AU9728598A - Stereo optic disc analyser - Google Patents

Description

WO99/20056 PCT/AU98/00863 - 1 STEREO OPTIC DISC ANALYSER The present invention relates to a computer imaging or 5 vision technique for the creation and analysis of three dimensional images, of particular but not exclusive application in the creation and analysis of images of the retinal wall of the eye, and in other three dimensional medical and industrial imaging, including fields such as 10 plastic surgery or aerial surveying and mapping. The invention also has application in the detection of anomalies of the ocular fundus, and in the early diagnosis, treatment and observation of diseases such as glaucoma and macular degeneration. 15 The ability to visualize objects in stereo, or in three dimensions, is a function of the position of the organs of sight, the eyes, and the manner in which the human brain processes visual information. The eyes are offset from one 20 another, resulting in a slightly different view of an object being presented to each eye. The brain 'combines' the left and right perspectives, such that a single image, conveying information about depth, is perceived. Unlike the eye, conventional imaging methods, such as slide, film 25 and video images, present only two dimensional images of an object. The ocular fundus and optic disc possess, like most objects, a three dimensional structure. A better 30 appreciation of fundus topography can, therefore, be gained from stereo photography and stereoscopic viewing. Stereo fundus photography can create three dimensional images of the optic nerve head. Using a fundus camera, the photographer produces two images of the ocular fundus, from 35 the perspective of his or her left and right eye. The two images must then be aligned, and viewed with a stereo slide viewer, or a light table coupled with a pair of plus (+) lenses. Alternatively, the images may be projected through WO99/20056 PCT/AU98/00863 - 2 a polarised material onto a screen, with the stereo pair polarised at 900 to each other. The observer must view the images through polarising glasses with a polarising filter in front of each eye. These devices enable the left and 5 right eye to "see" its corresponding image so that a stereo representation may be perceived (see Saine & Tyler (1997) for an overview of stereo imaging techniques). Stereo examination of the ocular fundus provides useful 10 information about the health of the eye, to guide diagnostic and treatment decisions. However, the clinician is most interested in observing the evolution of fundus topography over time. Comparing a patient's stereo fundus photographs at regular intervals may allow the clinician to 15 review subtle changes in the architecture of the optic nerve head. However, these images, often taken at different times, by different people or in different lighting conditions, may possess variable characteristics, in terms of magnification, colour and the positioning of 20 features in the image. These variations in image quality could be mistaken for changes in the topography of the optic nerve head. Computer technology can overcome some of these problems 25 through the use of image processing techniques. Colour matching techniques can eliminate colour and tonal differences between images of the same object taken on separate occasions, while image registration can minimise scale, translation and rotation variation. Regular 30 computerized imaging of the ocular fundus is, therefore, a useful ophthalmic technique, enabling the clinician to make diagnostic decisions, track the course of a disease and to measure the effectiveness of treatment. 35 A number of digitized systems of image analysis have been developed to aid in the quantitative analysis of stereo images, such as that illustrated in US Patent 5,519,485.

WO99/20056 PCT/AU98/00863 - 3 This patent describes a computerized, stereo image, measuring apparatus, suitable for topographical mapping and capable of displaying, and varying the magnification of, stereo images, and performing measurements relating to the 5 three dimensional structure of the object being imaged. A control device or central processing unit controls the function of this system. Left and right images are introduced, from a scanner or the like, into two separate optical disc drives. Images are displayed on a high 10 resolution, stereo, display device comprising; a left and right monitor, a half mirror, a polarizing filter in front of each display unit and orthogonal polarized glasses worn by the observer. A feature extractor may be used to extract features from the image data through designated 15 left and right measuring points. US Patent 5,270,924 describes an ophthalmic image processing system that is able to recognize the difference between the left and right images of a stereo pair and to 20 distinguish the top and bottom of the images, so that they may be stored without confusion. Another image processing system, the IMAGEnet, from Topcon Corporation, comprises a computerised image processing system for fluorescein angiography pictures, and fundus photography. This system 25 may digitally enhance stereo images using sharpening and contrast stretching tools. Analysis functions, such as line area measurement, enable quantitative analysis of a number of separate images. However, this product has proven to be somewhat impractical in a clinical setting, as 30 it requires long processing times and only registers images for translation differences in the X and Y directions. Heidelberg Engineering have also developed a method of imaging the fundus of the eye, using software which 35 captures images from a confocal scanning laser ophthalmoscope (cSLO). A cSLO image is constructed from a series of "slices" taken at varying levels of the fundus.

WO99/20056 PCT/AU98/00863 The slices are "stacked" together to form a single representation of fundus topography, with an accompanying sense of volume. To allow analysis of the same region of interest on respective slices, the operator defines this 5 region with a contour line. This defined area then is stored and aligned on subsequent images. A topographical representation of the fundus is produced by determining height measurements at each location on the cSLO's multiple captured images. Estimates are then made of topographic 10 variables, such as the mean height of the fundus contour, the optic cup volume and the volume of the optic nerve rim. Quantitative analysis in the Heidelberg system is based on the intensity of the light reflected from the fundus. The 15 area of highest reflectance is equivalent to the fundus contour, the edge surrounding the optic nerve head. At each level, or slice, the edge or fundus contour is determined, creating a topographic map of the fundus and enabling the calculation of the clinically important values 20 outlined above. However, if a lesion or vessel in the slice is more reflective than the contour, the position of that lesion will be considered the position of fundus contour, a situation which may result in a misleading topographical picture. 25 Current computerised stereo imaging systems, such as those outlined above, may suffer from a number of practical disadvantages. Difficulties with image registration challenge the accuracy of analysis, while long processing 30 times are a problem for clinical practice. Many of these systems produce only monochrome images which do not convey as much information as full colour images. In addition, none of the presently available systems provide a comparative measure for reviewing, in real time, three 35 dimensional images in rapid sequence. There remains a need for an imaging system capable of producing full colour, registered, stereo images in real time. A novel, stereo WO99/20056 PCT/AU98/00863 -5 imaging method and apparatus has therefore been developed, for constructing a three dimensional view of an object, and for performing quantitative analysis of the resultant stereo photographs. The present invention enables images 5 of a three dimensional subject, such as the ocular fundus, to be viewed in stereo, and for serial comparison to take place between colour matched and registered images of the same object. 10 It is therefore an object of the present invention to provide an improved imaging system capable of producing a virtual, three dimensional representation of an object, that also enables an observer to compare representations of the object taken at different times. 15 It is a further object of the present invention to provide an improved stereo image processing system which has the ability to colour correct and automatically or semi automatically register images in a stereo pair, or a set of 20 stereo pairs, compensating for differences in size, rotation and translation between the stereo images. According to the present invention there is provided a system for creating and visualising three dimensional 25 images of an object, including: imaging means for obtaining two images of the same object from different angles; digitizing means for digitizing said images; image processing means for colour matching and 30 registering the images; controller means for converting the two images into an interlaced image; display means for displaying the registered interlaced image; and 35 visualizing means for visualizing the image in three dimensions.

WO99/20056 PCT/AU98/00863 - 6 Preferably the system includes measuring means for measuring areas of interest in three dimensions, and calculating means for calculating desired measurements of the object. 5 Preferably the system includes a stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs. Preferably the stereo flicker chronoscope is operable to 10 serially display stereo pairs or sets of stereo pairs, The stereo pairs or sets of stereo pairs may have been registered and/or colour corrected, by means of the image processing means. 15 The measuring means may be a three dimensional cursor. Preferably the calculating means includes computer software. 20 Preferably the system includes result display means for displaying the results of the measurements. Preferably the result display means is a polar graph 25 centred on the optic nerve head. Preferably the imaging means is a stereo camera, a digital camera, a digital stereo camera, a video camera or a scanning laser ophthalmoscope operable to record two 30 different views of the object to be imaged. Preferably the digitizing means is a image scanner operable to digitize a slide film with high resolution, a digital camera, or any other apparatus operable to produce an image 35 in, or convert an image into, a digital format. Preferably the controller means is a computer or WO99/20056 PCT/AU98/00863 -7 microprocessor. Preferably the image processing means is software using the techniques of colour matching and image registration, 5 and/or includes means for changing image magnification in three dimensions and real time. Preferably the display means is a video display monitor or the like. 10 Preferably the visualizing means includes a pair of Liquid Crystal Display goggles. The present invention also provides an apparatus for 15 viewing three dimensional images of an object, including: imaging means for obtaining first and second images of a stereo pair; digitizing means for digitizing the two images; image processing means for determining and correcting 20 for colour, rotation, translation and scale differences between different images of the same object; controller means for converting the images into a stereo interlaced image; display means for displaying registered interlaced 25 images; and visualizing means for visualizing the images in three dimensions. Preferably the apparatus includes measuring means for 30 measuring specific characteristics of the object, calculating means for calculating desired measurements of the object and result display means for displaying the results of measurements. 35 Preferably the apparatus includes a stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs.

WO99/20056 PCT/AU98/00863 - 8 Preferably the stereo flicker chronoscope is operable to serially display stereo pairs or sets of stereo pairs. 5 Preferably the measuring means includes a three dimensional cursor. Preferably the measuring means includes a circular or elliptical template that may be superimposed over each 10 optic disc, and which may be used to measure one or more parameters including neuro-retinal rim width and optic disc cupping. Preferably the calculating means includes computer 15 software. Preferably the first and second images are left and right images. 20 Preferably the display means is for displaying alternately an approximately equal number of one or more horizontal lines of the first image and of the second image. Preferably the imaging means is a stereo camera, a digital 25 camera, a digital stereo camera, a video camera, a scanning laser ophthalmoscope or any other suitable imaging means that is able to record two different views of the object to be imaged. 30 Preferably the digitizing means is an image scanner that is able to digitize a slide film with high resolution, a digital camera, or any apparatus capable of producing or converting an image into a digital format. 35 Preferably the controller means is a computer or a microprocessor.

WO99/20056 PCT/AU98/00863 -9 Preferably the image processing means is custom software. Preferably the image processing means uses colour matching and image registration methods for the correction of 5 differences in colour, rotation, translation and scale, and/or includes means for changing image magnification in three dimensions and real time. Preferably the methods includes a colour matching technique 10 utilising a linear adjustment method to match the mean and standard deviation of each colour component, and an automatic or semi-automatic technique for rotation and translation effects. 15 Preferably the display means includes a video display monitor or the like. Preferably the visualizing means includes a pair of Liquid Crystal Display goggles. 20 Preferably the goggles are Vrex wireless or 3-D Max goggles, and more preferably the LCD goggles are electronically coupled to the display means. 25 Preferably the result display means includes a polar graph centred on the optic nerve head. The present invention still further provides an apparatus for visualizing three dimensional, recreated views of an 30 object, including: a stereo camera for obtaining first and second images of a stereo pair; digitizing means for digitizing the first and second images; 35 image processing means for determining and correcting for colour, rotation, translation and scale differences between two different interlaced images of the WO99/20056 PCT/AU98/00863 - 10 same object; controller means for converting the images into an interlaced image, in which an approximately equal number of one or more horizontal lines of the first and then of 5 the second image are displayed alternately; display means for displaying registered, interlaced images; and visualizing means for visualizing the images in three dimensions. 10 Preferably the apparatus includes measuring means for measuring specific characteristics of the object, calculating means for calculating desired measurements of the object, and result display means for displaying the 15 results of measurements. Preferably the apparatus includes a stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs. 20 Preferably said object may be any object in which three dimensional topographic data is desirable. Preferably said object includes human or animal tissue. 25 Preferably said object includes an animal or human body part. Preferably said tissue or body part is the fundus of the 30 eye, specifically the optic nerve head region, or other ocular features of interest. According to the present invention there is also provided a method for creating and visualising three dimensional 35 images of an object including: obtaining two images of the same object from different angles; WO99/20056 PCT/AU98/00863 - 11 digitizing said images; colour matching and registering the images; converting the two images into an interlaced image; 5 displaying the registered interlaced image for visualizing the image in three dimensions; measuring areas of interest; and calculating desired measurements of the object 10 Preferably the method includes comparing stereo pairs or sets of stereo pairs, or colour correcting and/or registering and displaying sequentially or flickering two or more stereo pairs in 3D to highlight change or differences in topography. 15 Preferably the method includes displaying the results of the measurements. Preferably said digitizing is performed in high resolution. 20 In order that the invention be more fully understood, some preferred embodiments will be described, by way of example, with reference to the following drawings in which: Figure 1 is a diagrammatic plan view of a system 25 according to the present invention; Figure 2 is an explanatory diagram illustrating the process of producing an interlaced image; and Figure 3 is an illustration of a novel colour matching process according to a preferred embodiment of the 30 present invention. Referring to Figure 1, the first arrangement of an apparatus of the present invention includes a Nidek simultaneous stereo camera 1 and 2, for recording two 35 different images 3 and 4, of the ocular fundus of patient's eye 9, taken from left and right viewing positions. Alternatively, the images may be captured on film and WO99/20056 PCT/AU98/00863 - 12 developed on photographic paper or slides, which may then be digitised for the controller means (see below) via a scanner, such as a Polaroid Sprintscan or the like. 5 An image file of digitized images 3 and 4 is generated and stored in the memory of a controller means in the form of an IBM compatible personal computer 5, although any appropriate computing system may be substituted. This image file is accessed via custom software. The left and 10 right stereo images are converted by the software into a single interlaced image 6, in which every second line is captured from both images. Referring to Figure 2, image A and image B are combined to form a single image C (corresponding to image 6 in Figure 1) containing 15 stereoscopic information. A horizontal line of pixels from image A is displayed as the first line of the interlaced image C, and a horizontal line from image B is displayed as the next line. Either image A or image B may be the left or right image. The process of capturing alternate lines 20 of pixels from the two images continues until the completion of an interlaced image C. This image C, therefore, contains every second line of the right stereo image and every second line of the left image. 25 Liquid Crystal Display goggles 7 are then used to visualize the interlaced image 6 in stereo, on a display unit in the form of a computer monitor 8 or similar video display screen. The LCD glasses 7 may be electronically coupled to the display unit, such as with those made by 3DMax, or they 30 may be a wireless version, such as Vrex wireless LCD glasses. The monitor 8 must be in interlaced mode, so that firstly, the odd numbered horizontal lines are written on the display monitor, and then the even numbered horizontal lines. When the odd numbered lines are displayed, one of 35 the two screens of the LCD goggles is darkened, while the other remains clear. The observer views the image with the eye under the clear screen and sees the information from WO99/20056 PCT/AU98/00863 - 13 the odd numbered lines (image A). After all of the odd numbered lines have been written, the LCD shutter alternates the darkened and clear vision windows and the even numbered lines are written (image B). This process 5 takes approximately fifty milliseconds, which is imperceptible to the human eye. The interlaced image C can then be visualised as a "virtual" stereo image and the topography of the optic nerve head can be perceived in three dimensions. An alternative embodiment would involve 10 a number of three dimensional glasses being connected, or used, in parallel with the video display monitor, so that several people could simultaneously view the interlaced image. 15 A novel image processing technique is incorporated into the custom software of PC 5 to compensate for differences in colour matching, scale, translation and rotation between stereo image pairs, or sets of stereo image pairs. Figure 3 illustrates the technique through which colour matching 20 is carried out. Linear adjustment is used to accommodate for differences in grey scale (colour) from one image of the same object to another. Linear adjustment of the input image 10, into the output image 14, occurs pixel by pixel, by calculation of the means and standard deviations from 25 the reference image 12. For a grey scale image, this will simply adjust the mean and standard deviation of the input image to the mean and standard deviation of the reference image. For colour images, however, linear colour correction will be applied separately on each colour 30 component of red, green and blue. The mean and standard deviation of each colour component of the input image will be appropriately matched to the reference image. Image registration is also applied to compensate for 35 translation, scale and rotation differences between stereo pairs or sets of stereo pairs. This may be completed via an automatic or a semi-automatic registration procedure.

WO99/20056 PCT/AU98/00863 - 14 Two different techniques may be used to align sequential input and reference images. The first method provides automated and precise image registration based on a normalized grey scale correlation. In this method, feature 5 matching is obtained in both the input and reference images, whereby the same feature in both images is identified. A unique template is automatically selected from the input image and a similar template is identified, if it exists, from the reference or target image. The 10 reference image is then registered according to the differences in the centre coordinates of the templates. To reduce the search time, the search area on the target image may be limited to double the size of the template surrounding the centre of the template. The normalized 15 grey scale correlation function reaches a maximum value of 1 when the input and reference image match exactly, or 0 when there is no correlation. By moving the template over the reference image, the correlation function is computed at each position. The position where the largest 20 correlation value is obtained is considered the best match. A second technique uses a semi-automatic method to register the stereo pairs. An even number of points from the input image and the approximately corresponding points from the 25 reference image are chosen. The best possible match for the points chosen on the reference image is found. The search area is limited to the area surrounding the points selected on the reference image. This may increase the speed as well as the accuracy of the correlation 30 computation. The differences in the x and y directions for each point (input and reference points) are computed and the average of the differences in the x and y direction obtained. This will correct for any translation differences. 35 By connecting two points and calculating the angles with respect to a horizontal axis in the input and the reference WO99/20056 PCT/AU98/00863 - 15 image, the difference in the angle can also be obtained. The average angle difference for all the pairs of points will give an estimation for the overall rotation of the reference image. This technique is faster than the 5 automatic method, but the fully automatic method may provide more accurate alignment. The apparatus of the present invention can also supply 10 means to view, in real time, registered, stereo images of the same fundus in rapid sequence (stereo flicker chronoscopy). This technique allows comparison of two or three dimensional fundus images from the same patient, taken on different occasions. For example, a stereo pair 15 photographed in 1995 may be registered with a stereo image taken in 1997. As the display jumps from one image to the other, subtle changes in the structure of the optic disc can be easily perceived. Flickering between a number of registered images may help the clinician visualize any 20 changes in fundus topography over time. A three dimensional mouse pointer can also be used to manually measure structures of the optic nerve head or other areas of interest. The three dimensional mouse 25 pointer is an indicator which can not only be moved back and forth across the image plane on the monitor, but also perpendicular to that plane. Using a keyboard or other controls (not shown in Figure 1), the perceived depth of the pointer can be changed. This 3D mouse is valuable for 30 measurements to be made or the precise location of objects or structures to be determined. It allows the cursor to be placed, in the eyes of the viewer, on the surface of the optic nerve or another three dimensional structure. 35 Measuring means, in the form of a circular or elliptic template, can then be displayed and positioned over the optic disc by the operator, to aid in obtaining WO99/20056 PCT/AU98/00863 - 16 measurements around the optic nerve head. Clinically important values regarding the extent of optic disc cupping and the width of the neuro-retinal rim can then be calculated. Differences in nerve-head rim measurements, 5 between two chronologically separate images of the same fundus, can then be plotted in a polar fashion around the disc, with positive changes advancing beyond the edge of the disc and negative changes plotted towards the centre of the disc. A very good representation is thus displayed, 10 allowing the operator to determine at a glance the size and position of any rim width changes. A quantitative measure of the change in optic nerve head rim measurements over time is therefore provided. 15 Thus, the present invention provides a novel system in which three dimensional images of an object may be constructed and analysed. Comparison between images taken at different times and at different orientations is possible using the present invention. 20 The advantages of the various embodiments of the apparatus and method of the present invention are thus that: * stereo images can be seen on a screen, rather the clinician having to bend over a light box; 25 * a series of stereo images can be flickered ("stereo flicker chronoscopy"), which is not possible using only the slides, and without using a mechanical system such as a Deltascope; * the edges of the optic disc, the start of optic disc 30 cupping and the start of the floor of the optic cup can be seen much easier than from monoscopic images; * the high resolution allows precise location of the edges of the neuro-retinal rim; * colour adjustment and correction minimize errors due to 35 change in colour of photographs attributable to the photographic process, pupil dilation, and lens changes; * the flicker system (chronoscopy) and the measurements WO99/20056 PCT/AU98/00863 - 17 system (chronometry) work together; * registered and colour adjusted images are stored, and so do not have to be done over and over again; and * a number of people can observe the stereo image on the 5 computer screen simultaneously. Modification within the spirit and scope of the invention may therefore be readily effected by a person skilled in the art. Other alternative embodiments would involve the 10 use of one or two video cameras or a scanning laser ophthalmoscope to directly capture the image in a digital format. Any other single or stereo camera or imaging device that is capable of creating an image of the optic nerve head from two viewing positions, simultaneously or 15 sequentially, may also be utilised. Thus, it is to be understood that this invention is not limited to the particular embodiments described by way of example herein above.

Claims (50)

1. A system for creating and visualising three dimensional images of an object, including: 5 imaging means for obtaining two images of the same object from different angles; digitizing means for digitizing said images; image processing means for colour matching and registering the images; 10 controller means for converting the two images into an interlaced image; display means for displaying the registered interlaced image; and visualizing means for visualizing the image in 15 three dimensions.

2. A system as claimed in claim 1, including measuring means for measuring areas of interest in three dimensions, and calculating means for calculating 20 desired measurements of the object.

3. A system as claimed in either claim 1 or 2, including a stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs. 25

4. A system for creating and visualising three dimensional images of an object, including: imaging means for obtaining two images of the same object from different angles; 30 digitizing means for digitizing said images; image processing means for colour matching and registering the images; controller means for converting the two images into an interlaced image; 35 display means for displaying the registered interlaced image; visualizing means for visualizing the image in WO99/20056 PCT/AU98/00863 - 19 three dimensions; stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs; measuring means for measuring areas of interest 5 in three dimensions; and calculating means for calculating desired measurements of the object.

5. A system as claimed in either claim 3 or 4, wherein 10 said stereo flicker chronoscope is operable to serially display stereo pairs or sets of stereo pairs.

6. A system as claimed in either claim 2 or 4, wherein said measuring means is a three dimensional cursor. 15

7. A system as claimed in either claim 2 or 4, wherein said calculating means includes computer software.

8. A system as claimed in any one of the preceding claims, 20 including result display means for displaying the results of the measurements.

9. A system as claimed in claim 8, wherein said result display means is a polar graph centred on the optic 25 nerve head.

10. A system as claimed in any one of the preceding claims, wherein said imaging means is a stereo camera, a digital camera, a digital stereo camera, a video camera 30 or a scanning laser ophthalmoscope operable to record two different views of the object to be imaged.

11. A system as claimed in any one of the preceding claims, wherein said digitizing means is a image scanner 35 operable to digitize a slide film with high resolution, a digital camera, or any other apparatus operable to produce an image in, or convert an image into, a WO99/20056 PCT/AU98/00863 - 20 digital format.

12. A system as claimed in any one of the preceding claims, wherein said controller means is a computer or 5 microprocessor.

13. A system as claimed in any one of the preceding claims, wherein said image processing means is software using the techniques of colour matching and image 10 registration, and/or includes means for changing image magnification in three dimensions and real time.

14. A system as claimed in any one of the preceding claims, wherein said display means is a video display monitor 15 or the like.

15. A system as claimed in any one of the preceding claims, wherein said visualizing means includes a pair of Liquid Crystal Display goggles. 20

16. An apparatus for viewing three dimensional images of an object, including: imaging means for obtaining first and second images of a stereo pair; 25 digitizing means for digitizing the two images; image processing means for determining and correcting for colour, rotation, translation and scale differences between different images of the same object; 30 controller means for converting the images into a stereo interlaced image; display means for displaying registered interlaced images; and visualizing means for visualizing the images in 35 three dimensions.

17. An apparatus as claimed in claim 16, including WO99/20056 PCT/AU98/00863 - 21 measuring means for measuring specific characteristics of the object, calculating means for calculating desired measurements of the object and result display means for displaying the results of measurements. 5

18. An apparatus as claimed in either claim 16 or 17, including a stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs. 10

19. An apparatus for viewing three dimensional images of an object, including: imaging means for obtaining first and second images of a stereo pair; digitizing means for digitizing the two images; 15 image processing means for determining and correcting for colour, rotation, translation and scale differences between different images of the same object; controller means for converting the images into a 20 stereo interlaced image; display means for displaying registered interlaced images; visualizing means for visualizing the images in three dimensions; 25 stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs; measuring means for measuring specific characteristics of the object; calculating means for calculating desired 30 measurements of the object and result display means for displaying the results of measurements.

20. An apparatus as claimed in either claim 18 or 19, wherein said stereo flicker chronoscope is operable to 35 serially display stereo pairs or sets of stereo pairs.

21. An apparatus as claimed in either claim 17 or 19, WO99/20056 PCT/AU98/00863 - 22 wherein said measuring means includes a three dimensional cursor.

22. An apparatus as claimed in any one of claims 17, 19 or 5 21, wherein said measuring means includes a circular or elliptical template that may be superimposed over each optic disc, and which may be used to measure one or more parameters including neuro-retinal rim width and optic disc cupping. 10

23. An apparatus as claimed in either claim 17 or 19, wherein said calculating means includes computer software. 15

24. An apparatus as claimed in any one of claims 16 to 23, wherein said first and second images are left and right images.

25. An apparatus as claimed in any one of claims 16 to 24, 20 wherein the display means is for displaying alternately an approximately equal number of one or more horizontal lines of the first image and of the second image.

26. An apparatus as claimed in any one of claims 16 to 25, 25 wherein said imaging means is a stereo camera, a digital camera, a digital stereo camera, a video camera, a scanning laser ophthalmoscope or any other suitable imaging means that is able to record two different views of the object to be imaged. 30

27. An apparatus as claimed in any one of claims 16 to 26, wherein said digitizing means is an image scanner that is able to digitize a slide film with high resolution, a digital camera, or any apparatus capable of producing 35 or converting an image into a digital format.

28. An apparatus as claimed in any one of claims 16 to 27, WO99/20056 PCT/AU98/00863 - 23 wherein said controller means is a computer or a microprocessor.

29. An apparatus as claimed in any one of claims 16 to 28, 5 wherein said image processing means is custom software.

30. An apparatus as claimed in any one of claims 16 to 29, wherein said image processing means uses colour matching and image registration methods for the 10 correction of differences in colour, rotation, translation and scale, and/or includes means for changing image magnification in three dimensions and real time. 15

31. An apparatus as claimed in claim 30, wherein said methods includes a colour matching technique utilising a linear adjustment method to match the mean and standard deviation of each colour component, and an automatic or semi-automatic technique for rotation and 20 translation effects.

32. An apparatus as claimed in any one of claims 16 to 31, wherein said display means includes a video display monitor or the like. 25

33. An apparatus as claimed in any one of claims 16 to 32, wherein said visualizing means includes a pair of Liquid Crystal Display goggles. 30

34. An apparatus as claimed in claim 33, wherein said goggles are Vrex wireless or 3-D Max goggles.

35. An apparatus as claimed in either claim 33 or 34, wherein said LCD goggles are electronically coupled to 35 the display means.

36. An apparatus as claimed in any one of claims 17 or 19, WO99/20056 PCT/AU98/00863 - 24 wherein the result display means includes a polar graph centred on the optic nerve head.

37. An apparatus for visualizing three dimensional, 5 recreated views of an object, including: a stereo camera for obtaining first and second images of a stereo pair; digitizing means for digitizing the first and second images; 10 image processing means for determining and correcting for colour, rotation, translation and scale differences between two different interlaced images of the same object; controller means for converting the images into 15 an interlaced image, in which an approximately equal number of one or more horizontal lines of the first and then of the second image are displayed alternately; display means for displaying registered, interlaced images; and 20 visualizing means for visualizing the images in three dimensions.

38. An apparatus as claimed in claim 37, including measuring means for measuring specific characteristics 25 of the object, calculating means for calculating desired measurements of the object, and result display means for displaying the results of measurements.

39. An apparatus as claimed in either claim 37 or 38, 30 including a stereo flicker chronoscope for comparison of stereo pairs or sets of stereo pairs.

40. An apparatus for visualizing three dimensional, recreated views of an object, including: 35 a stereo camera for obtaining first and second images of a stereo pair; digitizing means for digitizing the first and WO99/20056 PCT/AU98/00863 - 25 second images; image processing means for determining and correcting for colour, rotation, translation and scale differences between two different interlaced images of 5 the same object; controller means for converting the images into an interlaced image, in which an approximately equal number of one or more horizontal lines of the first and then of the second image are displayed alternately; 10 display means for displaying registered, interlaced images; visualizing means for visualizing the images in three dimensions; stereo flicker chronoscope for comparison of 15 stereo pairs or sets of stereo pairs; measuring means for measuring specific characteristics of the object; calculating means for calculating desired measurements of the object; and 20 result display means for displaying the results of measurements.

41. An apparatus as claimed in any one of claims 37 to 40, wherein said first and second images are left and right 25 images.

42. An apparatus as claimed in any one of claims 37 to 41, wherein said object is any object in which three dimensional topographic data is desirable. 30

43. An apparatus as claimed in any one of claims 37 to 42, wherein said object includes human or animal tissue.

44. An apparatus as claimed in any one of claims 37 to 43, 35 wherein said object is a human or animal body part.

45. An apparatus as claimed in any one of claims 37 to 44, WO99/20056 PCT/AU98/00863 - 26 wherein said object is an ocular feature such as the fundus of an eye or the optic nerve head region.

46. A method for creating and visualising three dimensional 5 images of an object including: obtaining two images of the same object from different angles; digitizing said images; colour matching and registering the images; 10 converting the two images into an interlaced image; displaying the registered interlaced image for visualizing the image in three dimensions; measuring areas of interest; and 15 calculating desired measurements of the object.

47. A method as claimed in claim 46, including comparing stereo pairs or sets of stereo pairs. 20

48. A method as claimed in claim 46, including colour correcting and/or registering and displaying sequentially or flickering two or more stereo pairs in 3D to highlight change or differences in topography. 25

49. A method as claimed in any one of claims 46 to 48, including displaying the results of said measurements.

50. A method as claimed in any one of claims 46 to 49, wherein said digitizing is performed in high 30 resolution.