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WO2008100332A1 - Système de topographie cornéo-sclérale - Google Patents

Système de topographie cornéo-sclérale Download PDF

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Publication number
WO2008100332A1
WO2008100332A1 PCT/US2007/074715 US2007074715W WO2008100332A1 WO 2008100332 A1 WO2008100332 A1 WO 2008100332A1 US 2007074715 W US2007074715 W US 2007074715W WO 2008100332 A1 WO2008100332 A1 WO 2008100332A1
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Prior art keywords
grid
image
node
camera
sum
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Inventor
Edwin J. Sarver
James Marous
Cynthia Robert
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VISION OPTIMIZATION LLC
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VISION OPTIMIZATION LLC
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Priority claimed from US11/674,985 external-priority patent/US20070195268A1/en
Application filed by VISION OPTIMIZATION LLC filed Critical VISION OPTIMIZATION LLC
Publication of WO2008100332A1 publication Critical patent/WO2008100332A1/fr
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/107—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for determining the shape or measuring the curvature of the cornea

Definitions

  • Embodiments of the invention relate to an ophthalmic topography measurement system and, more particularly, to an advanced rasterstereography-based corneo-scleral (“RCT”) topography measurement system; and to an image processing method used in conjunction with the system.
  • RCT rasterstereography-based corneo-scleral
  • the human cornea is the clear window of the eye. It provides as much as seventy-five percent of the refractive power of the eye; thus, it is of great interest to accurately assess the eye's topography (surface shape), and have the capability to map the topography particularly over the cornea, limbus and the neighboring scleral region.
  • This shape information can be used to diagnose corneal disease (such as Keratoconus), plan vision correction therapies involving the use and fitting of contact lenses and in intraoperative procedures, and in other ophthalmic applications as those skilled in the art will appreciate.
  • Commonly used and conventional corneal topography systems include, for example, Placido-based systems that measure a concentric light ring pattern that is specularly reflected from the cornea, and scanning-slit systems.
  • Scanning slit-based systems operate by capturing individual images of a bright slit of light that is diffusely reflected/scattered from various surfaces of the eye. This diffusely reflected image does not have image edges as sharp as those of the specularly reflected mire images. As a result, the inherent measurement accuracy is reduced.
  • the slits must be scanned over some finite time period in which the eye can be moving, there may be problems in providing an exact registration of the individual images relative to the eye being measured.
  • PAR Corneal Topography System Another topography measurement system that was commercially available in the 1990' s was known as the PAR Corneal Topography System (PAR CTS).
  • the PAR CTS is referred to as a rasterstereography-based system.
  • Rasterstereography-based topography is a method of obtaining contour or topographic information where one of the cameras in a stereogrammetric pair is replaced with a light source, which projects a cyan grid of parallel lines onto a surface to be measured. If the topography of a cornea is to be obtained, fluorescein solution is applied onto the tear film of the cornea so that the grid pattern becomes fluorescent and can be imaged.
  • the PAR CTS was advantageous in that its operation was not dependent on specular reflection of the grid, and therefore not dependent on high quality optical surfaces or strict alignment criteria.
  • the PAR CTS also was an "elevation" (height) system, distinguishing it from Placido-based systems, which measure surface slope rather than elevational height directly.
  • Elevation height
  • the interested reader is directed to US Patent Nos. 4,995,716 and 5,159,361, the disclosures of which are incorporated herein by reference in their entireties.
  • the PAR CTS also had a long working distance and long optical layout that made it difficult to use or integrate with surgical microscopes and other diagnostic and/or therapeutic devices, thus further limiting its utility.
  • Embodiments of the instant invention described herein as an advanced Rasterstereography Corneo-scleral Topography (RCT) system, overcome the abovementioned limitations, shortcomings, and disadvantages of the prior art devices and, in particular, the original PAR CTS system.
  • the RCT system will provide measurement and analysis capabilities that both include certain desirable features of past and currently available Placido-based, scanning slit-based, three-dimensional polar grid-based, Scheimpflug-based, or other topography measurement modalities, and others, which are not technically provided by those systems.
  • the RCT system according to the embodiments described herein will present a modern, efficient, and efficacious device that incorporates improved hardware and software over the obsolete PAR CTS system in particular, as well as other currently available corneal topography systems.
  • An embodiment of the invention is directed to an advanced rasterstereography- based corneo-scleral topography (RCT) system.
  • the system is referred to as a corneoscleral topography system rather than merely a corneal topography system because the unique system design accommodates mapping of the cornea, limbus and neighboring scleral (hereinafter 'target') region.
  • the RCT system is equipped to project a cyan grid pattern onto the target surface in which the tear film has been stained with a fluorescein solution. The stained tear film will fluoresce and diffusely reflect/scatter the projected cyan grid, and is imaged by a grid detection camera.
  • the RCT system is structurally and functionally equipped to capture a complete grid image that spans the target in a single image frame.
  • custom optics assemblies including tube-mounted imaging and grid projection systems having increased depth of field are provided.
  • the single frame acquisition capability eliminates a need for sequential imaging and image registration, which were problematic in the prior art for sequential image systems.
  • the RCT utilizes a customized, compact optical layout that additionally provides more efficient and improved operational integration with complementary devices such as, e.g., a surgical microscope.
  • the RCT system includes a novel mapping feature that provides a visual correlation between the display of a raw grid image on the cornea and a corneal elevation or curvature map generated by the RCT system. A marker indicia on the grid image can be displayed on the elevation or curvature map. This association allows measurement features on the raw image to be viewed on the processed map. This software feature may be selectable and is useful in identifying where on the processed map physical image features are located.
  • a novel image processing algorithm can extract and quickly process the grid features and yield an accurate and detailed corneal surface measurement, without the need for specialized image processing hardware (e.g., pc board/frame grabber) required by the prior art PAR system.
  • the total processing time for an image can be reduced to less than 2 seconds.
  • the processing time for the algorithm running on a 3GHz PC is 0.2 seconds.
  • the embodiments of the invention incorporate components and/or design considerations that include and/or provide, without limitation thereto, the following: digital imaging capability; controlled LED Illumination; adjustable illumination levels for alignment and measurement modes; efficacious head spacing for efficient integration with other diagnostic and/or therapeutic components; full corneoscleral coverage (up to 16.5mm x 13.25mm); improved depth of field (e.g., > 5mm); an adaptable core hardware platform that is modular and portable and which may include, e.g., a microscope, slit lamp; a faster, more robust grid detection algorithm; and, click- selectable raw image feature mapping/topo map overlay.
  • Figure 1 is a flow diagram illustrating image processing steps according to an embodiment of the invention
  • Figure 2 shows a reticle image on an exemplary input grid image according to an embodiment of the invention
  • Figure 3 is a schematic diagram useful in illustrating how row and column sums are used to find the location of the center of grid pattern according to an embodiment of the invention
  • Figure 4 illustrates a profile of column sums in a region of interest (ROI) for the image shown in Figure 2 according to an aspect of the invention
  • Figure 5 illustrates an algorithmic result of center finding for the image shown in Figure 2 according to an aspect of the invention
  • Figure 6 shows an exemplary grid image illustrating vertical linear feature enhancement via a convolution operation according to an aspect of the invention
  • Figure 7 is a schematic diagram that illustrates peak detection by the algorithm according to an aspect of the invention.
  • Figure 8 shows the image of Figure 6 after thinning, binarizing, and shot noise removal according to an aspect of the invention
  • Figure 9 shows an image similar to that of Figure 8, which illustrates the results of horizontal features processing after thinning, binarizing, and shot noise removal according to an aspect of the invention
  • Figure 10 is a diagram that illustrates an exemplary instance when a continuous horizontal linear feature and a continuous vertical linear feature cross at the boundary of a pixel;
  • Figure 11 shows an exemplary image illustrating the intersections of the vertical and horizontal line features as depicted in Figures 8 and 9 according to an aspect of the invention
  • Figure 12 is a schematic diagram that is used to illustrate the process of searching for nodes according to an aspect of the invention.
  • Figure 13 shows an exemplary image that illustrates the final results where found nodes overlay the original image according to an aspect of the invention
  • Figure 14 shows a top plan schematic of an advanced RCT system according to an embodiment of the invention.
  • FIGS 15(a-d) schematically show four respective views of an optical head of the RCT system of Figure 14;
  • Figure 16a schematically illustrates a top plan view of an optical assembly according to an exemplary embodiment of the invention
  • Figure 16b illustrates a side view of the optical assembly of Figure 16a
  • Figures 17(a, b) schematically show top and side views, respectively, that illustrate certain details of an optical mount according to an aspect of the invention
  • Figure 18 shows a schematic diagram of a Zemax optical analysis ray tracing of a front view camera according to an embodiment of the invention
  • Figure 19 shows a schematic diagram of a Zemax ray tracing of the grid camera according to an embodiment of the invention.
  • Figure 20 shows a schematic diagram of a Zemax optical analysis ray tracing for the grid projection according to an embodiment of the invention
  • Figure 21 shows a schematic diagram of a Zemax optical analysis ray trace for a grid illuminator according to an embodiment of the invention
  • Figures 22(a-d) illustrate a raw data/topo map overlay feature of the RCT system according to an aspect of the invention
  • Figure 23 is a schematic for a voltage power supply in a flash controller according to an exemplary embodiment of the invention.
  • Figure 24 is a schematic for the connectors and switches in the flash controller of Figure 23;
  • Figure 25 is a schematic for the LED array drivers in the flash controller of Figure 23;
  • Figure 26 is a schematic for a one shot trigger in the flash controller of Figure 23;
  • Figure 27 is a schematic for a programmable logic device (PLD) in the flash controller of Figure 23
  • Figure 28 is a schematic for a programmable current-mode power supply in the flash controller of Figure 23
  • PLD programmable logic device
  • Figure 29 shows a schematic illustration the advanced RCT system including the flash controller interface according to an exemplary embodiment of the invention.
  • An embodiment of the invention is directed to an image processing algorithm that involves process steps for determining the topography of a corneo-scleral target surface.
  • the process 100 allows one to extract the grid features from an advanced rasterstereography-based corneo-scleral topography (RCT) system captured grid image. Once the features have been extracted, the target surface topography can be reconstructed and displayed. It is particularly advantageous that the total time for processing the image can be less than 2.0 seconds. In an exemplary aspect, the processing time for the algorithm running on a 3GHz PC is about 0.2 seconds.
  • an exemplary cyan grid pattern is projected onto a fiuorescein-stained tear film of a corneo-scleral surface to be measured, and an image of the fluorescing grid is obtained.
  • the task at hand is to find the center of the grid and all grid intersections in the image.
  • a node as that term is used herein, is defined as the pixel space bounded by four associated intersection points of horizontal and vertical lines of the grid image.
  • the center box of the grid image is detected, according to an exemplary aspect, using histograms of row and columns sums around the center of the image.
  • This center box is denoted the center (starting) node.
  • Step 130 involves extracting horizontal and vertical line features of the grid image.
  • the step requires enhancing the vertical lines in the image via a filtering process and saving them in an array; enhancing the horizontal lines in the image via a filtering process and saving them in an array; post-processing the vertical line array to thin the vertical lines and remove small noise features; and, postprocessing the horizontal line array to thin the horizontal lines and remove small noise features.
  • intersections are found in the post-processed vertical and horizontal lines arrays.
  • a two dimensional node array (stack) for storing all nodes prior to resolving their pixel coordinate information is provided at step 150.
  • step 160 starting with the center node, all horizontal and vertical neighbors of a node (four-connected) are found and all new unresolved nodes are added to the stack. Each new node will have up to three neighbors yet to be found.
  • nodes are resolved (described in further detail below), they are removed from the stack until the stack is ultimately empty. If the stack is not empty, a node is popped off the stack and its neighbors are found at step 170.
  • step 180 new, unresolved nodes are added to the stack and processing the nodes continues until the stack is empty; i.e., until all intersection points are determined.
  • Step 190 is an optional processing step that discloses the use of prediction to estimate where neighboring nodes are expected to be located. By iterating over the set of found nodes and gradually relaxing processing thresholds, hard to locate node locations (for example, in areas of low contrast) may be extracted more reliably. Image processing algorithm details will now be described.
  • a reticle is provided with the grid projection optics (described in further detail below) that provides a centered cross pattern 205 as shown in Figure 2.
  • the first step in the image processing algorithm 100 is to detect the cross pattern 205 in the image 1000 as illustrated in Figure 2.
  • the cross pattern is brighter and has a higher contrast than surrounding pixels.
  • the horizontal and vertical sections 206, 207 of the center cross are generally aligned with rows and columns of the image, as further illustrated schematically in Figure 3. These characteristics are effectively exploited to properly locate the cross pattern.
  • Figure 3 illustrates the process of adding all pixels along a row inside a region of interest (ROI), representing approximately one-third of the image in an exemplary aspect, and saving the sum in a row sum array 310.
  • ROI region of interest
  • the same procedure is carried out for the columns in the ROI for a column sum array 320.
  • the peaks 315, 325, respectively, are found in the arrays as the maximum values.
  • the peak 315 in the row sum array 310 corresponds to the Y location of the cross center
  • the peak 325 in the column sum array 320 corresponds to the X location of the cross center.
  • Figure 4 is a profile 400 of an exemplary column sum array 320 in the center region of interest (ROI) for the image 1000 in Figure 2.
  • the profile of row sums (not shown) is similar.
  • Figure 5 illustrates the results of the center finding for the image of Figure 2.
  • the square 510 delimits the center ROI where the row and column sums are computed.
  • the central dot 520 shows the computed cross center.
  • the next process is to extract the vertical and horizontal line features of the grid image.
  • the first step in extracting the vertical and horizontal line features is feature enhancement.
  • a simple convolution operation is used to enhance the vertical and horizontal line features.
  • the illustrative convolution operation merely involves a point by point multiply and add operation to determine a final value for a particular sample. Once this point is centered on the image, the edge can conveniently be determined.
  • the filter is a zero-phase FIR filter.
  • the shape of the convolution kernel is illustrated below for the vertically oriented linear features. It is particularly advantageous in that it uses only constant values of (-1, 1).
  • the horizontal filter is an obvious rotation of the vertical filter as would be understood by a person skilled in the art.
  • Figure 6 shows the results of vertical linear feature enhancement using the convolution operation described herein. Other filter types may be used, such as recursive or Fourier filters, for example. As shown in Figure 6, the vertical (line) features are significantly enhanced. It can be noted, however, that the right hand side of the image is significantly darker (less contrast) than the left and center regions of the image.
  • the next step is to scan the image to detect the peaks.
  • the peaks are adaptively determined in a way that tolerates the non-uniform illumination present in the image.
  • H represents a high threshold
  • L a low threshold
  • the exemplary peak detection algorithm finds the local minima and maxima for a one dimensional profile. Two selected threshold values are used. A high threshold, H, must then be exceeded for a peak to be detected and a low threshold, L, must be exceeded in the negative direction for a valley to be detected. To compute the high and low threshold values, the algorithm sorts all values in the vector being processed and, in the exemplary aspect, takes the 45% point and 65% point as the low and high threshold values, respectively. This separation of the thresholds (as opposed to using 50% for both thresholds) provides a certain amount of noise immunity for the local minima and maxima. Other non-equal threshold values may alternatively be selected.
  • the thresholds are computed over regions along the profile vector.
  • the peak detection algorithm is applied to each row in the vertical feature enhancement image with four equally spaced sub- regions (e.g., ROI/4), where the thresholds are re-computed, according to an exemplary aspect.
  • the algorithm assigns the value of 255, while the value of zero is assigned to all other pixels. This has the effect of thinning and "binarizing" the vertical feature enhancement image.
  • the darker (vertically-oriented) squares 905 represent a discrete version of the vertical line 906 and the lighter gray squares 907 represent a discrete version of the horizontal line 908.
  • the linear features (906, 908) actually intersect, the discrete pixels do not have the same pixel in common indicating the intersection in the simple test described above. The probability of this occurring at a node is very low, but since there are over 1 ,000 nodes to process, it may occur one or more times per image. The situation may also occur when the continuous horizontal linear feature has a slight negative slope, the continuous vertical linear feature has a nearly vertical positive slope, and the continuous lines just happen to cross at the boundary of a pixel. To handle these situations, the line intersection test is modified as follows:
  • the current pixel being considered is at "00".
  • the pixel values for a 2x2 neighborhood in the vertical thinned image be V00, VOl, VlO, and VI l.
  • the output image from the thinned images in Figures 8 and 9 is shown in Figure 11. In the image of Figure 11 , the spots have been greatly expanded in size for viewing. In the actual image, each dot is a single pixel.
  • the next step is to find the nodes.
  • Each node will be considered to contain a "Point" object.
  • a Point object holds the (x,y) pixel location of the node.
  • the nodes are stored in a two-dimensional array so that it is easy to find the neighboring nodes.
  • the size of the node array is 101 x 101 (based on grid size and eye magnification).
  • the center node is located at element 50x50.
  • the array is indexed Nodes [x, y] where x indicates the column (center is 50), and y indicates the row (center is 50).
  • the node to the right of the center node would be stored at index (51,50) therefore x increases to the right.
  • the node above the center node would be stored at index (50,49), y increasing in the downward direction.
  • the nodes are almost regularly spaced so that the algorithm can predict where the neighbors should be located with little difficulty.
  • the predicted location is searched looking for an intersection as shown in Figure 11.
  • the closest pixel found to the predicted location is used as the actual location of the neighbor.
  • each direction is searched for a neighboring node, the following steps are performed: if the node is already found in a given direction, the node is not searched again; if the node has not yet been found (it has value Point (0,0)), the algorithm searches for the node; if the new neighbor node is found, its location is saved in the Nodes array. The node is also pushed onto the stack to look for the new node neighbors. The pixel value is set in the intersection image (and the pixels in the immediate neighborhood) to zero so as to prevent accidentally assigning another node to the same intersection in subsequent searches. Initially, the center node is pushed onto the stack and then the process executes the neighborhood finder until the stack is empty.
  • the nodes alternate in color (or contrast) between rows and columns to show proper topology of the nodes.
  • a common processing error is to assign a node to the wrong row or column.
  • the cyan connecting lines also help show that the nodes were properly placed in the correct relationship to their neighbors.
  • the RCT system 2000 comprises an optical head 2010 operationally connected to a controller/processor component(s) 2020.
  • the optical head 2010 includes a grid optical assembly (camera/detector/optics) 2050 aligned with a target 5000 along a system optical axis 2015; a front-view optical assembly 2070; and a grid projector assembly 2090.
  • the target surface has a location denoted by 2018.
  • Figures 15(a-d) show four respective schematic views of the optical head 2010.
  • Figures 16(a,b), respectively, show further plan and side schematic views of the optical head assembly in an exemplary aspect.
  • the optical assemblies of the grid camera assembly 2050 and front- view camera assembly 2070 each include an imaging optics enclosure 2052, 2072, and a prism 2054, 2074, respectively.
  • the grid projector 2090 as illustrated in Figures 15(b-d) includes a grid projection optics enclosure 2092 and a prism 2094.
  • the prisms provide optical path steering between the target, the cameras, and the grid projector.
  • the optics enclosures 2052, 2072, 2092 house optical assemblies as further described below, and are in the form of tubes.
  • Figure 16a shows the distance h from the system optical axis 2015 to the center of the grid camera tube 2052, given the full angle between the grid projector 2090 and grid camera being 35.8 degrees and the working distance from the plane containing the prisms to the target plane 2018 being equal to 170mm.
  • raw grid measurement data is obtained at an angular displacement in the horizontal plane.
  • the front view camera 2070 is 40mm lower than the grid view camera 2050.
  • the respective optical imaging lenses and apertures are enclosed in 28-30mm diameter tubes 2052, 2072.
  • the prisms 2054, 2074 are contained in an enclosure similar to that of the original PAR design.
  • the gray region 2080 in the top and side views is one possibility for providing a support structure for the three optical assembly tubes. Two of these triangular shapes can be aligned with standoffs to form a triangular cage. Set screws in the corners hold the optics tubes as illustrated in Figures 17(a, b).
  • the front view camera assembly (camera, optics/enclosure, prism) may not be required and, therefore, need not be integrated. This may occur, for example, if the optical head is connected to a microscope or laser system, as opposed to being a stand-alone system.
  • the distance between the center of the holes for the grid camera and grid projector is 110mm, as shown in Figure 16a.
  • Figures 17(a, b) Mounting details of an exemplary aspect is further shown in Figures 17(a, b).
  • Optical parts were primarily assembled from off the shelf components.
  • the tubes are 28mm OD and 25mm ID.
  • the prisms are held in place by a clevis mount at the end of the optical tube.
  • the prism was fixed relative to the camera optics in the optical tube.
  • the rotation of the prism to be aimed for the 17.8 deg angle was made by inserting the tube into the triangular frame, twisting the tube to the correct alignment and fixing the position with two set screws as illustrated in Figure 17a.
  • An advantageous aspect of the embodied RCT system is the comparatively shortened overall layout, as well as the device capability to measure and analyze the topography of the cornea, limbus and neighboring scleral region, rather than just over the corneal surface.
  • a telephoto lens design positive lens followed by negative lens
  • One criteria for the optical layout was that no vignetting of the images would be allowed.
  • a front view (at 710nm) for focusing and pupil acquisition was provided by a USB 2 camera.
  • the image sensor is 6.6mm x 5.3mm (8.46mm diagonal).
  • the grid reticle is chrome on glass with a 0.009mm line width, 0.075mm line spacing, and 19mm in diameter.
  • the optics are designed so that, at the target plane, the grid is 0.018mm line width, 0.15mm line spacing, 20mm diameter; thus more than sufficient to overlay the corneo-scleral region.
  • the view of the corneo-scleral target surface is such that the coverage is 16.5mm x 13.25mm (21.16mm diagonal — 10.58mm half diagonal). This scope of target coverage is unparalleled in the art.
  • the telephoto optical systems in conjunction with the limiting apertures also provide the generous depth of field, which equals or exceeds 5mm, and which is not found in conventional corneal topography systems (typically 3 mm).
  • the capability to map the cornea, limbus and neighboring sclera provides otherwise unavailable data that can be particularly useful for fitting contact lenses and/or in intra-operative procedures, and other applications.
  • the angle between the projection and measurement arms is 12 degrees.
  • the nominal working distance is 175mm.
  • the Zemax optical design layout for the exemplary front view camera 2070 is shown in Figure 18.
  • a 16.5 x 13.25mm target surface region at the corneal plane is imaged onto a 6.6 x 5.3mm camera sensor via the two element telephoto lens consisting of a +35mm lens (45210) and a -48mm focal length lens (45019).
  • the distance from the corneal plane to the front of the right angle prism (45109) is 214mm. This is 40mm longer than the grid camera working distance so that the physical extent of the cameras (41mm high, tapered) will not interfere with each other.
  • the distance between the edge of the prism and the positive lens is 10mm.
  • the distance between the positive and negative lenses is 11.5mm.
  • the distance between the negative lens and the image plane is 59.5mm.
  • the maximum diameter of the corneal region of interest is 21.16mm.
  • the Zemax ray tracing indicates that no vignetting occurs for up to a 10mm aperture at the positive lens.
  • the overall magnification of the front view camera is -0.4 (-0.3946).
  • the Zemax layout for the exemplary grid camera is shown in Figure 19.
  • a 16.5 x 13.2 mm region at the corneal plane is imaged onto a 6.6 x 5.3mm camera sensor via the two element telephoto lens consisting of a +35mm lens (45211) and a -48mm focal length lens (45018).
  • the distance from the corneal plane to the front of the right angle prism (45108) is 179mm.
  • the distance between the edge of the prism and the positive lens is 10mm.
  • the distance between the positive and negative lens is 17.5mm.
  • the distance between the negative lens and the image plane is 39.74mm.
  • the maximum diameter of the corneal region of interest is 21.16 mm.
  • the large corneo-scleral target areas are made available by the increased depth of filed provided by the telephoto lens and aperture designs.
  • the depth of field of the grid camera is equal to or greater than 5mm.
  • the Zemax ray tracing again indicates that no vignetting occurs for up to a 10mm aperture at the positive lens.
  • the overall magnification of the grid view camera is -0.4 (- 0.4041).
  • the Zemax ray tracing for the grid projection is shown in Figure 20.
  • a 10mm diameter region of the grid reticle (45221) is imaged onto a 20mm diameter (plus projection distortion) via the telephoto lens consisting of a -48mm (45220) lens and a +35mm (45212) lens.
  • the distance from the grid to the negative lens is 62mm.
  • the distance between the lenses is 10.5mm.
  • the distance between the positive lens and the prism (45106) is 10mm.
  • the distance from the prism to the corneal plane is 179mm, which is the same as for the grid camera.
  • the overall magnification of the grid projection is -2.0 (-2.06).
  • the exemplary grid illumination system is shown in an optical schematic in Figure 21. It consists of a 1 watt LED with its integral lens ground off so that the lens system can provide a uniform illumination pattern at the grid reticle.
  • the LED was mechanically mounted to an aluminum heat sink. The LED may be directly attached to the heat sink as the bottom of the LED package is electrically isolated from the contacts on top of the package.
  • the LED is imaged onto the plane of the first grid projector lens via a 30mm collimation lens (45211) and a 75mm focusing lens (32325).
  • the grid reticle image 27 is 6.6mm from the focusing lens. If the back surface of the lens and the grid reticle are at the same location, any dust on the focusing lens will be projected at the cornea. Since the distance is 6.6mm, this artifact is avoided.
  • the distance S from the LED element to the collimation lens is 22.23mm.
  • the distance between the lenses is about 5mm.
  • the distance from the focusing lens to the first grid projection lens is 68.37mm.
  • the LED illumination feature provides instrumentation capability not associated with earlier generation corneal topography systems.
  • the combination of a cyan grid and fluorescein dye may not be optimum under all contemplated conditions of use of the RCT system. It may be desirable to illuminate the target surface with IR light, in which case the use of a fluorescent substance such as Indocyanine Green (ICG) in place of fluorescein dye may be advantageous.
  • ICG Indocyanine Green
  • the capability for selecting an appropriate illumination wavelength can be provided by the LED illumination system of the RCT apparatus.
  • the controllable LED illumination system according to an embodiment of the invention allows a particular fluorescent compound to be targeted by an appropriate corresponding illumination wavelength.
  • the RCT system includes software and processing routines that provide what is referred to herein as a selectable 'feature overlay' 2200 as illustrated in conjunction with Figures 22(a-d).
  • the feature overlay provides correlative mapping of a visual marker between the display of a raw grid image (Fig. 22b) obtained from an angularly-displaced side-view as described hereinabove and a top-view target elevation or curvature (topography) map (Fig. 22d), for example, generated by the RCT system.
  • An indicia 2210 on the raw grid image can be mapped and displayed as marker indicia 2210' on the elevation or curvature map. This association allows features on the raw target image to be mapped and viewed on the processed topography map.
  • This software feature is useful in identifying where on the processed map physical image features are located.
  • the marker indicia 2210 (2210') is provided by a draw routine in the software.
  • Alternative marking indicia may be provided.
  • the feature overlay may be provided as a user-selectable option that could be accessed, for example, by a clickable mouse or keyboard stroke.
  • the flash controller components perform functions related to the grid illumination and digital input/output processing of the system. More specifically, the flash controller components turn the light emitting diode(s) (LED(s)) on and off, provide LED illumination at multiple intensities at a specific light wavelength, and processes digital input/output for switches, indicator lights, etc. Schematics of an exemplary flash controller are shown in Figures 22-27 '.
  • the flash controller 2003 is designed to accomplished two primary tasks.
  • the flash controller utilizes an available Input/Output (I/O) port (labeled 1-4 in Figure 29) on the digital camera 2050 of the RCT system 2000 to pass data to and from a host PC 2001 to the flash controller 2003.
  • I/O Input/Output
  • this interface is designed to provide fast communications and be easy to interface with by a programmer.
  • VHDL Verilog Hardware Definition Language
  • the interface utilizes only three I/O wires (1-3, Fig. 29). Data bits are sent serially to the flash controller 2003 from the PC 2001 through the camera I/O port.
  • the three wires (1-3) are implemented as one data clock, one data input, and one data latch to indicate that the full 24 bits have been written. A low to high
  • transition of the data latch causes the flash controller to immediately execute the command requested.
  • 24 bits (3 bytes) are sent for each command.
  • the 3 bytes are formatted as follows:
  • the first byte is the flash controller command byte. This byte holds the command that the flash controller must immediately execute.
  • the second 2 bytes are data bytes (1 and 2) as further described below.
  • the valid commands that may be issued in the first byte are:
  • Interface Command #3 0x02 - End Potentiometer programming, data bytes ignored
  • Interface Command #4 0x04 - Set Flash to on, data bytes ignored
  • the second two data bytes are the potentiometer interface command (16 bits). Programming of the potentiometer allows the host PC to control the intensity of the flash LED remotely.
  • the first data byte is the potentiometer programming command.
  • the command byte is sent to the board in reverse order (MSB first). The format of this byte is:
  • the second data byte is the wiper position to set the potentiometer to, or the resistance value that the potentiometer will be set to, after programming.
  • the format of this byte is:
  • Position 0 is the maximum LED intensity and position 255 is the lowest intensity
  • the flash controller can also send data to the host PC. This can be accomplished by utilizing a fourth wire (#4, Fig. 29) of the digital camera FO port. One wire then additionally is used for an acquire image function button. This button is latched until a specific command (Interface Command #6) is issued. This allows the flash controller to store a button press until the computer is able to read it. Upon writing interface command #6, this data is removed from latch. If a second external event occurs while data is latched, that event is ignored. The other 3 inputs are not latched; data is passed through the PLD 2003 to appropriate camera I/O wires (1-4).
  • the flash controller also can execute a test mode function so that the host PC can verify proper operation of the flash controller.
  • the input data lines will transition to all l's.
  • the test mode is cleared by writing of interface command #7 (Reset).
  • the flash controller also contains a reset mode so that the host PC can return the flash controller to a known state.
  • a reset is issued, all chips on the flash controller are deselected, the flash LED is turned off, and all test outputs are set to high impedance mode.
  • FIG. 22 Schematics for the voltage power supply ( Figure 22); connectors and switches (Figure 23); the LED array drivers (Figure 24); the one shot trigger (Figure 25); the PLD ( Figure 26); and the programmable 2 AMP current power supply (Figure 27) are shown.
  • An exemplary implementation for the flash controller follows: 4 TTL compatible inputs from the host PC. 4 TTL compatible outputs to the host PC. 4 TTL compatible inputs for external events. 2-wire serial interface to potentiometer. 1 flash enable line. 1 chip select output for potentiometer. 1 clock input for potentiometer serial interface. 8-wire JTAG port for programming the PLD chip.

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Abstract

La présente invention concerne un dispositif de topographie cornéo-sclérale avancé basé sur un stéréographe à tramage, incluant un ensemble de projection/illumination à trame à DEL, un ensemble de visualisation d'image de trame, et un ensemble caméra en vue avant pouvant être intégré en option. Lesdits ensembles incluent chacun des systèmes optiques téléphotographiques qui fournissent une structure compacte, une profondeur de champ accrue, et un champ de vue augmenté permettant l'acquisition suffisante de données dans une seule image acquise afin de fournir l'analyse de topographie cornéo-sclérale désirée. Le dispositif utilise un nouvel algorithme de traitement d'image. Ledit dispositif et le procédé présenté offrent la possibilité de cartographier une caractéristique à partir d'une image de trame brute sur une carte topographique de la région cornéo-sclérale, et d'afficher simultanément les images si elles sont sélectionnées par l'utilisateur. Les considérations relatives à la conception d'ordre matériel, logiciel, mécanique, électrique et optique, ainsi que l'intégration, fournissent des avantages et des bénéfices par rapport aux topographes antérieurs de type basés sur un stéréographe à tramage, Placido, et autres topographes cornéens traditionnels.
PCT/US2007/074715 2007-02-14 2007-07-30 Système de topographie cornéo-sclérale Ceased WO2008100332A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US11/674,985 US20070195268A1 (en) 2006-02-14 2007-02-14 Advanced corneal topography system
US11/674,985 2007-02-14
USPCT/US0762155 2007-02-14
US2007062155 2007-02-14

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WO2008100332A1 true WO2008100332A1 (fr) 2008-08-21

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3773145A1 (fr) * 2018-04-06 2021-02-17 AMO Development LLC Procédés et systèmes pour une topographie cornéenne au moyen d'une imagerie sclérale à focalisation
WO2023279172A1 (fr) * 2021-07-09 2023-01-12 Medmont International Pty Ltd Procédé, dispositif et système de combinaison de données de topographie sclérale et cornéenne

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5159361A (en) * 1989-03-09 1992-10-27 Par Technology Corporation Method and apparatus for obtaining the topography of an object
US20020159618A1 (en) * 2001-04-26 2002-10-31 Freeman James F. System to automatically detect eye corneal striae
US20030103189A1 (en) * 2001-09-11 2003-06-05 The Regents Of The University Of California Characterizing aberrations in an imaging lens and applications to visual testing and integrated circuit mask analysis
US20030227612A1 (en) * 2002-06-10 2003-12-11 Howard Fein Imaging system for examining biological material

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5159361A (en) * 1989-03-09 1992-10-27 Par Technology Corporation Method and apparatus for obtaining the topography of an object
US20020159618A1 (en) * 2001-04-26 2002-10-31 Freeman James F. System to automatically detect eye corneal striae
US20030103189A1 (en) * 2001-09-11 2003-06-05 The Regents Of The University Of California Characterizing aberrations in an imaging lens and applications to visual testing and integrated circuit mask analysis
US20030227612A1 (en) * 2002-06-10 2003-12-11 Howard Fein Imaging system for examining biological material

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3773145A1 (fr) * 2018-04-06 2021-02-17 AMO Development LLC Procédés et systèmes pour une topographie cornéenne au moyen d'une imagerie sclérale à focalisation
WO2023279172A1 (fr) * 2021-07-09 2023-01-12 Medmont International Pty Ltd Procédé, dispositif et système de combinaison de données de topographie sclérale et cornéenne

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