# US 10,441,168 B2 · Computer-implemented method for detecting a corneal vertex

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- Number: US 10,441,168 B2
- Document ID: US10441168B2
- Status: Granted
- Kind: B2
- Application number: 15/881,367
- Filed: 2018-01-26
- Published: 2018-08-02
- Granted: 2019-10-15
- Earliest claimed: 2017-01-27
- Assignees: Carl Zeiss Vision International GmbH; Carl Zeiss AG
- Applicants: Carl Zeiss Vision International GmbH; Carl Zeiss AG
- Inventors: Claudia Nieuwenhuis; Oliver Schwarz; Michael Gamperling
- Web page: https://patentgrep.com/patent/US10441168B2

## CPC

- A61B 3/14: Arrangements specially adapted for eye photography
- G06T 7/73: using feature-based methods
- A61B 3/10: Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
- A61B 3/1005: {for measuring distances inside the eye, e.g. thickness of the cornea (A61B3/11 takes precedence)}
- A61B 3/107: for determining the shape or measuring the curvature of the cornea
- G02C 13/003: {Measuring during assembly or fitting of spectacles}
- G02C 13/005: {Measuring geometric parameters required to locate ophtalmic lenses in spectacles frames (apparatus for testing or instruments for examining the eyes per se A61B3/00; machines or devices and accessories for grinding the edges of lenses using spectacles as a template B24B9/144)}
- A61B 3/111: {for measuring interpupillary distance}
- G01M 11/0207: {Details of measuring devices}
- G02C 7/061: {Spectacle lenses with progressively varying focal power}
- G02C 2202/22: Correction of higher order and chromatic aberrations, wave front measurement and calculation
- G06T 2207/30041: Eye; Retina; Ophthalmic
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G02C: SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES (trial frames for testing the eyes A61B3/04; goggles or eyeshields not having the same features as spectacles A61F9/00)
- G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR

## Abstract

A computer-implemented method detects the position of a corneal vertex of an eye from a frontal image of a head and a lateral image of the head. The front and lateral images are calibrated to one another, and the position of the corneal vertex in space is determined from the frontal image and the lateral image with a geometric position determination.

## Claims

### Claim 1

A computer-implemented method for detecting a position of a corneal vertex, the method comprising:
recording a frontal image of a head and a lateral image of the head,
calibrating the frontal image and the lateral image to one another,
determining a position of a corneal vertex in space from the frontal image and the lateral image with a geometric position determination, the geometric position determination including:
determining a position of the corneal vertex in space to a first approximation as the point of intersection q of:
a first view ray, tangential to the cornea, from a lateral camera recording the lateral image, with
a second view ray, directed onto the pupil, from a frontal camera recording the frontal image,
detecting at least one of a position of a pupil or detecting a position of a reflection point of a flash,
producing the flash when recording the frontal image and the lateral image and the position of the corneal vertex in space is determined to the first approximation as a position of the reflection point of the flash on the cornea, and
detecting the position of the pupil or detecting the position of the reflection point by performing at least one of:
extracting a feature, matching a feature, or comparing by machine learning a plurality of data known in advance.

### Claim 2 (depends on 1)

The computer-implemented method according to claim 1, further comprising:
selecting the frontal image and the lateral image to not overlap or selecting only mutually non-overlapping regions of the frontal image and the lateral image to detect the position of the corneal vertex.

### Claim 3

A computer-implemented method for detecting a position of a corneal vertex, the method comprising:
recording a frontal image of a head and a lateral image of the head,
calibrating the frontal image and the lateral image to one another, and
determining a position of a corneal vertex in space from the frontal image and the lateral image with a geometric position determination, the geometric position determination including:
selecting the frontal image and the lateral image to not overlap or selecting only mutually non-overlapping regions of the frontal image and the lateral image to detect the position of the corneal vertex.

### Claim 4 (depends on 1)

The computer-implemented method according to claim 1, wherein a view ray of the frontal camera directed to the corneal vertex is calculated from the frontal image and the view ray is projected into the lateral image, and wherein the position of the corneal vertex is detected on the view ray that is projected into the lateral image.

### Claim 5

A computer-implemented method for detecting a position of a corneal vertex, the method comprising:
recording a frontal image of a head and a lateral image of the head,
calibrating the frontal image and the lateral image to one another, and
determining a position of a corneal vertex in space from the frontal image and the lateral image with a geometric position determination, wherein a view ray of the frontal camera directed to the corneal vertex is calculated from the frontal image and the view ray is projected into the lateral image, and wherein the position of the corneal vertex is detected on the view ray that is projected into the lateral image.

### Claim 6 (depends on 1)

The computer-implemented method according to claim 1, wherein the geometric position determination includes a triangulation method.

### Claim 7 (depends on 1)

The computer-implemented method according to claim 1, further comprising:
performing a correction calculation of the position of the corneal vertex.

### Claim 8 (depends on 3)

The computer-implemented method according to claim 3, further comprising:
determining a position of the corneal vertex in space to a first approximation as the point of intersection q of:
a first view ray, tangential to the cornea, from a lateral camera recording the lateral image, with
a second view ray, directed onto the pupil, from a frontal camera recording the frontal image.

### Claim 9 (depends on 7)

The computer-implemented method according to claim 7, wherein the correction calculation comprises:
calculating the position of the corneal vertex according to a=q+μ*v+μ*w, wherein a denotes the position vector of the corneal vertex in space after carrying out the correction calculation, q denotes the position of the corneal vertex to a first approximation, μ denotes an empirical value or an actual value for the distance between a pupil center and the corneal vertex, v denotes a unit vector in the spatial direction from the pupil center to the frontal camera and w denotes a unit vector in the viewing direction extending through the center of a corneal sphere.

### Claim 10 (depends on 1)

The computer-implemented method according to claim 1, wherein the flash is produced when recording the images, and wherein the position of the corneal vertex in space is determined to a first approximation as the position of the reflection point of the flash on the cornea.

### Claim 11 (depends on 7)

The computer-implemented method according to claim 7, wherein the correction calculation comprises:
calculating the position of the corneal vertex in the horizontal direction proceeding from the reflection point by adding Δx=+/−r*sin (½*(arccos z/a+arctan x/(z−v))) to the x-coordinate, wherein r denotes an empirical value or an actual value for the corneal radius, a denotes the distance between the optical center of the frontal camera recording the frontal image and the reflection point, x and z denote the x- and z-coordinates of the reflection point in a coordinate system with the origin at the optical center of the frontal camera, wherein the viewing direction of the frontal camera corresponds to the z-direction and the x-direction is horizontally orthogonal to the z-direction and, when observed in the z-direction, points to the right, and v denotes the distance between the light source producing the flash and the optical center of the frontal camera in the z-direction.

### Claim 12 (depends on 7)

The computer-implemented method according to claim 7, wherein the correction calculation comprises:
calculating the position of the corneal vertex in the y-direction proceeding from the reflection point by adding Δy=+/−r*sin ½*(arctan l/(d−v)), wherein r denotes an empirical value or an actual value for the corneal radius, d denotes the distance between the optical center of the frontal camera and the reflection point in the z-direction, v denotes the distance between the light source producing the flash and the optical center of the frontal camera in the z-direction and l denotes the distance between the light source and the optical center of the frontal camera in the y-direction, wherein the y-direction is orthogonal to the x-direction and to the z-direction and points upward in space.

### Claim 13

A computer-implemented method for detecting a position of a corneal vertex, the method comprising:
recording a frontal image of a head and a lateral image of the head,
calibrating the frontal image and the lateral image to one another,
determining a position of a corneal vertex in space from the frontal image and the lateral image with a geometric position determination, the geometric position determination including:
determining a position of the corneal vertex in space to a first approximation as the point of intersection q of:
a first view ray, tangential to the cornea, from a lateral camera recording the lateral image, with
a second view ray, directed onto the pupil, from a frontal camera recording the frontal image, and
calculating the position of the corneal vertex according to a=q+μ*v+μ*w, wherein a denotes the position vector of the corneal vertex in space after carrying out the correction calculation, q denotes the position of the corneal vertex to a first approximation, μ denotes an empirical value or an actual value for the distance between a pupil center and the corneal vertex, v denotes a unit vector in the spatial direction from the pupil center to the frontal camera and w denotes a unit vector in the viewing direction extending through the center of a corneal sphere.

### Claim 14

A computer-implemented method for detecting a position of a corneal vertex, the method comprising:
recording a frontal image of a head and a lateral image of the head,
calibrating the frontal image and the lateral image to one another,
determining a position of a corneal vertex in space from the frontal image and the lateral image with a geometric position determination, the geometric position determination including:
performing a correction calculation of the position of the corneal vertex,
detecting a position of a reflection point of a flash,
producing the flash when recording the frontal image and the lateral image and the position of the corneal vertex in space is determined to the first approximation as a position of the reflection point of the flash on the cornea, and performing at least one of:
calculating the position of the corneal vertex in the horizontal direction proceeding from the reflection point by adding Δx=+/−r*sin (½*(arccos z/a+arctan x/(z−v))) to the x-coordinate, wherein r denotes an empirical value or an actual value for the corneal radius, a denotes the distance between the optical center of the frontal camera recording the frontal image and the reflection point, x and z denote the x- and z-coordinates of the reflection point in a coordinate system with the origin at the optical center of the frontal camera, wherein the viewing direction of the frontal camera corresponds to the z-direction and the x-direction is horizontally orthogonal to the z-direction and, when observed in the z-direction, points to the right, and v denotes the distance between the light source producing the flash and the optical center of the frontal camera in the z-direction; or
calculating the position of the corneal vertex in the y-direction proceeding from the reflection point by adding Δy=+/−r*sin ½*(arctan l/(d−v)), wherein r denotes an empirical value or an actual value for the corneal radius, d denotes the distance between the optical center of the frontal camera and the reflection point in the z-direction, v denotes the distance between the light source producing the flash and the optical center of the frontal camera in the z-direction and l denotes the distance between the light source and the optical center of the frontal camera in the y-direction, wherein the y-direction is orthogonal to the x-direction and to the z-direction and points upward in space.

### Claim 15 (depends on 3)

The computer-implemented method according to claim 3, further comprising:
extracting a feature, matching a feature, or comparing by machine learning a plurality of data known in advance.

### Claim 16 (depends on 1)

The computer-implemented method according to claim 1, wherein a view ray of the frontal camera directed to the corneal vertex is calculated from the frontal image and the view ray is projected into the lateral image, and wherein the position of the corneal vertex is detected on the view ray that is projected into the lateral image.

### Claim 17 (depends on 1)

The computer-implemented method according to claim 1, further comprising:
recording at least one further calibrated lateral image from a lateral position in respect of the head at the same time as the frontal image and the lateral image.

### Claim 18 (depends on 4)

The computer-implemented method according to claim 4, further comprising:
selecting the frontal image and the lateral image to not overlap or selecting only mutually non-overlapping regions of the frontal image and the lateral image to detect the position of the corneal vertex.

### Claim 19 (depends on 1)

The computer-implemented method according to claim 1, wherein a recording direction of the frontal image includes an angle of more than 60 and up to 120 degrees with the recording direction of the lateral image and, optionally, with the recording direction of the further lateral image.

### Claim 20 (depends on 1)

The computer-implemented method according to claim 1, wherein the position of the corneal vertex is determined to calculate a vertex distance of a spectacle frame or a spectacles-wearing subject.

### Claim 21 (depends on 1)

A computer program with program code for carrying out the method steps according to claim 1 when the computer program is loaded onto a computer and/or executed on a computer.

### Claim 22 (depends on 1)

An apparatus for carrying out the computer-implemented method according to claim 1, the apparatus comprising:
a camera carrier, which partly encloses an interior that is open to a top, to a bottom and to a rear side, the camera carrier including:
at least three cameras, which are arranged between two free ends of the camera carrier and directed onto the interior, and
an illumination device for illuminating the interior.

### Claim 23 (depends on 21)

A computer, comprising a memory, wherein the computer program according to claim 21 is stored in the memory, and a processor for executing the computer program stored in the memory.

### Claim 24 (depends on 23)

The computer according to claim 23, wherein the processor is configured to provide a frontal image of a head and a lateral image of the head, the images being calibrated to one another, and to determine the position of the corneal vertex in space from the frontal image and the lateral image by means of a geometric position determination.

### Claim 25 (depends on 21)

An apparatus for detecting a position of a corneal vertex comprising:
a frontal camera for recording a frontal image,
a lateral camera for recording a lateral image, and
a computer, which has a memory in which the computer program according to claim 21 is stored, and the computer having a processor configured to execute the computer program stored in the memory.

### Claim 26 (depends on 1)

A method for centering at least one spectacle lens in a spectacle frame, wherein, in a first method step, the position of at least one corneal vertex in space is detected using the method according to claim 1,
wherein, in a second method step, at least one centration parameter is determined using the position of the at least one corneal vertex in space, and
wherein, in a third method step, the at least one spectacle lens is centered in the spectacle frame using the centration parameter or parameters determined in the second method step.

### Claim 27 (depends on 1)

A method for grinding at least one spectacle lens into a spectacle frame, wherein, in a first method step, the position of at least one corneal vertex in space is detected using the method according to claim 1,
wherein, in a second method step, at least one centration parameter is determined using the position of the at least one corneal vertex in space, and
wherein, in a third method step, the at least one spectacle lens is ground in the spectacle frame on the basis of the centration parameter or parameters determined in the second method step for an arrangement.

### Claim 28 (depends on 27)

A method for producing a spectacle lens, comprising:
grinding at least one spectacle lens into a spectacle frame according to claim 27.

### Claim 29 (depends on 27)

A method for producing spectacles, comprising:
grinding at least one spectacle lens into a spectacle frame according to claim 27.