GB2364376A - Skin illumination and examination apparatus - Google Patents

Abstract

Apparatus for aiding diagnosis of skin disorder includes a light tube for illuminating the skin, and means for detecting light emitted from the skin at a selected wavelength and intensity. The light tube is fitted with a nose cone 7 having a transparent film 302 which prevents contamination through direct contact between a glass aperture 102 and the skin. The nose cone may also have devices for excluding ambient light, for limiting pressure applied to the skin, and for spacing the aperture 102 from the skin to allow a clinical view.

Description

2364376 Skin Diagnostic Aid

Field of the invention

The present invention relates to a skin diagnostic aid and more 5 particularly to a nose cone for use with skin illumination and remitted light detection apparatus as described in UK Patent Application Number 00 10 888.6.

Background to the invention

10 Conventional methods for the diagnosis of skin ailments involve the examination of the surface characteristics of a skin lesion. In addition, and dependant on the skin condition, a proportion or entire area of a skin lesion may be surgical excised and used for histological examination under a microscope.

15 There are a variety of skin conditions were the provision of histological information rapidly would be a valuable adjunct to enable the efficient diagnosis of a skin ailment. In the example of a malignant melanoma, histological information could be vital to determining the prognosis of the disease. For instance, the ingression of melanocytes into the papillary dermis 20 and in particular the depth of ingression has been correlated to the prognosis of the disease (Neville, C.D. "Melanoma: Issues of Importance to the clinician", British Journal of Hospital Medicine, 1995). For this reason, a device which could provide histological information about an area of skin rapidly and by a non-invasive technique would be a distinct advantage.

25 The principal chromophores located in the skin include melanin, haemoglobin, oxy-haernoglobin and collagen. In normal healthy skin, melanin is located exclusively in the epidermis, and haernoglobin and oxyhaemoglobin are located primarily in the papillary dermis and to a lesser extent the reticular dermis. Collagen is located throughout the dermis, with the highest concentration residing in the reticular dermis. Abnormalities in the distribution of such chromophores can provide valuable information about the 5 histology of a skin ailment and can be obtained by detecting and interpreting the distribution of different chromophores within the skin.

Our co-pending United Kingdom patent application numbers 99 12 908 and 99 25 414 relate to advances and improvements in the determination of the concentration and distribution of chromophores within 10 the skin. In particular, United Kingdom patent application number 99 12 908 relates to methods and apparatus by which the histology of the skin may be determined and the identification of the presence depth and concentration of chromophores within the skin. United Kingdom patent application number 99 414 relates to a method and apparatus for providing the information of the 15 skin structure, more particularly, to mapping the surface of dermal papillae.

Furthermore, our co-pending United Kingdom Patent Application Number 00 10 888.6 relates to an apparatus and methodology for determining the distribution of chromophores within the histological layers of the skin. An example of the skin illumination and remitted light detection 20 apparatus to which the present invention relates is illustrated in Figure A. The skin illumination and remitted light detection apparatus has a housing 1 onto which is mounted a display screen 2 with a touch screen operation. A handset 3 is stored on the housing I when not in use. The handset 3 is connected to the internal system of the equipment by a flexible metal tubing 4 25 which contains a bundle of optical fibres, which transmit light from a source contained with the housing 1, and carries signals from a detector to a computer located within the housing 1. The apparatus is supported by castors 5, which enable the equipment of the invention to be conveniently moved into a required location.

In use an operator 6 removes the handset 3 from its stored position in the housing 1 and holds the free end 7 of the handset 3 against the target 5 area 8 of the skin of a patient 9, as shown in Figure B. The operator 6 may then select options from the touch-screen 2 to initiate the illumination and imaging of the skin area.

The images obtained are displayed in a variety of formats on the display screen and the operator 6 can select specific representations and 10 view the presence of specific chromophore constituents of the skin by selecting options from the display screen 2. The images are interpreted by a suitably trained operator and differences in the distribution of chromophores between the image obtained and the predetermined models of normal healthy skin can be visualised.

15 Following the imaging of the skin, the light tube 3 is replaced within the housing and a printout of the images obtained for recording purposes.

It has been found that there are four distinct problems associated with the handset 3 and more particularly with the nose cone, which are detailed below.

20 Problem 1 It is clearly visible in Figure B that the nose cone is contacted directly onto the skin surface. It is during this procedure that the nose cone may be come contaminated with material associated with skin surface. The current approach to remove such material is to wipe the glass surface with an 25 alcoholic wipe. However, such a procedure may not result in complete removal contaminants from the skin surface or the glass aperture.

Problem 2 In addition, when the nose cone is located adjacent to areas of skin, such as a finger or nose, where the skin surface is not a smooth flat surface, ambient light or stray light from the surroundings may access the detector and give rise to errors in the measurement of remitted light.

Problem 3 A further disadvantage of the current nose cone is the absence of a mechanism for controlling the pressure by which the nose cone is applied to the skin surface. This is particularly significant in, for example, situations where the apparatus is used for mapping the topology of the dermal papillae 10 and applying too much pressure to the skin results in a flattening of these papillae.

Problem 4 A final disadvantage of the current nose cone is the requirement to provide a clinician with a clinical view. By clinical view we mean a view of the 15 macroscopic skin surface which is a valuable adjunct to the images of light remitted from an area of skin for which the apparatus to which the present invention pertains is designed.

The present invention is concerned with overcoming the above mentioned problems or at least significantly reducing them.

20 According to the present invention there is provided a skin illumination and remitted light detection apparatus, comprising a light tube defining a transparent glass aperture contactable with the skin, illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength 25 of light incident on said detection means, and illumination intensity selection means to select the intensity of light incident on the detection means, characterised in that said apparatus further comprises barrier means configured to prevent direct contact between said glass aperture and said skin.

According to a second aspect of the present invention there is provided a skin illumination and remitted light detection apparatus, 5 comprising a light tube defining a transparent glass aperture contactable with the skin, illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength of light incident on said detection means, and illumination intensity selection means to select the intensity of light 10 incident on the detection means, characterised in that said apparatus further comprises an ambient light exclusion means to prevent ambient light accessing said glass aperture.

According to a third aspect of the present invention there is provided a skin illumination and remitted light detection apparatus, comprising a light 15 tube defining a transparent glass aperture contactable with the skin, illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength of light incident on said detection means, and illumination intensity selection means to select the intensity of light incident 20 on the detection means, characterised in that said apparatus further comprises a pressure detection means configured detect a threshold level of pressure between said light tube and the skin.

According to a fourth aspect of the present invention there is provided a skin illumination and remitted light detection apparatus, comprising a light 25 tube defining a transparent glass aperture contactable with the skin, illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength of light incident on said detection means, and illumination intensity selection means to select the intensity of light incident on the detection means, characterised in that said apparatus further comprises a means for locating said glass aperture a defined distance from 5 said skin surface such that a clinical view of the skin surface is obtained.

Brief Description of the Several Views of the Drawings

How the invention may be carried out will now be described, by way of example only, with reference to the accompanying drawings, in which:

10 Figure A is a perspective view of an example of the equipment to which the present invention relates; Figure B is a schematic representation of the apparatus of Figure I in use; Figure I is a perspective representation of the nose cone of the 15 apparatus shown in Figures A and B; Figure 2a and 2b are perspective representations of an example of disposable nose cones; Figures 3 is a schematic representation of a nose cone fitted with a disposable film cover; 20 Figure 4 is a schematic representation of a transparent film coating that may be applied to the skin; Figure 5 is a cross-sectional view of the film shown in Figure 6, taken along the line X-X; Figure 6 is a schematic representation of a nose cone in contact with a 25 finger; Figure 7 is a flow chart illustrating an example of an operational sequence to detect the presence of stray light; Figure 8 is a schematic representation of a film cover attachment; Figure 9 is a schematic representation of an alternative film attachment shown in Figure 8; Figure 10 is a schematic representation of a nose cone in contact with 5 a skin surface; Figure 11 is a schematic representation of a nose cone configured to detect the pressure applied to the skin; Figure 12 is a schematic representation of an alternative embodiment of the nose cone shown in Figure 11; 10 Figure 13 is a schematic representation of a further nose cone equipped with a mechanical means for determining the pressure with which the nose cone is applied to the skin; Figure 14 is a flow chart showing an example of an operational sequence configured to prevent over pressurising the skin below; 15 Figure 15 is a perspective view of a nose cone with spacer legs in an upright position; and Figure 16 is a perspective view of a nose cone shown in Figure 15 with the legs in a down position.

In the drawings the same reference numerals are used for like or 20 corresponding parts in each of the Figures.

Best Mode for Carrying Out the Invention

Figure I shows a schematic representation of a light pipe 3 having a nose cone 7 with a transparent glass aperture 102 defined by the nose cone 25 ending 101. Illumination from the source, is transmitted from a source located within the housing I to the light pipe 3 (see Figures A and B) and illuminates the skin 103 through the transparent glass aperture 102. Also shown within figure 1 is a lesion 104, for example a mole, in which the distribution of chromophores is to be examined.

To obtain an image, the skin 103 is contacted directly against the aperture 102. Loose skin and material on the skin surface such as, for 5 example, skin oils, creams etc, leaves a residue on the glass aperture 102 and which, if not removed, will affect the quality of subsequent images.

A nose cone according to the present invention is illustrated in Figures 2a and 2b. Figure 2a illustrates a schematic representation of a disposable nose cone 7 with a nose cone ending 101 incorporating a glass aperture 102.

10 The nose cone 7 illustrated in Figure 2a comprises a male connection member 201 which is receivable within the handset body to form a resistive fit to secure the nose cone in position. Figure 2b illustrates another disposable nose cone similar to that shown in Figure 2a with the exception that the nose cone body 7 is elongated with a nose cone ending 101 and a glass aperture 15 102 of smaller dimensions to the corresponding nose cone illustrated in Figure 2a.

To accommodate the differing dimensioned nose cone, a means is provided to adapt the detective field of the detector to accommodate the appropriate sized glass aperture. This is achieved in the present embodiment 20 by the provision of an electrical contact on the nose cone such that, upon attaching the nose cone 7 to the handset 3, a contact is made with a second electrical contact provided on the handset 3. The contact will be configured such that each different dimensioned nose cone interacts with a specific electrical contact on the hand set. Upon electrical contact between a contact 25 on the nose cone and a contact on the handset, the lens which focuses the light remitted from the skin onto the detector is automatically moved to a predetermined position which adapts the detective field of the detector to correspond with that of the aperture of the nose cone fitted. Consequently, a variety of nose cones of differing dimensions are provided enabling the selection of different image areas.

Alternatively, the lens may be repositioned by a mechanical means, 5 wherein the nose cone carries a probe which, upon location of the nose cone on the handset, is received by the receptacle which moves a slidably mounted lens to the required position corresponding to the length of the probe. Each different dimensioned nose cone will possess a different length probe which determines the final lens position and hence ensure correct 10 focus of the image field of the detector within the handset onto which it is mounted.

The desired nose cone is provided within a sealed bag from which it is removed and mounted onto the handset. Upon use, the nose cone is contacted directly with the skin surface and the skin imaged as described in 15 our previous applications. Following use, the nose cone 7 is detached from the handset and discarded. For subsequent images, a second clean nose cone is attached to the handset.

An alternative embodiment of the present invention is illustrated in Figure 3. Attached to a nose cone 7 is a transparent film 302, which forms a 20 covering over the nose cone ending 101 and the transparent glass aperture 102. The film serves as a physical barrier between the glass aperture 102 and the skin and thus prevents contaminants on the skin adhering to the glass. The film 302 is mounted taught within a plastic clip 303 which comprises an arm 304 which extends adjacent to the external surface of the 25 nose cone body 7. In the preferred embodiment, the nose cone 7 is provided with an annular lip 301 which extends about the circumference of the nose cone. The arm of the plastic clip 304 comprises a recess 305 configured to receive the annular lip 301 of the nose cone 7, such that the plastic clip 303 and the transparent film 302 mounted therein is held flush with the nose cone end 101 and the glass aperture 102.

The film 302 is preferably prepared from material which is uniformly 5 transparent to light of visible and infra-red wavelengths. Examples of suitable materials would include polyethylene, polyesters, polypropylene, polystyrene, PBDF and polyvinylchloride. The plastic film may also be coated with an adhesive to improve the adherence of the film to the skin.

An example of an alternative film that may be incorporated into the clip 10 illustrated in Figure 3 is shown schematically in Figure 4. Located on a first side of the transparent film 302 is a second layer of an optical reflective index matching oil 401 within a defined area 402 which corresponds to the area of the glass aperture 102 of the nose cone 7. In the preferred embodiment the optical matching index oil is Heine Mineral Oil although any suitable optical 15 index matching oil would suffice such as olive oil or ultrasound coupling gel.

In use the optical matching oil reduce reflections from the skin surface. The oil coats the skin on contact diffusing into cracks and abrasions on the skin surface and reducing optical inhomogeneities due to the skin topology.

Also illustrated in Figure 4 is a further layer of adhesive 403 of defined 20 area 404 which encircles the optical index matching oil area 402. This arrangement provides for securing the film 302 to the skin surface of a subject providing an area of optical index matching oil 402 of comparable size to the glass aperture 102 such that, upon illumination, light incident from the skin encounters a layer of optical index matching oil prior to contacting 25 the surface of the skin.

Figure 5 shows a cross-section through the film illustrated in Figure 4 along the lines X-X'. The film 302 has, mounted on a first side, a second layer of optical index matching oil 401 surrounded by a further layer of adhesive 403. As previously described, the film is contacted with the skin via the first side, upon which the second layers of optical index matching oil and adhesive are mounted, and the second side is contacted with the glass 5 aperture preventing contaminants accessing the glass aperture of the nose cone.

Alternatively, the transparent film could be applied directly to the skin of the patient and the nose cone of the handset located against the exposed side of the film to image the area of skin. The film may be secured to the skin 10 by a layer of adhesive. In addition, a layer of optical index matching oil could be provided as previously described with reference to Figures 4 and 5.

The films incorporated in the present invention could also comprise a bar code which can be read by a bar code reader mounted within the handset or by the system intended for measuring the light remitted from the 15 skin itself. Consequently the image can be correlated with a specific patient by the bar code for recording purposes. Such a system, could also be used to prevent re-use of a film and hence, cross contamination with material collected from the skin during a previous image process. Example of alternative datamarkings which can be used instead of bar codes include 20 snowflake markings, alphanumeric codes or various forms of optical characters.

Furthermore, the film can be marked with a medical pen to identify areas of a lesion which may be excised. For example, in the case of a malignant melanoma, the images obtained by the apparatus of Figures A and 25 B will indicate the distribution of melanin beneath the surface layers of the skin. Consequently, it may be apparent that a larger area of the lesion requires removal compared to what is evident by a surface examination. A clinician will be able to mark or transfer a mark of the area to be excised onto the film which is subsequently used as a guide to a surgeon when removing the lesion.

The following section will describe examples of embodiments of the 5 invention designed to address the problem of stray light accessing the detector.

A schematic representation of an example of apparatus according to the invention in use imaging a skin surface of substantial curvature is illustrated in Figure 6. The light pipe 3 comprises a nose cone 7 which further 10 houses a nose cone end 101 with a glass aperture 102 mounted therein.

Located adjacent to the glass aperture is a finger, represented by the object 601. The finger 601, by virtue of the size and curvature, does not form a complete contact with the glass aperture and consequently stray light (or ambient light from the surroundings) accesses the detector increasing the 15 background intensity and obscuring the image of light remitted from the skin.

This makes the interpretation of the image less accurate and, in situations where the light remitted from the illuminated area of skin is low, the remitted light may be undetectable relative to the intensity of stray light accessing the detector.

20 To prevent images being obtained in a situation where too much stray light is present a safety operational sequence is incorporated into the operation of the apparatus to which the invention relates. The operational sequence is illustrated in Figure 7.

The light pipe is removed from the apparatus and located on the 25 desired area of skin 701. An image is recorded in the absence of incident illumination 702. The intensity of the image detected will depend on two factors, namely the dark current of the detector (which is known during normal operation) and the presence or absence of stray light accessing the aperture. Consequently, the intensity of the image at one or more points on the detector is set to a predetermined threshold level of stray light considered acceptable. If the image intensity at one or more points is below the defined 5 threshold 703 the normal imaging process continues 704. If the image intensity at one or more points is above a predetermined threshold level of illumination 705 the image will be rejected 706 and the operator alerted by an alarm or visual message 707 to signify that there is insufficient contact between the desired skin area and the glass aperture.

10 An example of an embodiment of the invention configured to prevent stray light accessing the detector is shown in Figure 8. The nose cone 7, with glass aperture 101 defined by nose cone end 102, is contacted with a finger, represented by oval object 601. Located in between the nose cone ending and the finger 601 is a transparent film 302, which prevents contaminants 15 from surface of the finger contacting the glass aperture. The transparent film 302 is fixed to the nose cone by an adhesive coating 802. A circular deformable foam ring 801 is attached to the film such that stray light from the surrounding is blocked from accessing the glass aperture 102. Any suitable deformable and optically opaque material would suffice in place of the foam 20 ring 801, suitable examples of which include pigmented silicone rubber and visco-elastic polymers such as a material known as "silly putty" or PlasticineRTm.

An alternative embodiment of the invention is shown in Figure 9. A nose cone 7 is provided with an annular lip 301. A finger 601 is orientated 25 adjacent to the glass aperture 102 with a transparent film located in between.

The transparent film 302 is mounted within a plastic clip 303 which receives the nose cone end 101 and is clipped into place by a groove 301 which receives the lip 301, as previously discussed with reference to Figure 3.

An opaque curtain 901 extends from the clip to associate with the finger 601 to prevent stray light from the surroundings accessing the glass aperture 102. The curtain can be made from any visually opaque material, 5 with fabric and polymer films the most preferred materials.

During skin imaging it is preferable to have the skin flat and pressed against the glass aperture of the handset such that an even illumination is provided across the skin surface. Consequently, a degree of force is required when pressing the handset onto the skin surface. An operator familiar with 10 the device will have experience of the amount of pressure required, but an unfamiliar operator may provide too much or too little force. Applying too much force is detrimental in situations where the apparatus to which the invention pertains is used for mapping the topology of the dermal- epidermal junction.

15 Figure 10 illustrates a schematic representation of a nose cone 7 of the skin illumination apparatus in contact with a skin surface 103. The skin is shown in cross section illustrating the stratum corneum 1001 dermo epidermal junction 1002 and the boundary between the dermis and the sub cutaneous tissue 1003. In normal skin the dermo-epidermal junction exists as 20 an undulating layer of peaks and troughs which define finger like projections or "papillae". In Figure 10 this layer is shown schematically as peaks 1004 and troughs 1005. If the nose cone 7 is pressed against the skin surface 103 with more force than is required the skin surface is compressed between the nose cone 7 and the pressure exerted by the underlying sub-cutaneous 25 tissue 1003. Hence, the thickness of the skin is reduced and the dermal papillae are squashed as illustrated at 1006. This may lead to false interpretation of the data, particularly in conditions where a flattening of the dermal papillae is diagnostic feature of a skin condition such as, for example, basal cell carcinoma.

Figure 11 illustrates a modified nose cone receivable on the handset of the apparatus to which the invention pertains. The nose cone 7 comprises 5 the usual nose cone end 101 which defines a transparent glass aperture 102 through which the skin is illuminated. In addition, mounted within the nose cone end 101 are two load cells 1101 and 1102 which are contacted with the skin. The load cells produces an electrical output corresponding to the pressure. The load cell is calibrated to detect an acceptable range of 10 pressure between the skin surface and the nose cone 7. If the pressure exceeds a predetermined threshold level, the apparatus is configured to prevent an image been obtained and thus prevent a false representation of the skin surface being imaged.

Figure 12 shows an alternative embodiment of the present invention 15 whereby the nose cone 7 is provided with a load cells 1101 and 1102 situated between the nose cone and handset 3. Applying pressure to the nose cone 7 in turn transfers pressure to the junction between the nose cone 7 and the handset 3. Similarly, to the embodiment illustrated in Figure 11, the load cells are configured to detect pressures above a predetermined 20 maximum.

A mechanical means by which a maximum threshold pressure is detected is shown in Figure 13. The nose cone 7 is provided with a circular skin-contacting member 1301 attached to a support 1302 on the nose cone by a resilient spring 1303. A transparent film 302 is mounted within the 25 aperture defined by the skin-contacting member 1301. The nose cone is orientated over an area of skin to be imaged and pressed against the surface 103. The skin contact member is forced towards the nose cone body 7, compressing the resilient spring 1303. If the pressure exceeds a defined threshold, the skin contact member is forced such that the protuberances 1304 contact the microswitch 1305 mounted on the nose cone 7. The actuation of the microswitch triggers an alarm or visual message alerting the 5 operator to the over pressuring of the skin area and prevents an image being obtained until the pressure is reduced below the predetermined threshold value.

Figure 14 is a flow chart illustrating an example of an operational sequence employed to prevent over pressurising an area of skin. The nose 10 cone is located over the desired area of skin to be imaged 1401. The load threshold is monitored by the pressure detection means 1402. If the pressure is too high 1405, indicated by a signal from the pressure detection means,

then the image is rejected 1404 and the operator alerted by audio alarm of visual signal 1407. If the pressure is below the defined threshold 1404, the 15 image is obtained as per the normal operational procedure of the skin measurement apparatus 1407. Consequently, when the operator is alerted to the over pressuring of the skin, the pressure applied may be reduced to below the threshold upon which an image is obtained as per the standard imaging procedure.

20 A further modification to the nose cone is illustrated in Figure 15.

During use of the apparatus to which the invention relates, it isadvantageous to provide a "clinical view" which, in other words, is an image of the skin surface. In Figure 15, the nose cone 7 of the handset is equipped with a two leg members 1501a and 1505b rotatably mounted onto a support 1502. In 25 Figure 15, the legs are in the "up position" and the handset is configured for illuminating the skin surface and detecting the light remitted. A lens 1503, mounted within a handset 3, focuses the remitted light onto a detector (not shown). To obtain a clinical view the legs are rotated into a down position, as illustrated in Figure 16. The nose cone end 101 is lifted from the skin surface 103 and the position of the lens adjusted to focus on the skin surface 103. In a preferred embodiment the detector is provided with an auto-focus system 5 which automatically moves the lens 1503 mounted within the handset to focus on the skin surface 103. Alternatively, the lens may be moved to predetermined position by a mechanical means associated with the rotatable leg members. For example, when the leg members are in a "up position" the lens resides in a fixed position 1503 during imaging of chromophores within 10 the skin and upon moving the leg members to a "down position" the lens is moved to a second predetermined position 1601 to focus on the skin surface.

Although the nose cone is spaced above the skin surface by the leg members in the embodiment illustrated in Figures 15 and 16, any spacing means would suffice, such as, for example, a spacer ring or foam ring of 15 defined dimensions such that the nose cone is spaced an optimal distance from the skin surface.

Claims (4)

Claims

1. A skin illumination and remitted light detection apparatus, comprising 5 a light tube defining a transparent glass aperture contactable with the skin, illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength of light incident 10 on said detection means, illumination intensity selection means to select the intensity of light incident on the detection means, characterised in that said apparatus further comprises barrier means configured to prevent direct contact between said glass aperture and said skin.

2. A skin illumination and remitted light detection apparatus, comprising a light tube defining a transparent glass aperture contactable with the skin, 20 illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength of light incident on said detection means, illumination intensity selection means to select the intensity of light 25 incident on the detection means, characterised in that said apparatus further comprises an ambient light exclusion means to prevent ambient light accessing said glass aperture.

3. A skin illumination and remitted light detection apparatus, comprising a light tube defining a transparent glass aperture contactable with the 5 skin, illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength of light incident on said detection means, 10 illumination intensity selection means to select the intensity of light incident on the detection means, characterised in that said apparatus further comprises a pressure detection means configured detect a threshold level of pressure between said light tube and the skin.

4. A skin illumination and remitted light detection apparatus, comprising a light tube defining a transparent glass aperture contactable with the skin, 20 illumination means configured to transmit light to said light tube, detection means to detect light remitted from the skin, wavelength selection means to select the wavelength of light incident on said detection means, illumination intensity selection means to select the intensity of light 25 incident on the detection means, characterised in that said apparatus further comprises a means for locating said glass aperture a defined distance from said skin surface such that a clinical view of the skin surface is obtained.