Abstract:
An apparatus ( 20 ) for directing electromagnetic radiation into a respective pupil of at least one eye of a user is disclosed. The apparatus comprises first radiation emitting means comprising at least one radiation emitting layer ( 8 ) adapted to emit electromagnetic radiation and second radiation emitting means ( 6 } adapted to direct electromagnetic radiation into at least one eye and/or onto at least one eyelid of a user. A light guide ( 1 ) is adapted to receive radiation emitted by the first radiation emitting means and to direct at least part of the radiation to the second radiation emitting means, wherein a total surface area of the first emitting radiation means from which radiation is emitted is larger than a total cross sectional area of a beam of radiation entering the or each pupil of the user in use, in a direction transverse to an optical axis of the beam.

Description:
[0001]    The present invention relates to apparatus for radiation treatment devices of the eye. The invention relates particularly, but not exclusively, to radiation treatment apparatus for treating diabetic retinopathy. 
       BACKGROUND OF THE INVENTION 
       [0002]    Light treatment of the eye can be used for a variety of therapeutic purposes, including retinopathy, modifying biological rhythms, psychiatric disorders and depression. For example, diabetic retinopathy is a condition caused by diabetes in which damage to the retina occurs, which can lead to impairment of vision or blindness. The condition can be treated by preventing the complete dark adaptation of the eye by illuminating the eyes/eyelids during sleep. The required wavelength for this treatment corresponds to the scotopic sensitivity of the eye, approximately 480 to 510 nm. Ideally a comfortable mask would be required for light treatments on the eye, especially if the therapy is conducted during sleep. 
         [0003]    Several examples of light therapy devices acting on the eye are known. Most of these utilize LEDs as light source. LEDs are substantially rigid and most configurations cause some degree of discomfort to the user, especially if the device is to be used while sleeping. In particular LED sources generate heat, causing discomfort. Some examples of LED based devices are below: 
         [0004]    GB2410903A (Arden) describes a light emitting device for preventing retinal disease. The device is based on LED emitters. 
         [0005]    U.S. Pat. No. 6,350,275 (Vreman) describes a radiation treatment device with LED emitters. The LEDs are integrated into the frames of eyeglasses. 
         [0006]    U.S. Pat. No. 4,858,609 (Cole) describes a bright light mask with the external light source coupled via fibre optics. Such a solution requires a separate light source, which is cumbersome for the wearer. Alternatively, the document suggests miniature light bulbs embedded in the mask. In this implementation, heat filtering is proposed. 
         [0007]    U.S. Pat. No. 4,396,259 (Miller) describes eyeglasses with a spectrum wheel. The device uses a lightbulb, making it cumbersome and bulky. 
         [0008]    EP 0495988 (Masuda) describes light emitting glasses to induce sleep, utilizing light emitting diodes. 
         [0009]    U.S. Pat. No. 5,486,880 (House) describes an apparatus for causing constriction of the pupil of an eye. The disclosure does not address the type of light source to be used in such devices. 
         [0010]    U.S. Pat. No. 4,938,582 (Leslie) describes a chromo therapy device that utilizes LEDs projecting light onto a screen in front of the eyes. The proposed device is essentially a pair of glasses which are bulky in construction. 
         [0011]    U.S. Pat. No. 6,319,273 (Chen) describes an illuminating device for treating eye disease. The invention utilizes LEDs and proposes the use of a focusing lens. 
         [0012]    US2008/0269849 (Lewis) describes pulsed phototherapy devices, including eyemasks employing LEDs or lasers. The invention does not offer efficient solutions for heat management. 
         [0013]    It is clear that LED and incandescent based devices have disadvantages in terms of either having rigid components or dissipation of heat generated by spot sources. The use of flat electroluminescent films is one possibility to make the device thin and deal with heat management. For example, some of the prior art suggests the use of so called AC electroluminescent (ACEL) films or wires. While the form factor of such films is ideal, they operate at high voltages and therefore are not preferred. 
         [0014]    US 2005/0278003 (Feldman) describes wearable devices to deliver light to the retina. The disclosure proposes the use of LED, electroluminescent wire or electroluminescent flat panels. The disclosure does not offer power efficient solutions. 
         [0015]    U.S. Pat. No. 4,777,937 (Rush) describes a mood altering facial mask with an electroluminescent strip that provides stimulus of a particular colour. The electroluminescent strip operates at high voltages and its power efficiency is not ideal. 
         [0016]    US 2010/0179469 (Hammond) suggests the use of OLED based phototherapy systems for the stimulation of the retina. The disclosure recognizes the need for heat management, and suggests heat sinks or other dedicated cooling such as cooling fans to solve the problem. The disclosure does not offer means to reduce the heat emitted per area. 
         [0017]    There is a need for improved eye masks for phototherapy that are comfortable to wear, dissipate little heat, and operate efficiently, with minimal power requirements. 
         [0018]    Preferred embodiments of the present invention seek to overcome one or more of the disadvantages discussed above of known arrangements. 
       SUMMARY OF THE INVENTION 
       [0019]    According to an aspect of the present invention, there is provided an apparatus for directing electromagnetic radiation into a respective pupil of at least one eye of a user, the apparatus comprising: 
         [0000]    first radiation emitting means comprising at least one radiation emitting layer adapted to emit electromagnetic radiation;
 
second radiation emitting means adapted to direct electromagnetic radiation into at least one eye and/or onto at least one eyelid of a user; and
 
radiation guide means adapted to receive radiation emitted by said first radiation emitting means and to direct at least part of said radiation to said second radiation emitting means, wherein a total surface area of said first emitting radiation means from which radiation is emitted is larger than a total cross sectional area of a beam of radiation entering the or each pupil of the user in use, in a direction transverse to an optical axis of said beam.
 
         [0020]    By providing first and second radiation emitting means such that a total surface area of said first radiation emitting means from which radiation is emitted is larger than a total cross sectional area of a beam of radiation entering the or each pupil of the user in use, in a direction transverse to an optical axis of said beam, this provides the advantage of enabling radiation directed into one or more eyes of the user to be generated over a larger area than in the prior art. This in turn provides the advantage of enabling the necessary therapeutic radiation doses to be generated at lower intensity than in the prior art, which reduces the heat generated per unit area, thus minimising discomfort to the user. In addition, under certain circumstances, this enables the radiation to be generated more efficiently. 
         [0021]    At least one said radiation emitting layer may be adapted to emit radiation in response to application of electrical power. 
         [0022]    At least one said radiation emitting layer may be adapted to emit radiation in response to irradiation of said layer. 
         [0023]    By suitable choice of materials, this provides the advantage of enabling a more comfortable and/or a disposable apparatus to be provided, for example an apparatus which emits radiation over an extended period in response to initial excitation. 
         [0024]    At least one said radiation emitting layer may comprise at least one organic light emitting diode (OLED). 
         [0025]    The radiation guide means may comprise a radiation transmitting portion including at least one first layer having a respective first refractive index and at least one second layer having a respective second refractive index, wherein said first refractive index of at least one said first layer is higher than the respective second refractive index of at least one second layer in contact with said first layer. 
         [0026]    This provides the advantage of minimising radiation loss out of said first layer by causing total internal reflection of the radiation. 
         [0027]    The radiation guide means may include at least one luminescent material. 
         [0028]    This provides the advantage of enabling the predominant wavelength of radiation entering an eye of the user to be selected. 
         [0029]    The degree of luminescence of at least one said luminescent material may vary with time. For example, in a case in which the luminance of a material in said first radiation means decreases with time, the radiation guide means may include at least one photochromic layer material having a transparency which increases with time, so that decay in the photochromic layer compensates decay in the material of the first radiation means. 
         [0030]    The luminescent material may be concentrated in a region adjacent said second radiation emitting means. This provides the advantage of minimising the amount of luminescent material needed to be used. 
         [0031]    The radiation guide means may further comprise at least one reflective layer. 
         [0032]    This provides the advantage of further minimising leakage of radiation from the radiation guide means, as a result of which the intensity of radiation directed to the eye of the user can be maximized, which in turn enables the intensity of the radiation source to be minimized, further reducing the degree of discomfort to the user. 
         [0033]    The radiation guide means may comprise a radiation transmitting portion having tapered thickness adjacent at least one edge portion thereof. 
         [0034]    This provides the advantage of enabling radiation leakage from the radiation guide means to be minimised under certain circumstances. For example, the radiation leakage could be minimised as a result of increasing angle of reflection from a second layer having lower refractive index adjacent to a first layer having higher refractive index, thus further contributing to total internal reflection. 
         [0035]    The radiation guide means may comprise a radiation transmitting portion, wherein the radiation transmitting portion is rounded adjacent at least one edge portion thereof. 
         [0036]    This provides the advantage of further minimising radiation leakage. 
         [0037]    The second radiation emitting means may be adapted to conform to a shape of at least one eyelid of the user. 
         [0038]    The second radiation emitting means may include at least one coolable material. 
         [0039]    The second radiation emitting means may include at least one material having a transmissivity to radiation varying with radiation intensity. 
         [0040]    This provides the advantage of enabling the intensity of radiation directed to an eye of the user to be regulated. 
         [0041]    At least one said radiation emitting layer may be adapted to be moved between a respective first position, in which said layer is adapted to direct radiation into said radiation guide means, and a respective second position, in which said layer is adapted to be exposed to exciting radiation. 
         [0042]    This provides the advantage of enabling a more compact apparatus to be provided. 
         [0043]    At least one said radiation emitting layer may be adapted to be moved between respective first and second positions thereof by folding. 
     
    
     
         [0044]    Preferred embodiments of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which: 
           [0045]      FIG. 1  is a perspective view of an eye mask of a first embodiment of the present invention; 
           [0046]      FIG. 2  is a perspective view of an eye mask of a second embodiment of the present invention; 
           [0047]      FIG. 3  is a perspective view of an eye mask of a third embodiment of the present invention; 
           [0048]      FIG. 4  is a side cross-sectional view of the eye mask of  FIG. 1 ; 
           [0049]      FIG. 5  is a side cross-sectional view illustrating a process of optically charging the eye mask of  FIG. 4 ; 
           [0050]      FIG. 6  is a side cross-sectional view of an eye mask of a fourth embodiment of the present invention; 
           [0051]      FIG. 7  is a side cross-sectional view of an eye mask of a fifth embodiment of the present invention; 
           [0052]      FIGS. 8(   i ) to  8 ( iii ) show a side cross-sectional view of an eye mask of a sixth embodiment of the present invention; 
           [0053]      FIG. 9  is a perspective view of the eye mask of  FIGS. 8(   i ) to  8 ( iii ); 
           [0054]      FIG. 10  is a side cross-sectional view of an eye mask of a seventh embodiment of the present invention; 
           [0055]      FIG. 11  is a side cross-sectional view of an eye mask of a eighth embodiment of the present invention; 
           [0056]      FIG. 12  is a side cross-sectional view of an eye mask of a ninth embodiment of the present invention; and 
           [0057]      FIG. 13  is a side cross-sectional view of an eye mask of a tenth embodiment of the present invention. 
       
    
    
       [0058]    The present invention is based on the discovery that heat dissipation in light sources for eye masks can be effectively solved by using area light sources and by extending their size so that they are significantly larger than the eye. The light intensity generated per unit area can therefore be reduced and thus the associated heat dissipation per unit area is also reduced. To compensate for the reduced luminance, the total light output is effectively coupled into a lightguide, collected and emitted into the eye or onto the eyelids. 
       DETAILED DESCRIPTION 
       [0059]    An eyemask of a first embodiment of the present invention is shown in  FIG. 1 , where  100  is the eyemask itself, and  101  illustrates an area light emitter combined with a lightguide and which is substantially larger than light exit windows  102  designed to illuminate the eyes. The mask can be attached, for example, by a strap  103  to the wearer&#39;s head. In a second embodiment of the invention, one or more area light sources such as  101 A and  101 B may be used as shown in  FIG. 2 .  FIG. 3  illustrates a third embodiment of the invention in which the emitter and lightguide  101  might take up substantially the entire area of the light mask to maximize the light output or to reduce the luminance required from the source. 
         [0060]    There are several important benefits with this approach. First, heat dissipation becomes negligible and no area of the mask feels warm to the wearer. Second, the invention enables the use of low intensity light sources or to operate light sources at extremely low luminance. The mask can utilize a number of light sources, for example OLED (organic light emitting diodes), electroluminescent films, chemiluminescent layers, phosphorescent layers or even bioluminescent materials. 
         [0061]    In one embodiment, OLED is used as the light source. The OLED source is ideally 2-1000 times larger than the emissive area required for the eyes. For example, the emissive OLED face can be 20×5 cm while the area illuminating the eyes can be 1×1 cm for each eye. The OLED area can take up substantially the whole area of the eye mask. Correspondingly, the OLED device is run at lower luminance. The device can be operated at reduced voltages and current density, which increases the lifetime of the OLED source. Reduced voltage operation is highly desirable for portable devices. In many OLED sources the power efficiency is improved at low luminance. Thus the invention also enables such devices to be run in a regime where they are more efficient. 
         [0062]    In another embodiment long decay phosphorescent materials are used as the light source. The phosphorescent source is ideally 2-1000 times larger than the emissive area required for the eyes. For example, the emissive phosphorescent layer can be 20×5 cm while the area illuminating the eyes can be 1×1 cm for each eye. The phosphorescent layer can take up substantially the whole area of the eye mask. In turn the light output of the phosphorescent layer is amplified to higher intensity by the light guide. The invention therefore enables very low intensity afterglow materials to be used, yet provides sufficient light levels for the treatment of the eye. 
         [0063]    In yet another embodiment, chemiluminescent or bioluminescent materials are used as the light source. The chemiluminescent source is ideally 2-1000 times larger than the emissive area required for the eyes. For example, the emissive chemiluminescent surface can be 20×5 cm while the area illuminating the eyes can be 1×1 cm for each eye. The chemiluminescent layer can take up substantially the whole area of the eye mask. In turn the light output of the chemiluminescent layer is amplified to higher intensity by the light guide. The invention therefore enables very low intensity chemiluminescent materials to be used, yet provides sufficient light levels for the treatment of the eye. 
         [0064]    The light guide used in the mask can propagate light towards the eye using adjacent layers of low optical index materials or reflective layers. The light guide in the mask may optionally comprise at least one luminescent dye to effectively capture the light emitted by the area source. The dye may be used to define the spectra of the light emitted into the eye. 
         [0065]    In order to compensate for variations of light intensity with time, the mask may comprise one or more photochromic layers. For example, phosphorescent or chemiluminescent sources exhibit decaying luminance with time. By including a photochromic member, it is possible to reduce the initial brightness and make the output illumination more even with time. As the luminance of the area source decays the photochromic layer becomes gradually more transparent, effectively providing a simple compensation mechanism. 
         [0066]      FIG. 4  is a crossection view of an area of the mask  20  with an area emitter with the eye region  6  emitting light into the eyes or onto the eyelids of the patient. The device comprises a lightguide  1  optionally doped with a luminescent dye. Layers  2  and  3  are low index materials designed to ensure total internal reflection of the light entering layer  1 . An emissive layer  8  is provided, with an area substantially larger than the eye region  6 . Light emitted by emissive layer  8  is absorbed by the dye  5  and is reemitted into layer  1 . The path of light  7  is then guided via internal reflection to the eye region  6 . The mask may further comprise optionally a reflective layer  9  and a protective layer  10 . The eye region  6  comprises a light outcoupling feature such as embossed or moulded features. This region may also contain pigment particles to scatter light for efficient outcoupling. Any suitable outcoupling technique can be used. 
         [0067]      FIG. 5  illustrates a technique for charging the mask when the emissive layer  8  comprises long afterglow phosphorescent materials. The layer  8  can be charged by external incident light  4 , which can be ambient light or any suitable light source. In this embodiment the device might be charged by a dedicated light charger unit. The charger may be an enclosure containing one or more illuminating sources such as LEDs or incandescent bulbs. The charger may also be in the form of an illuminator sheet with which the mask is brought into contact. 
         [0068]      FIG. 6  is a crossection view of a mask  20  with an area emitter  8  and the eye region  6  emitting light into the eyes or onto the eyelids of the patient. The device comprises a lightguide  1  optionally doped with a luminescent dye. Layers  2  and  3 A are low index materials designed to ensure total internal reflection of the light entering layer  1 . Layer  3 A may optionally be a reflective layer such as metal. The light emitting layer  8  has an area substantially larger than the eye region  6 . Light emitted by  8  is absorbed by the dye  5  and is reemitted into layer  1 . The path of light  7  is then guided via internal reflection to the eye region  6 . The mask may further comprise a protective layer  10 . 
         [0069]      FIG. 7  is a crossection view of a mask  30  with area emitters  8  and  8 A on both sides of the lightguide  1  in order to further increase the area of the source. An optional reflective layer  9 A is provided to prevent escape of the light from the surface of the mask. In this embodiment the total light output can be further increased or the luminance of the source reduced. The eye region  6  emits light into the eyes or onto the eyelids of the patient. The device comprises a lightguide  1  optionally doped with a luminescent dye. Layers  2  and  3 A are low index materials designed to ensure total internal reflection of the light entering layer  1 . The light emitting layers  8  and  8 A together have an area substantially larger than the eye region  6 . Light emitted by light emitting layers  8  and  8 A is absorbed by the dye  5  and is reemitted into layer  1 . The path of light  7  is then guided via internal reflection to the eye region  6 . The mask may further comprise protective layers  10  and  10 A. 
         [0070]      FIG. 8  illustrates a mask having a foldable structure with two sets of area emitters comprising segments  20 A and  20 B. In one embodiment, the emitters comprise long afterglow phosphorescent layers in each segment. This mask can be conveniently charged in the open state as shown in  FIG. 8(   i ). External light  4  from the ambient or from a light charger unit excites the phosphorescent material causing it to glow following excitation. The mask can be folded as shown in  FIG. 8(   ii ). The mask  35  is shown in its closed state in  FIG. 8(   iii ). Light irradiated from either side is captured in the lightguide and propagated toward the eye via internal reflection. In this embodiment the emissive area is significantly larger than the area to illuminate the eyes. For example, the total emissive area can be as large as 400 cm 2 , while each of the areas illuminating the eye can be 1 cm 2 . 
         [0071]      FIG. 9  further illustrates a foldable eyemask  35  with two parts  20 A and  20 B having absorbing/emitting layers. Preferably the part  20 A shining light on the eye is folded inwards to secure it to the head when strapped. 
         [0072]      FIG. 10  illustrates a preferred embodiment of the mask  40  in which the lightguide  1  is tapered or narrowed towards the edge of the mask. This reduces the number of reflections for the light emitted at the edge due to the gradually increasing angle of reflection from the low index layer  2  and/or reflective layer  9 . The edge of the lightguide might also be rounded to reduce outcoupling and loss of light at the edge. In this embodiment light emitted from the area source  8  is coupled into the lightguide material  1 . The lightguide may optionally be doped with a dye. Outcoupling is effected via regions  6 A and  6 B. 
         [0073]      FIG. 11  is further embodiment where an additional region is disposed within the lightguide. Region  12  is doped with a dye  5  to effect conversion or correction of the emitted wavelength of the light  7 . 
         [0074]      FIG. 12  illustrates another embodiment, in which the eyemask comprises a further optical element  13  to couple light in close proximity to the eye or eyelid. Element  13  may be a polymer optionally shaped into a lens. This portion may also comprise a gel material to make soft contact with the eyelids. The gel may have additional functionality of cooling, for example, by placing it in a refrigerator prior to use. 
         [0075]      FIG. 13 . illustrates a further embodiment with a light controlling layer  14 . This layer may comprise a photochromic material, which attenuates the light at high intensities while staying substantially transparent at low intensities. Such an element is an effective method to control light intensity variations from the source and is especially useful when the light source is phosphorescent or chemiluminescent. 
       Sources: 
       [0076]    The invention may utilize any area source, for example OLED, bioluminescent, phosphorescent coatings, e.g. luminophore, or chemiluminescent emitters. The mask might comprise one or more area sources, for example two sources on each side of the mask with the lightguide positioned in the middle. The two sides may form a foldable structure. To benefit from sources of low luminance the area of the source is at least twice the area of the outcoupling region provided to illuminate the eyes. Preferably the source is between 2 to 1000 times than the outcoupling region. More preferably, the source is between 4 to 200 times larger than the outcoupling region. Even more preferably the source is between 10 to 100 times the size of the area illuminating the eye. The area illuminating the eyes or eyelids is preferably between 1 mm 2  to 20 cm 2 . More preferably, the area illuminating the eyes or eyelids is between 0.1 cm 2  to 10 cm 2 . Even more preferably, the area illuminating the eyes or eyelids is between 1 cm 2  to 5 cm 2 . The source should be structured in a manner that improves light coupling into the waveguide or on to the wavelength conversion materials. Such structuring may include the formation of 2D or 3D photonic crystals to direct the light emission or larger scale structures formed by, for example, deposition onto non-planar surfaces such as microprisms, or moulding into non-planar shapes. 
       OLED Sources 
       [0077]    OLED sources might include luminescent or phosphorescent emitters. OLED films can be manufactured by any suitable technique, for example evaporation, solution coating techniques or printing. The source might comprise small molecule or polymeric materials. The emission colour can be defined by the choice of OLED materials. The OLED source comprises at least one emitting surface coupling to the lightguide. Optionally inorganic thin film luminescent or electroluminescent layers might be used. These may include inorganic quantum dots or inorganic luminescent or transport materials instead or in addition to OLED materials. The OLED source can be provided on a rigid substrate such as glass. Ideally the OLED source is provided on a flexible substrate such as polyester (PET) or polyethylene naphthalene (PEN). Any suitable polymeric substrate and barrier material can be used. Since the invention enables running the OLED at lower luminance, less perfect encapsulation is acceptable. It is estimated that in an optimized mask configuration, the luminance of the OLED source can be reduced by a factor of 2-100. 
         [0078]    When OLED area sources are used the mask comprises a power source such as a battery. Low voltage (&lt;10V) operation is preferred for safety reasons as well as for reducing the size and complexity of the power source. Ideally the power source is less than 6 V, more preferably less than 3 V. Importantly, the invention enables running OLED at low voltages and current densities. 
       Light Accumulation Sources 
       [0079]    In one embodiment the area light source comprises phosphorescent or luminescent materials that exhibit long glow after excitation. For example, following a light exposure they glow for minutes or hours. Such materials make it possible to provide battery free phototherapy devices with the capability to recharge the device for prolonged light emission. Materials with delayed phosphorescence excited by any electromagnetic radiation can be considered, for example infrared light or heat. Such materials can be formed into a film, sheet or coating to provide an area, light source. The sheet or coating may comprise substantially the entire area of the mask, coupling light into the lightguide described in the present invention. 
         [0080]    Materials particularly relevant to the invention are long decay luminophore materials where the re-emitted light is slowly released over a period of time after initial excitation. Suitable materials include, but are not limited to, those described in U.S. Pat. No. 5,424,006 and U.S. Pat. No. 5,686,022. Suitable materials include those manufactured by Nemoto &amp; Company, Tokyo and are available under the brand name LUMINOVA having the general formula MAl 2 O 4 , where M is one or more metals selected from strontium (Sr), calcium (Ca), barium (Ba), magnesium (Mg) activated by europium (Eu) and at least one co-activator selected from lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), terbium (Tb), thulium (Tm), ytterbium (Yb), lutetium (Lu), tin (Sn), manganese (Mn) and bismuth (Bi). Chemical compositions of exemplary materials for use in the invention include, but are not limited to: SrAl 2 O 4 :Eu; SrAl 2 O 4 :Eu, Dy; SrAl 2 O 4 :Eu, Nd; Sr 4 Al 14 O 25 :Eu; Sr 0.5  Ca 0.5  Al 2 O 4 :Eu, Dy; BaAl 2 O 4 :Eu, Nd; BaAl 2 O 4 :Eu, Sn; ZnS:Cu; ZnS:Cu, Co; ZnS:Mn; ZnS:Ag; BaMgAl 10 O 17 :Eu; BaMgAl 10 O 17 :Mn, Eu; Sr 2 P 2 O 7 :Eu; CaWO 4 ; CaWO 4 :Pb; SrGa 2 S 4 :Eu; CePO 4 :Tb; MgWO4; Y 2 O 3 :Eu; Y 3 Al 5 O 12 :Ce; (Ba 1-x Sr x ) 5  (PO 4 ) 3  (F, Cl):Eu; (Y 1-x-y Gd x Lu y ) 3  (Al 1-y Ga y ) 5 O 12 :Ce; (Y 1-x Gd x ) 2 O 3 :Bi, Eu; (Y 1-x P x ) 2 O 4 :Eu; YVO 4 :Eu; Y 2 O 2 S:Eu. 
         [0081]    Chemiluminescent Sources 
         [0082]    Chemiluminescent sources may also be provided as the area light emitter. Such light sources exploit the light emission associated with the product of the chemical reaction between at least two reactants. A common example of such light source is the so-called glow stick where a fluorescent dye is excited by the decomposition of the product of the reaction between hydrogen peroxide and oxalate ester. Particularly attractive to the invention in the case of a single use phototherapy device is a system where one of the reactants is contained in a vessel which is broken by application of pressure (or folding) to allow the reactants to mix and initiate the chemical reaction responsible for light emission. The reactants may be included in a sheet comprising a gel. The sheet may take up substantially the entire area of the mask, coupling light into the lightguide described in the present application. 
       Lightguides: 
       [0083]    The lightguide may comprise substantially the whole area of the eye mask. Preferably the lightguide comprises between 5% to 100% of the mask area. More preferably the lightguide comprises between 10% to 95% of the mask area. The lightguide is the same size or larger than the light source. Suitable lightguide constructions include a polymer core with a high index material and surrounding low index polymer layer(s), which may extend to both sides of the lightguide. Where required, for example in the case where the refractive index of the light source (i.e. OLED source) is substantially higher than the low index layer or even the higher index core, an additional high index coupling layer such as narrow angle high gain GRIN diffusers (for example those offered by Microsharp Ltd) can be placed in between the source and waveguide. Where a wavelength conversion layer is used, an appropriate position would be between the low index cladding and high index core, in order to take advantage of Supercritical Angle Fluorescence (SAF) which allows the preferential injection of converted light into waveguided modes of the high index core. Appropriate materials for the waveguide should have a high degree of transparency in the spectral region of interest, and where required should be flexible and appropriate for the particular method of manufacture. Low index materials therefore may include MY-132 (MY Polymers Ltd), with refractive index 1.32. A high index core could include material such as polysiloxanes (WO/2003/011944) with refractive index of up to 1.581. This combination of materials would have a critical angle of 58 degrees, and SAF emission from the interface would couple up to approximately 70% of light directly into the waveguided modes. 
         [0084]    These may include polystyrenes, poly(ethylene terephthalate), a transparent polyolefin, in particular a clarified polyolefin, for example clarified polypropylene, Poly(methyl methacrylate) (PMMA), transparent polyamide or polycarbonate and perfluorinated polymers such as polyperfluorobutenylvinylether, polysulphones, polyether sulphones and polyacrylates. PMMA and polycarbonate are two transparent thermoplastics of choice because of their ease of processing, their availability on the market, their high transparency in the visible range and refractive index in the visible range. Other materials which are recommended for use with fluorescent dyes include styrene-butadiene. For the low index cladding, polymers such as TEFLON FEP, PCTFE (polychlorotrifluoro-ethylene) or PVDF as well as UV curable low index polymers such as the OPTI CLAD (manufactured by Ovation Polymers) series, may be chosen, which have refractive indices as low as 1.33. Further examples of polymers can be found in “Encyclopedia of Polymer Science and Engineering”, 2nd Edition, J Wiley and Sons and “Polymer Handbook”, 4th ed.; John Wiley &amp; Sons, 1999. The lightguides may be further surrounded by reflectors, as described in a later section in order to recycle non-waveguided light, both allowing light from the initial light source to be down converted on later passes and also recycle non-SAF emitted light. In general, structures constructed so that the majority of the light is waveguided by Total Internal Reflection (TIR) will have better device performance. Additionally the high index core of the lightguide may be doped with light accumulation or wavelength converting chemical. The ends of the lightguides may be squared and mirrored, or they may be tapered to a point or curved edge such as a parabola such that waveguided light may be turned and reflected towards the centre of the guide again with minimal reflections from metallic surfaces. The lightguide may also be a gel material within a polymer shell. 
       Wavelength Conversion Materials 
       [0085]    The lightguide may comprise wavelength conversion materials such as dyes. Such materials can aid coupling of light into the lightguide. Wavelength conversion is also an approach to adjust the wavelength emitted into the eyes. By using such materials it is possible to convert less effective wavelength light into an effective spectrum. Suitable materials or mixtures of materials are those which absorb light at a first wavelength and subsequently emit light at a second wavelength which is different from the first wavelength. The emitted light might be result of fluorescence and/or phosphorescence depending on the type of material or mixture of materials. In addition the nature of the material or mixture of materials and associated energy conversion mechanisms will dictate if the wavelength emitted is larger or smaller than that of the absorbed light. Light can be absorbed by one species and re-emitted by a second species following non-radiative energy transfer. 
         [0086]    Suitable wavelength conversion materials may be of any type including but not limited to coumarins; perylenes; xanthenes; thioxanthenes; fluoresceins; rhodamines; azlactones; methines; oxazines; thiazines; phtalocyanines; stilbenes; distilbenes; distyrenes; azomethines; phenanthrenes; rubrene; quinacridones; naphtalimides; methines; pyrazolones; quinophthalones; perinones; anthraquinones. Materials particularly relevant to the invention are those which can be efficiently doped into light guide materials without compromising their optical function and which exhibit a high quantum yield. Of particular interest are fluorescent dyes manufactured by BASF and available under the brand name LUMOGEN F Dyes. Other commercial materials of interest include those available under the following brand names MACROLEX (Bayer), HOSTASOL (Clariant), THERMOPLAST (BASF), SOLVAPERM (Clariant), SANDOPLAST (Clariant), AMAPLAST (Color-Chem). 
         [0087]    Quantum dot materials may also be used to adjust the emission characteristics of the mask. Suitable quantum dots materials include but are not limited to CdSe, CdTe, ZnS, ZnTe, ZnSe, CdS, HgS, HgSe, HgTe, CdTeSe, CdTeS, ZnSSe, ZnTeSe, ZnSTe, CdZnSe, CdZnTe, CdZnS, GaAs, GaP, GaSb, GaN, InN, InP, InAs, InSb, InGaP, InGaAs, InGaN, AlInGaN, AlInGaP, AlInGaAs, Si, Ge. 
         [0088]    The above wavelength conversion materials may also be used as part of the area light source or the outcoupling region. 
         [0089]    Outcoupling Methods 
         [0090]    The mask comprises at least one outcoupling region as an exit window to shine light onto the eye. Outcoupling from this region may be achieved through the use of scattering, embedded nanoparticles and/or quantum dots which may be doped or undoped, of various shapes and orientations such as rods, triangles or spheres, optical interference structures such as diffraction gratings or holographic structures, photonic crystals which may be either 2D or 3D, macroscopic shaped structures such as, but not limited to, micropyramids and microprisms, microlenses, lens arrays, GRIN structures, fiber optics for either scattering or redirection of light through waveguiding or other coupling methods through variation of refractive index. The outcoupling region may either be directly on the side of the escape window area forming part of the window, it may be an external component attached to the window, or it may be on the opposite side of the waveguide to the window (i.e. diffractive components) Additionally bulk components such as scattering particles, nanoparticles and lumophores may be present in the waveguide near the window for outcoupling, or they may form part of external components. Concave or convex outcoupling schemes may be employed. 
       Reflectors 
       [0091]    Reflectors will have two primary purposes. The first is to ensure that light that is not wavelength converted and will be substantially reflected through the wavelength conversion region so that a significant proportion of light will be converted on later passes as opposed to being absorbed and lost. The second is to provide supplementary waveguiding to light intended for emission that has not been injected into supercritical waveguided modes in the waveguide core. In the case of the SAF layer above, this would make up around 30% of the light. The reflectors may consist of periodic or aperiodic dielectric multilayers which may be either isotropic or anisotropic in nature, with the particular arrangements of refractive indices, thicknesses and index ellipsoid orientations chosen to optimise reflections of light which is not captured within the waveguide to either ensure its passage to the outcoupling region or to increase the chances of absorption and re-emission at the wavelength conversion layers. Such materials may either be custom arrangements of layers which may be extruded or laminated onto the core or commercially available films. The choice of materials may also be chosen to allow their dual use as barrier layers to lengthen the lifetime of the devices. In the event that no practical arrangements can be found, it would also be possible to used metallic or metallised layers as a reflector. However for large numbers of reflections, the efficiencies of metallic layers are significantly poorer. 
       Optical Modulation Layer 
       [0092]    The mask may optionally comprise one or more optically variable layers for modulation of the light coupling. This may for example be a photochromic light absorber (such as silver chloride) or may change refractive index such that index matching between layers ( 3 ) or ( 5 ) and ( 9 ) increases and decreases according to the desired conditions. Such layers that change properties based on conditions including but not limited to, pH and chemicals (chemochromic), humidity (hydrochromic), temperature (thermochromic) and pressure may also be used. The optically variable layer may be between the light source and waveguide, in the waveguide outcoupling area, or in the additional pad ( 13 ). The layer may consist of pure photochromic chemical, a doped material such as polymer, or be dispersed in a solution. The range of suitable materials is large and includes inorganic materials such as zinc halides and silver chloride, as well as organic materials such as spirooxazines which have fast switching in gels and spiropyrans which can be cross linked with other molecules. Such organic molecules as these may be tuned to specific wavelength switching requirements. 
       Shape, Form of Implementation 
       [0093]    The eyemask is ideally flexible or conformal. The mask may be provided for both eyes or for one eye or as a patch. The form factor and bend angles of the waveguide should remain small with respect to the thickness of the waveguide in order to ensure an acceptable level of total internal reflection is maintained. The lightguide may comprise a soft material such as a gel. The gel may provide an additional cooling function to soothe the eyes. The external surface of the mask may be covered with a fabric material or other soft layer or layers such as a foam. These layers can have the function to provide vapour transmission. 
         [0094]    Method for Manufacturing 
         [0095]    The eyemask can be manufactured by a variety of techniques. The lightguide is preferably manufactured by moulding, lamination, stretching, forming of the lightguide as well as emissive components. The outcoupling features can be formed in a single moulding step when forming the mask or defined in a second step by embossing or coating further layers. The area light source such as OLED or phosphorescent source may be laminated or attached to the lightguide using an adhesive. The source may also be directly coated onto the lightguide by solution coating techniques such as screen-, flexo-, gravure-, or inkjet printing, spray coating or dip coating. The source may also be deposited on the lightguide by evaporation. 
       EXAMPLES 
     Example 1 
     Retinopathy Device 
       [0096]    In patent application GB2410903A, Arden describes an eye mask device using inorganic LED light sources to illuminate the eyes of patients suffering from retinal diseases during their sleep. Because the treatment is carried out during sleep a phototherapy device with minimum discomfort for the user is advantageous. Because of the low light intensity required and the long illumination time available a passive phototherapy device using luminophore for slow release of light is particularly suitable. This example describes such device. 
         [0097]    A light guide sheet element (less than 2 mm thick in thickness) could be moulded in the shape of an eye mask as to cover the eye of a patient as shown in  FIG. 1 . The element is formed by injection moulding silicone resin containing 0.1% of Lumogen F Green 850 (BASF). The light guide is coated on both sides with a 5 microns thick lower index polymer such as polychlorotrifluoro-ethylene. 
         [0098]    A blue light emitting OLED is formed on top of the lightguide using 4,4′-bis( 2 , 2 ′diphenilvinyl)-1,1′-biphenyl (DPVBi) as the emitter, for example by using a device structure described by Othman et al in Proc. IEEE of ICSE, 2004. The blue emission centered at 483 nm is then absorbed by the lightguide and transmitted to the emitting surface. 
         [0099]    On the opposite side of the OLED, two light delivery areas are defined to coincide with the eye of the patient so that the light emitted by the phototherapy device can illuminate the eye lids of the patient. These areas assist outcoupling by surface structuring to the attachment of a soft sac containing mineral oil or silicone gel of an equal or higher refractive index to the core. This allows light to be coupled directly from the lightguide core into a non-waveguiding structure directly over the eye, and allowing light into the eye. The use of a gel further assists comfort and coupling between the lightguide mask and eye. A large proportion of the light emitted by the OLED enters the lightguide, where it is absorbed by the fluorescent die and re-emitted as light with peak wavelength around 500 nm. The 500 nm light is emitted through the emitting surface is adequate for absorption rod cells. 
         [0100]    It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.