG. 4 , the juncture between edge surface  42  and exterior surface  38  is provided with a radius  48  so that the edge surface  42  and exterior surface  38  merge gradually into one another. 
     The exterior surface  38  of the fiber carrier has a spiral groove defining an inner turn  46   a  and an outer turn  46   b  corresponding to the turns  21   a  and  21   b  of radially dispersive optical fiber  20 . The outer turn  46   b  of the spiral groove terminates at an opening  48  extending through edge surface  42  of the fiber carrier. Turns  21   a  and  21   b  of fiber  20  are disposed in the turns  46   a  and  46   b  of the spiral groove, respectively. Thus, the axis  22  of fiber turns  21   a  and  21   b  also forms the central axis of the fiber carrier. The stub  24  of fiber  20  extends out of the fiber carrier through opening  48 . A transparent filler  49  ( FIG. 4 ) is disposed within the turns  46   a  and  46   b  of the groove. The filler defines surfaces that are flush with the exterior surface  38  of the fiber carrier. The features of the lens carrier, such as the edge surface  42  and the interior surface of hole  40 , are substantially in the form of surfaces of revolution about the central axis  22 . 
     The device further includes a mass  50  of an optically dispersive material disposed within the hole  40  in the fiber carrier  34 . For example, mass  50  may be formed from a transparent silicone polymer having microscopic particles of an opaque, reflective material such as titanium, titanium dioxide, or zinc dispersed throughout the polymer. The dispersive properties of a material of this nature can be controlled by varying parameters such as the particle material, the ratio of particles to polymer, the size of the particles, and the shape of the particles. 
     Mass  50  is in the form of a dome-like shell having a concave interior surface  52  and a convex exterior surface  54 . These surfaces generally conform to the dome-like configuration of the fiber carrier  34 , so that the fiber carrier and shell  50  form a continuous dome-like structure having substantially smooth interior and exterior surfaces. Shell  50  also has a generally cylindrical edge surface  56  extending between surfaces  52  and  54  and abutting the inner surface of the fiber carrier  34 , which defines hole  40 . Shell  50  can be formed by casting it in place in the hole  40  of the fiber carrier while holding the fiber carrier in a mold defining the desired dome shape. 
     Shell  50  constitutes a second optically dispersive element. Here again, the degree of dispersion in such an element can be characterized by the extinction length of the element. This embodiment is intended to produce uniform irradiation intensity across the area of the cornea to be treated. In this case, the extinction length of the mass or shell  50  typically is greater than the diameter of the cylindrical edge surface  50 . 
     A reflective element in the form of a film  58 , best seen in  FIG. 4 , covers the interior and exterior surfaces  36  and  38  of the fiber carrier and also covers the edge surface  42  of the fiber carrier and the transition  44  between the edge surface and the exterior surface. For example, film  58  may be formed from aluminum or other metals. Film  58  also covers the entire exterior surface  54  of dispersive shell  50 . Film  58  may extend beyond the edge surface  56  of the shell so that the film may cover a portion of the interior surface  52  of the dispersive shell remote from the central axis  22  of the device. However, a portion of the interior surface  52  adjacent the axis is left uncovered by the metallic film  58 , so as to define an aperture  60  surrounding axis  22 . As best appreciated with reference to  FIG. 4 , the reflective element  58  forms a cavity, and the dispersive mass  50  is disposed within this cavity. The reflective element  58  includes a reflective circumferential surface overlying the edge surface  42  of the wafer carrier and extending around axis  22 . This reflective circumferential surface is in optical communication with the edge surface  56  of mass  50 , through the clear fiber carrier  34 . The reflective element  58  also includes a surface facing in an inward direction, toward the bottom of the drawing, overlying the outer surface  54  of mass  50 , as well as an outwardly facing ledge surface overlying the inner surface  36  of the fiber carrier. 
     This embodiment is intended to correct myopia by flattening the cornea. For this purpose, the aperture is generally circular and has a radius approximately equal to the radius of a portion of the cornea to be treated. The aperture size appropriate for the particular patient is selected by the ophthalmologic professional. That is, aperture  60  is sized to cover only a portion of the cornea adjacent the center of the cornea. As explained below, this will provide crosslinking near the center of the cornea, so as to treat myopia. 
     Film  58  may be on the order of a few microns to a few tens of microns thick. Merely by way of example, film  58  may be formed by conventional methods of depositing metals onto polymers as, for example, electroless plating followed by electroplating, vapor deposition, sputtering, or the like. Alternatively, the reflective metallic element may be formed by other metalworking methods such as stamping, die casting or machining 
     The assemblage of the fiber carrier, radially dispersive fiber, dispersive shell, and reflective element is embedded in a housing  62 . Housing  62  has a dome-like central portion defining a first interior surface  64  with a shape adapted to conform to the shape of the cornea. The housing also includes a skirt portion defining a second interior surface  66  surrounding the first interior surface. The second interior surface has a shape adapted to conform to the shape of the sclera or opaque portion of the eye surrounding the cornea. The assemblage of the fiber carrier  34  and shell  50  is mounted centrally in housing  62  so that the central axis  22  defined by the fiber and fiber carrier is coincident with the central axis of dome-like portion  64  of the housing. Housing  62  also has an exterior surface  68  extending generally parallel to the interior surface portions  64  and  66  and covering the exterior surfaces of fiber carrier  34  and shell  50 . As best seen in  FIG. 4 , housing  68  includes a thin interior film  70  covering the interior surfaces of the fiber carrier  34  and shell  50  and overlying metallic film  58  on the interior surface of the fiber carrier. Housing  62 , apart from interior film  70 , may be formed from essentially any material, but typically is formed from a relatively soft polymer such as silicone. Interior film  70  desirably is formed from a material having good compatibility with the tissues of the eye as, for example, a hydrophilic polymer. The material of film  70  should also be capable of transmitting the light to be applied. 
     As best appreciated with reference to  FIG. 5 , the housing  62 , fiber carrier  34 , and shell  50  cooperatively form a contact lens structure substantially in the form and shape of a conventional scleral fit contact lens. Thus, the entire structure forms a relatively thin shell having interior and exterior surfaces generally conforming to the shape of the cornea and sclera. The thickness T of the entire contact lens structure desirably is no more than 3 mm, preferably no more than 2 mm, more preferably less than 1 mm, and most preferably less than 800 μm. 
     As best seen in  FIG. 6 , the fiber system (stub  24 , transmission fiber  26  and splice  28 ) extends out the housing  28  in a direction transverse to the central axis  22 . The fiber system exits the housing at an angle A relative to a line tangent to a circle concentric with central axis  22  and passing though the exit point. Angle A may have any value, including 0°, such that the fiber system exits parallel to the tangent line, and 90°, such that the fiber system exits perpendicular to the tangent line. Typically, an angle between 0° and 90° is chosen to mitigate both manufacturing challenges and contact with the patient&#39;s eyelid during the use of the device. 
     In a method according to a further embodiment of the invention, a device as discussed above with reference to  FIGS. 1-6  is placed over the front surface of the eye of a human or other mammalian subject as depicted in  FIG. 7 . The interior surfaces of the housing  62 , fiber carrier  34 , and dispersive shell  50  overlie the exterior surfaces of the sclera  72  and cornea  74  of the subject&#39;s eye. Typically, those portions of the device overlying the cornea are spaced slightly from the cornea so as to provide a small space between the outer surface of the cornea and the inner surface of the device. The central axis  22  of the device is substantially aligned with the central axis of the subject&#39;s eye. The central axis of the subject&#39;s eye, as referred to in this disclosure, is the axis extending through the center of the cornea and the center of the lens  76  of the eye, as well as the center of the pupil  78  of the eye. In this orientation, the fiber turns  21   a,    21   b  extend generally in planes transverse to the central axis of the eye, as indicated schematically by plane  80  in  FIG. 6 . Thus, the turns of the radially dispersive optical fiber extend generally parallel to the surface of the eye. Likewise, the interior and exterior surfaces of dispersive shell  50  extend generally parallel to the surface of the eye, and specifically the surface of the cornea. Also, the turns of the fiber surround the central axis of the eye, which, again, is substantially coincident with the central axis  22  of the device. 
     Before or during the application of the device to the eye, the eye is treated with a photo-reactive crosslinking agent  75  such as riboflavin and the crosslinking agent is allowed to permeate into the cornea  74 . As seen in  FIG. 7 , the device may be used as a reservoir to trap the agent in contact with the cornea during permeation. After a the agent has permeated into the cornea, and before light is applied as discussed below, the agent desirably is removed from the space between the device and the cornea as, for example, by flushing this space with a liquid such as saline solution or the patient&#39;s natural tears. Alternatively, the agent may be confined in contact with the cornea by another device such as another contact lens shaped shell, which is removed and replaced by the device. Optionally the epithelial layer forming the outermost surface of the cornea may be removed or disrupted using conventional techniques so as to enhance permeation of the crosslinking agent into the collagen of the cornea. 
     While the crosslinking agent is present in the cornea, the light source  30  ( FIG. 1 ) is actuated so as to direct light at a wavelength suitable for activating the crosslinking agent through the transmission fiber  26  and into dispersive fiber  20 . Where the agent is riboflavin, the light may be near UV light of 360 nm to 380 nm wavelength or blue light of about 425 nm to 475 nm wavelength. The light enters through stub  24  of the dispersive fiber  20  and passes lengthwise along the fiber through turns  21   a  and  21   b.  Thus, the light passing along the dispersive fiber in turns  21   a  and  21   b  is directed generally parallel to the surface of the eye. As the light passes along the turns of the fiber, a portion of the light is dispersed from the fiber, and the dispersed portion propagates in directions transverse to the length of the fiber, as indicated by arrows  82  ( FIG. 4 ). The light dispersed from the fibers passes through the transparent material of fiber carrier  34  into the dispersive shell  50  through the edge surface  56  of the shell. Some of the light dispersed by the fibers passes directly into the shell as indicated by arrow  82   a  in  FIG. 4 . Other light dispersed from by fiber passes into shell  50  by indirect paths, including one or more reflections from reflective film  58 , as indicated by arrows  82   b  and  82   c  in  FIG. 4 . A substantial portion of the light directed into shell  50  through peripheral surface  56  is propagating in directions generally parallel to the interior surface  52  of the shell and thus generally parallel to the surface of the cornea. As used in this disclosure, a propagation direction can be considered “generally parallel” to a surface if the propagation direction forms an angle of less than about 45° and preferably less than 30° to the surface. 
     The light propagating through dispersive shell  50  is dispersed. Some of the light dispersed in the shell is directed in the inward direction, towards the inner surface  52  of the shell. This light passes through the aperture  60  ( FIG. 4 ) and into the cornea  74 . Of course, dispersion in shell  50  is omnidirectional, and some of the light dispersed by the material of the shell will travel in directions other than the inward direction. Light initially dispersed in the outward direction will be reflected back toward the cornea by the metallic film  58  overlying the outer surface. Light dispersed in directions parallel to the inner and outer surfaces of the shell may pass out of the dispersive shell  50 , through the edge surface  56 , and into the transparent material of the fiber carrier  34 , but will be reflected back into the shell by film  58 . Likewise, some of the light passing from the fibers into the dispersive shell  50  will travel entirely across the dispersive shell and out into the fiber carrier  34  at another location. This light also will be reflected back into the shell by film  58 . Film  58  is not perfect, and some light will be lost during internal reflection. However, a substantial portion of the light dispersed by the fiber will ultimately pass out of the dispersive mass  50  through aperture  60  and into the cornea. The pattern of light travel discussed above is substantially symmetrical around the entire circumference of the device. 
     As the light passes from the inlet fiber  26  through the radially dispersive fiber  20 , it diminishes in intensity. Accordingly, slightly less light will be dispersed from the fiber near the terminal end  23  of the fiber than near the input end and stub  24 . However, this difference typically is minor. As pointed out above, the extinction length of the fiber is substantially greater than the length of fiber constituting turns  21   a  and  21   b.  Moreover, this difference is taken up over two full turns, i.e., 720° of travel in the circumferential direction around central axis  22 . Thus, the circumferential non-uniformity is minimal. Moreover, the effects of the multiple reflections and multiple passes of light through the dispersive shell  50 , as discussed above, compensate for any non-uniformity in the light dispersed from the fiber. Desirably, the light passing out from aperture  60  ( FIG. 4 ) is of uniform intensity over the entire surface area of the aperture to within about 20% or less. 
     The system is actuated to provide a dose of light to the cornea sufficient to perform the desired crosslinking. Merely by way of example, a dose of about 5.4 Joules/cm 2  may be delivered over a period of about 30 minutes in a typical procedure. While the device is present in the subject&#39;s eye, the subject may close his or her eye and blink freely to provide hydration to the eye. The thin contact lens-like structure of the device allows the patient to do this without discomfort. When the patient closes the eye or blinks, the eyelids close over and around the distal portion of the fiber system. The small diameter of the fiber system limits any discomfort caused by the fiber. The patient&#39;s eyelids desirably are not held open by an ophthalmology speculum or other device. Moreover, the patient&#39;s head does not have to be retained in a fixed position during the procedure. 
     The device and procedure discussed above may be varied in many ways. In one such variant, the coating  25  on the termination end  23  of the fiber is reflective rather than light-absorbing. In this variant, light which reaches the termination end of the dispersive fiber is reflected back toward the input end. The reflected light is also dispersed by the fiber, so that the intensity of the reflected light diminishes as it travels toward the input end of the fiber. By contrast, the light originally supplied through to the fiber at its input end diminishes in intensity as it travels toward the termination end. These effects counteract one another to reduce non-uniformity in the amount of light dispersed along the length of the fiber. 
     The radially dispersive optical fiber used in the embodiments discussed above may incorporate any number of loops as, for example, a single loop or three or more loops. The turns  21   a  and  21   b  of the spiral dispersive fiber  20  discussed above form loops extending around the central axis of the device. In other structures, where multiple loops are desired, these can be provided as separate radially dispersive optical fibers. 
     The fiber carrier  34  and filler  49  discussed above with reference to  FIGS. 3 and 4  may be replaced by a unitary mass of a clear material such as an epoxy or an acrylic which secures the dispersive fiber in one or more loops. The fiber may be embedded in the clear material as, for example, by casting the material around the fiber. In yet another variant, the clear material may serve as an adhesive so as to secure the fiber to another structural element of the device as, for example, the reflective element  58 . In yet another variant, the fiber may be embedded in the dispersive mass. For example, in the embodiment discussed above, the dispersive mass  50  may include a peripheral portion which occupies the space remote from the central axis occupied by the fiber carrier  34  in  FIGS. 3-5 . The dispersive fiber loops may be embedded in this peripheral portion of the dispersive mass, so that a central portion of the dispersive mass is disposed inside the loops. 
     The skirt portion of the housing  62  defining the second interior surface  66  depicted in  FIG. 5  may be omitted. In this variant, the device has the form and shape of a conventional corneal contact lens. 
     The embodiment discussed above with reference to  FIGS. 1-7  is intended to provide substantially uniform light intensity over the entire aperture. However, an intensity gradient in radial directions, towards and away from central axis  22 , may be provided by adjusting the properties of the dispersive mass. For example, the dispersive mass may have properties which vary with location within the mass as, for example, an extinction length which varies in the radial direction. In another example, the dispersive mass may be of uniform properties, but these properties may be selected to provide the desired gradient. For example, a mass having a short extinction length can produce a radial gradient. 
     In the embodiment discussed above, light application and, hence, crosslinking occurs only over a central portion of the cornea. This tends to flatten the central portion and thus correct some or all of a patient&#39;s myopic error. A device according to a further embodiment of the invention ( FIG. 8 ) has a dispersive shell  150  and other elements (not shown) similar to those discussed above with reference to  FIGS. 1-6 . However, the reflective film is patterned so that the aperture  160  is in the form of an annulus surrounding the central axis  122  of the device. Thus, the reflective film on the interior surface of the device includes a main portion  158   a  defining the outside of the annulus and a disc-like central portion  158   b  overlying a region immediately surrounding axis  122 . This device may be used to treat hyperopia. Thus, the UV light will be applied to a ring-shaped zone of the cornea, remote from the central axis of the eye, the parameters of which are selected to optimize the corneal shape change, thus tending to increase the curvature of the cornea. 
     A device according to yet another embodiment ( FIG. 9 ) incorporates a dispersive shell  250  and associated fiber (not shown) similar to the corresponding elements of the device discussed above with reference to  FIGS. 1-7 . In this embodiment, however, the reflective film  258  is patterned so as to provide an aperture that is non-uniform in the circumferential direction around axis  222 . In the particular embodiment shown, the aperture  260  includes two generally triangular, diametrically opposed portions, so that the aperture as a whole defines a “butterfly” shape. A structure according to this embodiment can be used to treat astigmatism. In this embodiment, the device is positioned on the eye so that the butterfly shape corresponds to a particular region of the eye where UV light application and crosslinking are desired. To aid in this process, the exterior surface of the device may have a mark indicating the orientation of the butterfly-shaped aperture. Also, the device may have a weight or other element to aid in maintaining the desired orientation during the treatment. Alignment also may be controlled by where the on the circumference of the device the fiber exits and the exit angle A discussed above with reference to  FIG. 6 . 
     A device according to a further embodiment of the invention ( FIG. 10 ) includes only one optically dispersive element in the form of a radially dispersive optical fiber  320 . The dispersive fiber  320  may be arranged in the form of a spiral extending around the central axis  322  of the housing. As in the embodiments discussed above, housing  362  may have the form and size of a scleral contact lens or a corneal contact lens. The spiral fiber may be disposed along a generally dome-like or disc-like surface of the housing extending transverse to the central axis  322  of the housing  362  of the device and facing toward the inner side of the housing. A reflective element (not shown) may be interposed between the fiber and the housing. The fiber may be secured to the housing surface or to the surface of the reflective element by a clear adhesive. In this arrangement, light dispersed from the fiber may pass directly into the cornea without passing through another optically dispersive element. In another arrangement, one or more optically dispersive layers (not shown) may be provided. For example, the adhesive that secures the fiber to the housing or reflective element may be optically dispersive. The dispersive adhesive may be disposed between turns of the spiral, and also may form a layer covering the fiber spiral on the side facing toward the eye. Alternatively or additionally, one or more other dispersive layers may be provided between the fiber and the eye. As depicted in  FIG. 11 , a more uniform light distribution can be achieved by reducing the spacing between turns of the spiral  321 . The turns of the spiral may touch one another to form a solid fiber mat. In these embodiments as well, light propagating along the fiber passes in a direction generally parallel to the surface of the eye, and the light that reaches the eye is light dispersed out of the fiber through the side walls of the fiber. The embodiments of  FIGS. 10 and 11  are arranged to treat a circular region around the central axis. In a further variant, the spiral dispersive fiber may extend only within an annular region so as to treat an annular region of the cornea. In yet another variant, the dispersive fiber may be arranged to provide illumination only within regions of other shapes and sizes as, for example, a “butterfly-shaped” region as discussed above with reference to  FIG. 9 . 
     A device according to yet another embodiment of the invention ( FIG. 12 ) includes an optically dispersive mass or shell  450 , similar to the optically dispersive shell  50  discussed above with reference to  FIGS. 3-6 . In this embodiment, the edge surface of the dispersive shell is surrounded by an array of LEDs  402  adapted to emit UV light. Light emitted by the LEDs passes into the optically dispersive shell  450  through the edge surface  456  of the shell in much the same way as light dispersed by the fiber in the embodiment discussed above with reference to  FIGS. 1-7 . Merely by way of example, the LEDs  402  may be mounted within a clear polymer diode carrier  434  generally similar to the fiber carrier  34  discussed above. Desirably, the diode carrier  434  and shell are equipped with a reflective element (not shown) similar to that discussed above, covering the outer surface of the shell  450 , facing away from the eye, and also covering the periphery and inner and outer surfaces of the diode carrier  434 . The diode carrier and shell are mounted in a housing  462  similar to that discussed above. The LEDs are powered by a simple electric circuit schematically indicated at  404 . Circuit  404  may be connected to power and ground wires  406 . In this embodiment as well, the entire structure desirably has shape and dimension similar to that of a conventional contact lens and, thus, desirably has a maximum thickness similar to that discussed above. The device may be placed in the eye of the subject with the wires extending out of the subject&#39;s eye between the eyelids. Here again, the subject may close his or her eye during the procedure. Alternatively, the LED&#39;s may be powered by wireless power transmission as discussed below. 
     A device according to yet another embodiment of the invention ( FIG. 13 ) includes a housing  562  in the form of a contact lens similar to the housings discussed above. The device of  FIG. 13  further includes an antenna  501  on or within housing  562 . The antenna, which may be in the form of a coil consisting of wire loops or tin oxide deposition for example, forms a near-field resonant tank circuit. For power transfer, the antenna is linked to a rectifier and storage capacitor unit  503 , which, in turn, is electrically connected to a power control circuit  505 . Power control circuit  505  provides regulated power voltages to other elements of the system. The structure further includes an illuminating element  530  adapted to apply light to the cornea as discussed above. For example, the illuminating element may include a dispersive structure connected to a source of light external to the housing by a transmission fiber as discussed herein in connection with  FIGS. 1-11 and 19-25 , or a dispersive element and an LED array mounted on or in the housing as discussed above in connection with  FIG. 14 . 
     A sensing element  532  is in optical communication with the illuminating element so that light from the illuminating element impinges on the sensing element. The sensing element is adapted to generate one or more signals which represent the light impinging on the sensing element, and thus represent the light applied by the illuminating element. 
     One form of sensing element  532  is depicted in  FIG. 14 . This sensing element includes one or more photosensors such as PIN diodes  534  sensitive to UV light mounted in a ring  536 . The ring is mounted on the housing  562  so that the ring structure encircles the dispersive mass included in the illuminating element  530 . For example, where the illuminating structure incorporates a fiber carrier and reflective element as discussed above with reference to  FIGS. 1-7 , the ring structure may be disposed within the reflective element and extend around the fiber carrier or between the fiber carrier and the dispersive mass. The ring structure may be integral with the fiber carrier. Where the illuminating structure includes a diode carrier and LED array as discussed above with reference to  FIG. 12 , the ring structure may encircle the diode carrier, or may be integral with the diode carrier, and some of the LEDs included in the array may be connected to act as the photosensors of the sensing element rather than as light emitters. The sensing element may include one or more signal processing circuits  538 . In the particular embodiment shown, the signal processing circuits  538  include three current-to-voltage converters, each incorporating an amplifier  540  and feedback resistor  542 . Only one of these converters is depicted in  FIG. 14  for clarity of illustration. 
     The device further includes an analog drive circuit  513  ( FIG. 13 ) arranged to supply power to the light source  509  associated with the light emitting element  520 . For example, where the light-emitting element includes an LED array, the drive circuit  513  supplies power to the LEDs. Where the light-emitting element includes an external light source such as a laser connected to a transmission fiber, the drive circuit supplies power to the laser. Drive circuit  513  has a set point value input connected to a control circuit  515 . The control circuit has one or more inputs connected to sensing element  511 . In some embodiments, all of the foregoing components can be are mounted on housing  562 . In other embodiments, the control architecture (circuits  513  and  515 ) is located remote from the housing  562  and communicates with the photosensor(s) of sensing element  530  either through fine wires the run between the lens and the control system, or wirelessly. For wireless communication, a telemetry transmitter (not shown) may be mounted on the housing and connected to antenna  501  or to another antenna mounted on or in housing  562 . The device further includes a radiofrequency (“RF”) transmitter  517  separate from housing  562 . 
     In operation, RF power as, for example, at about 100 kHz, is supplied by transmitter  517  through near field communication with antenna  501 . The power received by antenna  501  is rectified by rectifier  503  and conditioned by power control circuit  505 . The power control circuit  505  supplies power to the other electronic elements which are mounted on the housing as discussed above. The signal or signals from sensing element  532  will represent a proxy proportional to the amount of light available for UV corneal crosslinking and serves to aid in dosimetry. During delivery of the UV, control circuit compares the applied UV intensity represented by this photodetector generated signals to a signal representative of the desired applied intensity. The control circuit  515  desirably incorporates a calibration memory incorporating data representing the correlation between the signal or signals from the sensing element  532  and the actual dose applied to the subject&#39;s eye. The control circuit  515  varies the set point control signal applied to the control unit  513  so as to maintain the applied intensity at the desired level. 
     In a further variant, an additional intensity sensor (not shown) is located at a light source such as a laser external to the housing. In this variant, the sensing system will not only be able to control the applied intensity, it can also serve as an error or damage detector. Unaccounted for differences between launched optical power supplied by the light source and optical power detected by the sensing element are likely due to damage to the fiber system or to a lens or other optical element. 
     The concept of monitoring of applied dose discussed above with reference to  FIG. 13  also may be applied to the other embodiments discussed above. For example, the embodiment discussed above with reference to  FIGS. 1-6  may be provided with a sensing fiber. The sensing fiber may be connected through an output fiber extending parallel with transmission fiber to a diode or other photodetector mounted outside of the device housing as, for example, at the UV light source. Control circuitry responsive to the signal from the photodetector also may be mounted outside of the housing. 
     A device in accordance with a further embodiment of the invention ( FIG. 15 ) includes a contact lens-like structure  600 , which may be similar to any of the structures discussed herein. In addition, the device includes pairs of electrodes  601  adapted to overlie the patient&#39;s eye outside of the region to be treated. For example, the electrodes  601  may be fastened to the housing of the device so that the electrodes are exposed at the inner surface of the housing which faces toward the eye during use. Merely by way of example, the electrodes may be formed from materials such as tin oxide, or noble metals such as gold and silver. As discussed below, the electrodes are used as liquid level sensors to help maintain a constant liquid presence in the space between the device and the patient&#39;s eye. The pairs of electrodes are distributed over the circumference of the contact lens structure. In the particular embodiment illustrated, three pairs of electrodes are equally spaced around the circumference. The electrodes of each pair desirably have a known conductive surface area presented to the space and are spaced from one another by a calibrated distance D E . For example, the electrodes may be 0.03 inches (0.77 mm) diameter with 0.125 inches (3.2 mm) center-to-center spacing. In some cases, the inner surface of the housing is coated with a hydrophilic layer to aid the adhesion of the device to the eye. This hydrophilic layer can hold a layer of conductive fluid over the surfaces of the electrodes. Such layer may be sufficiently thick so that the impedance of the retained layer will approximate the impedance of a liquid present in the space between the housing and the eye. To prevent this, the hydrophilic layer may be omitted in areas  602  of the inner surface carrying the electrodes. 
     The device according to this embodiment further includes a port  603  communicating with the interior surface of the housing, so that the port is open to the space between the device housing and the patient&#39;s eye during use. Port  603  is connected to a liquid supply conduit  605 , so that the conduit communicates with the interior surface of the contact lens structure. Supply conduit  605  may be a small-diameter capillary conduit. The supply conduit  605  may extend alongside of the transmission fiber supplying light to the device. The supply conduit  605  may be a tubular fiber, such as a pipette or polyimide tube. In some embodiments, the conduit may additionally serve as the transmission fiber. Supply conduit  605  is connected to a pump  607 . Pump  607  is connected to a source  609  of a liquid to be applied prior to and/or during treatment depending on treatment protocol. 
     Each pair of electrodes  601  serves as an individual impedance measuring element to acquire individual measurements. The pairs of electrodes desirably do not interact with one another through leakage current paths. To accomplish this, each pair of electrodes  601  is connected to an individual sensor circuit  610 . 
     A single one of the sensor circuits  610  is shown in  FIG. 16 . It includes an error amplifier A 1 ,  628  that has one input connected to digital to analog converter (“DAC”)  631 . The output of error amplifier  628  is connected through a current sense resistor Rs,  626  to one electrode  601  of a pair. The opposite electrode of the pair is connected to ground. The impedance between the electrodes is shown schematically at  612 . An amplifier A 2 ,  627  has inputs connected on opposite sides of current sense resistor  626 . The output of amplifier A 2 ,  627  is connected to the other input of error amplifier A 1 ,  628 . A dedicated precision analog amplifier stage A 3 ,  630  is connected to a circuit node between the current sense resistor  626  and the electrode pair. In operation, error amplifier  628  receives a current set point signal from DAC  631  and maintains the current passing through the current sense resistor at a constant level such that the output from amplifier A 2 ,  627  is equal to the set point signal. The voltage at node  611  and the output signal  632  from amplifier stage A 3 ,  630  thus represent the impedance  612  between the electrodes of the pair. 
     As seen in  FIG. 15 , the DAC  631  may be common to all of the sensor circuits. The output signals  632  from the individual sensor circuits are combined with one another by an analog summing circuit  613 , and the combined signal is supplied to a control circuit  614 . This combined signal will vary with the degree of hydration of the space between the lens-like structure and the eye. The control circuit controls pump  607  so as to maintain the desired hydration. The sensor circuits and control circuits may be disposed outside of the contact lens structure, with the sensor circuits connected to the electrodes  601  with a simple multi-wire interface Alternately, the signal processing may be contained “on lens” by utilizing a localized silicon IC or ASIC. 
     Other sensing elements may be employed, such as an interdigitated finger array  623  ( FIG. 17 ) or circular interdigitated arrays  624  ( FIG. 18 ). The element&#39;s measurement of impedance may be by means of either a □A (microampere) precision DC current or, alternately, a kilohertz range, AC excitation. AC excitation is typically employed in most “wetted” measurement applications. 
     In other embodiments, multiple sensing elements such as multiple electrode pairs are placed on the inside surface of the device, exposed to the space between the device and the cornea. When this space is filled with a conductive solution, all sensing elements register the same impedance. As fluid drains or leaks out of the space, the impedances of various elements will deviate from one another. This deviation is used as a control signal to cause the pump to infuse additional fluid until the impedances of the sensors register that each is bathed in fluid. 
     In some embodiments, the sensing elements are not electrodes, but mechanically resonant elements. A shift in the measured resonant frequency or mechanical impedance can be used as a pump control signal in place of a shift in the electrical impedance discussed previously. 
     The feedback control system shown in  FIG. 12  can be varied and, indeed, in some embodiments, can be omitted. Thus, liquid can be supplied under pressure through conduit  605  without any feedback control. 
     Embodiments of the invention that incorporate a fluid sensing system can be employed in one method of the corneal collagen crosslinking procedure whereby the device is placed on the eye during the preparation phase of the procedure, and a photoactive agent containing solution is pumped into the space between the lens and the cornea to enable corneal saturation with the photoactive agent such as riboflavin. The sensing systems ensure the reservoir is full throughout this saturation phase. After sufficient time, the pump is activated to deliver a wetting solution without riboflavin to flush the reservoir space, as any riboflavin in this space will prevent some of the UV from reaching the cornea. Once flushed, the pump and sensing system then maintains a wet corneal surface throughout the UV delivery phase. 
     A device according to a further embodiment of the invention ( FIGS. 19-21 ) includes an optical structure  700  that incorporates a reflector  702 . Reflector  702  includes an inner element  704  that defines a first interior surface  706  in the form of a surface generally corresponding to the shape of the cornea and having a central axis  722 . The interior element additionally defines an aperture  710 , which, in this instance, is a circular aperture concentric with axis  722 . The interior element has a reflective circumferential surface  712  in the form of a cylinder concentric with axis  722 . The interior element  704  also has a ledge surface  714  extending from the aperture  710  to the circumferential surface  712 . Ledge surface  714  faces in the outward direction (towards the top of the drawing in  FIG. 21 ), as indicated by the arrow O. Ledge surface  714  desirably also is a reflective surface. 
     Reflector  702  further includes an outer element  716  overlying the outward extremity of the inner element  704 . Outer element  716  is shown in transparent, phantom view in  FIG. 19  for clarity of illustration. The outer element is secured to the inner element as, for example, by interlocking ridges  718  at the periphery of these elements, remote from axis  722 . The outer element  716  defines a reflective surface, referred to herein as the “cap surface”  720 , extending across axis  722  and spaced apart from ledge surface  714 . Reflector  702  thus defines a cavity  724  ( FIG. 21 ) communicating with aperture  710 . The cavity is bounded in part by the circumferential reflective surface  712  and the reflective cap surface  720  and. 
     The reflective surfaces  712 ,  720 , and  714  of the reflector may be arranged to provide either specular reflection or diffuse reflection. For example, the elements of the reflector may be formed from a metal such as aluminum with polished surfaces to provide specular reflection or with roughened surfaces to provide diffuse reflection. Alternatively, the elements of the reflector may be formed form a material such as a polymer coated with a metal such as aluminum. In yet another arrangement, the reflective surfaces may be formed by materials that provide a highly efficient diffuse reflection in the wavelengths to be applied. For example, films suitable for providing diffuse reflection of ultraviolet and blue light are commercially available from the 3M Company of Minneapolis, Minn. USA. 
     An optically dispersive element  726 , such as a mass of a dispersive composition as discussed above, is disposed within cavity  724 . The dispersive element is generally in the form of a disc concentric with axis  722 . It has an outer surface  728  facing outwardly and confronting the cap surface  720  of the reflector and an inner surface  730  facing inwardly. The inner surface includes a portion overlying ledge surface  714  of the reflector, as well as a portion extending across aperture  710 . This portion of the inner surface projects into the aperture so that it defines a surface region continuous with the first inner surface  706  of the reflector. The dispersive element  726  also defines an edge surface  732 , which is in the form of a cylinder concentric with axis  722 . The diameter of edge surface  732  is slightly smaller than the diameter of circumferential surface  712  of the reflector, so that the dispersive element and reflector cooperatively define an annular gap  734  extending around the dispersive element. Gap  734  is filled with a clear material, which may be a solid or gel, a liquid, or a gas such as air. The edge surface  732  of the dispersive element is in optical communication with the circumferential surface  712  of the reflector. 
     The reflector further defines a bore  740  ( FIGS. 19, 20 ) extending through the inner and outer elements in a plane transverse to the central axis  722 . In the particular embodiment depicted, the bore  740  extends in a plane perpendicular to the axis. Bore  740  communicates with the interior of cavity  724  and, in particular, with gap  734 . As best seen in  FIG. 20 , bore  740  communicates with the cavity and gap at a location near to the reflective circumferential surface  712 . A transmission optical fiber  742  extends through the port  740  and is held in place by a coupler  744  in the form of a sleeve that surrounds the fiber. The coupler  744  is secured to the fiber and to the internal wall of bore  740  as, for example, by an adhesive. 
     Fiber  742  has a distal end  746  and a proximal end (not shown). The proximal end is equipped with an appropriate coupler (not shown) for engagement with a light source such as light source  30  ( FIG. 1 ). The distal end  746  extends coaxially with bore  740  and thus extends in a plane transverse to and preferably perpendicular to axis  722 . The distal end  746  of the fiber is positioned within gap  734  adjacent the circumferential reflective surface  712 . As seen in  FIG. 20 , viewing the distal end of the fiber in a plane transverse to the axis, the distal end of the fiber may extend in a direction that is tangential to the circumferential surface  712  or that lies at an angle A DE  to such a tangent. 
     The optical structure  700 , including the reflector and dispersive element, is mounted in a housing  762 . As best seen in  FIG. 19 , the housing  762  may encompass a portion of the fiber  742  and coupler  744  extending out of the reflector. As in the embodiments discussed above, housing  762  is a generally shell-shaped structure, desirably less than 3 mm thick, having an interior surface generally conforming to the shape of a surface of the eye. For example, the housing  762  may have a first interior surface portion  764  that constitutes a continuation of the first interior surface  706  defined by the reflector and by the inner surface of dispersive element  726 , so as to form a composite first interior surface generally conforming to the shape of the cornea of the eye. In the particular embodiment depicted, housing  762  further includes a second interior surface portion  766  corresponding to the shape of the sclera of the eye. Here again, the assembly including the optical structure  700  and housing  762  forms a thin shell having an interior surface corresponding to the shape of the eye, so that the entire structure is generally of the form and size of a conventional scleral contact lens. As discussed above, the second surface portion  766  may be omitted so that the entire structure will have the form and size of a conventional corneal contact lens. Here again, the interior surfaces of the housing and of the optical structure may be covered with a film of a hydrophilic material (not shown). 
     In operation, the assembly is positioned on the eye with the inner surfaces overlying the corresponding surfaces of the eye in much the same manner as discussed above with reference to  FIG. 7 . In this condition, the inward direction of the optical assembly constitutes the direction toward the eye of the patient, whereas the outward direction is the direction away from the eye of the patient. Aperture  710  is aligned with the region of the cornea to be treated. 
     While the assembly is in this position, light is directed into cavity  724  through the transmission fiber  742 . Light passes from the distal end  746  of the fiber, strikes the reflective circumferential surface, and is reflected along a path around the periphery of the dispersive element. This path is schematically indicated in part by the path L in  FIG. 20 . 
     The light path L depicted in  FIG. 20  is simplified for purposes of illustration. For example, the light may be refracted as it passes between the gap  734  and the dispersive element  726 . Depending upon the indices of refraction of the medium in gap  734  and the dispersive element, the interface between the dispersive element and the gap may serve to confine the light to within the gap, so that the dispersive element and the circumferential reflective surface  712  serve as an annular light guide to help direct the light around the circumference of the structure. 
     As the light propagates around the structure, some of the light will be directed inwardly, toward axis  722 . Some of the light will be spread in the inward and outward directions ( FIG. 21 ) and thus may encounter the reflective cap surface  720  (id.) and the reflective ledge surface  714 . In general, the light propagates inwardly towards the central axis  722  and thus travels in directions generally parallel to the inner and outer surfaces of the dispersive element. As in the embodiments discussed above, the light passing through the dispersive element is dispersed in directions transverse to the inner and outer surfaces of the element, so that some of this light is dispersed in the inward direction and exits through aperture  710  into the eye. In the manner discussed above, the light performs the desired therapy as, for example, crosslinking of the collagen in the cornea. As in the embodiments discussed above, the eye desirably is treated with a crosslinking agent. 
     The embodiment discussed above with reference to  FIGS. 19 and 20  provides several significant advantages. It avoids the cost and complexity associated with the dispersive optical fiber. There is no need for a splice between the transmission fiber  742  and a dispersive fiber. Moreover, because the transmission fiber is optically coupled directly to the interior of the cavity and directly to the dispersive element  726 , without passing through any other dispersive element light transmitted along the transmission fiber will be efficiently coupled into dispersive element  726 . The structure according to this embodiment also provides advantages in patient comfort and ease of therapeutic applications similar to those discussed above. Here again, the patient need not hold his or her eye open during the procedure and desirably may close or blink his or her eye freely. 
     An optical structure  800  used in a further embodiment of the invention is schematically depicted in  FIG. 22 . This structure is identical to the optical structure  700  discussed above with reference to  FIGS. 19-21 . However, in structure  800 , the dispersive element  826  has a diameter equal to the diameter of the reflective circumferential surface  812 , so that the edge surface  832  of the dispersive element is in contact with the circumferential reflective surface. Also, in this embodiment, the distal end  846  of the transmission optical fiber is disposed within the dispersive element, near the edge surface  832  and circumferential surface  812 . Placing the distal end of the optical fiber within the dispersive element facilitates efficient optical coupling of the light emanating from the transmission fiber into the dispersive element. In the particular embodiment shown, dispersive element  826  has a graded composition. It has low dispersion (long extinction length) in a peripheral region  827  disposed remote from axis  822 , near the edge surface and near the circumferential surface  812  of the reflector, and has higher dispersion (shorter extinction length) in a central region  829  near axis  822  and thus near the aperture  810  of the reflector. As depicted, the gradation is stepwise. However, the gradation can be continuous. 
     The embodiments discussed above with reference to  FIGS. 19-22  can be varied in numerous other ways. For example, the circumferential surface of the reflector, and the edge surface of the dispersive element need not be cylindrical surfaces. For example, they may be surfaces of revolution other than cylinders. In one embodiment, the circumferential surface of the reflector may be a conical shape so as to direct light reflected from this surface along a path having a component of direction in the inward or outward direction. For example, in the embodiment of  FIGS. 19-21 , the reflective surface may be arranged to direct the light with a component in the outward direction so that the light encounters the reflective cap surface  720 , in the inward direction such that the light encounters the reflective ledge surface  714 , or both. More complex surfaces of revolution such as a surface defined by a curve of arbitrary shape revolved around the central axis  722  may be employed. Indeed, the edge surface of the dispersive element and the circumferential surface of the reflector need not be surfaces of revolution. For example, these surfaces may be polygonal or of irregular shape. Individual portions of such surfaces may be tilted at arbitrary angles so as to reflect the light along trajectories having inward or outward components. Also, the cap surface  720  need not be planar and need not be contiguous with the outer surface of the dispersive element. 
     The transmission fiber need not be secured to the optical structure which includes the dispersive element. As schematically represented in  FIG. 23 , an optical structure  900  as discussed herein may include a feature such as a socket  902 , and a transmission fiber  904  may have a distal end  906  arranged to mechanically engage with the socket  902  so as to place the distal end of the fiber in optical communication with the elements in the optical structure  900  that serves to disperse light. For example, in the embodiments of  FIGS. 19-22 , the socket would be arranged to hold the distal end of the fiber within the cavity of the reflector. In other embodiments, where a dispersive fiber is used, the socket and the distal end of the fiber would be arranged so that when the distal end of the fiber is engaged in the socket, the distal end of the fiber will be aligned with the dispersive fiber and in optical communication therewith. In the particular structure shown in  FIG. 25 , the distal end of the fiber is equipped with a collar  908  having a tapered exterior adapted to fit within a tapered interior defined by the socket  902 . However, other mechanical configurations can be employed. For example, the distal end of the fiber may be bare, and the feature may define an opening adapted to engage the outside of the fiber directly, without any intervening collar or other structure. Other expedients for promoting optical coupling between the transmission fiber and other elements of the system can be used. For example, where the transmission fiber is to be coupled to a dispersive fiber, elements such as index-matching gels may be used to provide an optically efficient splice. 
     Use of a transmission fiber that is detachable from the optical structure and from the contact lens structure as a whole allows reuse of the transmission fiber with a different contact lens structure. For example, the contact lens structure may be used once and discarded so as to avoid the risk of infection, whereas the transmission fiber may be reused. 
     The optical structure need not be permanently mounted to a housing that helps in positioning the optical structure on the eye of the patient. As schematically depicted in  FIG. 24 , an optical structure  1000  is used in conjunction with a separate, detachable housing  1062 . The optical structure  1000  may include any of the optical arrangements discussed above. Desirably, the optical structure  1000  includes the elements in the optical path between the transmission optical fiber  1002  and the aperture  1004 , including one or more optically dispersive elements and, desirably, one or more reflective elements as discussed herein. Housing  1062  has one or more inner surfaces  1006  with a shape generally corresponding to the shape of a surface of an eye. For example, the inner surface  1006  may include a first surface having a shape generally corresponding to the shape of the cornea and may also include a second surface generally corresponding to the shape of the sclera as discussed above, or may include only the first surface. The inner surface  1006  defines an axis  1022 , which extends towards and away from the eye when the inner surface  1006  overlies the surface of the eye. For example, axis  1022  may be aligned with the optical axis of the eye as discussed above. Housing  1062  also includes a wall  1008 , which extends across the axis. Desirably, wall  1008  is arranged to transmit light at a wavelength to be applied to the eye. In the embodiments discussed herein, which are arranged to provide crosslinking, wall  1008  may be arranged to transmit light in the UV or blue wavelength bands. 
     The housing further includes a feature  1010  adapted to releasably engage optical structure  1000 . In the embodiment depicted in  FIG. 24 , feature  1010  is shown as a simple tapered socket arranged to mate with a corresponding tapered wall on the outside of the optical structure  1000 . However, feature  1010  may include any other element capable of engaging the optical structure as, for example, other forms of mechanical features capable of mating with corresponding mechanical features on the optical structure. Feature  1010  is arranged to hold the optical structure so that the aperture  1004  of the optical structure is aligned with axis  1022  and wall  1008  and so that the optical structure is separated from the eye E by wall  1008 . 
     Desirably, housing  1062  is provided as a single-use device, whereas the optical structure  1000  is reusable. In a method according to a further embodiment of the invention, plural patients can be treated using the same optical structure. First, the optical structure with is assembled with a housing  1062 . The assembly is placed over the eye of a first patient, so that the wall of the housing is disposed between the optical structure and the eye and so that the housing engages the eye and maintains the optical structure out of contact with the eye. The optical structure is then actuated as discussed above so that light is dispersed within the optical housing and passes out of the aperture  1004  and through the wall  1008  of the housing into the eye of the patient to perform the desired therapy. Following this step, the optical structure is disassembled from the housing and the foregoing steps are repeated using a different housing and, typically, a different patient on each repetition. The different housings may have different shapes or sizes to accommodate the needs of different patients. 
     A structure according to a further embodiment of the invention ( FIG. 25 ) incorporates a dispersive element  1100  having an inner surface  1102  that faces inwardly toward the eye when the device is in place on the eye and an outer surface  1104  that faces outwardly away from the eye. The dispersive element has an axis  1122  extending through these surfaces. A transmission optical fiber has a distal end  1106  disposed on axis  1122  and spaced outwardly from the outer surface  1104 . An optically transmissive medium  1107  is provided between the distal end of the fiber and the outer surface, so that the distal end of the transmission fiber is in optical communication with the outer surface  1104 . The distal end of the fiber is equipped with one or more spreading structures schematically indicated at  1108 . The spreading structures may include elements such as a mass of dispersive material, one or more reflectors, refractive elements, and configuration of the cleaved fiber end. Alternatively or additionally, the medium  1107  may have dispersive or refracting properties that serve to spread the light. The spreading structures are arranged to direct light supplied through the fiber away from axis  1122  so that the light impinges on an outer surface over a substantial region of the outer surface and desirably over the entire outer surface. The structure may further include a reflective element defining one or more of a circumferential reflective surface  1112  extending around the axis, an inwardly facing reflective cap surface  1114  disposed outward of the fiber distal end, and an outwardly facing reflective ledge surface  1116  facing the inner surface of the dispersive element. 
     As these and other variations and combinations of the features discussed above can be utilized without departing from the present invention as defined by the claims, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by way of limitation of the present invention.