Device for measuring the eye length

Abstract

With regard to the problem of specifying a device that permits a simple and robust measurement of the eye length, in particular without hardware modification on a camera, an optical device for use in an apparatus (13) for carrying out optical coherence tomography (OCT), comprising a cylindrical optical channel (1) for guiding and refracting light, which has a first diameter (1a) and a first length (1b), is characterised in that the first channel (1) is, in some sections, surrounded annularly and concentrically by a second optical channel (2) for guiding and refracting light, the second channel (2) having a larger diameter (2a) but a shorter length (2b) than the first channel (1).

Description

[0001] Device for measuring the outer length

[0002] The invention relates to an optical device according to the preamble of claim 1.

[0003] Optical coherence tomography (OCT) is an imaging technique that can be used to obtain two- and three-dimensional images of light-scattering structures. This method typically involves splitting light with a specific bandwidth into two beams using a beam splitter. The first beam falls on the sample or object to be examined, while the second beam travels through a reference path. The light reflected from the sample or object interferes with the reference beam. Signals from the interference allow the sample to be examined with depth resolution, i.e., at the depth of the optical axis of the first beam, using so-called A-scans. It is also possible to scan the sample flatly or laterally with the first beam to obtain OCT images. A B-scan is made up of multiple A-scans.

[0004] Methods for measuring or estimating eye length using the aforementioned OCT technology are already known. Some of these methods require a relatively broad OCT spectrum. Other methods require additional optical components. Some methods are time-consuming or subject to distortion due to eye movements.

[0005] The invention is therefore based on the object of providing a device that enables a simple and robust measurement of the eye length, in particular without hardware modifications to a camera.

[0006] The present invention solves the above-mentioned problem by the features of claim 1.

[0007] According to the invention, it has been recognized that the creation of two optical channels with different diameters and lengths makes it possible to generate not only two focal planes but also two OCT reference planes with the same optical path length. Using these planes, a measurement of the eye length can optionally be carried out without the use of beam splitters, in particular conventional beam splitters, in the optical device or a device in which the device is installed. The described device does not require a broad OCT spectrum and can be used in many existing OCT devices. Furthermore, no hardware modifications to cameras of existing OCT devices are necessary in order to use the device, in particular, to measure the eye length. Furthermore, both the optical device and the eye length measurement carried out with it are very robust and precise.The retina and cornea can be imaged simultaneously and sharply using the optical device or the eye length measurement carried out with it.

[0008] Both optical channels could be formed by lenses arranged one behind the other in a collinear and concentric manner with respect to their respective optical axes, with at least one lens having a larger diameter than another lens and thus contributing to the second channel with its ring-like material portion projecting over the other lens, thereby forming a ring channel. Lenses are robust and can easily be joined together mechanically or materially, or optically connected in series. Furthermore, the optical properties of lenses are clearly defined by their refractive behavior and are essentially free from device influences such as heating or cooling. In such an optical device, central light rays pass through all lenses, while outer light rays only pass through one lens with a large diameter.

[0009] Several lenses with the same second diameter could be arranged as a bundle between at least two lenses with the same first diameter, where the first diameter is smaller than the second diameter. By using several lenses as a bundle, the refractive behavior of the entire bundle can be adjusted.

[0010] The optical device could have two focal planes, namely a first focal plane for light passing through the first, inner channel, and a second focal plane for light passing only through the ring-like second channel. Central and outer light rays are focused in each focal plane. The optical device can be designed so that one focal plane for the central light rays lies on the cornea and one focal plane for the outer light rays lies on the retina.

[0011] The optical device could have two reference planes, preferably with the same total optical path length, namely a first reference plane for light traveling through the first, inner channel, which forms a longer optical path for light, and a second reference plane for light traveling only through the ring-like second channel, which forms a shorter optical path. Ultimately, the optical path length up to both reference planes is identical; only a partial path, namely a first length, is considerably longer for the central ray, depending on the refractive index of the glass. The optical path length is considerably longer for the central light rays, resulting in different reference planes. The optical device can be designed such that the reference plane of the central light rays lies on the cornea and that the reference plane of the outer light rays lies on the retina.The division into two focal or reference areas is preferably achieved using concentric optics with different diameters. The central light rays of a scan field pass through all optics, while peripheral light rays do not pass through all optics.

[0012] The optical device can be designed as a lens or an interchangeable lens. A lens forms a prefabricated structural unit. The interchangeability of the lens allows an OCT device to be converted.

[0013] Such a lens can be used to measure eye length. In particular, such a lens can be designed as a multifocal lens.

[0014] In a method for determining distances between two structures, in which an optical device of the type described here is used, the first structure could be detected in a first focal plane and / or first reference plane of the optical device, wherein the second structure is detected in a second focal plane and / or second reference plane of the optical device, the distance between the structures being determined from data of their detection and / or from an image representation of both structures.

[0015] The first structure could be the cornea or a portion of the cornea of ​​an eye, and the second structure could be the retina or a portion of the retina of the eye. This specifies a method for measuring eye length using OCT technology.

[0016] A device for performing optical coherence tomography (OCT), which comprises an optical device of the type described here, could have, in particular as hardware with corresponding software, an electronic device which carries out the method described here for determining distances between two structures.

[0017] The electronic device controls the device's optics, in particular an interferometer, to detect the distances between the structures using the optical device. The electronic device then uses algorithms to automatically or user-definedly determine the distances between the detected structures. The electronic device could display the detected structures in an image. This allows a user to gain insights from the image that are helpful for diagnosis. The images can be stored and / or processed in a memory of the electronic device.

[0018] In the drawing show

[0019] Fig. 1 is a schematic representation of an optical arrangement in which an optical device is used for measuring eye length using OCT technology, and

[0020] Fig. 2 is a cross-sectional image showing that the cornea is sharply imaged in a central area and that the retina is sharply imaged in a peripheral area.

[0021] Fig. 1 shows an optical device for use in an apparatus 13 for performing optical coherence tomography. The optical device comprises or forms a cylindrical optical channel 1 for guiding and refracting light, which has a first diameter 1a and a first length 1b. The first channel 1 is partially surrounded in a ring-like and concentric manner by a second optical channel 2 for guiding and refracting light, wherein the second channel 2 has a larger diameter 2a but a shorter length 2b than the first channel 1.

[0022] Both channels 1, 2 are formed by lenses 3a-d, which are arranged one behind the other and collinear and concentric with respect to their respective optical axes 4a-d. In concrete terms, a single optical axis is therefore provided, with which the optical axes 4a-d coincide. At least one lens 3b, 3c has a larger diameter than another lens 3a, 3d and thus contributes to the second channel 2 with its ring-like material part protruding over the other lens, thereby forming an annular channel. In concrete terms, two lenses 3b, 3c with the same second diameter 2a lie as a bundle between two lenses 3a, 3d with the same first diameter 1a, wherein the first diameter 1a is smaller than the second diameter 2a.

[0023] The optical device has two focal planes 5, 6, namely a first focal plane 5 for light passing through the first, inner channel 1, and a second focal plane 6 for light passing only through the ring-like second channel 2.

[0024] The optical device has two reference planes 7, 8, namely a first reference plane 7 for light passing through the first, inner channel 1, which forms a longer optical path for light, and a second reference plane 8 for light passing only through the ring-like second channel 2, which forms a shorter optical path. The device is designed as an objective or interchangeable objective.

[0025] Fig. 1 also shows, based on the arrangement, a method for determining distances 9 between two structures, in which an optical device of the type described above is used, wherein the first structure is detected in a first focal plane 5 and first reference plane 7 of the optical device, wherein the second structure is detected in a second focal plane 6 and second reference plane 8 of the optical device, and wherein the distance 9 of the structures is determined from data of their detection and / or from a pictorial representation of both structures.

[0026] In the specific, but non-limiting, embodiment, the first structure is the cornea 10 or a region of the cornea 10 of an eye 11, and the second structure is the retina 12 or a region of the retina 12 of the eye 11.

[0027] Fig. 1 shows the specific optical structure of an objective, specifically an OCT objective for measuring the eye length of a human eye 11. The objective consists of several lenses 3a-d, which are arranged concentrically in a row and have different diameters. Thus, as shown in Fig. 1, the central light rays pass through all of the optics, while the outer light rays only pass through the optics with a larger diameter. This results in different focal planes 5, 6 for the central and outer light rays. In addition, the optical path length for the central light rays is considerably longer, resulting in different reference planes 7, 8 with the same total optical path length. The design of the objective is such that the focal plane 6 and the reference plane 8 of the outer rays lie on the retina 12. The focal plane 5 and the reference plane 7 of the central rays lie on the cornea 10.

[0028] Fig. 1 schematically shows a device 13 for performing optical coherence tomography (OCT), comprising the optical device and an electronic device 14 which carries out the method described above.

[0029] In an OCT procedure, light is typically split into two partial beams. A first partial beam falls on the sample to be examined, for example, the cornea 10 or the retina 12, while the second partial beam travels a reference path. Specifically, the first partial beam is guided to the respective focal plane 5, 6. The second partial beam travels a reference path of finite length. The position of the reference plane in which the OCT image is displayed is defined by the reference arm length. The "optical path lengths" of RE1 (reference plane 7) and RE2 (reference plane 8) are equal, so that both areas can be displayed simultaneously in the OCT image. Specifically, the respective reference plane 7, 8 coincides with the respective focal plane 5, 6. A light beam reflected from the sample interferes with the reference beam.Signals from the interference allow the sample to be examined with depth resolution, i.e. in the depth of the optical axis of the first partial beam, using so-called A-scans.

[0030] Fig. 2 shows the result of an application of the method described with reference to Fig. 1 to a human eye, wherein the first structure is the cornea 10 or a region of the cornea 10 of an eye 11 and wherein the second structure is the retina 12 or a region of the retina 12 of the eye 11. Fig. 2 shows that the electronic device 14 displays the structures in an image 15. Fig. 2 shows the image 15 as a sectional image. If a straight line scan (OCT-B scan) is performed radially through the optical axis 4a-d of the objective or the optical device, the sectional image according to Fig. 2 is produced. In the central area, the cornea 10 is sharply imaged, and in the peripheral area, the retina 12 is sharply imaged. The distance between

[0031] Cornea 10 and retina 12 can be calculated precisely.

[0032] Determining the exact eye length offers several advantages. For example, if the eye length is known, scaling can be calculated more accurately and eye structures can be represented more accurately.

[0033] List of reference symbols:

[0034] 1 cylindrical optical channel

[0035] 1a first diameter

[0036] 1 b first length

[0037] 2 second optical channel

[0038] 2a smaller length

[0039] 2b larger diameter

[0040] 3a-d lenses

[0041] 4a-d optical axis

[0042] 5 first focal plane

[0043] 6 second focal plane

[0044] 7 first reference level

[0045] 8 second reference plane

[0046] 9 Distance

[0047] 10 Cornea

[0048] 11 Eye

[0049] 12 Retina

[0050] 13 OCT device

[0051] 14 electronic device

[0052] 15 images

Claims

Patent claims 1. Optical device for use in a device (13) for carrying out optical coherence tomography (OCT), comprising a cylindrical optical channel (1) for guiding and refracting light, which has a first diameter (1a) and a first length (1b), characterized in that the first channel (1) is surrounded in sections in a ring-like and concentric manner by a second optical channel (2) for guiding and refracting light, wherein the second channel (2) has a larger diameter (2a) but a smaller length (2b) than the first channel (1).

2. Device according to claim 1, characterized in that both channels (1, 2) are formed by lenses (3a-d) which are arranged one behind the other and collinearly and concentrically with respect to their respective optical axis (4a-d), wherein at least one lens (3b, 3c) has a larger diameter than another lens (3a, 3d) and thus contributes to the second channel (2) with its part of material projecting over the other lens in a ring-like manner and thereby forms an annular channel.

3. Device according to claim 2, characterized in that several lenses (3b, 3c) with the same second diameter (2a) are arranged as a bundle between at least two lenses (3a, 3d) with the same first diameter (1a), the first diameter (1a) being smaller than the second diameter (2a).

4. Device according to one of the preceding claims, characterized by two focal planes (5, 6), namely a first focal plane (5) for light which passes through the first, inner channel (1), and a second focal plane (6) for light which passes only through the ring-like second channel (2).

5. Device according to one of the preceding claims, characterized by two reference planes (7, 8), namely a first reference plane (7) for light which runs through the first, inner channel (1), which forms a longer optical path for light, and a second reference plane (8) for light which runs only through the ring-like second channel (2), which forms a shorter optical path.

6. Device according to one of the preceding claims, characterized by a design as a lens or interchangeable lens.

7. Method for determining distances (9) between two structures, in which an optical device according to one of the preceding claims is used, wherein the first structure is detected in a first focal plane (5) and / or first reference plane (7) of the optical device, wherein the second structure is detected in a second focal plane (6) and / or second reference plane (8) of the optical device, and wherein the distance (9) of the structures is determined from data from their detection and / or from an image representation of both structures.

8. The method according to claim 7, characterized in that the first structure is the cornea (10) or a region of the cornea (10) of an eye (11) and that the second structure is the retina (12) or a region of the retina (12) of the eye (11).

9. Apparatus (13) for performing optical coherence tomography (OCT), comprising an optical device according to one of claims 1 to 6 and an electronic device (14) which carries out the method according to claim 7 or 8.

10. Device according to claim 9, characterized by an electronic Device (14) which displays the structures in an image (15).

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