AU2003283058B2

AU2003283058B2 - A corneal topographer

Info

Publication number: AU2003283058B2
Application number: AU2003283058A
Authority: AU
Inventors: Robert H. Eikelboom; Mark Gallop; Paul Van Saarloos
Original assignee: Clearmark Technologies Pty Ltd
Current assignee: Clearmark Technologies Pty Ltd
Priority date: 2002-11-20
Filing date: 2003-11-20
Publication date: 2009-11-05
Anticipated expiration: 2023-11-20
Also published as: AU2003283058A1

Description

Title A Comeal Topographer Technical Field 5 Qphthalmologists and optometrists would like to have an aCCurate representation of the comea of the eye, particularly its front surface and its thickness: This information Is used to prscribe contact lenses and eye glasses, and to reshape the come by surgical procedures, all to improve eyesight. Since it is not possible to measure the come with physical objects, 10 remote -sensing techniques are used to produce this data. Conmea Topography is the name given to this field of technology, and instruments that measure comeal topography are known as corneal topography machines, or comeal topographers. This invention concems- a comeal topographer; and a method for comeal topography. 15 Backgmund Art The basic and most common corneal topography systems usn a Placido disk to project a series of concentric rings onto the corneal surface. The 'disturbance to the concentric projections is imaged by a video camera, and 20 then complex algorithms calculate the topography. Unfortunately, this system relies on a number of assumptions and these make most measurements of irregularly shaped eyes very inaccurate. In general people who have irregularly shaped eyes also have the greatest need for accurate surgery. A much more complex and expensive system scans narrow bands, or 25 slita, of light across the surface of the cornea. The slits are imaged as they scan across the eye, and again complex algorithms calculate the topography. This method does not rely on any assumptions, generating accurate maps of both normal and irregularly shaped comeas. It has the added advantage of sriltaneously providing data to measure tlhe thickness of the coma. This is 30 because the projection of the slit produces a number of reflections as it passes through the come and anterior chamber'of the eye, The most common application of corneal topography Is for planning refractive surgery. This surgery has been sucessful in correcting the vision of many millions of people worldwide. However, In almost al cases, these 36 patients have had a simple variation or deviation from the normal comeal shape. There is a larger group of people with irregular variation in comeal 2 shape (irregular astigmatism). These require custom control of the laser that is reshaping the cornea, which ablates varying amounts of tissue over the cornea. It of course relies on accurate topography data of this Irregular astigmatism. Ideally the topography data is fed directly into the control system for the laser; this is called custom 5 ablation. It is not admitted that any of the information in this specification is common general knowledge, or that the person skilled in the art could be reasonably expected to have ascertained, understood, regarded it as relevant or combined it in anyway at the priority date. 10 Disclosure of the invention In an aspect of the present invention there is provided a corneal topographer, comprising: a light projection apparatus configured to project multiple slits of light onto different parts of the surface of a cornea of an eye; 15 a camera configured to capture still images of the projected slits; and an image processor coupled to the light projection apparatus and to the camera, wherein the image processor is configured to activate the light projection apparatus to project a sees of different stationary patterns of one or more of said multiple slits of light onto the surface of the cornea, wherein the stationary patterns include 20 combinations of slits which are substantially simultaneously projected onto the surface of the cornea of the eye, wherein the camera is configured to capture an image of each projected patten of the series, and the image processor is further configured to generate topographical information of the cornea based on the captured images of the series. 25 In another aspect of the present invention, there is provided a corneal topographer, comprising: an illumination projection subsystem comprising a plurality of light emitters configured to project a series of pre-selected different stationary patterns of one or more slits of light in ordered succession onto the surface of a come of an eye, wherein at least one of 30 said patterns comprises a plurality of slits, and wherein the plurality of slits of the at 3 least one pattern are substantially simultaneously projected onto the surface of the cornea of the eye; an image capture subsystem comprising a camera configured to capture an image of each projected pattem; and 5 an image processing subsystem executed on a computer, the image processing subsystem configured to convert the images into topographical information of the cornea. In yet another aspect of the present invention, there is provided a corneal topographer, comprising: 10 means for projecting a series of pre-selected different stationary patterns of one or more slits of light in ordered succession onto the surface of a cornea of an eye, wherein at least one of said patterns comprises a plurality of slits, and wherein the plurality of slits of the at least one pattern are substantially simultaneously projected onto the surface of the cornea of the eye; 15 means for capturing an image of each projected patten; and means for converting the images into topographical information of the cornea. A topographer in accordance with the invention may represent a relatively inexpensive device which may provide accurate topographical information of the cornea without relying on assumptions. In particular this is achieved by the use of multiple 20 stationary slits, and elimination of scanning, and therefore moving parts. The light source may be collimated LEDs, masked and focussed onto the eye. In total there may be many, such as forty-eight LEDs producing the same number of slits, and these may be projected in, say, fifteen to twenty different patterns to provide sufficient data to map the topography of the cornea. There may be more or 25 less slits; depending on the amount of resolution achieved. The size of the slits may also vary, and the draft angle.

3a The LEDs may be housed together in sets with a common focussing arrangement. A CCD video camera may be used, under the control of a computer to receive the images. The computer may also control a frame grabber to capture a still image 5 every time a new combination of slits is projected onto the cornea. Analysis may involve registration of the whole image sequence to compensate for saccadic or other eye movements that occur in the time interval between capture of successive images. Next, image processing may determine the two edges of the slits as they are 10 shown on the image. The edges of the slits define the anterior and posterior surfaces of the cornea. Other reflections may be off the iris and the two surfaces of the lens of the eye. The edges may then be converted into mathematical curves. The curves may then be used to determine the external shape of the cornea, 15 the inside surface of the cornea, and all the local shape variations in these surfaces. The thickness of the cornea can also be calculated. The reflections off other surfaces maybe used to calculate the volume of the anterior chamber and distances to the lens. The topography data may be displayed. In another aspect of the present invention, there is provided a method of 20 corneal topography, comprising: projecting a series of pre-selected different stationary patterns of one or more slits of light in ordered succession onto the surface of a cornea of an eye, wherein at least one of said patterns comprises a plurality of slits; capturing an image of each projected pattern; and 25 converting the images into topographical information of the cornea.

3b Brief Description of the Drawings An example of the invention will now be described with reference to the accompanying drawings, in which: Fig. I is a pictorial diagram of a corneal topographer having eight light emitters 5 and a controlling computer. Fig, 2 is a sectional view of one of the light emitters of Fig. 1; also showing the relationship between that light emitter, the camera and an eye during use of the topographer. Fig. 3 is a diagram of an eye showing the arrangement of light slits projected 10 onto it from the topographer of Fig. 1. Best Modes of the Invention Referring first to Fig. 1, the comeal topographer 1 comprises eight light emitters 5 mounted to focus slits of light at the same point 10 from different angles. A video camera 15 is arranged with its axis 20 through point 10 to image the slits. A computer 15 30 controls the emitters 5 and the video camera 15.

PCT/AU2003/001547 Received 8 October 2004 4 Referring now to Fig. 2. each emitter 5 comprises a tube 51 having an LED holder 52 and an electrical panel 53 at the remote end, and a lens 54 at the end closest to point 10. Six 5mm LEDs 55 are mounted in separate channels 56 through LED holder 52. A layer of stereo lithography material 58, 5 tinted to be opaque, is mounted to the end of the LED holder 52. A distance, say 100mm, of twice the focal length of lens 54 extends between the layer of stereo lithography material 58 and lens 54. Each channel 56 in the LED holder 52 collimates the light from the LED mounted in that channel. Slit-like openings in the stereo lithography material at 10 the end of each channel have a draft of 600 to produce a knife edge slit 59 that is 0.2mm wide. Light from LED 55 passes through knife edge slit 59 to produce a light slit 60 that is 24mm high. Lens 54 reduces the slit of light 60 from 24mm high to 15mm high for projection 62 onto the eye 100; as shown in Fig. 3. Light slit 62 is a vertical slit, relative to eye 100. The image of slit 62 projected 15 on the eye is captured by video camera 15. In total there are forty-eight LEDs 55 and they are all wired to electrical panels 53 at the remote end of the light tubes 51 so that they can be individually turned on and off under the control of the computer indicated schematically at 30. Should all the LED's be turned on at once they would 20 project over the entire visible surface of the cornea in a pattern of both horizontal and vertical contiguous slits. A significant amount of time may be devoted to the positioning of the light emitters, so that the entire corneal surface will be covered. Optimal resolution will be achieved when each part of the cornea is measured by at 25 least one slit projection. The topographer I is mounted on a conventional ophthalmic assessment stand (not shown), which supports the patient's head on a head and chin rest. The device is mounted so that its position is under the control of a mechanical joystick, allowing back and forth movement for focus, left and right movement 30 to move from one eye to the other, and smaller . horizontal and vertical movements to centre the device in front of the eye being assessed. In use, the topographer is aligned in front of the eye so that the light slits are properly focussed on the cornea, and so that the camera image is in focus. A single or series of LEDs or other lights will be mounted near the camera to 35 which the patient must fixate.

AMENDEDHEE

WO 2004/045400 PCT/AU2003/001547 5 Preselected different patterns of LEDs are then sequentially turned on and off under the control of the computer. The camera 15, a CCD video camera, operates under the control of the computer to receive the light reflected along axis 20 for each pattern. The computer also controls a frame a grabber to capture a still image every time a new combination of slits is projected onto the cornea. Each still image is stored as quickly as it is produced, on an image capture card. The topographer typically produces a series of between 15 and 20 images of each eye, in a total time period less than 2 seconds. The information 10 on the captured images is then converted into topographical Information of the cornea. This involves registration of the whole image sequence to compensate for the (very small) saccadic eye movements or eye drifts that occur in the time interval between capture of successive Images. This is done by the use of one 15 or two slits that will always be on, for instance the two slits furthest apart, and using landmarks on the eye to determine if and how far the eye has moved. Next, image processing determines the two edges of the slits as they are shown on the image. One of the edges determines the outside surface of the come, the other determines the inside surface of the cornea. 20 The edges are converted into mathematical curves. Using trigonometry, the data of all the curves are assembled* to determine the shape of the cornea, the inside surface of the cornea, and all the local shape variations in these surfaces. The thickness of the cornea can also be calculated. 25 The software then displays the topography data in various forms. For instance, the corneal data will be displayed as a series of colour coded providing axial, refractive, elevation and irregularity data. Other functions include showing a live view of the cornea before imaging to position the device, and export of data for control of refractive lasers during surgery. Standard data 30 handling functions are also performed, such as storage with patients' date, archiving, comparison between sessions, and printing. Although the invention has been described with reference to a particular example, it should be appreciated that it includes many variants and 36 alternatives. For instance, 3mm LEDs could be used, and this could lead to the use of fewer light emitters. Fewer or more LEDs may be used with differing WO 2004/045400 PCT/AU2003/001547 6 resolution requirements. The slits may be projected at varying angles; not only horizontal and vertical. It will be appreciated by persons skilled in the art that numerous 5 variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the Invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. A corneal topographer, comprising: a light projection apparatus configured to project multiple slits of light onto different parts of the surface of a cornea of an eye; 5 a camera configured to capture still images of the projected slits; and an image processor coupled to the light projection apparatus and to the camera, wherein the image processor is configured to activate the light projection apparatus to project a series of different stationary patterns of one or more of said multiple slits of light onto the surface of the cornea, wherein the stationary patterns include combinations of slits which are substantially simultaneously projected onto the surface of 10 the cornea of the eye, wherein the camera is configured to capture an image of each projected pattern of the series, and the image processor is further configured to generate topographical information of the cornea based on the captured images of the series.

2. A corneal topographer according to claim 1, wherein the light projection apparatus comprises 15 collimated LEDs, configured to be masked and focused onto the eye.

3. A corneal topographer according to claim 2, wherein the LEDs are housed in sets with a common focusing arrangement.

4. A corneal topographer according to claims 2 or 3, wherein there are up to forty-eight LEDs producing the same number of slits. 20

5. A corneal topographer according to claim 1 or 2, wherein the series of patterns comprises up to twenty different patterns.

6. A corneal topographer according to claim 1, wherein the camera is a CCD camera. 8

7. A corneal topographer according to any one of the preceding claims, wherein the image processor is executed on a computer and further comprises a frame grabber configured to capture a still image each time a new pattern is projected.

8. A corneal topographer according to any one of the preceding claims, wherein the image processor 5 is further configured to compensate for saccadic or other eye movements that occur between successive images, to convert two edges of the slits of each image of the patterns into mathematical curves, and to determine, based on the curves, one or more of a shape of the cornea, an inside surface of the cornea, a local shape variation of an external surface of the cornea, and a local shape variation of an internal surface of the cornea. 10

9. A corneal topographer according to claim 8, wherein the image processing subsystem is further configured to determine, using the curves, a thickness of the cornea.

10. A corneal topographer according to claim 8, wherein the image processing subsystem is further configured to use reflections off surfaces of one or more of an irs and a lens of the eye to calculate the volume of an anterior chamber and distances to the lens. 15

11. A corneal topographer, comprising: an illumination projection subsystem comprising a plurality of light emitters configured to project a series of pre-selected different stationary patterns of one or more slits of light in ordered succession onto the surface of a comea of an eye, wherein at least one of said patterns comprises a plurality of slits, and wherein the plurality of slits of the at least one pattern are substantially simultaneously projected onto the surface of the 20 cornea of the eye; an image capture subsystem comprising a camera configured to capture an image of each projected pattern; and an image processing subsystem executed on a computer, the image processing subsystem configured to convert the images into topographical information of the cornea. 25

12. A corneal topographer according to claim 11, wherein the illumination projection subsystem makes use of collimated LEDs, masked and focused onto the eye. 9

13. A corneal topographer according to claims 11 or 12, wherein a CCD video camera is used under the control of a computer to capture the images.

14. A corneal topographer according to claim 13, wherein the computer also controls a frame grabber to capture a still image every time a new combination of slits is projected onto the cornea. 5

15. A corneal topographer according to any one of claims 11 to 14, wherein the image processing subsystem is further configured to compensate for saccadic or other eye movements that occur in a time interval between successive images, to determine two edges of the one or more slits of the patterns of each image, to convert the edges into mathematical curves, and to determine, using the curves, one or more of a shape of the cornea, an inside surface of the cornea, and all local shape variations of external 10 and internal surfaces of the cornea.

16. A corneal topographer according to any one of the preceding claims, further comprising a display configured to display the topographical information.

17. A method of corneal topography, comprising: projecting a series of pre-selected different stationary patterns of one or more slits of light in ordered 15 succession onto the surface of a cornea of an eye, wherein at least one of said patterns comprises a plurality of slits; capturing an image of each projected pattern; and converting the images into topographical information of the cornea.

18. A method according to claim 17, wherein converting the images into topographical information of 20 the cornea comprises compensating for saccadic or other eye movements that occur in a time interval between successive images.

19. A method according to claims 17 or 18, wherein converting the images into topographical information of the cornea comprises determining two edges of the one or more slits of the patterns captured in each image. 10

20. A method according to claim 19, wherein converting the images into topographical information of the cornea comprises converting the edges into mathematical curves, and determining, using the curves, one or more of an external shape of the cornea, an inside surface of the cornea, and all local shape variations of external and intemal surfaces of the cornea. 5

21. A method according to claim 20, wherein converting the images into topographical information of the cornea comprises determining, using curves, a thickness of the cornea.

22. A method according to claim 21, further comprising calculating a volume of an anterior chamber and distances to a lens of the eye using reflections off surfaces of one or more of an iris and the lens of the eye . 10

23. A method according to any one of claims 17 to 22, further comprising displaying the topographical information.

24. A comeal topographer, comprising: means for projecting a series of pre-selected different stationary patterns of one or more slits of light in ordered succession onto the surface of a cornea of an eye, wherein at least one of said patterns comprises 15 a plurality of slits, and wherein the plurality of slits of the at least one pattern are substantially simultaneously projected onto the surface of the cornea of the eye; means for capturing an image of each projected pattern; and means for converting the images into topographical information of the cornea.