U.S. patent application number 17/327344 was filed with the patent office on 2021-10-21 for method and device for measuring an optical lens for individual wearing situations by a user.
The applicant listed for this patent is Carl Zeiss Vision International GmbH. Invention is credited to Carsten Glasenapp.
Application Number | 20210325276 17/327344 |
Document ID | / |
Family ID | 1000005692950 |
Filed Date | 2021-10-21 |
United States Patent
Application |
20210325276 |
Kind Code |
A1 |
Glasenapp; Carsten |
October 21, 2021 |
METHOD AND DEVICE FOR MEASURING AN OPTICAL LENS FOR INDIVIDUAL
WEARING SITUATIONS BY A USER
Abstract
An apparatus for measuring a cornea of a subject contains an
image capturing device configured to capture image data of an iris
of the subject from a plurality of viewpoints by imaging beam paths
which pass through the cornea and a computing unit for providing a
mathematical model of an anterior eye section of the subject
including a mathematical model of the cornea and the iris. The
model further identifies and registers image features of the iris,
which are present in a plurality of images of the image data;
determines deviations between actual positions of the image
features of the iris in the images captured from the plurality of
viewpoints and expected positions of the image features of the iris
in the images captured from the plurality of viewpoints in
consideration of the mathematical model of the cornea and the
position of the iris.
Inventors: |
Glasenapp; Carsten;
(Oberkochen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carl Zeiss Vision International GmbH |
Aalen |
|
DE |
|
|
Family ID: |
1000005692950 |
Appl. No.: |
17/327344 |
Filed: |
May 21, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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17074710 |
Oct 20, 2020 |
11099100 |
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17327344 |
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PCT/EP2019/060346 |
Apr 23, 2019 |
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17074710 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02C 7/024 20130101;
G01M 11/0264 20130101; G01M 11/0214 20130101 |
International
Class: |
G01M 11/02 20060101
G01M011/02; G02C 7/02 20060101 G02C007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2018 |
EP |
18 168 823.5 |
Claims
1. An apparatus for measuring a cornea of a subject, the apparatus
comprising: an image capturing device configured to capture image
data of an iris of the subject from a plurality of viewpoints by
imaging beam paths which pass through the cornea; and a computing
unit configured to: provide a mathematical model of an anterior eye
section of the subject including a mathematical model of the cornea
and the iris; identify and register image features of the iris,
which are present in a plurality of images of the image data;
determine deviations between actual positions of the image features
of the iris in the images captured from the plurality of viewpoints
and expected positions of the image features of the iris in the
images captured from the plurality of viewpoints in consideration
of the mathematical model of the cornea and the position of the
iris; adapt parameters of the mathematical model of the cornea so
as to minimize the deviations; and determine a metric of the cornea
from the adapted mathematical model of the cornea.
2. The apparatus as claimed in claim 1, wherein the computing unit
is configured to evaluate a refractive power or an astigmatism from
the adapted mathematical model of the cornea.
3. The apparatus as claimed in claim 1, wherein the mathematical
model comprises a relative position of the iris with respect to the
cornea.
4. The apparatus as claimed in claim 1, wherein the apparatus is
configured to calculate the cornea situated between the iris and
the image capturing device without prior knowledge about how the
iris looks.
5. The apparatus as claimed in claim 1, wherein the apparatus is
configured to perform a correlation of previously unknown image
features in images of the iris recorded from different
viewpoints.
6. The apparatus as claimed in claim 1, wherein the computing unit
is configured to calculate the shape of the cornea based on a
system of equations from imaging beam paths which are captured at
the respective known positions.
7. The apparatus as claimed in claim 1, wherein the image capturing
device comprises: a first camera configured to capture first image
data from a first viewpoint; and a second camera configured to
capture second image data from a second viewpoint, wherein the
computing unit is configured to determine the three-dimensional
shape of the cornea on the basis of the first image data and the
second image data.
8. The apparatus as claimed in claim 1, wherein the computing unit
is configured to iteratively determine the three-dimensional shape
of the cornea with an integration method.
9. The apparatus as claimed in claim 1, wherein the computing unit
is configured to determine the three-dimensional shape of the
cornea on a basis of back tracing the respective imaging beam paths
entering the image capturing device.
10. The apparatus as claimed in claim 1, wherein the computing unit
is configured to determine the three-dimensional shape of the
cornea by dividing at least one of a front surface or a back
surface of the cornea into surface elements and to determine an
alignment of the surface elements.
11. The apparatus as claimed in claim 10, wherein the computing
unit is configured to determine a three-dimensional shape of the
front surface and the back surface of the cornea on the basis of
the alignment of the surface elements.
12. The apparatus as claimed in claim 1, wherein the computing unit
is configured to determine the three-dimensional shape of the
cornea taking account of a boundary condition that a front surface
or a back surface of the cornea has a parameterizable area.
13. The apparatus as claimed in claim 12, wherein the
parameterizable area includes a sphere, a section of the sphere, a
torus, or a section of the torus.
14. The apparatus as claimed in claim 1, wherein the computing unit
is further configured to determine the three-dimensional shape of
the cornea taking account of one or more known contact points of
the cornea.
15. The apparatus as claimed in claim 1, wherein the computing unit
is configured to determine a spatial refractive index distribution
of the cornea to be measured.
16. A method for measuring the cornea of a subject, the method
comprising the steps of: capturing image data of an iris of the
subject from a plurality of viewpoints by imaging beam paths which
pass through the cornea; providing a mathematical model of an
anterior eye section of the subject including a mathematical model
of the cornea and the iris; identifying and registering image
features of the iris, which are present in a plurality of images of
the image data; determining deviations between actual positions of
the image features of the iris in the images captured from the
plurality of viewpoints and expected positions of the image
features of the iris in the images captured from the plurality of
viewpoints in consideration of the mathematical model of the cornea
and the position of the iris; adapting parameters of the
mathematical model of the cornea so as to minimize the deviations;
and determining a metric of the cornea from the adapted
mathematical model of the cornea.
17. The method of claim 16, further comprising a preceding step of
calibrating the camera system for capturing the image date of the
iris from the plurality of viewpoints.
18. A computer program product being stored on a non-transitory
storage medium and comprising instructions that, upon execution of
the program by a computer, cause the computer to perform the method
of claim 16.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 17/074,710, filed Oct. 20, 2020, which
is a continuation application of international patent application
PCT/EP2019/060346, filed Apr. 23, 2019, designating the United
States and claiming priority from European patent application EP
18168823.5, filed Apr. 23, 2018, and the entire content of all
three applications is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to the field of ophthalmic
optics and, in particular, an apparatus for measuring the optical
effect of an optical lens, in particular a spectacle lens, arranged
in a measurement volume. The present disclosure further relates to
an apparatus for measuring a spatial refractive index distribution
of an optical lens, in particular a spectacle lens, arranged in a
measurement volume. The present disclosure further relates to a
method for calibrating a corresponding apparatus and a
computer-implemented method for measuring the optical effect of an
optical lens arranged in a measurement volume.
BACKGROUND
[0003] The measurement value usually of interest in the case of
spectacle lenses is the vertex power (VP). The vertex power is an
effective variable of the lens under certain observation
situations. Consequently, the VP differs, depending on the distance
to the observer or the lens tilt. A measurement appliance which
ascertains a VP by way of a direct interpretation of the light
beams passing through a lens will always determine a VP in this
measurement appliance configuration. Such effective variables only
have a limited use for an unambiguous qualification of a component.
Therefore, the ISO VP was defined to remedy this. The ISO VP is the
VP measured perpendicular to the surface normal in the case of a
parallel incidence of light. To this end, specific measurement
appliances have been developed in the past, which determine the ISO
VP at individual positions of a lens.
[0004] The advantage of the ISO VP is that it is a unique component
variable and not an effective variable like the VP. A disadvantage
is that the ISO VP can deviate from the effect of a pair of
spectacles in the worn situation (also referred to as the worn
vertex power or worn value).
[0005] A lensmeter with a spectacles installation for checking
ready glazed spectacles is known from DE 1 238 690 B1. Using this,
it is possible to determine the vertex power of a spectacle lens
already set in a frame.
[0006] EP 2 101 143 A1 discloses a method and an apparatus for
capturing the shape of transparent refractive objects. In the
method for capturing the shape of transparent refractive objects,
the object to be measured is inserted in transmission into an
imaging system. Using the modified imaging system created in this
way, a grid with a known structure is imaged onto a receiver device
and the arising image is evaluated. Use is made of planar grids
with known structures, the grid points of which are assigned to
evaluable spatial coordinates in grid coordinate systems. One or
more of these planar grids is inserted at least at two different
positions with respect to the object to be measured.
[0007] US 2016/0109362 A1 discloses a method and apparatus for
determining a local refractive index.
[0008] Knauer et al., "Measuring the refractive power with
deflectometry in transmission," DGaO Proceedings, 2008, describes a
deflectometric method for determining the refractive power.
[0009] WO 2017/134275 A1 describes methods and systems for
determining an optical axis and/or physical properties of a lens
and the use of same in virtual imaging and in the case of
head-mounted display devices.
[0010] WO 2016/207412 A1 discloses an apparatus and a method for
measuring individual data of spectacles arranged in a measurement
position, the spectacles having a left and/or a right spectacle
lens. The apparatus comprises a display for displaying a test
structure. The apparatus comprises an image capturing device for
capturing the test structure with an imaging beam path that passes
through the left spectacle lens and/or the right spectacle lens of
the spectacles. The apparatus comprises a computer unit with a
computer program which determines a refractive power distribution
for at least a section of the left spectacle lens and/or the right
spectacle lens from the image of the test structure captured by the
image capturing device and a known spatial orientation of the
display relative to the image capturing device and also a known
spatial orientation of the spectacles relative to the image
capturing device.
[0011] DE 10 2013 219 838 A1 discloses a method and system for
ascertaining the spatial structure of an object. DE 10 2014 005 281
A1 discloses a method and an apparatus for determining the position
of at least one spectacle lens in space. DE 10 2011 089 704 A1
discloses storage of information on a spectacle lens, spectacle
lens blank or spectacle lens semifinished product.
[0012] The appliances known from the related art are effect
measuring appliances, in which the effect of an optical element is
initially determined in one measurement position.
SUMMARY
[0013] The claimed subject matter is defined in the appended
independent claims. Further refinements are provided in the
dependent claims.
[0014] Against this background, it is an object of the present
disclosure to provide a measurement apparatus which facilitates a
more flexible determination of the optical effect of an optical
lens.
[0015] According to a first aspect of the present disclosure, it is
therefore proposed to provide an apparatus for measuring the
optical effect of an optical lens, in particular the spectacle lens
arranged in a measurement volume, comprising a display device which
is configured to display a test structure; an image capturing
device which is configured to capture image data of the test
structure from a plurality of viewpoints by way of imaging beam
paths which pass through the lens; and a computing unit, wherein
the computing unit is configured to determine a three-dimensional
shape of the lens on the basis of the image data; and calculate an
optical effect of the lens on the basis of the three-dimensional
shape thereof. The lens can be a spectacle lens. The computing unit
can be configured to calculate the optical effect of the spectacle
lens for a specified wearing position of a user, which differs from
the measurement position in which the image data are captured.
[0016] Compared to conventional lensmeters, substantial advantages
of the disclosure may consist in an improved unambiguousness and/or
range of application, in particular. A reason for this is that the
optical effect of a lens always depends on the direction of passing
radiation. A measuring appliance which only measures the optical
effect can only determine the latter reliably for the case of the
measurement arrangement. Very precise statements can already be
made herewith for a multiplicity of applications.
[0017] However, a measurement situation and an actual wearing
situation or wearing position of a spectacle lens might not
coincide or might deviate from one another to such an extent that a
reliable statement is no longer possible. Thus, a further
measurement of the effect under wearing conditions would be
required to determine the optical effect in the wearing
position.
[0018] The solution according to the disclosure follows a different
approach: A two-stage procedure is proposed, in which the
three-dimensional shape of the lens is initially determined and
only then is the optical effect of the lens calculated. A known
three-dimensional shape or topography of the lens allows the
optical effect to be calculated subsequently for any viewing or
wearing situation. Advantages can comprise, in particular, more
accurate results and more individualized statements for a wide
range of user-specific requests.
[0019] The display unit displays a test structure. The test
structure is captured by the image capturing device from a
plurality of viewpoints. Since the test structure is known, an
association can be made between image data of the test structure
captured by the image capturing device for each of the plurality of
viewpoints. If an optical lens is now placed into a measurement
volume between the display device and the image capturing device,
the beam paths between the respective pixels of the image data and
the corresponding image elements of the test structure are
influenced.
[0020] However, in the process, it is not possible to determine
only a single virtual refractive plane, as indicated in WO
2016/207412 A1. By virtue of image data being captured from a
plurality of viewpoints in accordance with the proposed solution,
with the imaging beam paths passing through the lens, it is
possible, in particular, to make separate statements about a shape
of a front surface, through which beam paths emanating from the
test structure enter into the optical lens, and statements about a
shape of a back surface, via which beam paths emanating from the
test structure emerge from the optical lens. Thus, a system of
equations with a multiplicity of equations can be set up to this
end, on the basis of which there can then be a reconstruction of
the surfaces lying in the beam path. The three-dimensional shape of
the lens follows, in turn, from the shape of the front surface and
the shape of the back surface.
[0021] The calculation of the optical effect on the basis of the
three-dimensional shape can be implemented thereafter using known
methods.
[0022] It is understood that it is not necessary for the
three-dimensional shape of the entire lens to be determined. By way
of example, the calculation can be implemented only for a portion,
for example only the front and back surface, without side faces, or
only for a portion in a user's field of vision.
[0023] When determining the three-dimensional shape of the lens by
the computing unit, more in-depth information, such as for example
a known relative spatial position of the display device in relation
to the respective viewpoints, from which the capture is
implemented, can advantageously be taken into account.
[0024] According to a further aspect, an apparatus is proposed for
measuring the optical effect of an optical lens arranged in a
measurement volume, comprising a display device which is configured
to display a test structure; an image capturing device which is
configured to capture image data of the test structure from a
plurality of viewpoints by way of imaging beam paths which pass
through the lens; and a computing unit, wherein the computing unit
is configured to: determine a three-dimensional shape of the lens
on the basis of the image data; and calculate an optical effect of
the lens on the basis of the three-dimensional shape thereof. The
computing unit can be configured to determine the three-dimensional
shape of the lens further taking account of one or more known
contact points of the lens; wherein a position of the contact
points is used to assign to an algorithm, which determines the
shape of the spectacle lens, an expected value for the position of
the latter in the measurement volume.
[0025] According to a further aspect of the present disclosure, an
apparatus is proposed for measuring the optical effect of an
optical lens arranged in a measurement volume, comprising a display
device which is configured to display a test structure; an image
capturing device which is configured to capture image data of the
test structure from a plurality of viewpoints by way of imaging
beam paths which pass through the lens; and a computing unit,
wherein the computing unit is configured to: determine a
three-dimensional shape of the lens on the basis of the image data;
and calculate an optical effect of the lens on the basis of the
three-dimensional shape thereof. The computing unit can be
configured to determine the three-dimensional shape of the lens
taking account of a boundary condition, wherein the boundary
condition is determined by reading information about the lens to be
measured, wherein the boundary condition is determined by reading a
code on the lens.
[0026] According to a further exemplary aspect of the present
disclosure, which may assist with the understanding of the
disclosure, a method is provided for calibrating an apparatus for
measuring individual data of an optical lens arranged in a
measurement volume, wherein the method includes the following
steps: providing or displaying a test structure on the display
device; setting a first distance between the image capturing device
and the display device and capturing image data of the test
structure with the image capturing device from the first distance;
setting a second distance between the image capturing device and
the display device and capturing image data of the test structure
with the image capturing device from the second distance;
determining a direction of incident light beams, which are captured
by the image capturing device, and corresponding pixels in the
image data on the basis of the image data captured at the first
distance and the image data captured at the second distance.
[0027] An advantage of this solution consists of the fact that the
direction of incident light beams can be determined in a simple
manner. Here, the display device used for the measurement in any
case can also serve calibration purposes. The relative position of
the display device including its image points relative to the image
capturing device can typically be taken into account during the
calibration.
[0028] As a result of the height adjustment, there is a change in
the angle of the incident light beams relative to the image
capturing device, for example relative to the cameras of the image
capturing device. A direction of the incident light can be
determined from a relationship between the known change in height
and a change in an image representation of the test structure in
the image data accompanying this. This facilitates so-called "back
propagation" of the incident light beams.
[0029] According to a further aspect of the present disclosure, a
method, in particular computer-implemented method, is disclosed for
measuring the optical effect of an optical lens, in particular a
spectacle lens, arranged in a measurement volume, including the
steps of: providing a test structure for display on a display
device; capturing image data of the test structure from a plurality
of viewpoints by way of imaging beam paths which pass through the
lens; determining a three-dimensional shape of the lens on the
basis of image data; and calculating an optical effect of the lens
on the basis of the three-dimensional shape thereof.
[0030] According to further aspects of the present disclosure,
methods corresponding to the aforementioned aspects are
proposed.
[0031] According to a further aspect of the present disclosure, a
computer program product is proposed, comprising instructions that,
upon execution of the program by a computer, cause the latter to
carry out one of the aforementioned methods. It is understood that
the method steps in this case are designed to be carried out by
computer. By way of example, capturing image data can be understood
to mean receiving image data. Thus, the term can be understood as a
transmission of measurement data generated by a physical image
sensor. Accordingly, the test structure can be provided by the
provision of test structure data. In turn, the data can be
displayed by a display device.
[0032] The provision of the test structure can also be a preceding
step, which is not carried out by the computer program product.
[0033] If nothing else is specified, the terms used herein should
be understood within the meaning of the standard DIN EN ISO
13666:2012 by the Deutsches Institut fur Normung e.V. [German
Institute for Standardization].
[0034] Pursuant to section 5.8 of the DIN EN ISO 13666:2012
standard, the term front surface or object-side surface denotes
that surface of a spectacle lens intended to face away from the eye
in the spectacles. Pursuant to section 5.19 of the DIN EN ISO
13666:2012 standard, the term back surface or eye-side surface
denotes that surface of a spectacle lens intended to be fitted
facing to the eye. As an alternative to this, the term front
surface within the scope of the present disclosure can denote the
surface of the lens facing the display device. Accordingly, a back
surface within the scope of the present disclosure can refer to the
surface facing away from the display device.
[0035] In one configuration, provision can be made for the image
capturing device to comprise a first camera and a second camera,
wherein the first camera is configured to capture first image data
from a first viewpoint and the second camera is configured to
capture second image data from a second viewpoint; and wherein the
computing unit is configured to determine the three-dimensional
shape of the lens on the basis of the first and second image data.
As an alternative to the use of two cameras, the first and second
image data can also be captured by means of one camera at different
positions. A displacement device or positioning device can be
provided to move the camera between the first and the second
position.
[0036] In an optional development, the first camera and the second
camera can be arranged at an angle with respect to one another such
that the test structure can be captured from the first angle by the
first camera and from the second angle by the second camera.
[0037] The lens is a spectacle lens and the optical effect of the
spectacle lens is calculated for a given wearing position of a
user. One advantage can consist of the fact that, in particular,
the optical effect can also be calculated retrospectively for any
given specified or desired wearing position of the user. Here, the
wearing position could also differ significantly from the
measurement position, in which the image data are captured. The
computing unit can be configured to calculate the optical effect of
the spectacle lens for a specified wearing position of a user,
which differs from a measurement position in which the image data
are captured. In particular, there can be a user-specific
adaptation and a flexible calculation of used values. By contrast,
conventional lensmeters provide no individualized statement for the
user.
[0038] In one configuration, provision can be made for the
computing unit to be configured to iteratively determine the
three-dimensional shape of the lens by means of an integration
method.
[0039] In a further configuration, provision can be made for the
computing unit to be configured to determine the three-dimensional
shape of the lens on the basis of tracing back the light beams
entering the image capturing device. In particular, the light beams
entering the image capturing device can be traced back to known
original locations of the test structure displayed on the display
device. In particular, the relative position of the display device
and the positions or viewpoints, from which the image data are
captured, are known. Optionally, the relative positions can be
ascertained on the basis of the above-described camera calibration
by means of changes in distance or height. By way of example,
methods such as a back propagation or inverse ray tracing can be
used to determine the three-dimensional shape of the lens. In
simple terms, a surface reconstruction of the lens to be measured
can be implemented on the basis of the comparison of an intended
position and an actual position of one or more elements of the test
structure in the captured image.
[0040] In one configuration, determining the three-dimensional
shape of the lens can comprise a division of a front and/or back
surface of the lens into surface elements and a determination of an
alignment of the surface element, in particular a determination of
surface normals of the surface elements. In particular, this
determination can be undertaken on the basis of tracing back the
light beams entering into the image capturing device. Expressed
differently, an alignment of the surface can be determined for
individual surface elements (for each individual surface element).
By way of example, surface normals can be calculated for individual
sections or surface elements.
[0041] In a development, the computing unit can be embodied to
determine a three-dimensional shape of a front surface and/or a
back surface of the lens on the basis of the alignment of the
surface elements. A surface of the lens, for example the front or
back surface, can be composed of individual surface elements.
Typically, the surface is composed in such a way that no
(significant) jumps arise between adjacent elements.
[0042] In one configuration, the computing unit can be configured
to determine the three-dimensional shape of the lens taking into
account the boundary condition that a front surface or a back
surface of the lens is a parameterizable area, in particular a
plane, sphere, torus or a section thereof. An advantage consists in
a faster calculation and/or greater accuracy since the parameter
space is reduced by specifying boundary conditions.
[0043] In one configuration, provision can be made for the
computing unit to be configured to determine the three-dimensional
shape of the lens further taking account of one or more known
contact point(s) of the lens. As an alternative or in addition
thereto, provision can be made for the computing unit to be
configured to determine the three-dimensional shape of the lens
taking account of a boundary condition, wherein the boundary
condition is determined by reading information about the lens to be
measured, in particular by reading a marking or a code on the lens.
Once again, advantages can consist in the faster and/or more
accurate calculation since the degrees of freedom are reduced
further. It is understood that a plurality of known contact points
or a lens glass holder or a spectacle holder can also be taken into
account. By way of example, an engraving, a marker relating to a
curvature, a material or a refractive index, can be read as a code
on a lens and can be taken into account in the calculation.
[0044] In an exemplary configuration, which may assist with the
understanding of the disclosure, provision can be made for the
computing unit to be further configured to determine a refractive
index, in particular to determine a spatial refractive index
distribution, of the lens to be measured. A lens or spectacle lens
with one refractive index can be considered to be a special case.
Typically, the refractive index is constant in at least one
portion. Further, a spatial refractive index distribution of a
so-called GRIN (GRaded-INdex) lens can be determined. The inventors
have recognized that the proposed solution can serve not only to
capture a shape but also to determine the refractive index, i.e.,
to measure the interior of a transparent body. By way of example,
it is possible to determine an internal interface between regions
with different refractive indices. Possible applications include,
for example, multi-part lenses, lenses with materials that have
different refractive indices, achromatic lenses, optical systems or
objectives.
[0045] In one configuration, the apparatus can further comprise a
height adjustment device, which is configured to vary a distance
between the image capturing device and the display device. Further,
the computing unit can be configured to determine, on the basis of
image data captured from different distances between the image
capturing device and the display device, a beam direction of the
light beams captured by the image capturing device. Consequently,
an association between pixel and beam direction can be established
in a simple manner.
[0046] The advantages described in detail above for the first
aspect of the disclosure apply accordingly to the further aspects
of the disclosure.
[0047] It goes without saying that the aforementioned features 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
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] The disclosure will now be described with reference to the
drawings wherein:
[0049] FIG. 1 shows an exemplary embodiment of an apparatus for
measuring the optical effect of an optical lens arranged in a
measurement volume;
[0050] FIG. 2 shows an exemplary embodiment of a test structure
recorded through a lens;
[0051] FIG. 3 shows an exemplary embodiment of a test structure
recorded through a tilted spectacle lens;
[0052] FIG. 4 shows an illustration of beam paths through a
transparent object;
[0053] FIG. 5 shows an illustration of beam paths through a
lens;
[0054] FIG. 6 shows a lens composed of parameterizable surface
elements;
[0055] FIG. 7 shows a schematic illustration of an apparatus for
measuring the optical effect of an optical lens arranged in a
measurement volume;
[0056] FIG. 8 shows a further exemplary embodiment of an apparatus
for measuring the optical effect of an optical lens arranged in a
measurement volume;
[0057] FIG. 9 shows a flow chart of a configuration of a method for
measuring the optical effect of an optical lens arranged in a
measurement volume;
[0058] FIG. 10 shows a detailed flowchart of a configuration of
such a method;
[0059] FIG. 11 shows a flowchart of an exemplary embodiment of a
calibration method;
[0060] FIG. 12 shows a schematic illustration of an eye;
[0061] FIG. 13 shows an image representation of a plan view of the
eye with an image representation of the iris;
[0062] FIG. 14 shows a schematic illustration of an apparatus for
measuring the cornea;
[0063] FIG. 15 shows the association or correlation of image
features in images of the iris recorded from different
viewpoints;
[0064] FIG. 16 shows a further correlation of image features;
and
[0065] FIG. 17 shows a flowchart of an exemplary embodiment of a
method for measuring the cornea.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0066] The apparatus 10 shown in FIG. 1 serves to determine the
optical effect of an optical lens 100, in particular a spectacle
lens. The apparatus 10 comprises a display device 20, which is
configured to display a test structure 21. By way of example, this
could be a screen or display and to be able to display different
test structures.
[0067] The apparatus 10 further comprises an image capturing device
30 which is configured to capture image data of the test structure
21 from a plurality of viewpoints 31, 31', 31'' by way of imaging
beam paths 32 which pass through the lens 100. On the one hand, the
imaging beam paths from the various viewpoints could be recorded
successively by one camera, which is successively arranged at the
various positions. However, a plurality of cameras are typically
provided in order to capture the image data in parallel. It is
understood that mixed forms may also be provided. By way of
example, an image capturing device 30 can comprise a first camera
33 and a second camera 34, wherein the first camera 33 is
configured to capture first image data from a first viewpoint 33
and the second camera 34 is configured to capture second image data
from a second viewpoint 33''. The measurement volume 200 is located
between the test structure 21, which is displayable on the display
device 20, and the image capturing device 30.
[0068] The apparatus 10 further comprises a computing unit 40. By
way of example, the computing unit 40 can be a computer, a
microcontroller, an FPGA or the like. The computing unit 40 is
configured to determine a three-dimensional shape of the lens 100
on the basis of the image data; and to calculate an optical effect
of the lens 100 on the basis of the three-dimensional shape.
Expressed differently, a two-stage procedure is proposed, in which
the three-dimensional shape of the lens is initially determined and
only then is the optical effect of the lens calculated from its
three-dimensional shape.
[0069] This approach as per the present disclosure should be
explained in more detail below with reference to FIGS. 2 to 6.
[0070] FIG. 2 shows a plan view of a test structure 21 of a display
device 20 recorded through a lens 100. By way of example, this can
be the test structure 21 as per FIG. 1, recorded by the camera 33
through the lens 100. The test structure 21 is reproduced in
distorted fashion as a result of the lens 100. Conclusions about
the optical effect of the lens 100 can already be drawn from such a
deflection of the beams. However, it is only possible to make a
statement about the effect of the lens 100 as a whole.
[0071] FIG. 3 shows a further exemplary image, which has been
recorded by a camera.
[0072] However, in this case, the spectacles 101 with the optical
lens 100 are arranged with a large tilt in the measurement region,
and so the beam deflection caused by the optical lens 100 only
reproduces the actual optical effect in a wearing position with
limited accuracy.
[0073] FIG. 4 shows an exemplary illustration 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 beam
paths emanating from the defined point 22 enter the lens 101 at the
surface 102 and emerge from the lens at the surface 103.
Consequently, they pass through the lens 100. The light beams are
refracted both at the entry surface 102 and at the exit surface
103. A different optical effect may arise, depending on the
relative spatial position or orientation of the lens 100 with
respect to the display device 20 and the image capturing device
30.
[0074] The inventors have recognized that such uncertainty or
ambiguity of the optical effect can be resolved by virtue of
recording the test structure from a plurality of viewpoints and
consequently capturing a multiplicity of imaging beam paths (see
also FIG. 1), from which, in turn, the optical properties of an
interposed lens can be determined. Expressed differently, a system
of equations with a multiplicity of equations can be set up for the
imaging beam paths, which equations each establish an association
between imaging beams, which pass through the lens 100 and enter
the image capturing device from a plurality of viewpoints, and the
known origins thereof on the display device 20. From this, it is
possible, in turn, to determine the three-dimensional shape of the
lens 100 and also, optionally, its refractive index or a
brake-force distribution within the lens as well.
[0075] A simplified example of beam paths through a lens 100 is
reproduced in FIG. 5. The image point 22 on the display device 20
is captured by the camera 34. The beam path 110 enters the lens at
the point 104 on the front side 102 of the lens 100 and emerges
from the lens at the point 106 on the back surface 103 of the lens.
In simple terms, there is therefore an equation with two unknowns,
the entry point 104 and the exit point 105 including the spatial
orientation of the surface at these points, in the case of a
measurement with only one camera. By virtue of the image capturing
device 30 recording the test structure from further viewpoints, as
indicated by the further camera 33, it is possible to capture
further beam paths 111 and 112. In the case of the beam path 111,
an exit point 104 coincides with the beam path 110 of the camera
34. In the case of the beam path 112, an entry point 105 coincides
with the beam path 110 of the camera 34. Consequently, it is
possible to set up a plurality of equations, from which it is
possible to determine the properties of the lens 100 arranged
between the display device 20 and the image capturing device
30.
[0076] To this end, the computing unit can be configured to model
the lens 100, typically as a composed surface made of
parameterizable surface elements, as shown in FIG. 6 in exemplary
fashion. An orientation of the surface elements 106, 107 of the
front and back surface 102, 103 can be determined from the
deflection of the beams at the points 104 and 105. Optionally, a
further division can be undertaken within the lens 100. By way of
example, further interfaces can be determined within the lens 100.
Optionally, the computing unit can further be embodied to determine
a refractive index of the lens 100 or else spatial refractive index
distribution of the lens.
[0077] Optionally, the apparatus can be embodied as an apparatus
for measuring a spatial refractive index distribution of an optical
lens arranged in a measurement volume. To this end, provision can
typically be made of an interface which is configured to receive
lens geometry data, which describe a three-dimensional shape of the
lens. In this case, the shape of the lens need not be calculated;
instead, it can serve as an input parameter for calculating the
spatial refractive index distribution of the lens on the basis of
the image data and the lens geometry data.
[0078] Referring to FIG. 5 and FIG. 6, the computing unit can be
configured to determine three-dimensional shape of the lens on the
basis of tracing back the light beams entering the image capturing
device. The directions from which the light beams 110, 111, 112
enter the cameras 33, 34 of the image capturing device are known.
To this end, the image capturing device, as still described below,
can be calibrated. Consequently, the entering beams can be traced
back proceeding from the respective camera 33, 34. The lens 100 is
located in the beam path between the image capturing device or the
respective cameras (with a known position) and the test structure
(with a known position). Proceeding from a model of the lens 100,
this model can successively be parameterized by the computing unit
in such a way that the (known) test structure is imaged by the
model of the lens 100 in such a way that the image data captured by
the image capturing device arise. For the parameterization, it is
possible, in particular, to adapt the alignments of the surface
elements, represented here by the surface normals 129, 130, forming
the lens surface and vary a distance 131 between the surface
elements, and it is optionally possible to vary a refractive index
n or a refractive index distribution within the lens.
[0079] FIG. 7 and FIG. 8 show further exemplary embodiments of an
apparatus 10 for measuring the optical effect of an optical lens
100 arranged in a measurement volume. Corresponding assemblies are
denoted by the same reference sign and not explained again in
detail in order to avoid repetition.
[0080] FIG. 8 shows an exemplary embodiment in which the image
capturing device 30 comprises two cameras 30, 31'. The cameras see
a pattern or a test structure 21 from different viewing angles. The
computing unit is embodied to reconstruct the test object 4 from
the corresponding image data. To this end, it is possible to
determine a gradient field from the surface elements or from the
normals 129, 129', as explained in FIGS. 5 and 6.
[0081] Light from defined sources at defined origins of the test
structure 21 passes through the lens 100 and is captured by the
image capturing device 30 from different viewing angles by means of
a calibrated camera system. The refractive surfaces of the body are
reconstructed from the images arising.
[0082] The principle works with one camera, two cameras or more
cameras. Two cameras are used in an exemplary embodiment, as a good
cost/use ratio can be obtained in this case. Even more cameras can
be used to further increase the accuracy.
[0083] The image capturing device 30 or the cameras 31, 31' is/are
calibrated in such a way that a function is known, by means of
which a unique chief light ray (camera ray) can be derived in 3D
for each sensor coordinate from the origin and direction. This
calibration can be carried out according to the related art.
Alternatively, a known optical design of the camera and/or of an
employed objective can be included in the model of the camera
instead of the above-described camera calibration.
[0084] By way of example, the display device 20 can have
self-luminous sources, such as light-emitting diodes arranged in an
array, a TFT or LED display, a 3D display, laser sources, a
polarization display, or else a collimated, selectively structured
illumination unit. Light can also be shone on the display
apparatus. By way of example, a display apparatus on which light is
shone may have test charts (e.g., a point pattern or checker
pattern), an in particular regular 3D pattern, an unknown
feature-rich flat image (wherein positions can be estimated during
the operation) or else an unknown feature-rich 3D scene (positions
are estimated during the optimization).
[0085] The computing unit 40 can use further information for
determining the three-dimensional shape. The reconstruction of the
three-dimensional shape may in particular also be based on the
known viewpoints or positions of the camera, from which the image
data are captured, and a known position of the test structure. In
the present example, the image data can be locations of the imaging
of light beams, entering the cameras, on the camera detectors. The
light beams entering the image capturing device can be calculated
from the image data and the known viewpoints. A calibration of the
image capturing device can serve as a basis for this.
[0086] Optionally, the computing unit 40 can further be configured
to determine the three-dimensional shape of the lens taking account
of one or more boundary conditions. By way of example, a contact
point or stop 51 may be predetermined. The relative position of the
lens 100 is known at this point and can be taken into account when
determining the three-dimensional shape of the lens. Further,
information such as the shape of a front and/or back surface of the
lens, a refractive index or material, etc., may be predetermined.
Optionally, the apparatus can be embodied to read information
present on the lens, for example in the form of an engraving or a
marker 140, and take this information into account when determining
the three-dimensional shape and/or when calculating the optical
effect.
[0087] A particularly advantageous application of the present
disclosure lies in the measurement of spectacle lenses, in
particular the measurement of progressive spectacle lenses--also
known as varifocal spectacle lenses. Simpler spectacle lenses such
as spherical, aspherical, toric or prismatic lenses can, however,
likewise be measured using the apparatus proposed.
[0088] Optionally, the computing unit can be configured to
calculate an ISO vertex power or a vertex power in a specified
measuring appliance configuration in order to provide comparable
data. By providing wearer-specific data, such as the distance of a
pupil from the spectacle lens (vertex distance) and its relative
position (e.g., face form angle or "as worn" pantoscopic angle), it
is possible to calculate use vertex powers.
[0089] Optionally, a plurality of test objects can be measured
simultaneously in the measurement space. In the case where a pair
of spectacles with a left and a right spectacle lens is measured,
the computing unit can be further embodied to determine a position
and relative position of the spectacle lenses with respect to one
another. From this, it is possible to calculate further
information, such as the distance of the optical channels for
example. A transparent body with zones of different effects can
also be provided as a plurality of test objects. By way of example,
this can be a pair of spectacles with two lenses or a lens with a
plurality of zones--bifocal lens, trifocal lens or multifocal
lens.
[0090] FIG. 9 shows a flow chart of a method 900 for measuring the
optical effect of an optical lens, in particular a spectacle lens,
arranged in a measurement volume, including the steps set forth
below. 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 captured from a plurality of viewpoints by
way of imaging beam paths that pass through the lens. In a third
step 903, a three-dimensional shape of the lens is determined on
the basis of 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 on the basis of
its three-dimensional shape. The calculation can be implemented for
any usage situation. Consequently, the computing unit can be
configured to calculate a first optical effect, corresponding to an
ISO vertex power, and a second optical effect, corresponding to a
usage situation by a user.
[0091] Optionally, the measuring method can be preceded by step 905
for calibrating the apparatus.
[0092] A corresponding method for calibrating the apparatus may, in
turn, include 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 is set between the image
capturing device and the display device and image data of the test
structure are captured from the first distance by means of the
image capturing device.
[0093] As shown in FIG. 8, provision can be made of a height
adjustment device 150, which is configured to vary a distance
between the image capturing device and the display device. In this
context, the computing unit can be further configured to determine,
on the basis of image data captured from different distances
between the image capturing device and the display device, a beam
direction of the light beams captured by the image capturing
device.
[0094] In a further step of the method for calibrating the
apparatus, a second distance can be set between the image capturing
device and the display device and image data of the test structure
are captured from the second distance by means of the image
capturing device. From this, a direction of incident light beams,
captured by the image capturing device, and corresponding image
points in the image data can be determined in a further step.
[0095] FIG. 10 shows a detailed flow chart of an exemplary
embodiment of a method 1000 for measuring the optical effect of a
lens arranged in a measurement volume.
[0096] In a first step S1011, a test structure is displayed on the
display device. By way of example, this can be an entire point or
stripe pattern. In a further step S1012, image data of the test
structure are captured by the image capturing device. In step
S1013, it is possible to determine 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 capturing device). Here, there can be a camera calibration
step S1001, as explained above or described in detail in FIG. 11,
for example. In step S1014, it is then possible to determine the
light beams incident in the image capturing device or the
directions thereof. The light beams incident in the camera can be
determined as a 3D vector from the camera images of the displayed
pattern, as observed through the lens to be measured.
[0097] In a step S1021, a complete or partial pattern of a test
structure can be displayed on the display device. In a further step
S1022, image data of the test structure are captured by the image
capturing device. In step S1023, pattern points can be associated
with image points in the image data. In particular, it is possible
to provide a sequence of different test patterns in order to
resolve a possible ambiguity when associating pattern points with
image points in the image data. Expressed differently, luminous
spots in the image data captured by the image capturing device can
be assigned to a position of the luminous points on the display
device, and hence also to the calculated light beams, which were
incident in the image capturing device. As an alternative or in
addition thereto, the computing unit can be configured to determine
neighborhood relationships from an overall pattern of a test
structure.
[0098] In a step S1031, a planar illumination can be provided on
the display device. By way of example, all pixels of the display
device could display "white". As a consequence, a contour of the
lens could stand out and a contour of the lens can be determined in
step S1032. In a step S1033, a relative position and dimensions of
the lens can be determined on the basis of the captured contour.
Expressed differently, a relative position of the lens in the
measurement volume can be determined in a simple manner.
[0099] In step S1041, there can be a calculation of a "best
fitting" parameterizable lens. Typically, a "best fitting"
parameterizable lens, which could lie in the measurement volume of
the appliance, can be ascertained by back propagation of the camera
light beams. A parameterizable lens is understood to mean a lens
that can be described by few parameters such as radius, thickness
or the refractive index. These include spherical and toric lenses,
for example. Toric lenses are a general compromise, which may be
applied here. In a more specific exemplary embodiment, it may be
sufficient to define individual "toric zones" on the lens and only
describe the spectacle lens there. By way of example, a first of
these zones could be a "far region" of a progressive lens. By way
of example, a second of these zones could be a "near region" of a
progressive lens. In addition to the location of the lens or the
individual surfaces, further parameters could be the radii, the
thickness and the refractive index.
[0100] In step S1042, a "best fitting" gradient surface of the
front and/or back surface of the lens can be determined by inverse
ray tracing of the camera rays. Consequently, a surface of the
"best fitting" parameterizable lens determined in step S1041 can be
described as a gradient surface and the gradients at the locations
of the beam passage can be varied in such a way that the positions
of the luminous points on the display device are impinged perfectly
by back propagation of the camera rays. In simple terms, the
three-dimensional shape of the lens is therefore adapted in such a
way that the light beams received by the image capturing device and
the associated beam sources fit together on the display device.
[0101] In step S1043, a front and/or back surface of the lens can
be obtained by integration from the gradient surface. Expressed
differently, a (continuous) new surface is determined from a
piecewise gradient surface or a gradient surface determined for
surface elements. Here, this could be the front surface or the back
surface of the lens.
[0102] According to step S1044, steps S1042 and S1043 can be
repeated iteratively. By way of example, the steps could be
repeated until a quality criterion has been satisfied. Optionally,
if a sufficient quality cannot be reached, step S1041 can also be
included in the iteration loop, in order to take account of
alternative lens geometries. A three-dimensional shape of the lens
can be available as a result of the iteration.
[0103] In a further exemplary embodiment, which may assist with the
understanding of the disclosure, a shape of the lens can be
predetermined and, instead, a spatial refractive index distribution
within the lens can be iteratively determined in analog
fashion.
[0104] One or more variables can be subsequently determined from
the determined three-dimensional shape (optionally including the
refractive index). A use value, in particular a user-specific use
value, can be calculated in step S1052. To this end,
wearer-specific data, such as a distance between cornea and apex,
can be provided in step S1051. An ISO vertex power can be
determined in step S1053. A vertex power in an appliance
configuration can be determined in step S1054.
[0105] If a plurality of lenses or spectacle lenses were arranged
in the measurement volume at the same time, it is optionally
possible to determine additional parameters, such as the spacing of
the progression channels.
[0106] It is understood that the aforementioned steps can be
carried out by the computing unit and that the latter can be
configured accordingly for the purposes of carrying out the
steps.
[0107] FIG. 11 shows a flow chart of an exemplary embodiment of a
method 1100 for calibrating an apparatus for measuring individual
data of an optical lens arranged in a measurement volume, which may
assist with the understanding of the disclosure. The calibration
can serve, in particular, to provide a set of functions, which
assigns a beam direction such as a 3D vector to an image
point--typically each image point--of the image data captured by
the image capturing device, the 3D vector describing a beam
direction or a light beam entering the image capturing device. Such
a set of functions can have the following form:
r .fwdarw. .function. ( x , y ) = ( x 0 y 0 0 ) + .alpha.
.function. ( d .times. x d .times. y 1 ) ##EQU00001##
where (x.sub.0, y.sub.0, 0) describes a point of the light beam in
a reference plane of the image capturing device, typically a point
of the light beam in 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 set of
functions consists of four functions: x.sub.0(x,y), y.sub.0(x,y),
dx(x,y), and dy(x,y), where x and y describe the pixel coordinates
in image data of the image capturing device, a camera in this
case.
[0108] Such a set of functions can be determined by virtue of a
test structure, e.g., a point pattern, being displayed on the
display device and being observed by the cameras of the image
capturing device from different distances. For this purpose, the
apparatus as illustrated in FIG. 8 in exemplary fashion can
comprise a height adjustment device 150, which is configured to
vary a distance between the image capturing device and the display
device.
[0109] In the method shown in FIG. 11, steps S1101 to S1104 can
respectively correspond to steps S1011 to S1014 in FIG. 10, which
were described above. Steps S1111 to S1113 shown in FIG. 11 can
each correspond to the above-described steps S1021 to S1023.
However, a loop is provided, with a distance between the image
capturing device and the display device being varied in step S1121.
As shown in FIG. 8, a variation in the distance changes a direction
of the incident light beams. The computing unit can be configured
to determine a direction of the incident light beams on the basis
of the image data captured at the first distance and the image data
captured at the second distance. It is understood that this
determination can further depend on a relative position between the
display device and the image capturing device and on the variation
of the distance.
[0110] As shown in FIG. 11, an interpolation of 3D light beams of a
plurality of image points or pixels, typically for each image point
or pixel, of the image capturing device can be undertaken in a step
S1131. Subsequently, the variables x.sub.0, y.sub.0, dx, and dy can
be determined for the image points in step S1132. In a next step
S1133, a polynomial fit can be applied to the variables x.sub.0,
y.sub.0, dx, and dy. As a result, this can be used to determine a
set of functions which assigns a direction of an incident light
beam to each image point of the image data captured by the image
capturing device.
[0111] Optionally, a relative spatial position of a contact point
51, as illustrated in exemplary fashion in FIG. 8, can be
determined in a manner analogous to the camera calibration. To this
end, the display device 20 can be configured to display a single
color background or a background with a constant brightness as a
test structure. The image capturing device captures the display
without an inserted lens. In this case, the contact points lead to
shadow (e.g., circle in the case of contact spheres), which is
captured by the image capturing device and contained in the image
data. The computing unit can be embodied to determine a position of
the contact points 51 on the basis of these image data. In turn,
these can be used as boundary conditions when determining a
three-dimensional shape of a lens. When observing a contact point
by at least two cameras, its central point (the relative position)
can be ascertained by an intersection of the camera rays. The
position of the contact points can be used to assign to an
algorithm for determining the shape of the spectacle lens an
expected value for the position of the latter in the measurement
volume. An advantage of this configuration consists in an improved
accuracy.
[0112] It is understood that the explanations made above can apply
accordingly to the exemplary embodiments below, and vice versa. To
avoid repetition, further aspects, in particular, are intended to
be discussed below. Features of the aforementioned exemplary
embodiments and the exemplary embodiments below can advantageously
be combined with one another.
[0113] The inventors have recognized that the concepts described
herein can also be advantageously used for measuring the cornea.
FIG. 12 shows a schematic sectional illustration of an eye 1200.
The eye comprises a cornea 1201, an Iris 1202, a pupil 1203, and
the lens 1204. FIG. 13 shows a plan view of the eye with an image
representation of the iris 1202 and the pupil 1203. However, a
substantial contribution to the refractive error does not come from
the lens 1204 in this case, but from the cornea 1201. A substantial
contribution to the refractive error of a subject can be due to
corneal curvature. It would therefore be desirable to be able to
objectively determine the shape of the cornea.
[0114] FIG. 14 shows a schematic illustration of an apparatus for
measuring the cornea of a subject as per a further aspect of the
present disclosure. The apparatus may comprise the following: an
image capturing device (30), which is configured to capture image
data of an iris (1202) of the subject from a plurality of (known)
viewpoints by way of imaging beam paths (32) which pass through the
cornea (1201); and a computing unit (40). The computing unit is
configured to: provide a mathematical model of an anterior eye
section of the subject including a mathematical model of the cornea
and the iris; identify and register image features of the iris
which are present in a plurality of images of the image data;
determine deviations between actual positions of the image features
of the iris in the images captured from the plurality of viewpoints
and expected positions of the image features of the iris in the
images captured from the plurality of viewpoints taking into
account the mathematical model of the cornea and the relative
position of the iris; adapt parameters of the mathematical model of
the cornea in such a way that the deviations are minimized; and
determine a measured variable of the cornea from the adapted
mathematical model of the cornea.
[0115] The image capturing device 30 can again have the same or
similar configuration as described for FIG. 1. The image capturing
device captures image data of the iris 1202, with the beam paths
passing through the cornea 1201. To capture the image data from
different known viewpoints, a camera 33 can be successively
positioned at different known positions. To this end, provision can
be made of a positioning device (not shown). As an alternative or
in addition thereto, provision can be made of a plurality of
cameras 33, 34, which capture the image data in parallel. An
advantage of the parallel capture consists of the eye of the user
not moving between the various measurements.
[0116] The inventors have recognized that the cornea 1201 situated
between the iris 1202 and the image capturing device 30 can also be
calculated without knowledge about how the iris 1202 looks. The
iris 1202 has an unknown structure or an unknown pattern. However,
the iris 1202 is usually very structured. The inventors have
recognized that a multiplicity of image features of the iris can be
identified and subsequently evaluated in respect of their position
in a plurality of images of the image data, which were recorded
from different positions. To this end, a system of equations can be
set up from the imaging beam paths 32 which are captured at the
respective known positions; the shape of the cornea 1201 can be
calculated therefrom.
[0117] FIG. 15 and FIG. 16 show the association or correlation of
unknown image features in images of the iris recorded from
different viewpoints. The left image in FIG. 15 shows a first image
representation 1500a of the iris 1202--through the cornea--from a
first position, for example recorded by the camera 33 in FIG. 14.
The right image in FIG. 16 shows a second image representation
1500b of the iris 1202--through the cornea--from a second position,
for example recorded by the camera 34 in FIG. 14. Since the iris is
usually a very structured area, it is possible to determine a
correlation 1502 between the same initial points 1501a and 1501b of
the iris 1201. A further example of the corresponding points is
specified by the reference signs 1503a and 1503b, linked by 1502'.
Such an association 1500 can be undertaken for a multiplicity of
images 1500a to 1500d and image points, as shown in FIG. 16.
[0118] On the basis of this correlation or association analysis, it
is possible to reconstruct a multiplicity of beam paths, as shown
in FIG. 14. As is evident from the shown beam paths 32, the light
beams emanating from the same image point on the iris 1202 pass
through the cornea 1201 at different points and are captured at
different locations by the image capturing device 30. Should now
the same starting point be identified in the image representations,
it is possible to make statements about the cornea 1201, which is
located between the starting point on the iris 1202 and the entry
into the cameras 33, 34, as described above with reference to FIG.
14.
[0119] FIG. 17 shows a flowchart of an exemplary embodiment of a
method for measuring the cornea of a subject, which may assist with
the understanding of the disclosure. The camera system can be
calibrated in an optional preceding step. However, the manufacturer
may have already carried out the calibration. In a first step 1701,
image data of an iris of the subject can be captured from a
plurality of viewpoints by way of imaging beam paths that pass
through the cornea. In a second step 1702, a mathematical model of
an anterior eye section of the subject with a mathematical model of
the cornea (and the relative position of the iris with respect to
the cornea) can be provided. In a third step 1703, image features
of the iris which are present in a plurality of images (typically
in all images) of the image data can be identified and registered
(or assigned in the images). In a fourth step 1704, it is possible
to determine deviations between the actual positions of the image
features of the iris in the images captured from a plurality of
viewpoints and the expected positions of the image features of the
iris in the images captured from a plurality of viewpoints taking
into account the mathematical model of the cornea and the relative
position of the iris. In a fifth step 1705, parameters of the
mathematical model of the cornea can be adapted in such a way that
the deviations are minimized. Steps 1703 and 1704 can typically be
repeated iteratively. In a sixth step, it is now possible to
determine a measured variable of the cornea from the adapted
mathematical model of the cornea. By way of example, a refractive
power or an astigmatism can be evaluated.
[0120] In conclusion, the solutions disclosed herein can
facilitate, in particular, a simplified contactless measurement of
lens elements arranged in a measurement volume or else a
contactless measurement of the cornea, in particular with a reduced
impairment of a light-sensitive user, in the field of ophthalmic
optics.
[0121] The foregoing description of the exemplary embodiments of
the disclosure illustrates and describes the present invention.
Additionally, the disclosure shows and describes only the exemplary
embodiments but, as mentioned above, it is to be understood that
the disclosure is capable of use in various other combinations,
modifications, and environments and is capable of changes or
modifications within the scope of the concept as expressed herein,
commensurate with the above teachings and/or the skill or knowledge
of the relevant art.
[0122] The term "comprising" (and its grammatical variations) as
used herein is used in the inclusive sense of "having" or
"including" and not in the exclusive sense of "consisting only of"
The terms "a" and "the" as used herein are understood to encompass
the plural as well as the singular.
[0123] All publications, patents and patent applications cited in
this specification are herein incorporated by reference, and for
any and all purposes, as if each individual publication, patent or
patent application were specifically and individually indicated to
be incorporated by reference. In the case of inconsistencies, the
present disclosure will prevail.
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