Petitioner: Haag-Streit AG
`Petitioner: Haag-Streit AG
`
`Ex. 1007
`
`EX. 1007
`
`

`

`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`4,995,716
`
`Warnicki et al.
`
`[45] Date of Patent:
`Feb. 26, 1991
`
`[54] METHOD AND APPARATUS FOR
`OBTAINING THE TOPOGRAPHY OF AN
`OBJECT
`
`[75]
`
`Inventors:
`
`Joseph W. Warnicki, Pittsburgh; Paul
`G. Rehkopf, Murrysville, both of Pa;
`James L. Cambier, Rome; Salvins J.
`Strods, Waterville, both of NY.
`
`[73] Assignee:
`
`Par Technology Corporation, New
`Hartford, NY.
`
`[211 App]. No.: 321,252
`
`[22] Filed:
`
`Mar. 9, 1989
`
`
`[51]
`Int. Cl.5 .............................. A61B 2/10
`[52] US. Cl. ..................................... 351/212; 351/247
`[58] Field of Search ................ 351/212, 247: 356/395,
`356/396
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Marco S. Caceci and William P. Cacheris, "Fitting
`Curves to Data,“ Byte, (May, 1984), pp. 340—357.
`J. James Rowsey, M.D., A. E. Reynolds, Ph.D., Randy
`Brown. “Corneal Topography," Arch Opltt/zalmol. vol.
`99, (Jun. 1981), pp. 1093—1100.
`M. S. Moreland, M.D., C. A. Barce. B.A.. M. 11. Pope.
`Ph.D., “Moire Topography in Scoliosis: Pattern Recog-
`nition and Analysis,” Aloire Fringe Topography and Spi-
`nal Deformity, Pergamon Press. (1981), pp. 171—185.
`Marius C. VanWijk, “Accuracy of Moire Topogra-
`phy." Moire Fringe Topography Spinal Deformity, Perga-
`mon Press, (1981).
`J. D. Doss et al., “Method for Calculation of Corneal
`Profile and Power Distribution", Arch Ophthalmol.
`1261 (1981).
`T. Yatagai. M. Idesawa, H. Ohshima. and M. Suzuki,
`"Automatic Measurement of 3—D Shapes Using Scan-
`ning Moire Method, " Moire Fringe Topography. pp.
`249—257.
`
`(List continued on next page.)
`
`3.169.459 '2/1965 Friedberg ....................... 351/212 X
`4.685.140
`8/1987 Mount
`351/212 X
`
`OTHER PUBLICATIONS
`
`Primary Examiner—Rodney B. Bovernick
`Attorney, Agent, or Firm—Arnold B. Silverman;
`Suzanne Kikel
`
`Joseph W. Warnicki, Paul G. Rehkopf, Diane Y. Cur-
`tin, Stephen A. Burns, Robert C. Arffa, and John C.
`Stuart, “Corneal Topography Using Computer Ana-
`lyzed Rasterstereographic Images,” in Applied Optics.
`vol. 27, No. 6, (Mar. 15, 1988), pp. 1135—1140.
`Thomas Olsen, “On the Calculation of Power from
`Curvature of the Cornea," British Journal of Ophthal-
`mology, (1986), vol. 70, pp. 152-154.
`Carsten Edmund and Erik Sjontoft, "The Central—Peri-
`pheral Radius of the Normal Corneal Curvature,"Acta
`Ophthalmologica, (1985), vol. 63, pp. 670—677.
`Joseph W. Warnicki and Paul G. Rehkopf, “Develop-
`ment of an Imaging System for Ophthalmic Photogra-
`phy," Journal of Biological Photography. vol. 53, No. 1,
`(Jan. 1985), pp. 9-18.
`Stephen P. Klyce, “Computer—Assisted Corneal To-
`pography,” Investigative Opthalmology and Visual Sci-
`ence. vol. 25, (1984), pp. 1426-1435.
`
`[57]
`
`ABSTRACT
`
`A system. method, and apparatus for obtaining the cor-
`neal topography of an Object using computer analyzed
`rasterstereographic images. The object may be non-
`transparent and diffusing. or it may be transparent and
`nondiffusing, such as a cornea. Rasterstereographic
`images of a cornea are produced by staining the cornea
`with a fluorescein solution which projects a light and
`dark line pattern onto the cornea through a grid. When
`obtaining the topography of a cornea. several different
`filters are used for producing and obtaining a grid im—
`age. An image processor uses unique software to store
`and analyze data extracted from the grid pattern. A
`video camera, an illuminator, the filters. and the grid
`may be mounted on a microscope.
`
`50 Claims, 10 Drawing Sheets
`
`
`
`

`

`4,995,716
`
`Page 2
`
`
`OTHER PUBLICATIONS
`
`E. Hierholzer and W. Frobin, “Rasterstereographic
`Measurement and Curvature Analysis of the Body Sur-
`face of Patients with Spinal Deformities", Moire Fringe
`Topography. pp. 267—276.
`N. Ikeda, “Perspective Correction of the Moire Photo—
`graph,“ Journal of the Biological Photographic Associa-
`tion, vol. 47, No. 3, (Jul, 1979), pp. 107—110.
`M. S. Karlan, M.C., M. Madden, M.A., and M. 13. Ha-
`bal, M.D., “Biostereometric Analysis in Plastic and
`Reconstructive Surgery,” Plastic and Reconstructive
`Surgery, vol. 62, No. 2 (Aug, 1978), pp. 235—239.
`T. W. Smith, M.D., “Corneal Topography," Docu-
`menta Opthalmologica 43.2 (1977), pp. 249—276.
`
`S. Wittenberg and Wm. M. Ludlam. “Planar Reflected
`Imagery in Photokeratoscopy," Journal of the Optical
`Society of America, vol. 60, No. 7.
`(Jul., 1970), pp.
`981—985.
`
`H. Takasaki, "Moire Topography," Applied Optics, vol.
`9, No. 6. (Jun. 1970), pp. 1467—1472.
`Wm. M. Ludlam and S. Wittenberg. “Measurements of
`the Ocular Dioptric Elements Utilizing Photographic
`Methods,“ American Journal of Optometry Publishing
`Association, (Apr., 1966), pp. 249—267.
`S. Wittenberg and Wm. W. Ludlam. “Derivation of a
`System for Analyzing the Corneal Surface
`from
`Photokeratoscopic Data." Journal of the Optical Society
`ofAmerica. vol. 56, No. ll. (Nov., 1966). pp. 1612—1615.
`‘
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 1 of 10
`
`4,995,716
`
`
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 2 Br 10
`
`4,995,716
`
`
`
`FIG- 3
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 3 of 10
`
`4,995,716
`
`64
`
`
`
`
`CORRECT:
`correct for
`
`
`
`
`distortion in
`
`the optics
`
`and projection
`
`grid.
`
`68
`
`46
`
`SO
`
`54
`
`GET DATA
`
`48
`
`DET EDGES:
`
`tines.
`
`find the edges
`of the imaged
`
`52
`
`construct
`
`
`
`LINE SEGS:
`
`
`
`
`tine segments
`from the edge
`points.
`
`S6
`
`58
`
`BUILD MAT:
`
`
`
`tink the line
`
`
`
`segments to
`form a matrix
`
`
`
`of contiguous
`tines.
`
`
`
`
`
`7
`
`O
`
`74
`
`COMP ELEV:
`compute
`elevation
`
`information
`
`from the tine
`
`positions.
`
`
`
`
`
`
`
`
`
`72
`
`COMP CU RV:
`
`comp curve
`
`compute
`curvature
`
`information
`
`elevation data.
`
`from the
`
`76
`
`return
`
`78
`
`FIG.4
`
`6O
`
`REF LINE:
`
`find the
`
`
`
` 62
`
`
`
`
`
`reference tine
`in the
`
`projection
`
`space.
`
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 4 of 10
`
`4,995,716
`
`
`
`114
`
`DET EDGES
`
`50
`
`82
`
`84 IMG AVG:
`
`standard
`
`
`
`
`
`
`image
`averaging
`using 3X3
`convolution
`kernel
`
`86
`
`
` pixel is not
`
`an edge
`
`point.
`
`
`
`
`
`
`
`edge points
`
`
`in the tempor—
`
`ary array
`
`center lXN
`
`
`window on
`
`next pixel
`
`in image
`
`
`
`
`determine
`range of
`
`Dixel inten-
`
`sities in
`window
`
`
`
`pixel is an
`
`
`
`
`pixel in
`edge point,
`Upper halt
`
`
`
`
`add 10
`of intenSIty
`
`
`
`
`1erTlDorary
`range
`
`
`?
`point array
`
`
`116
`
`118
`
`
`
`124
`
`Yes
`
`126
`
`
`
`
`
`EDG APEX:
`find the
`center of
`
`
`
`
`
`
`
`lines by fit-
`ting curve to
`
`
`
`
`
`Dixel intensities
`
`
`
`128
`
`130
`
`
`
`
`
`add center point
`to line point
`array and remove
`edge points FROM
`temDOr‘ary array
`
`
`
`
`
`
`
`132
`
`have
`all the
`
`134
`
`Pixels in the
`
`image been
`examine.
`?
`
`.
`
`136
`
`Yes
`
`FIG. 5
`
`return
`
`138
`
`.
`
`

`

`
`
`check the
`length of the
`
`line segment
` formed by the
`
`found line
`
`
`
`all unlinked
`
`146
`
`Yes
`
`‘44
`
`US. Patent
`
`Feb. 26, 1991
`
`Sheet 5 of 10
`
`4,995,716
`
`54
`
`LINE 515
`
`l40
`
`l76
`
`points
`
`
`line points in
`remove all
`
`the image
`the line
`
`
`
`been
`points in the
`
`
`se ment lon
`.
`
`
`examined
`9
`9
`line segment
`
`
`
`
`7
`form the
`
`
`line point
` array
`
`
` search vertically
`
`
`within lXM
`
`
`line segment
`window for line
`
`
`
`as already
`
`
`included.
`
`148
`
`mark the line
`
`points in the
`
`
`add line
`
`segment to
` line point
`
`
`
`array or
`found
`
`
`line segments
`7
`
`
`
`163
`
`164
`
`
`'
`
`
`add the line
`
`
`
`point to a
`temporary line
`point array
`
`
`
`
` position over
`newly found
` FIG.6
`line point
`
`
`
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 6 of 10
`
`4,995,716
`
`BUILD MAT
`
`190 222
`
`192
`.
`is
`
`
`the end of
`the line met
`
`7
`
`
`
`
`find the longest
`line segment
`found and label
`as the
`
`58
`
`
`
`
`
`
`
`
`
`reference line
`Yes
`228
`
`194
`195
`remove any
`
`
`search in
`line points in
`
`
`
`the found line
`214
`specified direction
`
`
`
`that produce
`of the line
`
`
`spikes intheline
`withina lXN search
`
`
`
`window for a
`
`
`230
`label the area
`neighboring
`
`
`
`232
`has
`line segment.
`as a hole and
`
`
`
`
`the margin
`advance down
`
`
`the line one
`
`of the image
`point
`
`
`
`been met
` is a
`
`
`?
`
`line segment
`
`found
`
` Yes
`1;
`
`240
`
`is
` 244
`
`YES
`the margin
`
`
`return
`the right
`
`
`
`advance down
`
`
`margin
`’?
`
`line by length
`
`
`of found
`
`
` No
`line segment.
`
` change the
`specifed search
`
`
`direction
`from
`
`242
`
`250
`
`left to right.
`
`
`
`F107
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 7 of 10
`
`4,995,716
`
`7O
`
`COMP ELEV
`
`272
`
`252
`
`
`
`find the reference
`line of the
`projection space
`
`in the image
`
`2‘54
`
`256
`
`for each
`
`vertical
`
`gridline
`
`258
`
`260
`
`
`compute the
`
`simulataneous
`
`solution to
`the ray and
`plane equation
`to get the
`elevation at
`
`274
`
`276
`
`
`
`
`the point.
`
`
`
`
`
`has
`
`
`elevation
`
`278
`
`
`for all points
`
`
`in the grid
`
`line been
`
`found
`262
`equation for the
`
`?
` plane formed by
`
`the projected grid
`
`line.
`
`calculate the
`
`
`
`
`286
`
`282
`
`Yes
`
`
`
`for each point
`
`in the vertical
`
`grid line
`
`No
`
`
`
`
` has
`284
`elevation
`
`
`for all
`the grid
`
`lines been
`
`
` found
`
`?
`
`
` compute the
`equationfor
`
`the ray formed
`
`by the point
`on the line in
`
`
`288
`
`
`
`the image.
`
`YES
`
`290
`
`return
`
`FIG. 8
`
`

`

`U.S.' Patent
`
`Feb. 26, 1991
`
`Sheet m 10
`
`4,995,716
`
` ELEVATIO N ->
`
`~PROJECTEDCRID UNS—
`
`-Flé_q
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 9 of 10
`
`4,995,716
`
`_ (111.-..-
`‘II'.....
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`
`
`
`

`

`US. Patent
`
`Feb. 26, 1991
`
`Sheet 10 of 10
`
`4,995,716
`
`
`
`

`

`1
`
`4,995,716
`
`2
`
`METHOD AND APPARATUS FOR OBTAINING
`THE TOPOGRAPHY OF AN OBJECT
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`This present invention relates to a system, method,
`and associated apparatus for enabling the use of raster-
`stereographical principles for determining the curva-
`ture and surface detail across the surface of an object by
`using a computer analyzed rasterstereographic tech-
`nique. More specifically, a projected light and dark
`pattern on the object is picked up by a video camera and
`the image is digitized by an image processor which
`calculates the surface detail by evaluating the distortion
`of the grid lines.
`2. Description of the Prior Art
`In recent years there has been increased interest in
`both qualitative and quantitative measurements of an
`object by topography. Particularly this increased inter-
`est has been in regard to corneal topography especially
`relating to keratorefractive procedures. Since keratore-
`fractive procedures correct the refractive error of the
`eye by altering the curvature of the corneal surface,
`topographic measurements of the corneal curvature are
`important in planning, performing, and assessing the
`effect of these procedures.
`Corneal topography has been proven of value for
`numerous uses including predicting the result of radial
`keralotomy, evaluating the design of epikeratophakia
`for myopia, diagnosis and staging of ke'ratoconus, and
`guiding suture removal after corneal transplantation.
`There have been previously reported photographic
`methods based on the keratoscopic disk system. (See
`“Corneal Topography,” J. J. Rowsey, et al., Arch.
`Ophthalmol, Vol. 99, 1093 [1981]). This keratoscopic
`system consists of a series of black and white concentric
`rings on a circular disk. When this disk is placed in front
`of the eye, the rings are reflected by the corneal surface
`and their position, size, and spacing in the reflected
`image are determined by the corneal shape.
`Current commercial systems utilizing illuminated
`concentric circular rings surrounding a viewing port
`through which photographs are taken have been
`known. If the cornea is spherical,
`the rings appear
`round and regularly spaced. If the cornea is oval or
`astigmatic, the rings are oval and the spacing varies in
`different axes. This is known as the placido disk tech-
`nique.
`These techniques, while providing a visual represen-
`tation of the corneal surface, do not provide quantita-
`tive information. Computer programs have been devel-
`oped which calculate the corneal profile and the optical
`power distribution on the corneal surface from placido
`disk images. See “Method for Calculation of Corneal
`Profile and Power Distribution,” J. D. Ross, et al., Arch
`Ophthalmol., 1261 (1981).
`Computer analyzing techniques have been developed
`for deriving quantitative information about the corneal
`shape from keratoscope photographs and displaying the
`results both numerically and graphically in easily under—
`stood forms. See “Computer-Assisted Corneal Topog-
`raphy, High Resolution Graphic Presentation and Anal-
`ysis of Keratoscopy,” S. D. Klyce, et al., Investigative
`Ophthalmology and Visual Science, Vol. 25, 1426
`(1984).
`
`5
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`45
`
`50
`
`55
`
`65
`
`Placido disk techniques for recording and quantifying
`the corneal surface have inherent
`limitations which
`reduce their clinical usefulness.
`There are three main factors which limit the useful-
`ness of the placido disk system. These factors are as
`follows: (1) The most central portion of the cornea is
`not imaged. This is due in part to the fact that there is a
`hole in the central portion of the placido disk through
`which the optical system for this technique views the
`cornea. This viewing port is devoid of any lighted spots
`or rings, and therefore there can be no reflected images
`on the cornea in this area. (2) The diameter of the pla-
`cido disk determines how much of the corneal surface is
`covered by the reflected images. The smaller the diame-
`ter, the smaller the area of the cornea. The larger the
`diameter, the larger the area of the cornea that will be
`covered extending more toward the limbus or periph-
`ery of the cornea. (3) The distance between the cornea
`and the placido disk system also determines how much
`of the cornea is covered. The farther away the disk is
`from the cornea, the less the corneal coverage will be.
`The closer the disk is to the cornea, the greater the
`corneal coverage will be.
`Other limitations of the placido disk techniques are
`that they do not extend to the corneal limbus due in part
`to shadows being cast from the eye lashes, brow and
`nose of the patient, nor do they work on corneas which
`do not have the necessary qualities to reflect an image
`of the disk due to conditions such as epithelial defects,
`scarring, or highly irregular shape.
`Current computer methods being used to obtain
`quantitative measurements have been known to utilize
`photographic images acquired with the commercially
`available placido disk keratoscopes and are, therefore,
`subject to the same limitations discussed hereinbefore.
`In some such systems the data are entered into the com-
`puter by hand digitizing from these photographs, re-
`quiring a considerable amount of time, and the possible
`introduction of error during the digitization process.
`While hand digitizing with some manually manipu-
`lated device is still being practiced, there is also known
`at
`least
`two systems for direct digitizing purposes,
`which systems have imaging cameras attached to the
`optics which, in turn, view through the central portion
`of the placido disk. These images are then taken directly
`into the computer for manipulation in calculating the
`corneal curvature and for determining the diopter pow-
`ers.
`‘
`
`These systems with direct digitization are still subject
`to the same problems as the placido disk systems having
`hand digitization. Although several attempts have been
`made to extend farther out into the limbus or periphery
`of the cornea, none of these systems have achieved this
`capability. These systems still inadequately handle cor-
`neas with very steep curvature or with a highly irregu-
`lar surface.
`It has been known to employ a rasterstereography
`method for measuring large body surfaces, curvature of
`the back, and reconstructive plastic surgery. Raster-
`stereography is an intermediate between stereography
`and moire topography and 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 grid of vertical parallel
`lines Onto a subject.
`One type of rasterstereographic system employs an
`electronic camera with a linear sensor, an x-y translator
`for image shifting, and a light source or projector. The
`
`

`

`3
`camera and translator are connected to an on-line com-
`puter which produces an image scan of the large sur-
`face. See “Rasterstereographic Measurement and Cur-
`vature Analysis of the Body Surface," E. Hierholzer, et
`al., Biol. Photogr., Vol. 51, 11 (Jan. 1, 1983).
`It has been known to employ a Rhonchi ruling in
`moire technique, which is normally a technique used for
`measuring the topography of a solid, nontransparent
`object. In moire topography a light source illuminates
`the Rhonchi ruling to cast shadows on the object to be
`measured. These shadows and the lines of Rhonchi
`
`ruling when viewed by either the eye or a camera inter-
`fere to produce contour lines of the object. See “Bios-
`tereometric Analysis in Plastic and Reconstructive Sur-
`gery,” M. S. Karlan, et al., Plastic and Reconstructive
`Surgery, Vol. 62, (1978).
`It has been known to attempt to determine corneal
`topography including moire techniques. A drawback is
`the low reflectivity of the cornea in that the cornea is a
`transparent, nondiffusing member, which does not
`allow for a good image of the grid to be formed on it.
`It has been known to employ a microscope with a
`reticule referred to as a toposcope which uses the moire
`technique. A recticule is a grid or scale that is a standard
`piece of equipment in the moire technique. A series of
`straight parallel lines is imaged on the object. In the
`eyepiece of the microscope there is a reticule with the
`same number of lines. The two patterns interfere to
`produce the contours This instrument has been used to
`analyze contact lenses, but there is no evidence of using
`it
`to determine the contour of an eye. A drawback
`would be the low reflectivity of the cornea.
`It has been known to use a fluorescein solution on a
`the eye, and a contact lens to determine the topography
`of a cornea. The fluorescein solution is placed on the
`eye followed by the placement of a contact lens. Blue-
`violet radiation produces a fluorescence pattern which
`gives an indication of the variable clearance between
`the known surface of the contact lens and the unknown
`cornea. For the measurements to be valid, the lens must
`be kept stationary, and in practice, diagnostic contact
`lenses are used to verify ‘K’ readings in conjunction
`with refractive findings. See “Corneal Topography,” T.
`W. Smith, M.D., Documenta Opthalmologica 43.2, pg.
`262 (1977).
`It has been known to determine corneal topography
`by stereographic techniques, in addition to holographic
`interferometric, and profile techniques See “Corneal
`Topography,” pg. 263 cited in the preceding paragraph.
`As the cornea is a transparent member which is non-
`diffusing to light, a grid projected onto the cornea is not
`visible unless a diffusing material is used to provide a
`surface on which an image can be visualized. It has been
`known to spray talcum powder on anesthetized corneas
`to obtain stereo photographs of the cornea.
`Stereophotography is traditionally used to obtain the
`topography of a solid, nontransparent light diffusing
`object that has some texture. Stereophotography may
`utilize two cameras which view an object of interest
`from two different angles relative to a fixed center line
`between them. Stereophotography can also be accom-
`plished by taking two sequential images with one cam-
`era. This is accomplished by focusing the camera on a
`fixed point and taking an exposure. The camera is then
`moved laterally a fixed distance, again focusing on the
`same point previously used in the first image and an—
`other exposure is made.
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`The two stereo photos are analyzed and one of the
`images is chosen as a reference image. Some object of
`interest is chosen and the displacement of the object in
`the opposite stereo image can be measured. From this
`displacement and the angle between the two shots, an
`elevation of an object can be calculated.
`As the Stereophotography method is used on solid
`objects, it has not been known to adequately obtain the
`topography of a cornea in that sufficient topographic
`detail of the cornea cannot be extracted.
`
`It has been known to use an image processing system
`with a video camera, flash unit, and computer and dis-
`play units in the field of opthalmology where the eye
`images are handled electronically. However, most of
`the study in the ophthalmology field has been in evalu-
`ating the optic nerve, retina, and corneal surface de-
`fects, and not for determining the curvature and related
`topographic details of the cornea. See “Development of
`An Imaging System for Ophthalmic Photography,” J.
`W. Warnicki, et al., J. Biol. Photog. 53, 9 (1985).
`is
`it
`In the holographic interferometric technique,
`known to use a beam splitter to direct the laser beam in
`one direction toward a camera and in the other direc-
`tion toward an object. See “Corneal Topography,” pg.
`264 cited hereinbefore.
`
`‘
`
`In spite of these known systems, methods, and instru-
`ments, there remains a very real and substantial need for
`a system, method, and device which more accurately
`and quickly determine quantitatively and qualitatively
`the contour of both a light diffusing, nontransparent
`object and a light nondiffusing, transparent object, such
`as a cornea.
`
`SUMMARY OF THE INVENTION
`
`The present invention has met the above-described
`needs. A system, a method, and an apparatus of the
`present
`invention provide more accurate and easily
`obtainable means for determining the topography of an
`object particularly that of a cornea as defined hereinaf-
`ter.
`
`The apparatus may provide a support means with
`built-in optical means and a beam splitter along a center-
`line of the support means. The apparatus and associated
`method may involve providing an illuminator/flash
`unit, a grid, a cobalt blue filter, and an infrared cutoff
`filter on one side of the support means, and a video
`camera, and a yellow barrier filter on the other side of
`the support means.
`If the topography of a cornea is to be obtained, fluo—
`rescein solution is applied onto the tear film of the cor-
`nea so that the grid pattern created through the grid of
`a Ronchi ruling becomes fluorescent when excited by
`light passing through the cobalt blue filter. The yellow
`barrier filter is employed to increase the contrast of the
`grid image by the video camera. When the topography
`of an object, other than that of a cornea is to be deter—
`mined, the filters preferably are not used. The recorded
`image of the object is used to identify the central area of
`the lines of the grid pattern, to calculate the elevation of
`the lines of the grid pattern, and to display the eleva-
`tional results in a contour plot representative of the
`topography of the object.
`The apparatus preferably comprises a microscope
`with two beam splitters, a video camera and optics
`along a centerline in line with a support for resting and
`placement of an object, which in the instance of the
`cornea is the head of a patient. A video camera and the
`yellow barrier filter are located at an angle relative to
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`and along the centerline of the apparatus, and an illumi-
`uating source, a grid, and the cobalt blue and infrared
`cutoff filters are located in a line relative to each other
`
`and at an angle relative to the centerline opposite to that
`of the video camera. An image processor is employed to
`determine the topography of the object through the use
`of software which identifies, and calculates the eleva-
`tion of the grid lines, and displays the results in a con-
`tour plot representing the topography of the object.
`The system, method, and apparatus may be used for
`obtaining the topography of an object which is trans-
`parent and nondiffusing to light, such as a cornea, or
`which is nontransparent and diffusing to light.
`It is a broad object of the invention to provide a
`system, an apparatus, and a method for quickly and
`efficiently determining" the topography of an entire
`surface of an object, which object is transparent and
`nondiffusing to light, such as a cornea, or which is non-
`transparent and diffusing to light.
`It is a further object of the present invention to pro—
`vide a system, an apparatus, and a method for quickly
`and efficiently determining the topography of an entire
`cornea of a patient, which is a member of the animal
`kingdom particularly a human.
`It is a further object of the present invention to pro-
`vide a system, a method, and an apparatus for achieving
`the preceding objective by obtaining information on
`curvature and surface detail across the full cornea sur-
`face including the central optical axis and the periphery
`beyond the limbus.
`It is a further object of the invention to provide a
`system, a method, and an apparatus for effectively pro-
`jecting a grid onto the object and shortening the com-
`puter time by digitizing a video image of the grid by an
`image processor which calculates surface detail by eval-
`uating the distortion of the grid lines.
`It is another object of the invention to provide such a
`system which attaches to an examination slit lamp mi-
`croscope and which is compact, economical, providing
`valid clinical information regarding curvature and to-
`pography, particularly of a cornea, and which is easily
`operated by medical personnel.
`It is yet another object of the invention to provide
`such a system which attaches to a microscope which is
`used in an operating room.
`It is a further object of the invention to provide a
`system, an apparatus, and a method for quickly and
`efficiently determining the topography of an entire
`surface of an object and reproducing the results, and
`which system and apparatus are easy to operate, are
`inexpensive to buy and operate, and which system,
`apparatus and method are harmless to the object, espe-
`cially a cornea, and are generally not unpleasant for the
`patient.
`It is a further object of the invention to provide a
`system, a method and an apparatus for obtaining the
`topography of a cornea which enables a grid image to
`be reflected from the cornea.
`It is a further object of the invention to provide a
`system, an apparatus, and a method whereby digital
`imaging processing techniques are used to find eleva-
`tion information, from which, in turn, curvature infor-
`mation is extracted.
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`It is a further object of the invention to provide a
`system, an apparatus, and a method relative to the pre-
`ceding objective whereby from the extracted data, an
`assessment of the shape of the object and the refractive
`power of the front surface of a cornea can be made.
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`A further object of the invention is to provide such a
`system which is compact, economical, and together
`with computer hardware and appropriate software is
`capable of making calculations in an operating room
`where time is of the essence.
`
`It is therefore an object of the present invention to
`more effectively and efficiently obtain the topography
`of an object, such as a cornea, and to achieve this
`through a rasterstereographic technique.
`It is a further object of the invention to project a grid
`image onto a transparent, nondiffusing object, such as a
`cornea rather than have the grid image reflected by the
`cornea, so that the projected image is not affected by
`surface defects and irregularities.
`It is a further object of the invention to electronically
`acquire the image of an object, electronically digitize
`and analyze the imaging system, and display the data
`obtained from the analysis of these images in easily
`understood formats.
`
`It is a further object of the invention to apply a digital
`image processing technique to the projected image in
`order to find the projected lines and to convert the lines
`into elevation information.
`It is a further object of the invention to extract curva-
`ture information and in the instance where the cornea is
`being examined, diopter powers from the curvature
`information.
`It is a still further object of the invention to use the
`elevation and curvature information to obtain an intu-
`itive and quantitative assessment of the shape and re-
`fractive power of the front surface of the cornea.
`A further object is to utilize computer processing
`techniques including a main program with a number of
`subroutines including an edge determining subroutine, a
`line segment constructing subroutine, a matrix building
`subroutine, an elevation computing subroutine, and a
`curvature computing subroutine.
`It is a further object of the invention to adapt a Zeiss
`or a Topcon exam slit lamp microscope, which may
`generally have been used in stereophotographic tech-
`niques for obtaining the topography of a cornea, to a
`rasterstereographic method for obtaining the topogra-
`phy of a cornea.
`A still further object of the invention is to adapt a
`Zeiss or a Topcon exam slit lamp microscope to a ras-
`terstereographic method for obtaining the topography
`of any object.
`'
`It is a further object of the invention to provide in a
`rasterstereographic technique a cornea surface with a
`grid image projected thereon.
`It is a further object to achieve the immediately pre-
`ceding objective by applying a fluorescein solution onto
`the surface of the eye.
`These and other objects of this invention will be more
`fully understood from the following description of the
`invention on reference to the illustrations appended
`hereto.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. la is an illustration of a normal spherical cornea
`with a placido disk used in the prior art;
`FIG. 1b is an illustration of a corneal transplant pa-
`tient with astigmatic central cornea using the placido
`disk technique of the prior art;
`FIG. 2 is an illustration of an image of a vertical grid
`projected onto the eye obtained by the present inven-
`tion;
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`FIG. 3 is a schematic diagram of a microscope with
`beam splitter and projection system employed in the
`present invention;
`FIG. 4 is a logic flow diagram of the main program
`for digitizing the image on the cornea of FIG. 2 by a
`computer;
`FIGS. 5, 6, 7, and 8 are logic flow diagrams of sub-
`routines utilized in the main program of FIG. 4 includ-
`ing respectively a determination of the edges subrou-
`tine; a construction of the line segments subroutine a
`forming of a matrix subroutine; and a computation of
`the elevation in formation subroutine;
`FIG. 9 is a schematic diagram showing grid lines
`displaced on the cornea from an assumed normal posi-
`tion and a trigonometric solution for elevation em-
`ployed by the present invention;
`FIG. 10 is an illustration showing on the left hand
`side an orthogonal view of a normal cornea, and on the
`right hand side the same cornea with the common curve
`removed which are derived by the display methods
`used in the present invention; and
`FIGS. 11, 12, and 13 are illustrations of contour plots
`of the cornea derived by the display methods employed
`in the present invention.
`
`DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`The invention may be used to obtain through raster-
`stereographical techniques the topography of an object
`which is nontransparent and diffusing to light or which
`is transparent and nondiffusing to light, such as a cor-
`nea. The invention has particular application but is not
`limited as a clinical tool for the evaluation of topo-
`graphic abnormalities of the corneal surface of a patient
`being a member of the animal kingdom, particularly a
`human. The invention will be described in terms of
`obtaining the topography of the cornea of a human, but
`is not limited thereto, and may be employed to deter-
`mine the surface features or surface contour of an exter-
`nal body portion. The invention may also be used in
`dentistry, particularly in surgery, and also in plastic
`surgery practices.
`Eyes that are emmetropic and eyes with keratoconus
`and severe astigmatism can be detected, analyzed and
`corrected through surgery and contact lenses. The in-
`vention can be easily used in an examination room or in
`an operating room.
`As used herein, “limbus” is the border or edge of the
`cornea or clear optical zone and the sclera portion of
`the eye. The sclera is the white, fibrous outer envelope
`of tissue surrounding the cornea.
`As used herein, “cornea” is the transparent anterior
`portion of the outer fibrous tunic of the eye, a uniformly
`thick, nearly circular convex structure covering the
`lens.
`
`As used herein, a pixel is an individual picture ele-
`ment constituting a matrix used in a digital computer
`system for the resolution of images.
`As used herein, the term “search window” applies to
`a size dimension which denotes how far from a refer-
`ence line a search for a line segment will take place.
`Increasing or decreasing a “search window” means to
`look within a larger or smaller area abo