DE102018109726B4 - Method and device for measuring the cornea - Google Patents

Abstract

The present invention relates to the field of ophthalmic optics and in particular to a device (1) for measuring the cornea of a test subject, the device comprising the following: an image capture device (30) set up for capturing image data of an iris (1202) of the test subject from a plurality of points of view by means of imaging beams - passages that penetrate the cornea (1201); and a computing unit (40), the computing unit being set up to: provide a mathematical model of a front part of the subject's eye with a mathematical model of the cornea (1201) and iris (1202) (1702); Identifying and registering image features (1501a, b; 1503a, b) of the iris (1202) which are present in several images (1500a-d) of the image data (1703); Determining deviations between actual positions of the image features of the iris in the images acquired from multiple viewpoints and expected positions of the image features of the iris in the images acquired from multiple viewpoints, taking into account the mathematical model of the cornea and the position of the iris (1704); Adapting parameters of the mathematical model of the cornea such that the deviations are minimized (1705); and determining a measured variable of the cornea from the adapted mathematical model of the cornea (1706).

Description

The present invention relates to the field of optics and in particular to a device for measuring the cornea of a subject. The present invention further relates to a method for cornea measurement and a corresponding computer program product.

Devices for cornea measurement are already known from the prior art. The solutions known from the prior art essentially use two measuring methods.

On the one hand, projection methods in which the cornea is illuminated with a ring pattern of concentric circles and the reflection of the ring pattern on the cornea is measured. Distortions of the ring pattern allow conclusions to be drawn about the shape of the anterior surface of the cornea. An exemplary device is the E300 Corneal Topographer from Medmont International PYT Ltd. LTD (Nunawading, Australia).

Another known measurement method is the so-called 3D Scheimpflug Corneatomography. A corresponding measuring device is commercially available from Oculus Optikgeräte GmbH (Wetzlar, Germany). Furthermore, from the publication US 2015/0 190 046 A1 another device for analyzing the shape of the cornea and a method for determining the thickness of the cornea are known. From the publication US 2012/0 033 179 A1 a method and a device for determining an eye pivot point position are known.

However, there is still the problem that such test methods are perceived as unpleasant by some test subjects. In particular for users with light-sensitive eyes, several attempts are sometimes necessary to obtain a measurement result.

Against this background, it is desirable to make a cornea measurement more convenient for the user. In particular, it would be desirable to reduce glare during the measurement.

• - eine Bilderfassungseinrichtung, eingerichtet zum Erfassen von Bilddaten einer Iris des Probanden aus mehreren (bekannten) Blickpunkten durch Abbildungsstrahlengänge, welche die Cornea durchsetzen; und
• - eine Recheneinheit, wobei die Recheneinheit eingerichtet ist zum:
  • - Bereitstellen eines mathematischen Modells eines vorderen Augenabschnitts des Probanden mit einem mathematischen Modell der Cornea und der Iris;
  • - Identifizieren und Registrieren von Bildmerkmalen der Iris, welche in mehreren (vorzugsweise allen) Bildern der Bilddaten vorhanden sind;
  • - Bestimmen von Abweichungen zwischen tatsächlichen Positionen der Bildmerkmale der Iris in den aus mehreren Blickpunkten erfassten Bildern und erwarteten Positionen der Bildmerkmale der Iris in den aus mehreren Blickpunkten erfassten Bildern unter Berücksichtigung des mathematische Modells der Cornea und der Lage der Iris;
  • - Adaptieren von Parametern des mathematischen Modells der Cornea derart, dass die Abweichungen minimiert werden; und
  • - Bestimmen einer Messgröße der Cornea aus dem adaptierten mathematischen Modell der Cornea.

According to a first aspect of the invention, it is therefore proposed to provide a device for measuring the cornea of a subject, the device having the following:

• an image capturing device configured to capture image data of an iris of the subject from several (known) viewpoints through imaging beam paths which penetrate the cornea; and
• a computing unit, the computing unit being set up to:
  • - Providing a mathematical model of an anterior segment of the subject with a mathematical model of the cornea and iris;
  • - Identifying and registering image features of the iris which are present in several (preferably all) images of the image data;
  • Determining deviations between actual positions of the image features of the iris in the images acquired from a plurality of viewpoints and expected positions of the image features of the iris in the images acquired from a plurality of viewpoints, taking into account the mathematical model of the cornea and the position of the iris;
  • - Adaptation of parameters of the mathematical model of the cornea in such a way that the deviations are minimized; and
  • - Determination of a measured variable of the cornea from the adapted mathematical model of the cornea.

The inventors have recognized that an active measurement does not necessarily have to be carried out to the effect that the cornea must be illuminated with a defined ring or slit pattern. Rather, it is proposed to evaluate ray paths of the iris lying behind the cornea. The iris has an unknown structure or pattern. However, the iris is usually very structured. The inventors have recognized that a large number of image features of the iris can be identified and subsequently evaluated for their position in a plurality of images of the image data recorded from different positions.

An advantage of the solution according to the invention can thus be that a passive measurement can be carried out without the cornea having to be illuminated with a defined ring or slit pattern. For users with sensitive eyes in particular, glare can be reduced during the measurement and the cornea measurement can thus be made more pleasant.

In other words, the same object, namely the iris with the cornea above it, is taken from different perspectives. Without the influence of the cornea, the images only differ in the different perspective from which the iris is taken. The optical effect of the cornea, however, results in additional distortions, which are reflected in the images taken from the various points of view. Even if the picture content is unknown, since the iris differs from subject to subject, for example, similar image features can be identified by a correlation analysis. These features can be tracked in images taken from different perspectives or viewpoints and deviations between actual and expected positions of the features in the images can be determined. The deviations are caused by the cornea. The shape and / or the refractive index (which can be regarded as constant in a first approximation) can be inferred from the effect on the image data. In particular, a shape, thickness and / or thickness distribution can be determined as the measurement variable.

• - Erfassen von Bilddaten einer Iris des Probanden aus mehreren Blickpunkten durch Abbildungsstrahlengänge, welche die Cornea durchsetzen; und
• - Bereitstellen eines mathematischen Modells eines vorderen Augenabschnitts des Probanden mit einem mathematischen Modell der Cornea und der Lage der Iris relativ zur Cornea;
• - Identifizieren und Registrieren von Bildmerkmalen der Iris, welche in mehreren (vorzugsweise allen) Bildern der Bilddaten vorhanden sind;
• - Bestimmen von Abweichungen zwischen tatsächlichen Positionen der Bildmerkmale der Iris in den aus mehreren Blickpunkten erfassten Bildern und erwarteten Positionen der Bildmerkmale der Iris in den aus mehreren Blickpunkten erfassten Bildern unter Berücksichtigung des mathematische Modells der Cornea und der Lage der Iris;
• - Adaptieren von Parametern des mathematischen Modells der Cornea derart, dass die Abweichungen minimiert werden; und
• - Bestimmen einer Messgröße der Cornea aus dem adaptierten mathematischen Modell der Cornea.

According to a second aspect of the present invention, a method for corneal measurement of a subject is proposed, the method comprising the following steps:

• - Acquisition of image data of an iris of the test subject from several points of view by means of imaging beam paths which penetrate the cornea; and
• - Providing a mathematical model of an anterior segment of the subject with a mathematical model of the cornea and the position of the iris relative to the cornea;
• - Identifying and registering image features of the iris which are present in several (preferably all) images of the image data;
• Determining deviations between actual positions of the image features of the iris in the images acquired from a plurality of viewpoints and expected positions of the image features of the iris in the images acquired from a plurality of viewpoints, taking into account the mathematical model of the cornea and the position of the iris;
• - Adaptation of parameters of the mathematical model of the cornea in such a way that the deviations are minimized; and
• - Determination of a measured variable of the cornea from the adapted mathematical model of the cornea.

According to a further aspect of the present disclosure, a computer program product is proposed, comprising instructions which, when the program is executed by a computer, cause the computer to carry out the aforementioned method. It is understood that the method steps are designed for execution by a computer. For example, capturing image data can be understood to mean receiving image data. The term can thus be understood as a transmission of measurement data generated by a physical image sensor.

Unless otherwise specified, the terms used herein are intended to be used within the meaning of Standard DIN EN ISO 13666: 2012 of the German Institute for Standardization eV

In one embodiment it can be provided that the image capture device has a camera array for capturing image data of the subject's iris from several (known) viewpoints. One advantage of a camera array is that the positions of the cameras, ie the viewpoints from which the image data are acquired, have already been defined. For example, the image capture device can have a first camera and a second camera, the first camera being set up for capturing first image data from a first viewpoint and the second camera being set up for capturing second image data from a second viewpoint.

In one embodiment it can be provided that the computing unit is set up to identify the image features of the iris on the basis of a correlation analysis between images of the image data. One advantage of this solution is that matching features can be identified even with unknown images, here images of the iris. Alternatively or additionally, the computing unit can be designed to carry out an edge detection in order to recognize an edge of the pupil or an inner and / or outer edge of the iris. These can be identified as image features in the images taken from the different angles.

In one embodiment it can be provided that one of the parameters of the mathematical model of the cornea is a form of the cornea and the computing unit is set up to adapt the shape of the cornea (or of parameters of the mathematical model of the cornea). The mathematical model of the cornea can have a front and a back surface. The front surface faces away from the user in the viewing direction. The rear surface faces the user in the direction of view. The computing unit can be set up to determine the shape of a front and a back surface of the cornea. The front and / or back surface can be determined by adapting the parameters of the mathematical model of the cornea. In other words, the cornea can be determined as a combination of a 3D topography of the front surface and a 3D topography of the back surface. The 3D topographies can be specified separately. Alternatively, a 3D topography and a thickness of the cornea can be specified. The computing unit can optionally be set up to provide a Evaluate the distance between the front and rear surface, in particular whether the distance is below a predetermined threshold. It is therefore possible to make a (spatially resolved) statement about the thickness of the cornea. This is particularly advantageous when preparing a laser treatment or laser ablation in order to avoid excessive material removal. In the case of solutions known from the prior art, two measuring devices are used here: First, the shape of the front surface is determined by means of a projection method in which the cornea is illuminated with a ring pattern of concentric circles. The thickness is then determined using an ultrasound measurement. The proposed solution enables an efficient determination of the shape and thickness in one work step. Alternatively or additionally, one of the parameters of the mathematical model of the cornea can be a refractive power distribution of a front and / or back surface; and the computing unit can be set up to adapt the refractive power distribution.

A mathematical model of a front section of the subject's eyes can be provided, which comprises a mathematical model of the cornea and iris. The model can have a front and a back of the cornea. Preferably, the model of the anterior segment of the eye can further comprise a model of aqueous humor between the cornea and the iris. The iris can, but need not, be modeled simply as a two-dimensional disk. In the mathematical model, each surface can be modeled as a 3D topography, at least in sections. Areas between the respective areas can be described with an individual refractive index. The computer program can be set up to reconstruct this model from the detected beam paths. In the simplified case, the surfaces can be assumed to be toric or spherical surfaces. The refractive indices can optionally be assumed to be known. Known values for the refractive index of the cornea and aqueous humor can be used here. In one configuration, a thickness or the thickness distribution of the cornea can optionally be determined (pachymetry). The thickness of the cornea is an important parameter in refractive eye surgery as well as in the correction of tonometry data. In one configuration, the device can have a measuring device for acquiring measurement data of a front surface of the cornea and the mathematical model of the cornea can also be provided or adapted based on the acquired measurement data of the front surface of the cornea. In particular, it can be a deflectometric measuring device. By providing further information about the front surface, the subsequent optimization can be improved and simplified.

In a further development it can be provided that the measuring device is set up to determine an orientation, in particular a surface normal, in at least one point on the front surface of the cornea. For example, the ZEISS IOL Master500 (Zeiss, Germany) can be used.

In one embodiment it can be provided that the computing unit is set up to model the iris as a two-dimensional plane. One advantage of this solution is that good results can be achieved with only moderate computing effort. Alternatively, other approximations of the iris can be provided, on the basis of which a further improvement in accuracy can be achieved. In general, the iris can be understood as a 3D structure and can also be modeled as this. The computing unit can therefore be set up to model the iris as a 3D topography. Such a 3D topography can have, for example, a sphere, a torus, a plane or combinations thereof.

In one configuration it can be provided that the mathematical model models a circular iris edge. The inner and / or outer edge of the iris can be approximated as a circle. For example, the iris can be modeled as a ring with a circular circumference and a circular pupil in the middle. By specifying a boundary condition for the shape of the iris, calculations can be simplified. For example, a tilt of the iris edge can be determined in images taken from different positions. The orientation of the circle can be used as a starting point for further optimization.

In one embodiment it can be provided that the computing unit is also set up to carry out a deflectometric evaluation of reflections from an environment on the eye and to take this into account when determining the mathematical model of the cornea. Instead of giving the test subject potentially unpleasant test light in the eye, deflectometric analysis of reflections from the surroundings can be carried out. Such an evaluation may not necessarily offer sufficient accuracy for a final determination of the cornea, but it can be used as a further input parameter, e.g. be taken into account when adapting the mathematical model of the cornea.

In one embodiment it can be provided that the computing unit is set up to determine a refractive index of the cornea. An advantage of this configuration is that In addition to the shape, the refractive index or a spatial refractive index distribution can also be determined.

In one embodiment it can be provided that the computing unit is set up to carry out calculations using photometric measurements.

In one embodiment it can be provided that the device also has an illumination device which is set up to illuminate the iris. This enables the image capture device to capture the image data even without ambient light or in low ambient light.

In one embodiment it can be provided that the lighting device is set up for projecting a pattern onto the iris. An advantage of this configuration is that a known pattern on the iris can be generated and evaluated. This can be particularly advantageous if the iris has only a few structural features.

The advantages described in detail above for the first aspect of the invention apply accordingly to the further aspects of the invention.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own without departing from the scope of the present invention.

• 1 zeigt eine schematische Darstellung einer Vorrichtung zum Vermessen der optischen Wirkung einer in einem Messvolumen angeordneten optischen Linse;
• 2 zeigt eine beispielhafte Darstellung einer durch eine Linse aufgenommenen Teststruktur;
• 3 zeigt eine beispielhafte Darstellung einer durch ein verkipptes Brillenglas aufgenommenen Teststruktur;
• 4 zeigt eine Darstellung von Strahlengängen durch ein transparentes Objekt;
• 5 zeigt eine Darstellung von Strahlengängen durch eine Linse;
• 6 zeigt eine aus parametrierbaren Flächenelementen zusammengesetzte Linse;
• 7 zeigt eine schematische Darstellung einer Vorrichtung zum Vermessen der optischen Wirkung einer in einem Messvolumen angeordneten optischen Linse;
• 8 zeigt eine weitere Ausführungsform einer Vorrichtung zum Vermessen der optischen Wirkung einer in einem Messvolumen angeordneten optischen Linse;
• 9 zeigt ein Flussdiagramm einer Ausgestaltung eines Verfahrens zum Vermessen der optischen Wirkung einer in einem Messvolumen angeordneten optischen Linse;
• 10 zeigt ein detailliertes Flussdiagram einer Ausgestaltung eines solchen Verfahrens;
• 11 zeigt ein Flussdiagram einer Ausführungsform eines Verfahrens zum Kalibrieren;
• 12 zeigt eine schematische Darstellung eines Auges;
• 13 zeigt eine Abbildung einer Draufsicht auf das Auge mit einer Abbildung der Iris;
• 14 zeigt eine schematische Darstellung einer Vorrichtung zur Cornea-Vermessung;
• 15 zeigt die Zuordnung bzw. Korrelation von Bildmerkmalen in aus unterschiedlichen Blickpunkten aufgenommenen Bildern der Iris;
• 16 zeigt weitere Korrelationen von Bildmerkmalen; und
• 17 zeigt ein Flussdiagram einer Ausführungsform eines Verfahrens zur Cornea-Vermessung.

Embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

• 1 shows a schematic representation of a device for measuring the optical effect of an optical lens arranged in a measurement volume;
• 2 shows an exemplary representation of a test structure recorded by a lens;
• 3 shows an exemplary representation of a test structure recorded by a tilted spectacle lens;
• 4 shows a representation of beam paths through a transparent object;
• 5 shows a representation of beam paths through a lens;
• 6 shows a lens composed of parameterizable surface elements;
• 7 shows a schematic representation of a device for measuring the optical effect of an optical lens arranged in a measurement volume;
• 8th shows a further embodiment of a device for measuring the optical effect of an optical lens arranged in a measuring volume;
• 9 shows a flow diagram of an embodiment of a method for measuring the optical effect of an optical lens arranged in a measurement volume;
• 10 shows a detailed flow diagram of an embodiment of such a method;
• 11 shows a flow diagram of an embodiment of a method for calibration;
• 12 shows a schematic representation of an eye;
• 13 shows an image of a top view of the eye with an image of the iris;
• 14 shows a schematic representation of a device for cornea measurement;
• 15 shows the assignment or correlation of image features in images of the iris taken from different points of view;
• 16 shows further correlations of image features; and
• 17 shows a flow diagram of an embodiment of a method for cornea measurement.

In the 1 shown device 10 is used to determine the optical effect of an optical lens 100 , in particular an eyeglass lens. The device 10 has a display device 20 on what to display a test structure 21 is set up. For example, it can be a screen or a display in order to be able to display different test structures.

The device 10 also has an image capture device 30 which is set up for capturing image data of the test structure 21 from several points of view 31 . 31 ' . 31 " through imaging beam paths 32 which the lens 100 push through. The imaging beam paths from the different viewpoints can be recorded one after the other with a camera, which is arranged one after the other at the different positions. However, a plurality of cameras are preferably provided in order to capture the image data in parallel. It goes without saying that mixed forms can also be provided. For example, an image capture device 30 a first camera 33 and a second camera 34 have, the first camera 33 for capturing first image data from a first point of view 33 is set up and the second camera 34 for capturing second image data from a second point of view 33 " is set up. The measurement volume 200 lies between that on the display device 20 displayable test structure 21 and the image capture device 30 ,

The device 10 also has a computing unit 40 on. At the computing unit 40 it can be, for example, a computer, microcontroller, FPGA or the like. The computing unit 40 is designed to determine a three-dimensional shape of the lens 100 based on the image data and for calculating an optical effect of the lens 100 based on the three-dimensional shape. In other words, a two-stage procedure is proposed in which the three-dimensional shape of the lens is first determined and only then is the optical effect of the lens calculated from its three-dimensional shape.

This approach, in accordance with the present disclosure, is set out below with reference to FIG 2 to 6 are explained in more detail.

2 shows a top view of a through a lens 100 recorded test structure 21 a display device 20 , This can be, for example, the one with the camera 33 through the lens 100 recorded test structure 21 according to 1 act. The test structure 21 is through the lens 100 reproduced distorted. Such a deflection of the rays can already draw conclusions about the optical effect of the lens 100 to be pulled. However, only a statement can be made about the effect of the lens 100 be taken in their entirety.

3 shows another exemplary image, which is recorded with a camera. Here is the glasses 101 with the optical lens 100 however, strongly tilted in the measuring area, so that through the optical lens 100 caused beam deflection reproduces the actual optical effect in a wearing position with limited accuracy.

4 shows an exemplary representation of beam paths through a transparent object, such as a lens 100 , The origin of the beam paths is a defined point 22 on the display device 21 , The from the defined point 22 outgoing beam paths appear on the surface 102 into the lens 101 on and on the surface 103 out of the lens. They penetrate the lens 100 Consequently. Both on the entrance surface 102 , as well as on the outlet surface 103 , the light rays are refracted. Depending on the spatial position or orientation of the lens 100 relative to the display device 20 and to the image capture device 30 there may be a different optical effect.

The inventors have recognized that such vagueness or ambiguity of the optical effect can be resolved by taking the test structure from several points of view and thus capturing a large number of imaging beam paths (see also 1 ), from which the optical properties of an intermediate lens can be determined. In other words, an equation system with a multiplicity of equations can be set up for the imaging beam paths, each of which represents the association between imaging rays entering the image capturing device from several points of view, the lens 100 enforce, and their known places of origin on the display device 20 getting produced. This in turn can be the three-dimensional shape of the lens 100 and optionally also their refractive index or a braking force distribution within the lens can be determined.

A simplified example of beam paths through a lens 100 is in 5 play. The pixel 22 on the display device 20 is from the camera 34 detected. The ray path 110 occurs at the point 104 on the front surface 102 lens 100 into the lens and in point 105 on the back surface 103 out of the lens. When measuring with only one camera, in simple terms, there is an equation that has two unknowns, the entry point 104 and the exit point 105 including the spatial orientation of the surface at these points. By the image capture device 30 takes the test structure from further points of view, like through the additional camera 33 indicated, can further beam paths 111 and 112 be recorded. With the beam path 111 an exit point falls 104 with the beam path 110 the camera 34 together. With the beam path 112 falls an entry point 105 with the beam path 110 the camera 34 together. Thus, a plurality of equations can be set up, from which the properties of the between the display device 20 and the image capture device 30 arranged lens 100 let determine.

For this purpose, the computing unit can be set up to use the lens 100 preferably modeled as a composite surface from parameterizable surface elements, as in 6 shown as an example. From the deflection of the rays in the points 104 and 105 can be an orientation of the surface elements 106 . 107 the front and back surface 102 . 103 be determined. Optionally, a further division within the lens can also be carried out 100 be made. For example, other interfaces within the lens 100 be determined. Optionally, the computing unit can also be designed to provide a refractive index of the lens 100 or to determine a spatial refractive index distribution of the lens.

The device can optionally be designed as a device for measuring a spatial refractive index distribution of an optical lens arranged in a measurement volume. For this purpose, an interface can preferably be set up to receive lens geometry data that describe a three-dimensional shape of the lens. In this case, the shape of the lens need not be calculated and can serve as an input parameter for calculating the spatial refractive index distribution of the lens based on the image data and the lens geometry data.

Referring to 5 and 6 For example, the computing unit can be set up to determine the three-dimensional shape of the lens based on a backtracking of the light rays entering the image capturing device. The directions under which the rays of light 110 . 111 . 112 into the cameras 33 . 34 the image capture device are known. For this purpose, the image capturing device can be calibrated as described below. Starting from the respective camera 33 . 34 the incoming rays can thus be traced. The Lens 100 is located in the beam path between the image capture device or the respective cameras (with a known position) and the test structure (with a known position). Starting from a model of the lens 100 This model can be successively parameterized by the computing unit in such a way that the (known) test structure in this way by the model of the lens 100 it is shown that the image data recorded by the image capture device result. In particular, the orientations of the surface elements forming the lens surface, represented here by the surface normals, can be used for parameterization 129 . 130 , be adjusted and a distance 131 of the surface elements are varied, and optionally a refractive index n or a refractive index distribution within the lens are varied.

7 and 8th show further embodiments of a device 10 for measuring the optical effect of an optical lens arranged in a measuring volume 100 , Corresponding modules are identified by the same reference numerals and are not explained again in detail in order to avoid repetition.

8th shows an embodiment in which the image capture device 30 two cameras 30 . 31 ' having. The cameras see a pattern or a test structure 21 from different angles. The computing unit is designed to use the corresponding image data to determine the measurement object 4 to reconstruct. For this purpose, a gradient field can be determined from the surface elements or from the normals 129 . 129 ' , as in 5 and 6 explained.

Light from defined sources at defined points of origin of the test structure 21 penetrates the lens 100 and is used by the image capture device 30 taken with a calibrated camera system from different angles. The breaking surfaces of the body are reconstructed from the resulting images.

The principle works with one, two or more cameras. In an advantageous embodiment, two cameras are used, since a good cost / benefit ratio can be achieved. Additional cameras can be used to further increase accuracy.

The image capture device 30 or the cameras 31 . 31 ' is calibrated in such a way that a function is known with which a unique main light beam (camera beam) can be derived from origin and direction in 3D for each sensor coordinate. This calibration can be done according to the state of the art. Alternatively, instead of the camera calibration described above, a known optical design of the camera and / or a lens used can be included in the model of the camera.

The display device 20 can have, for example, self-illuminating sources, such as light-emitting diodes arranged in an array, a TFT or LED display, a 3D display, laser sources, a polarization display, or also a collimated, optionally structured lighting unit. The display device can also be illuminated. For example, an illuminated display device can test charts (e.g. dot pattern or plaid pattern), in particular a regular 3D pattern, an unknown feature-rich flat image (where positions can be estimated during optimization) or an unknown feature-rich 3D scene (positions are estimated during optimization).

The computing unit 40 can use further information to determine the three-dimensional shape. The reconstruction of the three-dimensional shape can in particular also be based on the known viewpoints or positions of the cameras from which the image data are acquired and on a known position of the test structure. In the present example, the image data can be locations of the images of light rays entering the cameras on the camera detectors. The light rays entering the image capturing device can be calculated from the image data and the known viewpoints. A calibration of the image capture device can serve as a basis.

The computing unit can optionally 40 also be set up to determine the three-dimensional shape of the lens taking into account one or more boundary conditions. For example, a contact point or stop 51 be given. At this point is the location of the lens 100 known and can be taken into account when determining the three-dimensional shape of the lens. Furthermore, information such as a shape of a front and / or back surface of the lens, a refractive index or material, etc. can be specified. Optionally, the device can be designed to present information on the lens, for example in the form of an engraving or a marker 140 , read out and take into account when determining the three-dimensional shape and / or when calculating the optical effect.

A particularly advantageous application of the present invention is the measurement of spectacle lenses, in particular the measurement of progressive spectacle lenses - also known as progressive lenses. Simpler glasses, such as spherical, aspherical, toric or prismatic glasses, can however also be measured with the proposed device.

The computing unit can optionally be set up to calculate an ISO peak power or a peak power in a predetermined measuring device configuration in order to provide comparable data. By providing carrier-specific data, such as Distance of a pupil to the spectacle lens (cornea-vertex distance HSA) and its position (e.g. frame lens angle or inclination). utility peak powers can be calculated.

Optionally, several objects can be measured simultaneously in the measuring room. In the event that glasses with left and right glasses are measured, the computing unit can also be designed to determine a position and position of the glasses relative to each other. From this, further information, such as the distance of the visual channels can be calculated. A transparent body with zones of different effects can also be provided as several measurement objects. This can e.g. be glasses with two lenses or be a lens with several zones - bi-, tri-, or multifocal lens.

9 shows a flow diagram of a method 900 for measuring the optical effect of an optical lens arranged in a measuring volume, in particular a spectacle lens, with the steps. In a first step 901 a test structure is provided for display on a display device. In a second step 902 Image data of the test structure are acquired from several points of view through imaging beam paths that penetrate the lens. In a third step 903 a three-dimensional shape of the lens is determined based on image data (and the known positions of the viewpoints and the display device relative to one another). In a fourth step 904 an optical effect of the lens is calculated based on its three-dimensional shape. The calculation can be made for any use situation. The computing unit can therefore be set up to calculate a first optical effect in accordance with an ISO vertex refractive index and to calculate a second optical effect in accordance with a usage situation of a user.

One step can optionally be added to the measuring method 905 upstream for calibrating the device.

A corresponding method for calibrating the device can in turn have the following steps: In a first calibration step, a test structure is provided on the display device. In a second calibration step, a first distance between the image acquisition device and the display device is set and image data of the test structure are acquired with the image acquisition device from the first distance.

As in 8th shown, a height adjustment device 150 be provided, which is set up to vary a distance between the image capture device and the display device. In this context, the computing unit can also be set up to determine a beam direction of the light beams detected by the image detection device based on image data acquired from different distances between the image detection device and the display device.

In a further step of the method for calibrating the device, a second distance between the image acquisition device and the display device can be set and image data of the test structure can be acquired with the image acquisition device from the second distance. In a further step, a direction of incident light beams, which are detected by the image capturing device and corresponding pixels in the image data, can be determined from this.

10 Figure 10 shows a detailed flow diagram of an embodiment of a method 1000 for measuring the optical effect of a lens arranged in a measuring volume.

In a first step S1011 a test structure is displayed on the display device. For example, this can be an entire dot or stripe pattern. In a further step S1012 image data of the test structure are captured by the image capture device. In step S1013 positions of features of the test structure, for example the positions of pattern points in the image data (corresponding to positions on a detector surface of the image capture device), can be determined. This can be done in step S1001 camera calibration takes place, as explained above or described in detail in FIG. 11. In step S1014 light rays incident in the image capturing device or their directions can then be determined. From the camera images of the displayed pattern, viewed through the lens to be measured, the light rays that enter the camera can be determined as a 3D vector.

In one step S1021 a full or partial pattern of a test structure can be displayed on the display device. In one big step S1022 image data of the test structure are captured by the image capture device. In step S1023 an assignment of sample points to pixels can be made in the image data. In particular, a sequence of different test patterns can be provided in order to resolve any ambiguity in the assignment of pattern points to pixels in the image data. In other words, luminous spots in the image data recorded with the image capture device can be assigned to a position of the luminous dots on the display device and thus also to the calculated light beams which have entered the image capture device. As an alternative or in addition, the computing unit can be set up to determine neighborhood relationships from an overall pattern of a test structure.

In one step S1031 A flat illumination can be provided on the display device. For example, all pixels of the display device can display "white". As a result, a contour of the lens can emerge and in step S1032 a contour of the lens can be determined. In one step S1033 a position and dimensions of the lens can be determined based on the detected contour. In other words, a position of the lens in the measurement volume can be determined in a simple manner.

In step S1041 a "best fitting" parameterizable lens can be calculated. A “best fitting” parameterizable lens, which could be in the measuring volume of the device, can preferably be determined by backward propagation of the camera light beams. A parameterizable lens is understood to be a lens that can be described with a few parameters, such as radius, thickness, refractive index. These include, for example, spherical and toric lenses. Toric lenses are a general compromise that can be used here. In a more specific version, it may be sufficient to define individual “toric zones” on the lens and only to describe the spectacle lens here. A first of these zones can be, for example, a “far area” of a progressive lens. A second of these zones can, for example, be a “close range” of a progressive lens. In addition to the location of the lens or the individual surfaces, further parameters can be the radii, the thickness and the refractive index.

In step S1042 a "best fitting" gradient surface of the front and / or rear surface of the lens can be determined by inverse ray tracing of the camera beams. An area of the in step S1041 Certain "best-fitting" parameterizable lens can thus be described as a gradient area and the gradients at the locations of the beam passages can be varied such that the positions of the luminous dots on the display device are hit perfectly by backward propagation of the camera beams. In simple terms, the three-dimensional shape of the lens is adjusted in such a way that the light beams received by the image capturing device and the associated beam sources on the display device match.

In step S1043 a front and / or back surface of the lens can be obtained by integration from the gradient surface. In other words, a (continuous) new surface is determined from a gradient surface determined in sections or for surface elements. This can be the front surface or the back surface of the lens.

According to step S1044 can the steps S1042 and S1043 can be repeated iteratively. For example, the steps can be repeated until a quality criterion is met. Optionally, if a sufficient quality is not achieved, the step can also be carried out S1041 be included in the iteration loop in order to take alternative lens geometries into account. The iteration may result in a three-dimensional shape of the lens.

In a further embodiment, a shape of the lens can be predetermined and instead a spatial refractive index distribution within the lens can be determined iteratively analogously.

One or more sizes can subsequently be determined from the determined three-dimensional shape (possibly including the refractive index). In step S1052 can calculate a use value, in particular a user-specific use value become. You can do this in step S1051 carrier-specific data are provided, such as a distance from the cornea to the apex. In step S1053 an ISO vertex refractive index can be determined. In step S1054 a peak power can be determined in a device configuration.

If several lenses or glasses were arranged in the measurement volume at the same time, additional parameters such as e.g. the distance between the progression channels can be determined.

It goes without saying that the above-mentioned steps can be carried out by the computing unit and this can be set up accordingly to carry out the steps.

wobei (x₀, y₀, 0) einen Punkt des Lichtstrahls einer Bezugsebene der Bilderfassungseinrichtung, vorzugsweise einen Punkt des Lichtstrahls einer Bezugsebene im Linsensystem einer Kamera der Bilderfassungseinrichtung beschreibt und (dx, dy, 1) den Richtungsvektor des einfallenden Strahles. Folglich besteht der Funktionensatz aus den vier Funktionen x₀(x,y), y₀(x,y), dx(x,y) und dy(x,y), wobei x und y die Pixelkoordinaten in Bilddaten der Bilderfassungseinrichtung, hier einer Kamera, beschreiben. 11 10 shows a flow diagram of an exemplary embodiment of a method 1100 for calibrating a device for measuring individual data of an optical lens arranged in a measuring volume. The calibration can in particular serve to provide a function set which assigns a beam direction, such as a 3D vector, to a - preferably each - pixel of the image data captured by the image capture device, which describes a beam direction or a light beam that penetrates into the image capture device. Such a function set can look like this: $$\overrightarrow{r}\left(x.y\right)=\left(\begin{array}{c}{x}_0\\ y_0\\ 0\end{array}\right)+\alpha \left(\begin{array}{c}dx\\ dy\\ 1\end{array}\right).$$

where (x ₀ , y ₀ , 0) describes a point of the light beam of a reference plane of the image capturing device, preferably a point of the light beam of a reference plane in the lens system of a camera of the image capturing device and (dx, dy, 1) describes the direction vector of the incident beam. Consequently, the function set consists of the four functions x ₀ (x, y), y ₀ (x, y), dx (x, y) and dy (x, y), where x and y are the pixel coordinates in image data of the image capture device, here a camera.

Such a set of functions can be determined by displaying a test structure, for example a dot pattern, on the display device and viewing it at different distances with the cameras of the image capture device. For this purpose, the device, as in 8th illustrated by way of example, a height adjustment device 150 which is set up to vary a distance between the image capture device and the display device.

At the in 11 The procedure shown can include the steps S1101 to S1104 the steps described above S1011 to S1014 in 10 correspond. In the 11 shown steps S1111 to S1113 can each follow the steps described above S1021 to S1023 correspond. In addition, however, a loop is provided, whereby in step S1121 a distance between the image capture device and the display device is varied. As in 8th shown, a direction of the incident light rays changes by varying the distance. The computing unit can be set up to determine a direction of the incident light beams based on the image data captured at the first distance and the image data captured at the second distance. It goes without saying that the determination can also be based on a relative position between the display device and the image capture device and the variation of the distance.

As in 11 shown can in one step S1131 an interpolation of 3D light beams from a plurality of, preferably for each pixel or pixel of the image capture device. The following can be done in step S1132 a determination of the sizes x ₀ . y ₀ , dx and dy can be made for the pixels. In a next step S1133 can fit a polynomial to the sizes x ₀ . y ₀ , dx and dy. As a result, a function set can be determined which assigns a direction of an incident light beam to each pixel of the image data captured by the image capturing device.

Optionally, analogous to camera calibration, a spatial position of a support point can be used 51 as exemplified in 8th represented, determined. For this, the display device 20 be set up to display a monochrome or background with constant brightness as the test structure. The image capture device captures the display without an inserted lens. In this case, the support points lead to a shadow cast (for example a circle in the case of support balls), which is captured by the image capture device and is contained in the image data. For this purpose, the computing unit can be designed based on this image data a position of the support points 51 to determine. These can in turn be taken into account as boundary conditions when determining a three-dimensional shape of a lens. When looking at a support point of at least two cameras, its central point (the location) can be determined by cutting the camera beams. The position of the support points can be used to assign an algorithm that determines the shape of the spectacle lens an expected value for its position in the measurement volume. An advantage of this configuration is improved accuracy.

It is understood that the above explanations for the following exemplary embodiments can apply accordingly and vice versa. In order to avoid repetitions, the following section will deal in particular with further aspects. Features of the above and subsequent exemplary embodiments can advantageously be combined with one another.

The inventors have recognized that the concepts described here can also be used advantageously for cornea measurement. 12 shows a schematic sectional view of an eye 1200 , The eye has a cornea or cornea 1201 , an iris 1202 , a pupil 1203 and the lens 1204 on. 13 shows a top view of the eye with an image of the iris 1202 and the pupil 1203 , However, the lens does not make a significant contribution to ametropia 1204 but from the cornea 1201 , A major contribution to a subject's ametropia can be due to astigmatism. It is therefore desirable to be able to objectively determine a shape of the cornea.

14 shows a schematic representation of a device for cornea measurement of a subject according to a further aspect of the present disclosure. The device can have the following: 30 ) set up for capturing image data of an iris ( 1202 ) of the subject from several (known) points of view through imaging beam paths ( 32 ) which the cornea ( 1201 ) push through; and a computing unit ( 40 ). The computing unit is set up for: providing a mathematical model of a front section of the subject's eyes with a mathematical model of the cornea and iris; Identifying and registering image features of the iris that are present in several images of the image data; Determining deviations between actual positions of the image features of the iris in the images acquired from a plurality of viewpoints and expected positions of the image features of the iris in the images acquired from a plurality of viewpoints, taking into account the mathematical model of the cornea and the position of the iris; Adapting parameters of the mathematical model of the cornea in such a way that the deviations are minimized; and determining a measured variable of the cornea from the adapted mathematical model of the cornea.

The image capture device 30 can again be configured the same or similar as for 1 describe. The image capture device captures image data of the iris 1202 , with the ray paths through the cornea 1201 pass. A camera can be used to capture the image data from various known viewpoints 33 can be positioned successively at different known positions. A positioning device (not shown) can be used for this. Alternatively or additionally, multiple cameras can be used 33 . 34 be provided, which capture the image data in parallel. One advantage of parallel detection is that the user's eye does not move between the different measurements.

The inventors have recognized that there is a difference between the iris 1202 and the image capture device 30 lying cornea 1201 even without knowing the appearance of the iris 1202 can be calculated. The iris points 1202 an unknown structure or pattern. However, the iris 1202 usually highly structured. The inventors have recognized that a large number of image features of the iris can be identified and subsequently evaluated for their position in a plurality of images of the image data recorded from different positions. For this, from the imaging beam paths 32 , which are recorded at the respective known positions, an equation system can be set up, from which the shape of the cornea 1201 can be calculated.

15 and 16 show the assignment or correlation of unknown image features in images of the iris taken from different points of view. The left picture in 15 shows a first the iris 1202 - Through the cornea - from a first position, for example taken with the camera 33 in 14 , The right picture in 16 shows a second the iris 1202 - Through the cornea - from a second position, for example taken with the camera 34 in 14 , Since the iris is usually a strictly structured surface, a correlation can be made 1502 between the same starting points 1501a and 1501b the iris 1201 be determined. Another example of corresponding points is by reference numerals 1503a and 1503b connected by 1502 '. Such an assignment 1500 can be used for a variety of images 1500a to 1500d and pixels are made as in 16 shown.

Based on this correlation or assignment analysis, a large number of beam paths can be reconstructed, as in 14 shown. As from the beam paths shown 32 As can be seen, the light rays emanate from the same pixel on the iris 1202 at different points through the cornea 1201 through and are at different locations by the image capture device 30 detected. If an identical starting point is now identified in the illustrations, statements can be made about the starting point on the iris 1202 and entering the cameras 33 . 34 lying cornea 1201 as above with reference to 14 described.

17 shows a flow diagram of an embodiment of a method for corneal measurement of a subject. The camera system can be calibrated in an optional upstream step. However, the calibration can already be done by the manufacturer. In a first step 1701 Image data of an iris of the test subject can be acquired from several points of view by means of imaging beam paths which penetrate the cornea. In a second step 1702 For example, a mathematical model of an anterior segment of the subject can be provided with a mathematical model of the cornea (and the position of the iris relative to the cornea). In a third step 1703 image features of the iris, which are present in several (preferably all) images of the image data, can be identified and registered (or assigned in the images). In a fourth step 1704 deviations between the actual positions of the image features of the iris in the images acquired from several viewpoints and the expected positions of the image features of the iris in the images acquired from multiple viewpoints can be determined taking into account the mathematical model of the cornea and the position of the iris. In a fifth step 1705 parameters of the mathematical model of the cornea can be adjusted so that the deviations are minimized. The steps 1703 and 1704 can preferably be repeated iteratively. In a sixth step, a measured variable of the cornea can now be determined from the adapted mathematical model of the cornea. For example, a refractive power or an astigmatism can be evaluated.

In summary, the solutions disclosed herein in the field of ophthalmic optics can enable, in particular, simplified non-contact measurement of lens elements arranged in a measurement volume or also non-contact measurement of the cornea, in particular with reduced impairment of a light-sensitive user.

Claims (15)

Device (1) for measuring a subject's cornea, the device comprising: - an image capturing device (30) set up for capturing image data of an iris (1202) of the subject from a plurality of viewpoints through imaging beam paths which penetrate the cornea (1201); and - a computing unit (40), the computing unit being set up to: - Providing a mathematical model of an anterior segment of the subject with a mathematical model of the cornea (1201) and iris (1202) (1702); - Identifying and registering image features (1501a, b; 1503a, b) of the iris (1202) which are present in several images (1500a-d) of the image data (1703); - determining deviations between actual positions of the image features of the iris in the images acquired from several viewpoints and expected positions of the image features of the iris in the images acquired from multiple viewpoints, taking into account the mathematical model of the cornea and the position of the iris (1704); - Adapting parameters of the mathematical model of the cornea in such a way that the deviations are minimized (1705); and - Determination of a measured variable of the cornea from the adapted mathematical model of the cornea (1706). Device after Claim 1 , characterized in that the image capture device (30) has a camera array (33, 34) for capturing image data of the subject's iris from a plurality of viewpoints. Device according to one of the preceding claims, characterized in that the computing unit (40) is set up to identify the image features of the iris (1202) on the basis of a correlation analysis between images (1500a-d) of the image data. Device according to one of the preceding claims, characterized in that one of the parameters of the mathematical model of the cornea is a shape of the cornea (1201) and the computing unit is set up to adapt the shape of the cornea; and / or one of the parameters of the mathematical model of the cornea is a refractive power distribution of a front and / or back surface; and the computing unit (40) is set up to adapt the refractive power distribution. Device according to one of the preceding claims, characterized by a measuring device for recording measurement data of a front surface of the cornea, in particular a deflectometric measuring device; and wherein the mathematical model of the cornea is further provided or adapted based on the acquired measurement data of the front surface of the cornea (1201). Device after Claim 5 , characterized in that the measuring device is set up to determine an orientation, in particular a surface normal, in at least one point on the front surface of the cornea (1201). Device according to one of the preceding claims, characterized in that the Computing unit (40) is set up to model the iris as a two-dimensional plane. Device according to one of the preceding claims, characterized in that the mathematical model models a circular iris edge. Device according to one of the preceding claims, characterized in that the computing unit (40) is also set up to carry out a deflectometric analysis of reflections from an environment on the eye and to take this into account when determining the mathematical model of the cornea. Device according to one of the preceding claims, characterized in that the computing unit (40) is set up to determine a refractive index of the cornea. Device according to one of the preceding claims, characterized in that the computing unit (40) is set up to carry out calculations using photometric measurements. Device according to one of the preceding claims, characterized by an illumination device, configured to illuminate the iris (1202). Device after Claim 12 , characterized in that the lighting device is set up for projecting a pattern onto the iris (1202). Method (1700) for cornea measurement of a subject, the method comprising the following steps: - Acquisition of image data of an iris of the test subject from several points of view by imaging beam paths which penetrate the cornea (1701); and - Providing a mathematical model of an anterior segment of the subject with a mathematical model of the cornea and the position of the iris relative to the cornea (1702); - Identifying and registering image features (1501a, b; 1503a, b) of the iris which are present in several images of the image data (1703); - Determining deviations between actual positions of the image features (1501a, b; 1503a, b) of the iris (1202) in the images (1500a-d) acquired from multiple viewpoints and expected positions of the image features of the iris in the images acquired from multiple viewpoints below Consideration of the mathematical model of the cornea (1201) and the position of the iris (1202) (1704); - Adapting parameters of the mathematical model of the cornea in such a way that the deviations are minimized (1705); and - Determination of a measured variable of the cornea from the adapted mathematical model of the cornea (1706). A computer program product comprising instructions that cause the computer to execute the program following the method (1700) Claim 14 perform.

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