Abstract:
Medical treatment apparatus that treats conditions selected from the group consisting of phantom limb pain, stroke, visual neglect syndrome, and complex regional pain syndrome, and worn on a head of a user to view an object in front of an eye of the user includes a support configured for location and use of the apparatus near the eye; solely one optical device including at least one prism that defines a plane at which the field of view is reflected supported by the support such that, in use, the optical device is within a visual field of solely one eye of the user, the optical device reversing a field of view of the user&#39;s eye through the optical device laterally with respect to the user&#39;s eyes, and configured such that the plane defined by the at least one prism is substantially in a sagittal plane of the user; and a member that obstructs a field of view of the eye of the user other than the eye with which the optical device is operable.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 12/302,689, filed Nov. 26, 2008, which is a §371 of International Application No. PCT/GB2007/002026, with an international filing date of Jun. 1, 2007 (WO 2007/138330 A1, published Dec. 6, 2007), which claims priority of British Patent Application No. 0610914.4, filed Jun. 1, 2006, the subject matter of which is incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to optical apparatus and in particular but not exclusively to optical apparatus suitable for treatment, investigation and diagnosis of pain, for stroke rehabilitation, for brain injury rehabilitation or for treatment of physical and visual dysfunction or as an experimental apparatus. 
       BACKGROUND 
       [0003]    The above mentioned medical conditions can be treated by means of what is termed a mirror box. A mirror box consists of two separate, side-by-side compartments and a mirror arrangement. A user either inserts his or her left arm in the left compartment or his or her right arm in the right compartment. The compartment into which the arm is inserted is covered to hide the inserted limb from view. The mirror arrangement inside the mirror box inverts the image of the inserted limb so that it appears to the user to be present in the other compartment and thus appears to be his or her other limb. For example, if the user inserts his or her left arm he or she sees a reversed view of his or her left arm such that it appears to be his or her right arm. This optically created illusion of the presence of the right arm tricks the user&#39;s brain into believing that movement of the left arm is actually the right arm moving. As a result, it is understood that the brain undergoes re-mapping that could improve the above mentioned medical conditions stated in the technical field section. 
         [0004]    The mirror box has disadvantages. More specifically, the mirror box can be impractical for frequent use and can be unsuited to use with the leg. 
         [0005]    Recently much activity has been seen in the development of drug treatments for PLP. However, drug treatments can produce undesirable side effects. 
         [0006]    Conversely in dyslexia and similar syndromes visual perceptual reversals occur and the potential in this has yet to be investigated. 
         [0007]    Other asymmetric neurological conditions, such as stroke, visual neglect syndrome and complex regional pain syndrome, may benefit from mirror box therapy. Furthermore, other ophthalmic conditions, such as cyclotorsion of the eye or diplopia, may be diagnosed using image reversal such as is provided by the mirror-box. In addition, rehabilitation of patients following limb injury and surgery, including the rehabilitation of athletes, may also benefit from optical illusions created by the mirror box. 
         [0008]    It could therefore be helpful to provide for an apparatus suitable for treatment of the above mentioned medical conditions. 
         [0009]    More specifically, it could be helpful to provide an optical apparatus for treatment of the above mentioned medical conditions. 
         [0010]    According to a first aspect there is provided optical apparatus comprising: a support configured for location and use of the optical apparatus near an eye of a user of the optical apparatus; and an optical device supported by the support such that, in use, the optical device is within a visual field of the eye of the user, the optical device being configured to reverse a field of view of the user&#39;s eye through the optical device laterally with respect to the user&#39;s eyes. 
         [0011]    As an example of the use of the device in the treatment of Phantom Limb Pain (PLP), a user locates the support of the optical apparatus in front of one of his eyes and views his remaining limb, e.g., his arm, through the optical device. The optical device reverses the field of view of the user&#39;s eye laterally with respect to his eyes. Reversal of the field of view of the user&#39;s eye laterally with respect to his or her eyes means that the field of view is reflected about a sagittal plane. Thus, for example if the user views his left arm through the optical device it appears to him that his right, amputated arm is present. 
         [0012]    An advantage of the optical apparatus is that the optical apparatus is more portable and less obstructive than the mirror box, thereby allowing for greater freedom of movement by a user. The optical apparatus also provides for a closer approximation to a normal visual environment for a user. This provides for ease of storage and transportation and for use in a home environment. In addition, the optical apparatus provides for greater ease of use with a lower limb than the mirror box. 
         [0013]    More specifically, the optical device may comprise an optical component that defines a reflecting plane about which the field of view is reflected. 
         [0014]    More specifically, the optical device may be configured such that the reflecting plane defined by the optical component is substantially in the sagittal plane. 
         [0015]    Alternatively or in addition, optical apparatus may be configured such that the reflecting plane faces towards one of a temporal side and a nasal side of the user&#39;s visual field. 
         [0016]    Alternatively or in addition, the optical device may comprise a mirror. 
         [0017]    Alternatively or in addition, the optical device may comprise at least one prism. For example, the optical device may comprise a pair of prisms. 
         [0018]    More specifically, the prism may be configured to provide for total internal reflection. The prism may be triangular. 
         [0019]    Alternatively or in addition, the prism may be truncated in form, e.g., a Dove prism. 
         [0020]    Alternatively or in addition the optical device may comprise at least one Fresnel-type prism. For example, the optical device may comprise a pair of Fresnel-type prisms. 
         [0021]    Alternatively or in addition, the optical device may comprise a pair of astigmatic lenses. 
         [0022]    Alternatively or in addition, the optical device may be configured to provide, in use, a field of view that extends in the meridional plane at least one of: above the eye and below the eye. Extension of the field of view in the meridional plane below the eye can provide for an adequate view of a lower limb of a user. 
         [0023]    More specifically, the optical device may be truncated distally and towards an eye of a user. Thus, a portion of the optical device outwith a field of view of the optical device may be absent. This can provide for a reduction in weight of the optical apparatus. 
         [0024]    Alternatively or in addition, when the optical device comprises a prism, the optical device may further comprise at least one lens. 
         [0025]    More specifically, the optical device may comprise one positively powered lens. Thus, the positively powered lens may magnify an object viewed by the user. 
         [0026]    More specifically, the positively powered lens may be disposed in relation to the prism such that, in use, the positively powered lens is one of: closer to the viewer&#39;s eye than the prism; and further away from the viewer&#39;s eye than the prism. An extent of magnification of the viewed object depends on a distance between the user&#39;s eye and the positively powered lens. 
         [0027]    Alternatively or in addition, the optical device may comprise one negatively powered lens. Thus, the negatively powered lens may minify an object viewed by the user. 
         [0028]    More specifically, the negatively powered lens may be disposed in relation to the prism such that, in use, the negatively powered lens is one of: closer to the viewer&#39;s eye than the prism; and further away from the viewer&#39;s eye than the prism. An extent of minification of the viewed object depends on a distance between the user&#39;s eye and the negatively powered lens. 
         [0029]    Alternatively or in addition, the optical device may comprise at least one astigmatic lens. The astigmatic lens may be disposed in the optical apparatus such that, in use, an image of an object viewed by a user may be meridionally distorted. 
         [0030]    More specifically, where the optical device comprises a plurality of astigmatic lenses, astigmatic axes of the astigmatic lenses may be parallel. Also, differences of focal lengths of the lenses in each meridian may be the same. Thus, meridians of such an arrangement may be in optimal focus. 
         [0031]    Alternatively or in addition, when the optical device comprises a prism, the optical device may further comprise a pair of lenses. 
         [0032]    More specifically, the pair of lenses may consist of a positively powered lens and a negatively powered lens. 
         [0033]    More specifically, the optical apparatus may be configured such that, in use, the positively powered lens is disposed further away from a user&#39;s eye than the prism and the negatively powered lens is disposed closer to the user&#39;s eye than the prism. Such a configuration may provide for magnification or, less readily, minification of a viewed object. 
         [0034]    An extent of magnification of a viewed object may be determined by a ratio of focal lengths of the positively and negatively powered lenses. Alternatively, an extent of minification of a viewed object may be determined by a ratio of focal lengths of the positively and negatively powered lenses and where the focal length of the negatively powered lens is greater than the focal length of the positively powered lens. 
         [0035]    Alternatively, the optical apparatus may be configured such that, in use, the negatively powered lens is disposed further away from a user&#39;s eye than the prism and the positively powered lens is disposed closer to the user&#39;s eye than the prism. Such a configuration may provide for minification or, less readily, magnification of a viewed object. 
         [0036]    An extent of minification of a viewed object may be determined by a ratio of focal lengths of the positively and negatively powered lenses. Alternatively, an extent of magnification of a viewed object may be determined by a ratio of focal lengths of the positively and negatively powered lenses and where the focal length of the negatively powered lens is greater than the focal length of the positively powered lens. 
         [0037]    Alternatively or in addition, the optical apparatus may be configured for viewing parts of a user&#39;s body. 
         [0038]    More specifically, a distance between the pair of lenses may be greater than a difference of the focal lengths of the lenses. 
         [0039]    Alternatively or in addition, the optical apparatus may be configured for viewing objects further away from the optical apparatus than parts of a user&#39;s body. 
         [0040]    More specifically, a distance between the pair of lenses may substantially equal to a difference of the focal lengths of the lenses. 
         [0041]    Alternatively or in addition, the optical device may comprise a pair of Fresnel-type astigmatic lenses. 
         [0042]    Alternatively, the optical device may comprise a pair of cylindrical lenses spaced apart from each other in a direction away from the user&#39;s face when the optical apparatus is in use. 
         [0043]    More specifically, the lower optically powered surfaces of the pair of cylindrical lenses may face each other. 
         [0044]    Alternatively or in addition, respective focal lengths of the astigmatic lenses may be substantially the same. This can provide for a magnification factor of one of an object viewed with the optical apparatus. 
         [0045]    Alternatively, respective focal lengths of the astigmatic lenses may be unequal. Thus, where the focal length of the lens closer to a face of the user is less than the focal length of the other lens a lateral field of view through the optical device is decreased with resultant horizontal magnification of less than unity. Conversely, where the focal length of the lens closer to the face of the user is greater than the focal length of the other lens, the lateral field of view through the optical device is increased with resultant horizontal magnification of greater than unity. 
         [0046]    Alternatively or in addition the lenses may comprise a curved surface, such as a hyperbola. Such a curved surface provides for optimisation for optical performance. 
         [0047]    The optical apparatus may further comprise another optical device which is supported by the support such that the two optical devices are spaced apart from each other, the other optical device being configured to reverse a field of view of a user&#39;s other eye when in use. 
         [0048]    More specifically, the optical apparatus may be configured and the two optical devices spaced apart from each other such that when the optical apparatus is located and used near the eyes of the user, a respective one of the two optical devices is within a visual field of a respective one of the user&#39;s two eyes. Thus, the optical apparatus can be used to reverse the field of view of both eyes of the user simultaneously. 
         [0049]    Alternatively or in addition, an orientation of one of the two optical devices in relation to the support may be fixed and an orientation of the other of the two optical devices in relation to the support may be changeable. 
         [0050]    Alternatively or in addition, the two optical devices may be oriented such that, in use, their respective fields of view are directed to substantially the same object. 
         [0051]    In a form of our apparatus, the optical apparatus may be configured to be worn by a user of the optical apparatus. 
         [0052]    More specifically, the, optical apparatus may be configured to be worn on the head of a user of the optical apparatus. Thus, the optical apparatus may form part of a pair of spectacles. 
         [0053]    Alternatively or in addition, the support may be configured for attachment of the optical apparatus to wearable apparatus configured to be worn by the user. 
         [0054]    More specifically, the support may be configured for attachment of the optical apparatus to wearable apparatus configured to be worn on the head of the user, such as a pair of spectacles. 
         [0055]    Alternatively or in addition, the support may be configured for releasable attachment of the optical apparatus to the wearable apparatus. 
         [0056]    More specifically, the support may comprise a clip configured to engage the wearable apparatus. 
         [0057]    More specifically, the support may comprise a biasing device, such as a spring, that is operative to bias the clip and provide for tight engagement of the clip and the wearable apparatus. 
         [0058]    In another form, the optical apparatus may be configured to be held by a user of the optical apparatus. Thus, the support may comprise at least one gripping surface configured to be gripped by the user. Thus, the user can hold the optical apparatus with the gripping surface and bring the optical apparatus near to one of his eyes for use of the apparatus with that eye. 
         [0059]    Alternatively or in addition, the optical apparatus may have a weight of less than about 50 grams. 
         [0060]    More specifically, the optical apparatus may have a weight of less than about 25 grams. 
         [0061]    Alternatively or in addition, optical apparatus may comprise a restricting member configured to restrict the field of view of the user&#39;s eye through the optical device. Thus, the field of view can be tailored to view a limb of the user, e.g., an arm or leg, and less of the environment around the limb. 
         [0062]    More specifically, the restricting member may define the field of view of the user&#39;s eye through the optical device. 
         [0063]    Alternatively or in addition, the restricting member may be configured to extend away from the user&#39;s face when the optical apparatus is in use. 
         [0064]    More specifically, the restricting member may define a space extending away from the user&#39;s face when the optical apparatus is in use. Thus, the restricting member may form a tunnel through which the user looks with his eye when the optical apparatus is in use. The restricting member may, for example, define a tunnel of rectangular cross-section. 
         [0065]    Alternatively or in addition, the restricting member may be attached to the support. 
         [0066]    More specifically, the restricting member may be integrally formed with the support. 
         [0067]    Alternatively or in addition, the optical apparatus may be configured to vary a centration distance. Variation of centration distance provides for use of the optical apparatus with different users, such different users having different eye spacings. 
         [0068]    More specifically, the optical device may be movable laterally on the optical apparatus. 
         [0069]    Alternatively or in addition, the optical device may be rotatable in relation to the optical apparatus. Thus, the optical device may be moved laterally. 
         [0070]    More specifically, the optical device may be a prism that is inherently decentered, such as a Dove prism. 
         [0071]    Alternatively or in addition, where the optical device is rotatable, the optical apparatus may comprise spaced apart indications which cooperate with an indicator that moves with the optical device to indicate an extent of rotation of the optical device. 
         [0072]    Alternatively or in addition, the optical apparatus may comprise an inclination indication device operative to indicate a level of the optical apparatus with respect to the ground, such as by reference to the gravitation field of the earth. 
         [0073]    More specifically, the inclination indication device may be operative to indicate when the optical apparatus is substantially level with respect to the ground. 
         [0074]    More specifically, the inclination indication device may comprise a spirit level. 
         [0075]    According to a second aspect of this disclosure, there is provided a pair of spectacles comprising optical apparatus according to the first aspect. 
         [0076]    More specifically, the pair of spectacles may comprise a first lens apparatus, which comprises the optical apparatus, and a second lens apparatus configured to obstruct a field of view of one of the user&#39;s eyes through the second lens apparatus. 
         [0077]    More specifically, the second lens apparatus may comprise one of an opaque member configured to substantially block the passage of light therethrough and a translucent member configured to reduce the passage of light. 
         [0078]    Alternatively or in addition, the pair of spectacles may be configured such that the optical apparatus is operative with either of both eyes of the user. 
         [0079]    More specifically, the pair of spectacles may be configured such that they are wearable one way up or turned upside down and wearable a second way up. Thus, when worn the first way up the optical device can be used with one of the left and right eye of the user and when worn the second way up the optical device can be used with the other of the left and right eye of the user. 
         [0080]    More specifically, the first and second lens apparatus may be spaced apart from each other and connected by a bridge, the bridge having at least one resilient member provided on the bridge such that when the spectacles are worn either way up the at least one resilient member is interposed between the nose of the user and the rest of the bridge. 
         [0081]    Alternatively or in addition, the pair of spectacles may be configured such that the field of view of the user&#39;s eye through the optical device of the optical apparatus may be changed. 
         [0082]    More specifically, the pair of spectacles may be configured such that the field of view may be moved laterally with respect to the user&#39;s eyes. 
         [0083]    More specifically, the optical device may be movable in relation to the pair of spectacles. 
         [0084]    More specifically, the optical device may be rotatable in relation to the pair of spectacles. 
         [0085]    In one form, the optical device may be movable such that a lateral direction of the movable device may be changed. Thus, the optical device may be rotatable about the coronal plane. For example, where the optical device is a prism, a direction of a face of the prism may be changed to change an orientation of a plane of reflection of the prism such that the plane of reflection can be made substantially in the sagittal plane. This feature can be used to provide an appropriate field of view when the pair of spectacles is used a first way up and when the pair of spectacles is turned upside down and used a second way up. 
         [0086]    In a second form, the optical device may be rotatable within a plane that is parallel to a plane generally defined by the user&#39;s face when the pair of spectacle is in use. Thus, the optical device may be rotatable about an axis that is generally perpendicular to the plane defined by the user&#39;s face. 
         [0087]    Alternatively or in addition, the pair of spectacles may have a weight of less than 200 grams. 
         [0088]    More specifically, the pair of spectacles may have a weight of less than 100 grams. 
         [0089]    Further examples of the second aspect may comprise one or more features of the first aspect. 
         [0090]    According to a third aspect, there is provided a kit of parts comprising a Magnetic Resonance Imaging (MRI) scanner and optical apparatus according to the first aspect, the optical apparatus being configured for use by a subject of the MRI scanner. 
         [0091]    Examples of the third aspect may comprise one or more features of the first and second aspects. 
         [0092]    According to a fourth aspect, there is provided a kit of parts comprising a Positron Emission Tomography (PET) scanner and optical apparatus according to the first aspect, the optical apparatus being configured for use by a subject of the PET scanner. 
         [0093]    Examples of the fourth aspect may comprise one or more features of the first and second aspects. 
         [0094]    According to a further aspect, there is provided a method of treatment comprising the steps of: locating an optical device near an eye of a user; and the user looking through the optical device, the optical device being configured to reverse a field of view through the optical device laterally with respect to the user&#39;s eyes. 
         [0095]    Examples of the further aspect may comprise one or more features of the first to fourth aspects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0096]    Further features and advantages will become apparent from the following specific description, which is given by way of example only and with reference to the accompanying drawings. 
           [0097]      FIG. 1  is a perspective view of a pair of spectacles according to one example. 
           [0098]      FIGS. 2   a  and  2   b  are perspective schematic views of a pair of spectacles according to alternative example. 
           [0099]      FIGS. 3   a ,  3   b  and  3   c  are schematic side views of different prisms. 
           [0100]      FIGS. 4   a  to  4   d  are schematic plan views of optical devices. 
           [0101]      FIGS. 5   a  and  5   b  are schematic plan views of cylindrical lens arrangements. 
           [0102]      FIG. 6   a  is a schematic side view of a cylindrical lens arrangement. 
           [0103]      FIG. 6   b  is a schematic view of a Fresnel lens arrangement. 
           [0104]      FIGS. 6   c  and  6   d  show alternative Fresnel lens arrangements. 
           [0105]      FIG. 7  is a perspective view of a pair of spectacles according to a further example. 
           [0106]      FIGS. 8   a  to  8   h  show examples configured to be releasably attached to a pair spectacles worn by a user. 
           [0107]      FIGS. 9   a  to  9   c  show examples configured to be worn either way up by a user. 
           [0108]      FIG. 10  shows an optical device mounted for rotation on a pair of spectacles. 
           [0109]      FIGS. 11   a  to  11   f  show various examples having a prism and at least one lens. 
       
    
    
     DETAILED DESCRIPTION 
       [0110]    In  FIG. 1 , a pair of spectacles  10  according to one example is shown. The spectacle frame  12  constitutes a support, which supports a prism  14  in front of a first lens  16  of the spectacles. In  FIG. 1 , the area of the casing tube indicated by the letter ‘a’ indicates a portion of the prism that can be removed without compromising the operation of the prism. The second lens  18  of the spectacles is opaque to substantially block the passage of light through the lens. In addition, a surface of a lens surrounding the prism  14  is opaque to restrict a field of view through the first lens  16 . The field of view is further restricted by covering the top, bottom and side surfaces  20  of the prism  14  with an opaque material. The opaque material may have the form of a coating or a covering, e.g., of plastics. The pair of spectacles of  FIG. 1  has a weight of about 90 grams. 
         [0111]      FIGS. 2   a  and  2   b  provide schematic views of pairs of spectacles  30 ,  40  according to alternative examples. As shown in  FIG. 2   a , a mirror  32  is attached in front of a first lens  34  of a pair of spectacles  30 . A reflecting surface  36  (which constitutes a reflecting plane) of the mirror  32  faces towards a nasal side of a wearer of the spectacles  30 . An alternative arrangement is shown in  FIG. 2   b , in which a mirror  42  is attached in front of a second lens  44  of a pair of spectacles  40 . A reflecting surface  46  of the mirror  42  faces towards a temporal side of a wearer of the spectacles  40 .  FIGS. 2   a  and  2   b  are both schematic in nature and do not show how the mirrors  32 ,  42  are attached to the spectacles. Nevertheless, each mirror  32 ,  42  may be attached by means of an attachment member formed of plastics or the like which extends from the spectacle frame to a side of the mirror opposing the reflecting surface  36 ,  46 . Furthermore, the lens of the spectacles  30 ,  40  without the mirror  32 ,  42  is opaque in the same manner as described above with reference to the spectacles shown in  FIG. 1 . 
         [0112]      FIGS. 3   a ,  3   b  and  3   c  are schematic side views of alternative forms of prisms used in the example shown in  FIG. 1 . In  FIGS. 3   a  to  3   c , a field of view of a user&#39;s eye  52 ,  62 ,  66  is represented by the lines bearing arrows. In  FIG. 3   a , the prism  50  is comparatively shorter and thus provides for a limited vertical field of view. In  FIG. 3   b , the prism  60  is comparatively longer below eye level and thus provides for an increased vertical field of view. The dotted portion  64  of the prism can be removed as it falls outside a field of view of the user  62 . In  FIG. 3   c , the prism  67  is comparatively longer both above and below eye level and thus provides for a further increased field of view. Thus, when the arrangement shown in  FIG. 3   c  is used with the invertible examples shown in  FIGS. 9   a  to  9   c  or with the rotatable example shown in  FIG. 10 , the field of view extending below eye, which achieved by the arrangement of  FIG. 3   b , can be achieved by the arrangement of  FIG. 3   c  irrespective of whether or not the prism  67  is upside down. The dotted portions  68  of the prism  67 , which are towards the upper and lower extents of the prism and towards the user&#39;s eye, can be removed as they fall outside a field of view of the user  66 . 
         [0113]      FIGS. 4   a  to  4   d  show schematic plan views of optical devices used in the examples of  FIGS. 1 ,  2   a  and  2   b . In  FIGS. 4   a  to  4   d  lines bearing arrows illustrate rays of light passing through the optical devices and serve to illustrate the operation of the optical devices.  FIG. 4   a  shows a dove prism  70 . The dotted portion  72  of the prism  70  can be removed without affecting the operation of the prism. As can be seen from  FIG. 4   a , the incident light rays are reflected off the lower internal surface  74  (which constitutes a reflecting plane) of the prism  70 . The effect of the reflection is to reverse an image viewed by a user through the prism.  FIG. 4   b  shows a prism  80  like that of  FIG. 4   a , the sole difference being that, as indicated by the lines bearing arrows, a user views an image through the prism at an angle. Nevertheless, the effect of the reflection of the image by the prism  80  is the same as for  FIG. 4   a  in that the image is reversed. In both  FIGS. 4   a  and  4   b , the surfaces of the prisms  70 ,  80  are refracting as indicated by the change in direction of rays of light upon passing the respective surface.  FIG. 4   c  shows another prism  90  having refracting surfaces  92 . Normal incidence of light rays at the refracting surfaces  92  provides for unaffected passage of light through the surfaces of the prism  90 . The prisms  70 ,  80 ,  90  of  FIGS. 4   a  to  4   c  are used in the example shown in  FIG. 1 . Turning now to  FIG. 4   d , a schematic plan view of a mirror  100  used in the examples of  FIGS. 2   a  and  2   b  is shown. As with  FIGS. 4   a  to  4   c , light rays are indicated by lines bearing arrows. As can be seen from  FIG. 4   d , the incident light rays are reflected off the lower internal surface  102  (which constitutes a reflecting plane) of the prism  100 . The effect of the reflection is to reverse an image viewed by a user through the prism. 
         [0114]      FIGS. 5   a  and  5   b  are schematic plan views of cylindrical lens arrangements. The cylindrical lens arrangements can form part of a pair of spectacles as shown in  FIG. 1 ,  2   a  or  2   b  by substituting the prism of  FIG. 1  for a cylindrical lens arrangement or by substituting the mirror of  FIG. 2   a  or  2   b  for a cylindrical lens arrangement. In  FIG. 5   a  the cylindrical lens arrangement  110  comprises first and second cylindrical lenses  112 ,  114 , which are spaced apart from each other and oriented such that their planar surfaces face one another. As can be seen by the lines bearing arrows, which represent light rays, the cylindrical lenses reverse an image viewed by a user through the lenses. In view of the cylindrical form of the lenses, image reversal is in one direction, i.e., about a plane perpendicular to the planar surfaces of the cylindrical lenses. An alternative arrangement of cylindrical lenses is shown in  FIG. 5   b , in which the cylindrical lens  122  closer to an eye  124  of a user is smaller than the other cylindrical lens  126 . As can be seen from the light rays, reducing the size of the lens  122  closer to the eye results in no loss of field of view. 
         [0115]      FIG. 6   a  shows a schematic side view of the cylindrical lens arrangements shown in  FIGS. 5   a  and  5   b . As can be seen from  FIG. 6   a , the smaller cylindrical lens  132  is located in front of an eye  134  of a user. As described above, the cylindrical lens arrangement  130  forms part of a pair of spectacles. As can be seen from  FIG. 6   a , the vertical aperture of the eyepiece lens is increased. This allows for an increase in the tolerance of alignment of the arrangement in the vertical direction with respect to the eye&#39;s visual axis. 
         [0116]    As shown in  FIG. 6   b , an astigmatic Fresnel lens arrangement  140  may be used instead of the cylindrical lens arrangement. Use of such an arrangement can provide for reduction in weight. 
         [0117]    One of two alternative Fresnel lens arrangements may be used instead of the cylindrical lens arrangement. In the first alternative arrangement shown in  FIG. 6   c , a Fresnel prism array  142  is provided in which each of the two surfaces of the array has a refracting angle. In the second alternative arrangement shown in  FIG. 6   d , two Fresnel prism arrays  144  separated by an air gap  146  are provided. A reflecting surface  148  is provided between the bases of the final prism pair of the arrays. 
         [0118]    A further example is shown in  FIG. 7 . As can be seen from  FIG. 7 , a pair of spectacles  150  has a prism  152 ,  154  in front of each lens  156 ,  158  of the spectacles. Each prism  156 ,  158  is as described above with reference to  FIGS. 3   a  to  4   c . The presence of a prism  152 ,  154  in front of each lens  156 ,  158  provides for an image reversal for each eye of a wearer of the spectacles. 
         [0119]    For example, a user with an arm amputation who is suffering from PLP wears one of the spectacles shown in  FIGS. 1 ,  2   a  and  2   b  in the normal fashion and directs his gaze towards his remaining arm, e.g., his left arm. The image reversing properties of the optical device (i.e., prism, mirror or cylindrical lens arrangement) reverses the view of the left arm seen through the optical device laterally with respect to the user&#39;s eyes. The effect of this is that the viewed left arm appears to the user as his right arm, thereby tricking his brain into believing that the amputated right arm is present. As a result, it is understood that the user&#39;s brain undergoes re-mapping and this, in turn, reduces the PLP suffered by the user with an amputation. 
         [0120]      FIGS. 8   a  to  8   h  show different examples having optical devices. In each example, the optical device (e.g., prism, mirror or cylindrical lens arrangement) is configured to reverse a field of view of a user through the optical device as described above and is configured to be releasably attached to a pair spectacles (which constitutes wearable apparatus) worn by a user. More specifically,  FIG. 8   a  shows a pair of spectacles  160  lacking sides having an optical device  162  mounted over one lens and a spring clip  164  that allows the pair of spectacles to be clipped to a pair of spectacles (not shown) worn by a user. The spring clip  164 , which may be formed from a metal or plastics material, and projects from the rear of the pair of spectacles  160 . The spring force of the spring clip  164  may be predetermined to provide for a secure grip or for looser grip, whereby the pair of spectacles shown in  FIG. 8   a  can be suspended from the worn pair of spectacles. The spring clip arrangement shown in  FIG. 8   a  is also suitable for a uniocular arrangement in which the pair of spectacles consist of one lens only with occlusion of the fellow eye being provided by a separate occluding member. The arrangements shown in  FIGS. 8   a  to  8   g  have a weight of about 25 grams. 
         [0121]      FIG. 8   b  shows an alternative example to that shown in  FIG. 8   a  in which a pair of spectacles lacking sides  170  has an optical device  172  mounted over one lens and a number of un-sprung clips  174  spaced apart around the periphery of the frame of the pair of spectacles. In use, the un-sprung clips  174  are used to attach the pair of spectacles  170  to a pair of spectacles (not shown) worn by a user. 
         [0122]      FIG. 8   c  shows a further example in which a pair of spectacles lacking sides  180  has an optical device  182  mounted over one lens and a magnetic clip  184 . In use, the magnetic clip  184  is used to attach the pair of spectacles  180  to a metal part, e.g., the frame, of a pair of spectacles (not shown) worn by a user. 
         [0123]      FIG. 8   d  shows a rear perspective view of a further example in which a pair of spectacles lacking sides  190  has an optical device  192  mounted over one lens and a spring clip  194  of a kind similar to that shown in  FIG. 8   a . The example of  FIG. 8   d  is clipped in much the same fashion as the example of  FIG. 8   a  to a pair of spectacles (not shown) worn by a user. 
         [0124]      FIG. 8   e  shows a front perspective view of a further example in which a pair of spectacles lacking sides  200  has an optical device  202  and an un-sprung clip  204  at each side of the pair of spectacles. The clips  204  are used to attach the pair of spectacles  200  to a pair of spectacles (not shown) worn by a user. A handle  206  is provided at one side of the pair of spectacles  206 . Such a handle  206  can form part of any one of the examples shown in  FIGS. 8   a  to  8   h.    
         [0125]      FIG. 8   f  shows a side view of a pair of spectacles having sides  210  to which a pair of spectacles  212  according to the examples shown in  FIGS. 8   a  to  8   e  is clipped. The clipped on pair of spectacles  212  according to one of the examples is provided with a hinge  214 , which allows for the clipped on pair of spectacles  212  to be rotated up out of the line of sight of the wearer. The clipped on pair of spectacles  212  may be modified by relocation of the hinge  214  to provide for rotation of the clipped on pair of spectacles sideways (or temporally of the wearer) out of the line of sight of the wearer. The hinge  214  can form part of a monocular spectacle arrangement in which rotation is either upwards or sideways. 
         [0126]      FIG. 8   g  shows an example  220  having an optical device  222  that is the same as the example shown in  FIG. 8   a  with the exception of the provision of gripping members  226  of the spring clip  224  towards the temporal sides of the pair of spectacles. The example of  FIG. 8   d  can be modified in the same fashion. 
         [0127]      FIG. 8   h  shows a rear perspective view of a monocular arrangement  230  having an optical device  232  and a spring clip  234 . The gripping members  236  of the spring clip  234  are spaced apart such that they are located towards each side of the arrangement. 
         [0128]    Where a spring clip is present in the examples of  FIGS. 8   a  to  8   h , the spring may have the form of a leaf spring, a helical spring or the like. 
         [0129]      FIGS. 9   a  to  9   c  show pairs of spectacles having an optical device mounted over one lens. The spectacles of  FIGS. 9   a  to  9   c  are configured to be worn either way up by a user. The capability to wear the spectacles either way up allows the optical device to be used with either the left or the right eye of the user. 
         [0130]      FIG. 9   a  shows a pair of spectacles  250  having an optical device  252  mounted over one lens. The distal portions  254 ,  256  of the sides  258  of the pair of spectacles  250  are each shaped to fit around the ear of a wearer of the pair of spectacles. The first  254  and second  256  distal portions extend in substantially opposite directions such that in use one of the first and second distal portions  254 ,  256  engage with an ear. For example, when the pair of spectacles  250  is worn a first way up (as shown in  FIG. 9   a ), the first distal portion  254  engages with the wearer&#39;s ear. When the pair of spectacles is worn upside down, the second distal portion  256  engages with the wearer&#39;s ear. 
         [0131]      FIG. 9   b  shows a pair of spectacles  260  which is the same as the pair of spectacles shown in  FIG. 9   a  with the exception that the spectacles have straight sides  262 . In use, each of the straight sides  262  rests on a respective ear of a wearer of the pair of spectacles irrespective of whichever way up the pair of spectacles is worn. 
         [0132]      FIG. 9   c  shows a pair of spectacles  270  which is the same as the pair of spectacles of  FIG. 9   b  with the further feature of a strap  272  attached to the distal portions of the sides  274  of the pair of spectacles. In use, the strap is fitted around the head of the wearer of the pair of spectacles  270  to help keep the pair of spectacles in place. 
         [0133]      FIG. 10  shows a pair of spectacles  300  having an optical device  302  mounted over one lens. The other lens is occluded. The optical device is mounted over the lens for rotation of the optical device in relation to the pair of spectacles about the coronal plane. The arrangement of  FIG. 10  is used with the pairs of reversible spectacles shown in  FIGS. 9   a  to  9   c  as follows. The pair of spectacles  300  is worn a first way up such that the optical device is positioned in front of the wearer&#39;s right eye. When the pair of spectacles is turned upside down on the head of the wearer, the optical device  302  is positioned in front of the left eye of the wearer. Depending on the configuration of the optics in the optical device  302 , positioning of the optical device in front of the wearer&#39;s left eye instead of his right eye can result in the field of view through the optical device being directed such that the pair of spectacles cannot be used properly. Rotation of the optical device  302  in relation to the pair of spectacles allows the wearer to redirect the field of view for proper use of the pair of spectacles. Furthermore, rotation of the optical device  302  through substantially 180 degrees provides for a change between two centration distances, i.e., spacings between the eyes of different users. In  FIG. 10 , the solid lines show the optical device at a first centration distance and the dotted lines show the optical device at a second centration distance. Where the optical device is an inherently decentered device, such as a Dove prism or the like, a change in centration distance can be achieved even where such an optical device is located centrally on the lens. 
         [0134]    Various examples having a prism and at least one lens are shown in  FIGS. 11   a  to  11   f.  In each of  FIGS. 11   a  to  11   f,  the eye  400  is shown in relation to each example. Each of the examples comprises a prism  402 , which functions as described above. 
         [0135]      FIGS. 11   a  and  11   b  show examples in which a lens is provided between the eye  400  and the prism  402 . The example of  FIG. 11   a  has a negatively powered lens  404 , which provides for minification, and the example of  FIG. 11   b  has a positively powered lens  406 , which provides for magnification. 
         [0136]      FIGS. 11   c  and  11   d  show examples in which a lens is provided on the other side of the prism  402  from the eye  400 . The example of  FIG. 11   c  has a positively powered lens  406 , which provides for magnification, and the example of  FIG. 11   d  has a negatively powered lens  404 , which provides for magnification. 
         [0137]    For the examples of  FIGS. 11   a  and  11   d,  image quality depends on the focusing ability of the user&#39;s eye to overcome or at least reduce defocusing caused by the lens. The disposition of the lenses of the examples of  FIGS. 11   a  to  11   d  in relation to the eye  400  and the prism  402  and the optical characteristics and dimensions of the lenses determine factors, such as extent of magnification, extent of minification, extent of field of view and the distance of objects that can be seen clearly. The disposition, optical characteristics and dimensions can be determined to meet specific requirements in accordance with well known optical design practice. The disposition of the lens further away from the eye in  FIGS. 11   c  and  11   d  compared with  FIGS. 11   a  and  11   b  has an effect, in accordance with well known optical design practice, on the extent of magnification or minification. In forms of the examples, an astigmatic lens is used to provide meridional distortion of a viewed object. 
         [0138]      FIGS. 11   e  and  11   f  show examples having one positively powered lens  406  and one negatively powered lens  404  disposed on opposing sides of the prism  402 . 
         [0139]    The example of  FIG. 11   e  will be recognised as a Galilean configuration in which the negatively powered lens  404  is disposed between the prism  402  and the eye  400 ; such an example is more readily configured to provide for magnification than minification. Minification is possible where the focal length of the negatively powered lens  404  is greater than the focal length of the positively powered lens  406 . The example of  FIG. 11   f  will be recognised as a reverse Galilean configuration in which the positively powered lens  406  is disposed between the prism  402  and the eye  400 ; such an example is more readily configured for minification than magnification. The magnification or minification is determined by the ratio of the focal lengths of the lenses. 
         [0140]    The examples of  FIGS. 11   e  and  11   f  are configured such that the distance between the lenses is the difference in their focal lengths; this provides for ease of viewing of objects further away from the apparatus than parts of the user&#39;s body. Alternatively, the examples are configured such that distance between the lenses is greater than the difference in their focal lengths; this provides for ease of viewing of parts of the user&#39;s body. In forms of the examples, the lenses are astigmatic to provide for meridional magnification differences. To provide for all meridians to be optimal focus the astigmatic axes of the lenses are parallel and the differences of the focal lengths in each meridian are the same. As with the examples of  FIGS. 11   a  to  11   d,  the disposition, optical characteristics and dimensions of the lenses of the examples of  FIGS. 11   e  and  11   f  can be determined to meet specific requirements in accordance with well known optical design practice. 
         [0141]    In un-illustrated forms of the above described examples the optical apparatus has a spirit level of conventional design and operation, which is operative to indicate when the optical apparatus is level with respect to the ground. In addition, in un-illustrated forms of optical apparatus in which the optical device is rotatable, such as is shown in  FIG. 10 , a graduated scale is provided on the optical apparatus and a moving indicator, such as a mark, is provided on the optical device. As the optical device rotates, the mark moves in relation to the graduated scale to indicate and extent to which the optical device is rotated. Thus, an orientation of the optical apparatus with respect to a bodily plane may be determined.