Ophthalmic pachymeter and method of make opthalmic determinations

ES 2 138 012 T3

DESCRIPTION

Ophthalmic instrument for the anterior segment of the eye.

Field of the invention

This invention relates, in general, to certain new and useful improvements to ophthalmic parameters that help to determine the thickness and relative anoptic density of the cornea of ​​the eye in real time.

Brief description of the prior art

The planning of anterior segment surgery has been the object of increasing attention in recent years, such as, for example, through the documents of Lehrman et al., 'Medicioan of the diameter of the anterior chamber' and 'Biometrics of the anterior segment by Scheimpflug 'slit lamp photography, published in Investigative Ophthalmology and Visual Science, Volume 32, No. 3, March 1991, pages 529-532.

The slit lamp is an instrument used by many optometrists and ophthalmologists to examine the front of the eye. Many different versions of the instrument have been produced over the last hundred years, although all slit lamps have three main common elements, including a projector to provide a collimated image of an oaptic slit focused on the eye, a biomicroscope, or camera. to observe the image, and a mechanical support system. In this slit lamp system, the biomicroscope or camera, which has been designed to observe the image formed by the projector, is cofocal with the projector. The mechanical support system must be designed in such a way that it supports at least the object, the projector and the observation system. In addition, the elements must be positioned in a mutual relationship that allows an adequate examination of the eye.

There are pachymetry accessories for the slit lamp that are used in clan settings. These accessories work in a way that moves half the image through a parallel flat glass block interposed in the viewing path. The thickness of the cornea is thus measured at a single point. The drum reading that is part of this accessory is then manually recorded as the local thickness of the cornea. Although these modified forms of slit lamp that act as parameters are able to accurately define the thickness of an unknown point, they are slow, expensive, and fragile. Furthermore, they are quite difficult to operate and require considerable operator instruction. General description of the invention

One of the main problems of the prior technique was that it was not possible to accurately measure the various phasic parameters of the cornea, such as the depth of the corneal tissue and the like, without using invasive techniques. As a simple example, it was very difficult to accurately measure the distance between a first ocular tissue surface and a second ocular tissue surface.

Accordingly, the present invention has as its main objective to overcome this basic problem by providing an ophthalmic analysis system that can also act as a densitometer.

Following the invention, said object is solved by the characteristics of claim 1.

In essence, the device can perform the phasic measurements that the ophthalmo-analog or oaptic needs to use. In addition, the device allows to perform a measurement and generate a map that shows the surface contour of the eye.

The ophthalmic analysis system according to the invention is used to determine the aforementioned and other phasic characteristics of the eye, particularly those of the anterior segment of the eye. The analysis system comprises a light projector means that projects a light through a slit lens; thus, the light projector means functions with a slit lens means to illuminate defined areas of the anterior segment of the corneal tissue.

The ophthalmic analysis system of the invention also includes an imaging means that operates effectively with a type of cathode ray tube system that provides a television image of parts of the illuminated areas of the eye. It also includes a means of causing movement of the cleft relative to the anterior segment. A series of selected images can thus be obtained through the eye.

Furthermore, there is a video medium positioned relative to the projector medium to receive these generated images corresponding to selected parts of the corneal tissue. The video medium generates and transmits video signals representative of these images.

The ophthalmic analysis system also comprises a converter means for converting parts of the video signals to digital format. Furthermore, the ophthalmic analysis system of the invention includes an analysis means that detects and stores relative brightness levels within said areas of the anterior segment of the corneal tissue from which the images have been formed. These gloss levels are directly correlated with the physical characteristics to be determined. The axis of the cleft means is held in a fixed position relative to the cornea of ​​the eye, and the cleft means is displaced transversely through the anterior segment of the corneal tissue.

The aforementioned system solves the problems of the prior art in the sense that it allows making images of the eye and measurements of the physical characteristics of the eye using the slit lamp projector system, which moves in relation to the eye. The use of a pair of slit lamps is highly effective in achieving depth of measurement into the eye.

The procedure of the invention, which is practiced with the aforementioned ophthalmic analysis system, makes it possible to calculate the shape of the anterior and posterior surfaces of the cornea and determine parameters such as the thickness and, consequently, the distance between a surface of a primer. eye tissue and a surface of a se2

ES 2 138 012 T3 second ocular tissue. At least one of these surfaces is posterior to the anterior surface of the eye. Accordingly, this procedure includes moving a first slit through a part of the eye and lighting the eye tissue during said movement. This enables scanning of the first ocular tissue, such as the anterior segment, and scanning at a first preselected angle relative to the ocular tissue.

The procedure also includes moving a second slit through one part of the eye and illuminating a second part of the ocular tissue, such as a posterior part of the cornea. This second movement also occurs during the movement of the second slit through the eye, although it occurs following a second preselected angle relative to this ocular tissue.

Next, the method includes generating an image of the first ocular tissue by movement of the first slit and an image of the second ocular tissue, during scanning, by movement of the second slit. This makes it possible to determine, at chosen points and through these images, the distance between the first and second ocular tissue.

The invention is also capable of acting as a densitometer that helps to determine the thickness and relative oaptic density of corneal tissue. This analysis system includes the imaging means described above, which generates digitally encoded television images of segments of the eye. A projector means illuminates these preselected areas during movement of the slit means to allow registration of the images in question. The analysis means also includes a processing means for receiving the digitally coded images and generating the data used in the determination of the ooptic thickness and the ooptic density. The processing means generates this data in relation to the digitally encoded images substantially at the same time that the images are being generated, whereby the system operates on a real-time basis.

In order to appreciate the invention more fully, the following overview of the invention is also presented, identifying parts of it that find some counterparts in other systems.

Densitometer is a term applied to the measurement of the oaptic density of areas of photographs. Densitometers normally measure the logarithm of the reciprocal of the percentage of light transmission of a defined area at a given wavelength or waveband. Typically, the measurement of the relative reflection of scattered light is used to define the turbidity of water samples. The amount of light scattered, and therefore retroreflected, is compared in this process with a known reference value to determine the reflection of the scattered light.

The densitometer of the present invention measures the relative amount of light reflected by scattering within the ocular tissue as an indication of the oaptic density. In the strictest sense, it is not a true density measurement, but rather provides a measure of the relative transparency of carnous tissues. The contact of the cornea with the air is not affected by the opacity that the stroma acquires, and serves as a reference of the relative density for medicioan. The minimum reflectance value for the calibration derives from the signal that the anterior chamber represents on the pupil, in which the mean reflectance is lower. The optical density of the small and large areas of the cornea often provides diagnostic information to determine the need for surgical intervention. In addition, the surface contour and thickness of the cornea are quantified to produce a complete, three-dimensional corneal thickness plot that includes the local thickness of the membrane.

The present invention uses light from an incandescent lamp to analyze the thickness and the oaptic density of the cornea at one or more wavelengths. By taking successive exposures with a small linear movement of a slit image between each exposure, a series of density image sections can be generated. These images are then stored in digital format.

The present invention also serves to produce a map of localized opacities used to plan a corneal replacement surgery. Corneal wounds and ulcers can also be mapped which provides accurate diagnostic information to the physician using the parameter of the invention. The refractive index changes associated with scars and ulcers create foci of light scattering and loss of transparency. The refractive index of the thickness of the cornea is lower in the fluid than in the fiber cytoplasm, producing dispersion due to the optic discontinuities. The degree of opacity can be observed through visual acuity loss, although night vision loss due to lack of image contrast can occasionally be debilitating, while Snellen acuity is only slightly affected.

Slit lamp examination may reveal the presence of these abnormalities, although direct visual examination does not provide an accurate and repeatable assessment of the location, density, and area of ​​the lesion, or of any changes in size or opacity produced by the pass of the time. The present invention provides a tool for a repeatable evaluation of potential loss of vision under adverse lighting conditions. In the present invention, the focal illumination provided by a modified conventional Kohler projector is used. The focal plane object is one or more oaptic slits that can be moved either manually or through an associated computer controlled mechanism.

'Tyndall phenoamine' is the term used to describe this procedure of generation of a loose oaptic section, which is well known in ophthalmic technique. The diffuse reflection of the first of the layers of the cornea that provides the image of the oáptic section is used

ES 2 138 012 T3 in the present invention as a reference against which to compare the diffuse reflection from the other parts of the cornea in determining relative transparency.

The present invention does not use the conventional common slit lamp biomicroscope, but rather employs a television camera system that produces digital images to analyze the anterior part of the eye. Correlation of a sequence of individual still-image photographs is difficult due to the change in gaze fixation in relation to the ooptic axis of the camera. The present invention solves this problem by employing a rectilinear scanner system that provides rapid density and thickness measurement of the entire cornea in an easy-to-interpret format.

The ophthalmic pachymeter of the present invention measures the elemental brightness of a selected part of a Tyndall image of the eye. The selection of a part of the field of view of a slit lamp system is carried out with computer control, using a table of valued fiducial marks that outline certain areas of the video image.

In the system described in the present invention, a 'clock' signal is derived from a high precision crystal controlled oscillator to provide a subdivision of the lattice lines that produces perfectly defined elements in time and size. The preferred embodiment uses a medium resolution solid state television camera.

The present invention provides a system that also reduces the number of positions used in the calculations involved in the elaboration of the graph by circumscribing parts of the visible frame in order to cover the area of ​​interest. Thus, the resulting information is stored more compactly and without loss of resolution or precision. The gamma curve for film images shows the relationship between log exposure and log image density.

The shape of the anterior and posterior surfaces and the thickness of the cornea of ​​the human eye can be mapped by means of the slit projection system of this invention. The gaze fixation line is made to coincide with the ooptic axis of the camera by means of a target observed by the subject through a beam splitter. The beam splitter and fixation target are positioned so as to produce the desired alignment of the eye and the camera, and consequently the slit beam.

Once the anterior surface of the cornea has been generated, the posterior surface can be defined using the ondx of refraction of the cornea and the angle of incidence of each beam that are derived from the data of the anterior surface by applying Snell's law. .

The calculation of the surface shape is performed in the present invention by the analysis of similar tri-angles, as illustrated in Figures 13 and 15. The contour of the anterior surface is defined first. The procedure requires a simple geomometric analysis of the Tyndall image. The angle between the slit beam and the optical angle is set at 45 degrees, in the center. The distance between the mirror and the eye is also fixed at a known distance. The image point for each pixel is shifted from the ooptic axis as a direct function of the height of the point above the reference base plane. In a preferred embodiment of the present invention, the image to be analyzed is generated by projecting the narrow bands of light into the eye through optical projectors of a conventional 'Kohler' design.

In one of the preferred embodiments a pair of projectors is employed, each of which actuates an individual slit assembly. Furthermore, each slot assembly is moved under computer control perpendicular to the longitudinal axis of the slot. Each slit is moved, furthermore, from an opposite side of the eye.

The computer-generated alignment points, called 'fiducial points', are represented along with the image of the eye. The user positioned these fiducial points on the corneal image by moving the instrument. The operator moves the instrument until the corneal image falls within the defined area, focuses the camera by axial movement until the desired focus figure is centered on the limbus within the frame, and operates the switch to accept the data sample and start the data collection sequence.

Brief summary of the description

In general terms, the present invention provides a new system for measuring corneal thickness and ooptic density as well as a method for measuring corneal thickness and ooptic density. Both the system and the procedure provide relative transparency plots of many types of corneal lesions. In addition, the invention provides pachymetry with almost instantaneous data representation that allows evaluating the need for surgical intervention. Consequently, one of the most important contributions of the present invention is essentially that it operates on a real-time basis, providing almost immediate results.

The pachymeter of the present invention, as indicated above, is made up of three main subsystems, which are a modified slit lamp to project light beams onto the eye to be examined, a television camera system and a lens to obtain images of the eye. , and an electronic circuit to define and quantify a part of the television image. Drive mechanisms are also provided to move the ooptic slit to produce successive images for analysis. The associated computer software performs the necessary control of the drive mechanism, the selection of images, the digital conversion of the analog television signals for the computer processing, and the numerical analysis. This converts the information into a perceptible measurement of surface shape, thickness, area of ​​optical density, and even a visual representation of derived information for clonal use. Obviously, a

ES 2 138 012 T3 video output for teaching purposes through pictures and / or record keeping.

Furthermore, the clinical pachymeter of the invention includes an amplitude detection circuit from which the positions of the image brightness discontinuities that could be associated with a lesion are derived. The invention includes memory storage for these image points, which are digital representations of the magnitude of the image brightness discontinuities. These image brightness discontinuities exist in pixel terms. A conventional electroinic computer is used to obtain the relative optic density and the thickness profile of the cornea. The pachymeter of the present invention also generates an image of the derived density and thickness information for immediate use.

Broadly speaking, the invention could be described as an ophthalmic pachymeter that helps to determine the thickness, surface contour and transparency of the anterior segment of the eye. The ophthalmic pachymeter generally comprises a light projection means, such as a projector, for illuminating a defined area of ​​the line. An image production medium, such as a television camera, provides a television image of selected parts of the illuminated area of ​​the eye. A video medium, such as a video amplifier, receives the image of the eye and transmits a video signal representing the image of the eye.

The video signals derived from the video medium acted in conjunction with a converter medium to convert said video signals to digital format. The converter means may take the form of an analog-to-digital converter that works in conjunction with a data memory computer. A fiducial medium outlines parts of the video image for focus and alignment. A suitable computer program outlines these parts of the video signal to be converted into digital format. Finally, an analytical means is provided to detect and store the relative brightness levels within the delineated areas in said data memory. A directional counter is also used that allows the subsequent addressing of the stored information.

Furthermore, the invention can be described as a system for producing graphics of the superficial contour of the cornea of ​​the eye comprising a projection lighting means to produce a definable spatial delineation of the corneal contour. A television camera medium converts illuminated areas into electrical signals in analog format. The analog signals are converted into a digitizing medium for computer-readable operation. A computer means calculates the shape of the corneal surface from the digital signals.

Brief description of the drawings

Having described the invention in general terms, reference will be made to the accompanying drawings (seven sheets), in which:

Figure 1 is a schematic view showing some of the main components of the system of the present invention;

Figure 2 is a top plan view, partially in horizontal section, of the optic pachymeter constructed according to the present invention, and incorporating it;

Figure 3 is a perspective view of an alternative construction of a focus assist mechanism that forms part of the system of the present invention;

Figure 4 is a front elevation view of the ophthalmic pachymeter of the present invention;

Figure 5 is a side elevation view of the ophthalmic pachymeter of the present invention, partially in section, illustrating the main components inside the same;

Figure 6 is a schematic view showing the optic and the optic trajectories involved in producing a slit image in the eye of a subject;

Figure 7 is a plan view of a television screen showing, in enlarged detail, a portion of the television grid for the screen;

Figure 8 is a schematic diagram of a part of the electrical circuit used in the system of the present invention;

Fig. 9 is a graphical illustration showing a television waveform that can be produced in the system of the present invention;

Figure 10A illustrates a front elevational view of the eye with superimposed half Tyndall images for focus and alignment;

Figure 10B illustrates a front elevation view of the eye, similar to Figure 10A, with the half Tyndall images aligned and in the position where they would be centered on a fiducial mark;

Figure 11 is a schematic view showing the fiducial figure used for alignment in the present invention;

Figure 12 is an illustration of a horizontal cross section of the eye for reference purposes;

Figure 13 is a graphical illustration showing the image analysis geometry employed in the Placido method and in the present invention;

Figure 14 is a schematic illustration of an oyptic beam trace for obtaining thicknesses of a transparent member; Y

Figure 15 is a schematic illustration showing the geometric relationship of the image obtained according to the present invention with respect to a projector lens and a camera lens.

Detailed description of the preferred embodiments

With more detailed reference to the drawings - by reference characters - and particularly to Figure 1, it can be appreciated that the ophthalmic meter of the present invention comprises a television camera 20 provided with a conventional lens that was aligned with and receives an image of an eye 22 of a subject through a beam splitter 24 for further quantification and to provide a television image of the eye for anaolysis purposes. With reference to Figure 3, it can be seen that the apparatus comprises a conventional incremental motor 26 for positioning an elongated aperture, for example a slit 28, of a slit shape 30 in the focal plane of the light projector depicted in Figure 1 by a lamp 32. The slit shape 30 may be operatively connected to an appropriate slide assembly 31, as also better illustrated in Figure 3 of the drawings.

The slit format 30, and particularly the slit 28 thereof, together with the lamp 32, produces an image in the eye 22 thanks to a projection lens 34, as shown in figure 1, intended for the selection of sequential images for analysis. Referring to Figure 6, a Kohler device 36 is illustrated comprising a lamp 32 provided with a dense filament 38. In this case, and referring again to FIG. 6, it can be seen that the image of the filament 38 is formed at the entrance pupil of the projection lens 34 by means of a condenser lens 34.

Adjacent to the condenser lens 40, and in ooptic alignment with said condenser lens 40, is the slot format 30 that contains the o-optical slot 28. Preferably, this slot format 30 was mounted on a support (not shown in detail) . The bracket can move in a direction perpendicular to the slot 28 driven by the incremental motor 26 mentioned above. The slit images are focused in the same plane as the television camera 20 by the projection lens 34 and a system of mirrors and prisms designated schematically by the reference number 42 in Figures 1, 2, 4 and 5. Also provided is a fixation lamp 44, occasionally referred to as a 'target fixation lamp', as shown in FIG. 1, which operates with beam splitter 24 as shown. This combination of lamp 32, lenses 34 and 40, and mirrors and prisms 42, coupled with slit format 30, acted as a slit lamp projector.

Referring again to FIG. 1, it can be seen that the television camera 20 generates a signal representative of the eye image, which is transmitted to a video amplifier 46 which amplifies and mixes the video signals for analysis. An analog to digital flash converter 48 receives the output from the video amplifier 46 which processes and digitizes the analog signals received from the television camera 20. A data separator 50 receives an output from the analog-to-digital converter 48 to direct the digital data to and from a storage in the form of digital data memory 52. ​​For example, the data separator 50 and the data memory 52 may be part of a conventional computer that is not illustrated in detail herein. In this sense, it would be observed that many of the components are shown schematically (rectangular boxes) in Figure 1.

The digital data sent to the digital data memory 52 constitutes a storage of the numerical brightness of each element within the fiduciary boundary. A counter 54 is provided to determine the location and storage of pixel brightness data for each pixel in the image. A mode controller 56 is connected to address counter 54 to determine the sequence of system operations. Mode controller 56 receives input from a computer interface 58 which, in turn, is connected to data separator 50 and analog-to-digital converter 48, as illustrated in FIG. 1.

Computer interface 58, acting in conjunction with a computer, controls the elements of the system through the associated computer. In this case, an image driver 60 is provided to control the aforementioned fixation target lamp 44, which is visible by the reflection of the beam splitter 24. This serves to provide the apparent location of the fixation target lamp 44, that is, from the beam splitter 24 coincident with the ioptic center of the television camera 20 and its associated lens system.

Referring to Figure 10, it can be seen that it is a representative image of eye 22. The anatomical features illuminated by slit beam 28 are visible in the form of a Tyndall image 62 representing parts of the eye, such as the epithelium of the cornea, stroma, and endothelial layer, which scatter light. An iris 64 of the eye does not constitute the area to be measured, so the illumination of this area is carried out by means of a Tyndall lighting device. The image of iris 64 can be further reduced by limiting the spectral distribution of the slit beam 28 by using a color filter (not shown), also a slit projector - or slit projectors, if more than one is used. one - it produces some specular reflections 66, as shown in figure 10, which were located in the space of the 'X, Y' coordinates, depending on the surface curvature of the cornea of ​​the eye 22.

The operator of the ophthalmic pachymeter is provided with a computer generated figure that is used as a fiducial mark system, as illustrated by reference number 68 in figure 11. The fiducial marks of this fiducial mark system 68 were located around in the center of the image monitor.

With reference to Figures 4 and 5, it can be seen that the components of the lamp illuminator

ES 2 138 012 T3 slit - for example, the lamp 32 and the slit format 30, as well as the television camera system 20 - are mounted on a movable base 70 comprising a molded frame. A vertical composition element, such as a vertically disposed support stem 72, acts from its mounting on the molded base 70, as illustrated. Generally, the sprocket support shafts 74 (not shown) are located in the molded base 70, are best seen in FIG. 5, and have movement towards the subject and in the opposite direction. The device also comprises dust guards 78 that cover the sprockets. The sprockets 76 located under the dust shields 78 serve to restrict movement relative to a table 80 and, consequently, the patient, so that movement occurs only in a given area. The molded base 70 is provided with a vertical handle 82 for manual manipulation by an operator of the apparatus, and allows the instrument to be positioned relative to a subject, which is described in more detail below.

Beam splitter 24 may be mounted on base plate 84 of a housing 86 that houses many of the ophthalmic pachymeter components, such as, for example, the television camera 20, the condenser lenses 40, the slit format 30, lamp 32, and mirrors and / or prisms 42. Located under beam splitter 24 is a printed circuit assembly (not shown). This printed circuit assembly may contain fixture lamp 44. Alternatively, fixture lamp 44 may be mounted on beam splitter 24 as best illustrated in Figures 4 and 5 of the drawings.

Motors 26 that move slit format 30 will rotate the full size slits 28 of Figure 3 through the eye, from each side and sequentially, to provide the sequence of data that will ultimately be stored for analysis. The data is masked by the software in order to remove any foreign material. The arc of Tyndall images is located only at one side of the section of the iris illuminated by light passing through the cornea, and has a defined maximum number of pixel positions at the apex from the iris line.

The television image has a lattice form, as shown in Figure 7. The television set has a monitor 100 that displays the visual information following a sequence of time. The beam current is low for black areas 102 and high for white areas 104, and is scaled to recreate the range of brightness of the original scene. The television camera 20 generates the analogue lighting tension of the scene, to which synchronization signals are supplied that guarantee that the reproduced time sequence is a faithful recreation of the scene being photographed.

Image processing and handling

The following section more specifically describes the process used to determine the thickness and topography of the cornea. Although the circuit shown in figure 8 literally constitutes a part of the apparatus, it will nevertheless be described in relation to said image handling and processing since it is integrally related to said image handling and processing.

Figure 13 shows the relationship between the Tyndall 62 image and the topography of the cornea. Along each lattice line of the television image there is a detectable edge of the Tyndall image that has a virtual image location offset according to delta d (Ad). This distance of displacement goes from the point where the beam may have intersected the optical axis in case of not being deviated, it is still better shown in figure 15. From this pixel position of the image, the height of the data above the reference plane delta h (Ah) can be calculated. Calculations are performed for all intercepts of all data frames in order to provide an array of X coordinate positions from which the topography can be drawn.

With reference to Figure 9, the waveform of the tension produced by the television camera of the parameter is illustrated. Following the above, the beam is low for the black areas 102 and high for the brighter areas 104. The brightness amplitude ratio of the anterior edge of the corneal section to the dark area of ​​the pupil representing the anterior chamber is used as reference value to evaluate the reflection of the lenses. Pixel amplitudes are averaged for all elements in the reference areas in order to provide the baseline reflectance value.

The waveform of the voltage of the television signal, as shown in figure 9, is a single lattice line of video information in which there are bright areas 108 from the corneal image and a brighter image of iris 64 (represented by bright areas 104) illuminated by the slit beam after it passes through the cornea. A synchronized pulse signal 112 precedes each line of pictorial information carrying voltage levels. The synchronized pulse 112 is followed by a short period of low-level blanking pulses 114. The blanking pulse 114 ensures that the image will be off while the beam is tracked back to the beginning of the new line. The black level, represented by reference number 116, is the most negative of the pictorial data voltages of the composite video signal. This level is determined by a synchronized level clamp circuit of a conventional design in which a selected point of the image representing the anterior chamber signal is sampled that is used as a determinant of minimum brightness. As the tension increases, so does the brightness in the rendered image from black to the maximum white 118, which is equal to the saturation of the signal. The level of stress produced at the saturation point by a 'white' image 118 is shown by the dotted line at the top of the illustration. The brightness profile of the corneal image varies as the local oaptic density and the refractive index vary.

ES 2 138 012 T3

At the leading edge of time of the corneal reflex signal, the signal rises to a maximum 119, which represents the interface between the flesh and the air. The amplitude of this signal is fairly constant from one subject to another and from time to time. This constant interface signal is used as a reference to the signal against which reflex measurements are made to quantify corneal transparency. Next, each successive grid line will provide a density profile for a different part of the cornea.

Each exposure containing the Tyndall image or images 62 is converted into digital form by the analog-to-digital converter 48. Through the action of the data separator 50, the mode controller 56, the address counter 54, and memory. of digital data 52, these sequential amplitude values ​​are stored for use. The stored data represent the brightness of the pixels against the location of each slice of the cornea to be analyzed. Next, each successive pixel in each successive frame is multiplied by a constant derived from the mean of the corneal-to-air interface signal and the lower normal brightness-correcting oaptic constant. As they are calculated, each point is returned for storage in the same sequence and for later computation and image representation. Tyndall lighting provides sequences of three-dimensional data that are transferred to the computer via computer interface 58.

Figure 8 represents a schematic diagram of part of the electronic circuit used in the preferred embodiment of the present invention. The composite video signal from the television camera 20 is applied to the input 120 of a signal conditioning amplifier.

The terminated signal is separated by an emitter follower 122 that drives the DC restoration networks and the synchronism separator 124 and 126. The video with DC restored and limited is separated by a second emitter follower, and serves to drive the clamping amplifiers. and mixes 128 and 130.

A computer-derived black reference timing signal 132 is generated time-synchronized with the image area of ​​the television camera 20 defining the area of ​​the pupil closest to the center of the image. This pulse is conditioned by monostable circuits 134 to provide a constant-width, constant-amplitude sampling pulse. This sampling pulse allows, through capacitor 136, that capacitor to store a voltage sample of the raw video representing the 'black' level. The black reference level thus generated drives amplifier 130 for use in analog-to-digital converter 48.

The signals from the computer are used for regeneration of the television timing in a conventional integrated circuit device 140 employing a composite timing signal 142 and a dot clock signal 144 from the computer image driver. The fiducial signal 146 and the composite sync regenerated through the computer are mixed by means of resistors 148 and the video signal from a follower emitter 150 in order to provide the monitor signal. The monitor signal is used to drive a conventional CRT image used for image search by the user of the parameter of the present invention.