Device for obtaining cornea geometry information

Abstract

A system for obtaining corneal topography information comprising a chamber 101 having a concave surface 105a and a central axis, with a plurality of light sources 107 configured to illuminate the cornea located meridianally (109, figure 2) on the concave surface. A detector 108 receives light emitted from the light sources and reflected by the cornea. The location of the light sources is defined by a reference cornea with a central radius of 7.8mm and a shape factor of between 0.8 and less than 1.0. The light sources may be LEDs, IR / NIR sources or fibre optics, configured to emit light of a wavelength 380-300nm. The plurality of meridians may be in the range of 3-32. The detector may be a camera integrated with or external to the chamber. The chamber may comprise a reflective inner surface.

Description

[0001] This invention relates to a system and a method for obtaining curved geometry information with application to corneal topography. BACKGROUND

[0002] The cornea is the main refractive component of the eye, whose shape has a direct bearing on visual acuity. A number of prevalent diseases, such as keratoconus, affect corneal microstructure, leading to surface distortion and serious loss of vision clarity.

[0003] Keratoconus (KC) affects young individuals from the early teens until young adulthood. In European populations, its prevalence is about 1:375, in Latin countries 1.8%, in middle east 5% and in Africa increases to 8%, becoming the most prevalent corneal disease resulting in corneal transplant. KC carries a high potential for morbidity as it is progressive, leading to corneal irregularities and loss of clear vision. This has a direct impact on the quality of life of these young patients, with many suffering from depression and anxiety. Early diagnosis is essential so that treatment to halt progression could be introduced in good time to avoid need for corneal transplant.

[0004] KC is commonly associated with the development of localised distortion, which takes a conical form, with bulging that increases in height as the disease progresses. KC is therefore identified through irregularities seen in topography maps depicting the distribution of curvature and elevation across the corneal surface.

[0005] Several devices are regularly used to measure corneal topography and produce the curvature and elevation maps needed for KC diagnosis and for following up its progression. Most of these devices are based on Scheimpflug (www.sciencedirect.com / topics / medicine-and-dentistry / scheimpflug-imaging) or Orbscan (https: / / www.lasikmd.com / technology / orbscan-topography) technology.

[0006] Other devices use the Placido disk technology or employ the techniques used, for example, in the Cassini type devices (https: / / cassjni-technotoqies.com / ). The Placido disk technology uses a series of concentric illuminated rings that are reflected off the cornea and viewed with a detector array, such as a charge-coupled device or video camera. The location and width of the rings are computed in such a way that the image of the rings reflected off a reference sphere is a uniform distribution of rings, i.e., rings equally spaced and all with the same width. The radius of curvature of the reference sphere is made equal to the mean radius of the cornea (about 7.8mm). Then the image of the rings reflected off an aberrated cornea will be distorted rings, and from this distortion it is possible to obtain the shape of the cornea.

[0007] The Cassini technology employs a combination of up to 700 multicoloured and / or infrared LEDs that are located inside the dome of the device. The location of the LEDs is sectorial and the points are positioned equidistantly on the flat surface of each sector. The light emitted by the LEDs is reflected from the surface of cornea and then a 3D model is built thus providing a topographical picture of the corneal surface.

[0008] All the known techniques have their drawbacks, for instance, difficulties to map the central corneal region or problems with alignment. Last but not least, most known devices are expensive, specialised and bulky, beyond the means of primary care units in developed countries and even secondary and tertiary care units in many developing countries.

[0009] For this reason, there is a need for affordable and simple technology that can capture corneal topography information with at least similar accuracy and precision as current commercial devices.

[0010] It is therefore an object of embodiments of the invention to at least mitigate one or more of the problems associated with the prior art. BRIEF SUMMARY OF THE DISCLOSURE

[0011] In accordance with the present invention there is provided a system for obtaining corneal topography information, the system comprising: a chamber comprising a structure having a concave surface and a central axis; a plurality of light sources configured to emit light to illuminate the cornea and located meridianally on the concave surface with respect to the central axis forming a plurality of meridians; a detector configured to receive light emitted from the plurality of light sources and reflected from the cornea, wherein the location of the plurality of the light sources is defined by a reference cornea having a central radius of 7.8 mm and a shape factor of between 0.8 and less than 1.0. Advantageously, it allows for a simple and accurate determination of the corneal topography information wherein the corneal surface irregularities can be determined quickly and precisely in both axial and circumferential directions.

[0012] In an embodiment, the shape factor is 0.8.

[0013] In an embodiment, the plurality of light sources are light emitting diodes (LEDs) or IR / NIR light sources or fibre optics.

[0014] In another embodiment, the plurality of light sources are configured to emit light of a wavelength between 380 nm and 3000 nm. Advantageously, using a broad light spectrum allows a good Modulation Transfer Function (MTF) to match the camera and light source and addresses light and colour aberration. Changing the wavelength improves image processing as certain wavelengths reduce the noise of tiny details captured by the camera. Using different wavelengths helps to identify segments of the image associated with particular meridians or light spots of the device. Using IR / NIR enables capturing information that is invisible to the human eye as it penetrates through the tissue, for instance, changes in the thickness of the cornea, diameter of the pupil, and changes in the tear film.

[0015] In an embodiment, the plurality of light sources are mounted on the concave surface. Advantageously, this provides a simple geometrical solution for the system without requiring complex technology to correctly position the light sources within the device.

[0016] In another embodiment, light is delivered to the plurality of light sources from at least one second light source located behind apertures in the concave surface, whereby light emitted from the second light source can pass through the apertures. Advantageously, if light is delivered to the light sources from a second light source located behind apertures, additional features, such as one or more reflective surfaces, can be included in the chamber to enhance the emitted light before it passes through the apertures.

[0017] In an embodiment, the LEDs are of the same colour.

[0018] In another embodiment, the LEDs are of different colours.

[0019] In an embodiment, the plurality of meridians are in the range of 3-32. Advantageously, the minimum number of meridians allows for obtaining useful corneal topography information, wherein the maximum number of meridians increases the accuracy of measurements but still does not overcrowd the set up.

[0020] In another embodiment, the system further comprises a filter to change wavelength.

[0021] In an embodiment, the detector is a camera. Advantageously, using an off the shelf camera simplifies the set up and thus decreases the cost.

[0022] In another embodiment, the camera is integrated with the chamber.

[0023] In yet another embodiment, the camera is external to the chamber. Advantageously, the system can be supplied to users without the camera, and a user can use their own camera, for example that of their mobile phone, to perform the measurements and obtain the results.

[0024] In an embodiment, the chamber further comprises a reflective inner surface. Advantageously, the reflective surface enhances the light emitted by the second light sources before it passes through the apertures on the concave surface, thus further improving accuracy of measurements,

[0025] In an embodiment, the system comprises an external power source. Advantageously, this provides a reliable and stable power supply to the device.

[0026] In another embodiment, the system further comprises a battery. Advantageously, this allows for the device to be portable.

[0027] In an embodiment, the battery is rechargeable. Advantageously, by using a rechargeable battery the ecological impact on the environment is minimised.

[0028] In yet another embodiment, the system further comprises a light diffuser, which is preferably a transparent cone. Advantageously, this allows for optimising the intensity of the light and a significant reduction in the number of light sources, while still ensuring a uniform intensity of light emitted at each of the light points.

[0029] In an embodiment, the system further comprises a processor for processing the output and providing information on the topographical information about the cornea of the eye. Advantageously, this enables capturing, transferring and processing images of the cornea.

[0030] According to another aspect of the present invention there is provided a method of obtaining corneal topography information comprising the steps of: positioning the system described above in front of the eye; illuminating the cornea of the eye with the light emitted from the plurality of the light sources; using the detector to detect light reflected from the cornea; outputting the reflected light as a plurality of reflection points; processing the plurality of reflection points to produce an output; and determining the corneal topography information from the output. Advantageously, the method enables determining corneal topography in a simple and precise manner, so as to determine localised deviations on the corneal surface having a predetermined central radius and shape factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments of the invention are further described hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a system according to an embodiment of the invention. Figure 2 is a front view of the system depicted in Figure 1. Figure 3 is a schematic view of a position of the system of Figure 1 when used on a patient. Figures 4-7 are graphic representations of the spacing between reflection points for different central radii and / or shape factors. Figure 8 and 9 are the schematic representations of the spacing between reflection points when corneal abnormality is present. Figures 10-13 are schematic views of a system according to alternative embodiments of the invention. DETAILED DESCRIPTION

[0032] Figure 1 shows a system 100 according to an embodiment of the present invention. The system 100 has a chamber 101 within which is a structure 105 that, when in use, faces an eye 103 of a patient. It is understood that the structure 105 can be conical or take the shape of a prolate ellipsoid. The chamber 101 has an opening 104 configured to accommodate a detector 108. The detector can be, for example, a camera. The camera can be a standalone camera, powered from the mains. Alternatively, it can be a USB camera powered via a USB connection and connected to a PC or USB connected to mobile phone or tablet, it can also be a mobile phone camera. It is also understood that the camera can be built in the system and thus form an integral part of the system.

[0033] The illustrated chamber 101 is generally cylindrical, however other shapes, such as conical or having rectangular or square cross-sections, are also anticipated. For example, irregular shape can be used to compensate for facial features and improve ergonomics of the device. The chamber 101 has a structure 105 having a concave surface 105a on the side facing the patient’s eye. The degree of concavity can vary and is defined by camera specifications such as focal distance to the cornea and space between the device and facial features. The walls of the chamber 101a, 101b, 101c and the structure 105 define an inner space 106.

[0034] The structure 105 has a plurality of light sources in the form of LEDs 107 located meridianally on the concave surface 105a with respect to the central axis of the system 100. The location of the meridians can be best seen on Figure 2 demonstrating how the LEDs 107 are positioned on the structure 105.

[0035] The location of the LEDs 107 on the structure is chosen in the following way. A reference cornea, which has a central radius of 7.8 mm and a shape factor of P = 0.8, is used as these values for the central radius and the shape factor are the mean values of a healthy human cornea across the population. However, it is understood that any shape factor that is between 0.8 and less than 1.0 can be used in choosing the location of the LEDs, and the shape factor of 0.8 is only used hereinabove as an exemplary embodiment.

[0036] The cornea has two surfaces: the inner (or posterior) surface, and the outer (or anterior) surface. Both surfaces are commonly prolate with the steepest curvature (smallest radius) at the centre and flatter curvature towards the periphery. While the central radius ( R) depicts the radius at the corneal centre or apex, the shape factor (P) denotes the degree by which the shape deviates from a spherical surface. It is understood that the mean values of the reference cornea are normally assumed to be R=7.8 mm and 0.8 <P <1.0, as described above. It is also understood that as the cornea does not necessarily have rotational symmetry, the values of R and P may vary from one meridian to another.

[0037] In order to provide equal spacing between the reflection points on the detector 108 the following calculation is made. The rays of light from the desired location of the reflection points on the detector 108 are propagated backwards from the detector 108 onto the surface of a reference cornea having mean values of R = 7.8 mm and 0.8 <P <1.0. The light rays are then reflected from its surface and projected on one meridian 109 on the concave surface 105a. The location of the light points 107 on the meridian 109 (as seen on Figure 2) is then defined by the positions where the light reflected from the corneal surface intersects the concave surface 105a of the structure 105.

[0038] It is understood that the minimum number of meridians 109 in order to obtain corneal topography information is 3. Preferably the number of meridians 109 does not exceed 32. More preferably, the number of meridians is equal to 12. In the illustrated example, the number of meridians is 12. It is understood that more meridians will give better accuracy of the measurements, however the balance between obtaining an acceptable level of accuracy and overcrowding the structure 105 with the light points should be considered.

[0039] The plurality of light sources can be, for example, LED lights, as shown in the embodiment in Figure 1. Alternatively, the plurality of light sources can be fibre optics. Each of the LED lights can be of the same colour, or monochrome, or can be of different colours, or heterochrome. In an alternative embodiment, light sources can be infrared (IR) or near-infrared (NIR). The LED lights and / or IR / NIR can emit light of a wavelength varying between 380 nm to 3000 nm. It is also understood that when monochrome LEDs are used, the system can optionally have a filter that changes the output wavelength. It is further understood that any suitable light source can be implemented.

[0040] Figure 3 shows the system 100 in use. In more detail, the user of the system approaches the patient’s face and positions the system 100 in the vicinity of the patient’s eye. It is understood that the system can be handheld and various gripping means can be additionally provided to improve grip. For the generally cylindrical chamber 101 of Figure 1, the user grabs around the outer surface with their thumb and four fingers.

[0041] Next, the system illuminates the open eye of the patient with the plurality of the light sources located on the concave surface of the structure . Light received from each light source is refracted through the anterior surface of the cornea and reflected by the posterior surface of the cornea.

[0042] Light reflected from the cornea is received as a set of spaced reflection points on the detector. The detector, that can be a camera, then takes an image of the cornea. A processor then processes the data obtained by the detector and provides information on the topography of patient’s eye. Any misalignment of the central axis of the system 100 and the central axis of the eye 103 can be corrected in the processing software.

[0043] In order to understand how deviations from the expected corneal shape are determined, reference is made to Figures 4-6.

[0044] Figure 4 shows how the spacing between the spaced reflection points will look if R remains constant and P is variable. Thus, if R = 7.8 mm and P = 0.8 , all the reflection points will have an equal spacing of approximately 0.25 mm. Other spacing can be used but taking into account that locating the light sources further apart may reduce accuracy of measurements, whereas locating the light sources too close to one another may be difficult from a manufacturing point of view. If P changes to P = 0.6 the slope of the pattern formed by the plurality of the reflection points increases upwards. If, on the contrary, P = 1.0, the slope of the pattern decreases downwards.

[0045] Figures 5-7 show how the spacing between the reflection points changes if P remains constant and R is variable. Thus, in Figure 5, P is constant at a value of 0.6 and the central radius R changing from 6.8 mm to 8.8 mm is illustrated. It can be seen that the spacing between the reflection points increases as the reflection point is further from the central axis of the eye. In figure 7, on the contrary, when P is constant at a value of 1.0, the spacing between the reflection points decreases with the increase of the distance from the central axis of the eye.

[0046] In figure 6, wherein the central radius changes from 6.8 mm to 8.8 mm, but the shape factor is set at P = 0.8, the spacing between the reflection points does not change. This is because the location of the plurality of light sources in the system 100 is chosen based on a mean value for the shape factor equal to 0.8. Therefore only the spacing corresponding to identically located reflection pointswill change and will increase with the increase of the central radius. Thus, from Figures 4-7 it is clearly seen that the same working principle applies when the shape factor changes between 0.8 and 1.

[0047] The trends explained above can be exploited to estimate the curvature of the cornea associated with each reflection point and, in turn, the curvature across the whole corneal surface. While Figures 4-7 describe the location between the reflection points for a cornea without localised surface changes, figures 8-9 demonstrate how the reflection points will be visualised when mild and / or moderate keratoconus is present.

[0048] In an exemplary situation depicted in Figures 8-9, the presence of keratoconus is evaluated by the presence of reflection points that lie outside the predicted trend for a healthy cornea. In figures 8-9 such a situation is demonstrated by the deviation of the reflection points having an index 6-10, thus meaning that the surface irregularity is present in the area results in larger diffraction of the light rays where the reflection point deviates from the predicted position.

[0049] Figures 10-13 represent alternative embodiments of the system of the present invention. Where the same reference numerals are used to relate to the same features as described above, their description will not be repeated.

[0050] In the embodiment shown in figure 10, instead of LEDs, the plurality of light sources 107 located on the concave surface 105 comprises a plurality of apertures 107’. The device 100 is further provided with a second light source 110 located within the inner space 106. The second light source 110 can be one or more discrete light sources that emit light into the chamber 111. The second light sources 110 can be placed anywhere in the chamber 101 as long as they do not block the apertures 107. The second light source 110 is configured to transmit light through the apertures 107’. The second light source 110 can be a light bulb, fibre optics, one or more LED lights of the same colour, or monochrome, or of different colours, or heterochrome, or any other source of light. In a further embodiment, the second light source 110 can be infrared (IR) or nearinfrared (NIR). The LED and / or IR / NIR lights can emit light of a wavelength varying between 380 nm to 3000 nm.

[0051] As used herein, the term “plurality of light sources located on the concave surface” is not limited to LED and / or IR / NIR lights or fibre optics 107 but also encompasses a plurality of apertures 107’ that allow the light from a second light source to pass through in order to reach the eye. In other words, in the embodiment depicted in Figure 2, the plurality of light sources are LEDs, wherein in the embodiments depicted in figures 10-13, the plurality of light sources are apertures that passively transmit the light generated by the second light source 110. Consequently, the term “emit” or “emission” of light is not limited to an active emission by a source of light, but can also encompass the passive transmission through an aperture in order to reach the eye of a patient.

[0052] The inner chamber 106 has a reflective surface 111 that is used to reflect light emitted from the at least one light source 110. Advantageously, the reflective surface 111 enhances the light that is passed through a plurality of openings 107 by adjusting its intensity to ensure more even distribution in the chamber 106, in order to maximise the brightness of the light that reaches the patient’s eye.

[0053] In the figure 10 embodiment, the detector 108 is a camera external to the chamber and located adjacent the opening 104. The external camera can be a smartphone camera used to obtain images of the reflection points formed by reflecting the emitted light from the plurality of light sources 107.

[0054] Figure 11 illustrates an embodiment, wherein the light from the second light sources 110 is transmitted through the plurality of light sources 107’. Instead of the opening 104, the detector 108, which is a camera, is integral with the system.

[0055] Figure 12 illustrates another embodiment, wherein both the camera and a power source 112 are integrated into the device 100. It is understood that the integrated power source 112 can be a battery, preferably a rechargeable battery.

[0056] Figure 13 illustrates yet another embodiment, wherein the structure 105 is less concave. If the focal distance of the camera and the device distance to the surface are not constrained, it enables the device to become more compact in length and improve portability and ergonomics.

[0057] The system 100 may further comprise a light diffuser 113, which is preferably a transparent cone. It can sit inside or outside the structure 105 or even be placed inside the apertures 107’, as further demonstrated in Figures 14-16. It helps to diffuse and soften the light by improving the distribution of light and its intensity that emit to the cornea surface resulting in more even geometry and intensity of reflection points on the surface of the cornea.

[0058] It will be understood that the data received by the detector 104 can be transmitted either via USB cable or Ethernet cable, or wirelessly, for example via WI-FI, Bluetooth, or internet. Optionally the data can be stored using a cloud connection service.

[0059] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0060] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0061] It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

[0062] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A system for obtaining corneal topography information, the system comprising:a chamber comprising a structure having a concave surface and a central axis;a plurality of light sources configured to emit light to illuminate the cornea and located meridianally on the concave surface with respect to the central axis forming a plurality of meridians;a detector configured to receive light emitted from the plurality of light sources and reflected from the cornea,wherein the location of the plurality of the light sources is defined by a reference cornea having a central radius of 7.8 mm and a shape factor of between 0.8 and less than 1.0.

2. The system of claim 1, wherein the shape factor is 0.8.

3. The system of claim 1, wherein the plurality of light sources are light emitting diodes(LEDs) or IR / NIR light sources or fibre optics.

4. The system of any of claims 1-3, wherein the plurality of light sources are configured to emit light of a wavelength between 380 and 3000 nm.

5. The system of any of claims 1-4, wherein the plurality of light sources are mounted on the concave surface.

6. The system of any of claims 1-4, wherein light is delivered to the plurality of light sources from at least one second light source located behind apertures in the concave surface, whereby light emitted from the second light source can pass through the apertures.

7. The system of claim 3, wherein the LEDs are of the same colour.8.The system of claim 3, wherein the LEDs are of different colours.

9. The system of any of the preceding claims, wherein the plurality of meridians are in the range of 3-32.

10. The system of claim 6, further comprising a filter to change wavelength.

11. The system of any of the preceding claims, wherein the detector is a camera.

12. The system of claim 11, wherein the camera is integrated with the chamber.

13. The system of claim 11, wherein the camera is external to the chamber.

14. The system of claims 6-13, wherein the chamber further comprises a reflective inner surface.

15. The system of any of the preceding claims, further comprising an external power source.

16. The system of claims 1-14 further comprising a battery.

17. The system of claim 16, wherein the battery is rechargeable.

18. The system of any of claims 6-17, further comprising a light diffuser, which is preferably a transparent cone.

19. The system of any preceding claim further comprising processor means for processing the output and providing information on the corneal topography information .

20. A method of obtaining corneal topography information comprising the steps of:positioning the system of any of claims 1-19 in front of the eye;illuminating the cornea of the eye with the light emitted from the plurality of the light sources;using the detector to detect light reflected from the cornea;outputting the reflected light as a plurality of reflection points;processing the plurality of reflection points to produce an output; and determining the corneal topography information from the output.

Images