Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2000-04-12
2001-08-21
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06276799
ABSTRACT:
The present invention relates to a computer imaging or 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 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.
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 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 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 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 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 a polarised material onto a screen, with the stereo pair polarised at 90° 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 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 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 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
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ighting conditions, may possess variable characteristics, in terms of magnification, colour and the positioning of 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 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 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.
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 U.S. Pat. No. 5,519,485.
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 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 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 left and right measuring points.
U.S. Pat. No. 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 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 computerized image processing system for fluorescein angiography pictures, and fundus photography. This system 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 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 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.
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 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 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 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 arnd enabling the calculation of the clinically important values 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.
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 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 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 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 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.
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
Eikelboom Robert Henry
Van Saarloos Paul Phillip
Yogesan Kanagasingam
Baker & Botts LLP
Manuel George
The Lions Eye Institute of Western Australia Incorporated
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