EP4178415A1

EP4178415A1 - Arrangement and method for determining eye lengths

Info

Publication number: EP4178415A1
Application number: EP21724243.7A
Authority: EP
Inventors: Björn MARTENSEN; Michaela GAENS; Andreas Fritz
Original assignee: Heidelberg Engineering GmbH
Current assignee: Heidelberg Engineering GmbH
Priority date: 2020-07-10
Filing date: 2021-05-05
Publication date: 2023-05-17
Also published as: JP2023533910A; DE102020118331A1; US20230284898A1; WO2022008116A1

Abstract

In view of the problem of specifying an arrangement and a method by means of which an eye can be measured preferably without artifacts and quickly, an arrangement for measuring an eye (1), comprising a light source (2) which is suitable for emitting light rays (3, 4) to the cornea (5) of an eye (1) and a control unit (6) which drives the light source (2) to emit the light rays (3, 4) and is suitable for converting reflected light rays (3a, 4a, 4b) entering the arrangement into signals (7, 8), is characterized in that the light source (2) when driven by the control unit (6) emits a central light ray (3) and emits a plurality of peripheral light rays (4) which are radially offset with respect to the central light ray (3) or in that the light source (2) when driven by the control unit (6) emits a plurality of peripheral light rays (4) radially offset with respect to one another. Moreover, a method is specified.

Description

P a t e n t a n g

Arrangement and method for determining eye lengths

The invention relates to an arrangement and a method according to the preambles of the independent claims.

In addition to other organs, the human eye has the cornea or cornea, the lens, the vitreous body or corpus vitreum, the retina or retina, the pigment epithelium, the choroid and the optic nerve or optic nerve. The so-called retinal pigment epithelium separates the retina from the choroid.

In order to be able to get a comprehensive picture of the dimensions of the eye, biometry of the eye is usually carried out. It is often of interest to measure the length of the eyeball from the cornea to the retina, the so-called axial length. The length of the eye is usually measured using ultrasound, time-domain OCT or low-coherence interferometry (partial coherence interferometry), the modes of action of which can be found in the literature. The abbreviation OCT is understood to mean optical coherence tomography (in English “optical coherence tomography”, usually abbreviated to OCT), the functioning of which can be found in the relevant literature. A measurement of an eye using the so-called time-domain OCT is subject to artifacts, is slow and prone to false signals. In the technologies mentioned, faulty signals can occur from layers, which then have to be identified by a user in order to determine a correct signal from a wrong one. This can be done automatically by algorithms. The artefact determination and its compensation is complex.

The invention is therefore based on the object of specifying an arrangement and a method with which an eye, in particular the human eye, can be measured as quickly and without artifacts as possible.

The present invention solves the aforementioned problem by the features of the independent claims.

First of all, it has been recognized that a reliable signal from the retina, in particular from the retinal pigment epithelium, is necessary for a measurement of eye length or other dimensions. It was then recognized that the signal from the retina or the retinal pigment epithelium must be free from disturbing influences and artefacts as well as from false signals from other layers, in particular the interface between the vitreous body and the retina. In addition, it has been recognized that a length reference of the retina to the cornea must be determined in order to determine the length of the eye.

Against this background, it has been recognized that several light rays emitted by the light source are essentially refracted by the lens and are directed approximately to the same point or area of the retina after these light rays have passed through the cornea at different points. According to the invention, it was then recognized that this enables a decentralized scanning approach, namely that light beams can be directed onto the eye not only along the optical axis of the eye, but also around the optical axis, preferably parallel to it, scattered onto the eye can be steered. Controlled by the control unit, the light source therefore emits a plurality of peripheral light beams that are radially offset from a central light beam or to the optical axis and are preferably parallel to one another and generates a point pattern of decentralized incident light beams or light beam bundles on the cornea. The peripheral light rays can be incident on the cornea consecutively or simultaneously. It is also conceivable that the peripheral light beams are incident at the same time as the central light beam or are incident with a time offset relative to it.

In this way, at least the specular reflection in the vertex of the cornea can be compensated and an associated artefact can be suppressed or compensated for. The vertex is the point of intersection of the lens surface facing an incident light ray with the optical axis.

According to the invention, however, artefacts that originate from deeper layers in the eye, in particular from the interface between the vitreous body and the retina, can also be compensated for or suppressed by the decentralized approach of the light irradiation.

The peripheral light beams, which are preferably parallel to one another, could lie within a circular area with a diameter of 3 to 12 mm, namely orthogonally pass through this circular area. A dot pattern can thereby be generated on a cornea. Controlled by the control unit, the light source therefore emits the peripheral light beams and generates a dot pattern on the cornea of the eye, scattered around the vertex of the cornea. The dot pattern can be spread more narrowly, i.e. it can also lie within a circular area with a diameter of 3 to 6 mm or 6 to 9 mm. The size of the circle or dot pattern field can be chosen appropriately in order to use sub-apertures appropriately, since due to the telecentric imaging, all light rays within the dot pattern field are directed by the lens approximately to the same point on the retina.

The control unit could automatically detect the vertex of the cornea. Alternatively or additionally, the light source controlled by the control unit could emit the peripheral light beams onto the cornea at defined distances from the central light beam and/or at defined distances relative to one another. In this way, phase information can be obtained from the reflected light beams, in particular the reflected peripheral light beams, with an adjustable resolution. The distances can be determined automatically by the control unit, in which the characteristics of the cornea are recorded, or by presetting possible distances.

The control unit could detect first peripheral light beams reflected from the eye, which are reflected upon the incidence of the peripheral light beams and which each show different intensities, with the control unit detecting second peripheral light beams reflected from the eye, which are reflected from the incidence of the peripheral light beams and each have the same size or show intensities lying within a predefined interval. In this way, peripheral light rays that are reflected at a boundary layer between the vitreous body and the retina can be distinguished from those peripheral light rays that are reflected at the retina or the retinal pigment epithelium. Peripheral light rays that are reflected at the boundary layer between the vitreous body and the retina show intensities that depend on the angles of incidence on this boundary layer. The angle of incidence determines the strength of the reflection.

The intensities of peripheral light rays reflected from the retinal pigment epithelium are essentially angle-invariant. Backscatter from the retinal pigment epithelium is essentially isotropic. Against this background, the control unit could use the respective detected intensities of all reflected peripheral light rays to distinguish an organ to be detected from an organ or structure not to be detected and/or to distinguish an artifact from an organ or structure not to be detected to suppress or remove the structure to be detected. In concrete terms, it can be determined whether an emitted peripheral light beam was reflected by the retinal pigment epithelium or the retina or by a boundary layer between the vitreous body and the retina. In this way, a further artefact can be eliminated in addition to the reflections on the cornea that have already been eliminated by subapertures.

The arrangement described here could be part of an FD-OCT device, namely a Fourier domain OCT device. Such devices are also called frequency domain OCT devices. Within the meaning of this description, FD-OCT devices are also understood to mean swept-source OCT devices (SS-FD-OCT devices). With the arrangement described here and the method described below, a reliable, rapid and largely artifact-free determination of the eye length is possible with an FD-OCT device. The eye length can be determined with a smaller image depth than the eye length to be measured. For the Measurement provides a reliable signal from the retina, particularly the retinal pigment epithelium.

This signal is free from disturbing influences and artefacts, false signals from other layers, in particular from the vitreous body/retina transition, and from ambiguities. Ambiguities can occur in FD-OCT methods due to the Hermitian symmetry of results. When transferring from TD-OCT to FD-OCT, it must be taken into account that a signal cannot be clearly assigned to the Hermitian level. That is, there are two eye lengths that match a given signal. However, FD-OCT is superior to TD-OCT in terms of sensitivity, so that the arrangement and method described here offers a practicable solution for FD-OCT.

Against this flickering background, the control unit could differentiate a complex conjugate signal from a normal signal based on phase information of reflected light rays, particularly reflected peripheral light rays. Various algorithms have already become known for generating imaging, which enable a “full-range OCT” by introducing additional phase information. Due to the differentiation mentioned, however, no "full-range imaging" is required. By differentiating the complex-conjugate signal from a normal signal based on additional phase information, a clear length reference to the cornea can be established.

To determine the length of the eye, a length reference of the retina to the cornea can be determined. The length reference can be determined by switching alternately between a front area of the eye and the retina, but this will not be discussed in detail here. However, so that the length reference can be determined independently of movement artifacts, an axial movement trajectory of two data sets is determined and taken into account for the length reference.

The retinal pigment epithelium is advantageously automatically recorded by the arrangement and/or by the subsequent method.

When performing a method for measuring an eye, light beams are sent onto the cornea of an eye by a light source, a control unit being used which controls the light source, and light beams being reflected from the eye onto the emitted light beams and being detected by a control unit and be converted into signals. A central light beam is emitted and a plurality of peripheral light beams, radially offset from the central light beam, are emitted to produce a dot pattern on the cornea of the eye which is scattered around the vertex of the cornea. Multiple radially offset peripheral light beams could also be emitted to create the dot pattern on the cornea of the eye which is scattered around the vertex of the cornea.

When determining the retinal pigment epithelium, it is important to ensure that the correct structure or organ is identified. A significant artefact is removed or at least substantially suppressed by the decentralized scanning approach described by the method and the arrangement, namely a specular reflex at an interface with the cornea. Instead of a central scan along the optical axis of the eye, the telecentric optical scanning arrangement described here allows a distribution of different points outside of this reflex. Nevertheless, all light rays emitted by the light source are imaged on approximately the same point on the retina where the central light ray falls. The points are advantageously scanned at defined distances from the preferably automatically detected vertex of the cornea. The telecentric image is driven through sub-apertures of approximately the same point, which are suggested in the technical literature to avoid so-called speckles.

This makes it possible to suppress a second artifact, because first peripheral light rays reflected from a boundary layer between the vitreous body and the retina could be detected, which are reflected upon the incidence of the peripheral light rays and which each show different intensities depending on the angle of incidence, with the retinal pigment epithelium reflected second peripheral light beams are detected, which are reflected upon the incidence of the peripheral light beams and which each show intensities of the same size or lying within a predefined interval, regardless of the angle of incidence. The respective detected intensities can be used to distinguish the retina or the retinal pigment epithelium from an organ or structure not to be detected and/or to distinguish said second artefact from the organ or structure not to be detected to suppress or remove. The second artifact is due to a reflex at the transition from the vitreous body to the retina.

Against this background, an arrangement of the type described here could be used to implement the method in order to either suppress or eliminate the first artifact and/or the second artifact. The arrangement of the type described here is preferably used for examining a human eye. The final diagnosis is subject to a doctor. The method described here is not a diagnostic method, but only provides data that a doctor must then evaluate. Show in the drawing

1 shows a schematic representation of an arrangement which guides parallel light beams onto a human eye, which is represented in a sectional view,

Fig. 2 is a plan view of a human eye showing the points of incidence of parallel rays of light which are scattered about the optical axis and thereby produce a dot pattern on the pile skin, and

Fig. 3 shows a reduction of an artifact, with two signals from structures or organs at different viewing angles or angles of incidence of light rays being shown in comparison, with the upper signals being recorded at an almost vertical incidence on the vitreous body/retina interface and with the lower signals were detected at an angle of incidence of peripheral light rays that differed greatly from 90°.

1 shows an arrangement for measuring a human eye 1, comprising a light source 2, which is suitable for emitting light beams 3, 4 onto the cornea 5 of the human eye 1, and a control unit 6, which controls the light source 2 for emitting the light beams 3, 4 and is suitable for converting reflected light beams 3a, 4a, 4b entering the arrangement into signals 7, 8 and displaying them.

Controlled by the control unit 6, the light source 2 emits a central light beam 3 and emits a plurality of peripheral light beams 4 that are radially offset from the central light beam 3 and are parallel thereto. 2 shows that the peripheral light beams 4 lie within a circular area 9 with a diameter of 3 to 12 mm, namely pass through this circular area 9 orthogonally. This is shown in FIG. 1 using the dashed circular area 9 . The light source 2 controlled by the control unit 6 emits the peripheral light beams 4 in order to generate a dot pattern on the florescence 5 of the human eye 1 which is scattered around the vertex 10 of the cornea 5 . To this extent, the control unit 6 generates the geometry of the dot pattern.

The control unit 6 automatically determines the vertex 10 of the cornea 5, or its local position. The light source 2, controlled by the control unit 6, emits the peripheral light beams 4 at defined distances from the central light beam 3 and relative to one another onto the cornea 5.

The control unit 6 detects first peripheral light beams 4a reflected by the human eye 1, which are reflected upon the incidence of the peripheral light beams 4 and which each have different intensities. The control unit 6 also detects second peripheral light beams 4b reflected by the human eye 1, which are reflected upon the incidence of the peripheral light beams 4 and which each show intensities of the same magnitude or lying within a predefined interval.

The control unit 6 uses the respective detected intensities to distinguish an organ to be detected from a structure not to be detected and to suppress or remove an artifact from a structure not to be detected.

The arrangement is integrated into a superordinate FD-OCT device 11 . The method for measuring the human eye 1 is carried out in that light beams 3, 4 are sent through the light source 2 onto the cornea 5 of the human eye 1, with the control unit 6 being used, which controls the light source 2 for this purpose. Light beams 3a, 4a, 4b are reflected by the human eye 1 onto the emitted light beams 3, 4 and are detected by the control unit 6 and converted into signals 7, 8. The reflection of the light beams 3, 4 is shown in Fig. 1 by the double arrows. The reflected light beams 3a, 4a, 4b run back to the control unit 6 after being reflected on structures of the eye 1.

A central light beam 3 is emitted and a plurality of parallel peripheral light beams 4 radially offset from the central light beam 3 are emitted to produce a dot pattern on the cornea 5 of the human eye 1 which is scattered around the vertex 10 of the cornea 5 .

First peripheral light beams 4a reflected by a boundary layer 12 between vitreous body 13 and retina 14 are detected, which are reflected upon the incidence of the peripheral light beams 4 and which show different intensities depending on the angle of incidence 16, with second peripheral light beams 4b reflected by the retinal pigment epithelium 15 being detected , which are reflected upon the incidence of the peripheral light beams 4 and which each show intensities of the same magnitude or lying within a predefined interval. The intensity of these reflected second peripheral light beams 4b is independent of the angle of incidence of the incident peripheral light beams 4 assigned to them.

The respective detected intensities are used to distinguish the retina 14 or the retinal pigment epithelium 15 from a structure not to be detected and to suppress or remove a second artifact from the structure not to be detected. 3 shows that signals 7, 8 from the control unit 6 are shown in a display of the arrangement. In this respect, the arrangement has a display 20 for the optical representation of the signals 7, 8 of the detected organs or structures.

The display 20 shows two signals 7, 8 in the top and bottom views, the first signal 7 coming from an artefact that goes back to the vitreous body/retina interface, and the second signal 8 coming from the retinal pigment epithelium 15.

The signals 7, 8 of the upper representation of the display 20 were recorded when a light beam or light bundle was incident almost perpendicularly on the boundary layer 12 between the vitreous body and the retina. The signals 7, 8 of the lower representation of the display 20 were recorded at angles of incidence of peripheral light rays that deviate greatly from 90°.

It is clearly evident that there is a clear reduction in the signal 7 of the artifact, namely that it is smaller than the signal 8 to be detected, which comes from the retinal pigment epithelium.

Reference list:

1 eye

2 light source

3 Central light beam

3a reflected central light beam

4 peripheral light beam

4a first reflected peripheral light beam

4b second reflected peripheral light beam

5 cornea

6 control unit

7 signal out of 12

8 signals out of 14 or 15

9 circular area

10 vertices from 1

10a optical axis

11 FD OCT device

12 boundary layer between 13 and 14

13 Vitreous

14 retina

15 Retinal pigment epithelium

16 angles of incidence

17 choroid of 1

18 lens of 1

19 optic nerve

20 display or screen of 6

Claims

patent claims

1. An arrangement for measuring an eye (1), comprising a light source (2) which is suitable for emitting light beams (3, 4) onto the cornea (5) of an eye (1), and a control unit (6) which controls the light source (2) to emit the light beams (3, 4) and is suitable for converting reflected light beams (3a, 4a, 4b) entering the arrangement into signals (7, 8), characterized in that the light source (2) controlled by the control unit (6) emits a central light beam (3) and emits a plurality of peripheral light beams (4) radially offset from the central light beam (3) or that the light source (2) controlled by the control unit (6) emits a plurality of peripheral light beams (4 ) emits.

2. Arrangement according to Claim 1, characterized in that the peripheral light beams (4) lie within a circular area (9) with a diameter of 3 to 12 mm, namely pass through this circular area (9) orthogonally, and/or that the light source (2) controlled by the control unit (6), emits the peripheral light beams (4) in order to generate a dot pattern on the cornea (5) of the eye (1) which is scattered around the vertex (10) of the cornea (5).

3. Arrangement according to claim 1 or 2, characterized in that the control unit (6) automatically determines the vertex (10) of the cornea (5) and/or that the light source (2) controlled by the control unit (6) transmits the peripheral light beams (4 ) at defined distances from the central light beam (3) and/or at defined distances relative to one another onto the cornea (5).

4. Arrangement according to one of the preceding claims, characterized in that the control unit (6) detects first peripheral light beams (4b) reflected by the eye (1), which are reflected upon the incidence of the peripheral light beams (4) and which each show different intensities, and that the control unit (6) detects second peripheral light beams (4b) reflected by the eye (1), which are reflected upon the incidence of the peripheral light beams (4) and which each show intensities of the same size or within a predefined interval.

5. Arrangement according to claim 4, characterized in that the control unit (6) uses the respective detected intensities to distinguish an organ to be detected from an organ not to be detected or a structure not to be detected and/or to distinguish an artifact from a non suppress or remove an organ to be detected or a structure that is not to be detected.

6. Arrangement according to one of the preceding claims, characterized by integration into or use with an FD-OCT device (11).

7. Arrangement according to one of the preceding claims, characterized in that the control unit (6) differentiates a complex conjugate signal from a normal signal on the basis of phase information from reflected peripheral light beams (4a, 4b).

8. A method for measuring an eye (1), wherein a light source (2) light rays (3, 4) are sent to the cornea (5) of an eye (1), wherein a control unit (6) is used, which the light source (2) drives, being reflected from the eye (1) light beams (3a, 4a, 4b) to the emitted light beams (3, 4) and from a control unit (6) and converted into signals (7, 8), characterized in that a central light beam (3) is emitted and a plurality of peripheral light beams (4) offset radially to the central light beam (3) are emitted, so that a dot pattern is generated on the cornea (5) of the eye (1), which is scattered around the vertex (10) of the cornea (5), or that a plurality of radially offset peripheral light beams (4) are emitted so that a dot pattern on the cornea ( 5) of the eye (1) scattered around the vertex (10) of the cornea (5).

9. The method as claimed in claim 8, characterized in that first peripheral light beams (4a) reflected by a boundary layer (12) between the vitreous body (13) and retina (14) are detected, which are reflected upon the incidence of the peripheral light beams (4) and which show different intensities depending on the angle of incidence (16), with second peripheral light beams (4b) reflected by the retinal pigment epithelium (15) being detected, which are reflected upon the incidence of the peripheral light beams (4) and which are each of the same size or within a predefined interval lying intensities, and wherein the respective detected intensities are used to distinguish the retina (14) or the retinal pigment epithelium (15) from an organ or structure not to be detected and/or to detect an artifact from which to suppress or remove the organ to be detected or from the structure not to be detected.

10. The method according to any one of the preceding claims, characterized in that an arrangement according to any one of claims 1 to 7 is used to carry out the method.