DE102014210787A1 - Distance-compensated measuring device for topographical and keratometric measurements on the eye - Google Patents

Abstract

The present invention relates to a distance-compensated measuring device with which ophthalmological devices are capable of being able to realize not only keratometric but also topographical measurements on the eye irrespective of distance. The proposed distance-compensated measuring device for topographical and keratometric measurements on the eye consists of a surface radiator for illuminating the eye with structured patterns and an imaging optical unit arranged in a detection beam path and an image recording device, as well as a control and evaluation unit. According to the invention, an aperture stop is arranged in the detection beam path between the imaging optics and the image recording device for limiting the beam. The present solution makes it possible to carry out topographical and keratometric measurements at the operating point of the ophthalmological device regardless of distance. The solution thus combines the advantages of keratometric and topographic measurements on the eye with little technical effort. In this case, the present invention is suitable for various ophthalmic devices while maintaining the defined condition.

Description

The present invention relates to a distance-compensated measuring device for topographical and keratometric measurements on the eye. As a result, ophthalmological devices are able to realize not only keratometric but also topographical measurements on the eye regardless of distance.

While keratometry is understood to mean the measurement of the curvature of the cornea (or cornea), the topography concerns the three-dimensional measurement of geometric surfaces, in our case the cornea of an eye.

Corneal curvature is usually measured by illuminating the cornea in a structured manner and detecting the light rays reflected by the cornea. According to the prior art, two different optical approaches to this problem are known.

In the first, more traditional approach, structures such as single luminescent structures or Placido ring systems are used to illuminate the cornea and view the resulting images with conventional optical imaging systems. Due to the nature of the illumination, it is absolutely necessary to determine the distance between eye or cornea and measuring device for an exact evaluation of the reflection images. In the following, brief reference will be made to corresponding arrangements.

In the methods that have been known for a long time and are predominantly used in so-called keratometers or keratographs, individual luminous structures or placido rings are imaged by the tear film in front of the cornea and the reflected signals are observed with imaging optics or recorded and evaluated with a camera. Depending on the curvature of the cornea, the reflected and detected by the camera pattern is scaled in size. In order to obtain a determination of the curvature from these reflection signals, the size of the reflected patterns must be compared to a known shape, which usually results in a sphere with a radius of 7.8 mm. Such a solution is for example in the Scriptures US 4,685,140 A described.

The Placido discs used for topographers to produce concentric rings need not necessarily be a flat disc. Such plane Placido discs are indeed well known in the art and, for example, in US 5,110,200 A and US 5,194,882 A However, more widespread are funnel-shaped ( US 5,684,562 A . US 6,116,738 A ) or even spherically curved ( US 5,864,383 A ) Placido slices.

In the scriptures US 6,575,573 B2 and US Pat. No. 6,692,126 B1 solutions to ophthalmometers (also known as keratometers) are described, which are supplemented by slit illumination units. While the imaging of placido-ring systems is provided for measuring the surface curvature of the cornea of the eye, the gap illumination unit generates sectional images of the eye from which the thickness of the cornea of the eye can be determined. As a result of this combination, a corneal thickness profile can be determined.

A disadvantage of such solutions is the fact that the accuracy of the measurement is highly dependent on the angular relationships and thus on the measuring distance. Various methods are used to determine or control the correct measuring distance. For example, the measurement can be triggered automatically when the correct working distance has been reached. On the one hand, this can be done by correcting the erroneous distance before each measurement by determining the distance or the position with the aid of light barriers, contacts or additional measuring systems and, if necessary, correcting them.

Exemplary for this are the writings US 6,048,065 A and US 6,070,981 A called. The solutions described therein represent topographers who are based on a Placidoscheibe. To control the correct measurement distance, both solutions have a point light source that illuminates the cornea, reflects it, and images it onto a CCD camera as a point image. The position of the dot image within the catchment area provides information about the distance between the placido disk and the eye. For exact positioning, the Placido disk is moved until the distance is optimized. Only then will the measurement be started.

The pattern projection for the distance-dependent approach in the form of a surface radiator requires little technical effort and also allows large-scale and complex measurement structures. However, in this case, the virtual image resulting from reflection on the curved cornea depends on the distance of the eye to the surface radiator. This virtual image is imaged by the observation optics on a camera. Accordingly, the result with a conventional observation optics also depends on the distance. Therefore, complex and precise methods for measuring or adjusting the distance between eye and device are required.

Failure to set or measure this distance with the requisite precision will result in variations in the measurement results that will be particularly detrimental to determining the radius of curvature of the cornea. Particularly in the calculation of intraocular lenses, a reduced precision of this value makes a negative impact, so that the result obtained does not correspond to the desired accuracy.

In the second approach, the structures are projected from the infinite onto the cornea, that is, in the form of parallel rays, and the cornea-reflected image is observed with a telecentric optical array. Due to the projection of parallel beams, this approach is independent of distance, so that in this case the determination of the distance between eye and meter is unnecessary.

For this purpose exists a in WO2000 / 33729 A2 described approach in which 6 point structures are projected from the infinite on the cornea with the help of 6 separate lenses. The document describes a combination device for non-contact determination of axial length (AL), anterior chamber depth (VKT) and corneal curvature (HHK) of the eye, in particular for the calculation and selection of an intraocular lens (IOL) to be implanted. The 6-point keratometer used to measure the curvature of the cornea is supplemented by a Michelson interferometer (to measure the AL) and slit illumination (to determine the VKT) as well as fixing and adjusting devices. A disadvantage here is that the measurements to avoid mutual interference of the individual measuring systems take place in succession, which significantly prolongs the measuring process.

The US 4,660,946 A describes a corneal shape measurement solution based on a disk-shaped Fresnel cylindrical lens. To project the ring structure onto the eye, each ring of the Fresnel cylindrical lens is individually illuminated annularly by means of ring cylindrical lenses. On the one hand, the number of rings that can be realized is limited by the disc-shaped structure, and on the other hand, with increasing number of rings, this type of illumination can only be realized with difficulty.

Another solution will be in the WO 2012/160049 A1 described. In this case, an element embodied as a fused axicon is arranged in the beam path and is illuminated over its entire surface by plane waves by a lighting unit. In addition to the telecentric, distance-independent image acquisition, the styled axicon has ring-shaped structures with different radii. Although this solution makes it possible to generate a large number of parallel beams with different directions of incidence, this places very high demands on accuracy and precision both in terms of its manufacture and its adjustment. In addition, this solution takes up much free space, which precludes integration in multifunctional ophthalmic devices.

In evaluating the solutions known from the prior art, it should be noted that for the measurement of the cornea, in particular in connection with the calculation of an intraocular lens (IOL), the distance-independent approach has distinct advantages. However, due to the principle, high technical effort for the projection in commercial devices only up to 6 individual points are detected. This prevents detection of deviations of the corneal surface from an ellipsoidal shape, which can adversely affect the accuracy of an optimal IOL selection.

The present invention has for its object to develop a measuring device for topographical and keratometric measurements on the eye, which eliminates the known disadvantages of traditional solutions in which structures, such as placido ring systems are projected onto the cornea, and reduces their dependence on distance or even eliminated. In this case, the measuring device should have as simple a structure as possible in terms of the generation of structured patterns as well as the reduction or elimination of the distance dependence and be easy to handle.

This object is achieved by a distance-compensated measuring device for topographical and / or keratometric measurements on the eye consisting of a surface radiator for illuminating the eye with structured patterns and an imaging optical unit arranged in a detection beam path, and a control and evaluation unit the beam is arranged in the detection beam path between the imaging optics and the image pickup device an aperture diaphragm.

According to the invention the object is solved by the features of the independent claims. Preferred developments and refinements are the subject of the dependent claims.

The present solution makes it possible to carry out topographical and keratometric measurements at the operating point of the ophthalmological device regardless of distance. The solution thus combines the advantages of keratometric and topographic measurements on the eye at a low level technical effort. In this case, the present invention is suitable for various ophthalmic devices while maintaining the defined condition.

The invention will be described in more detail below with reference to exemplary embodiments. Show this

1 : the basic structure of a distance-compensated measuring device with a planar surface radiator,

2 : the basic structure of a distance-compensated measuring device with a conical surface radiator,

3 : the basic structure of a distance-compensated measuring device with a parabolically curved surface radiator,

4 : the basic structure of a distance-compensated measuring device with a spherically curved surface radiator,

5 : Diagrams to illustrate the dependence of the image size on the distance between the measuring device and the eye for different measuring devices and

6 : A diagram with enlarged ordinate scaling to illustrate the dependency of the image size on the decentering of the eye for a distance-compensated measuring device.

The proposed distance-compensated measuring device for topographical and keratometric measurements on the eye consists of a surface radiator for illuminating the eye with structured patterns and an imaging optical unit arranged in a detection beam path and an image recording device, as well as a control and evaluation unit. According to the invention, an aperture stop is arranged in the detection beam path between the imaging optics and the image recording device for limiting the beam.

An aperture stop (also aperture stop) in an optical system limits its aperture, i. H. its free opening through which the light rays are received. The resolution is due to the wave diffraction of the diameter in relation to the wavelength of the radiation used. The area of the aperture determines the power absorbed by a plane wave, which is distributed on the surface of the image in the case of imaging optics.

An aperture stop is always located away from the image plane, object plane and intermediate image plane. The aperture diaphragm can therefore not be arbitrarily positioned in the beam path, as it would otherwise act as a visual field diaphragm. The images of the aperture diaphragm are called entrance pupil (object side) and exit pupil (image side).

With this special optical design, in particular by the fixed insertion of an aperture diaphragm, the distance dependence for an operating point is compensated.

d

dem Abstand des Oberflächenstrahlers zum Auge im Arbeitspunkt des Gerätes und

R

dem mittleren Krümmungsradius der Kornea entsprechen.

The position of the aperture diaphragm, the image of which forms the entrance pupil of the detection beam path, is to be selected such that the distance D between the entrance pupil and the surface radiator is sufficient D = 2 · d + R (1) results in the

d

the distance of the surface radiator to the eye in the working point of the device and

R

correspond to the mean radius of curvature of the cornea.

The mean radius of curvature of the human cornea can be given as 7.8 mm, for example.

From these specifications, the position of the aperture diaphragm in the detection beam path can be calculated. The position varies depending on the imaging optics used.

As a result, the size of the image, which arises from the surface radiator by reflection on the cornea and the imaging optics in the observation plane, does not change to a first approximation when the distance to the eye is varied.

According to an advantageous embodiment, the distance D between entrance pupil and surface radiator should at least approximately correspond to that calculated using equation (1), wherein a deviation of ± 15%, preferably ± 10% and particularly preferred ± 5% should not be exceeded.

According to a further advantageous embodiment, the surface radiator may have a plane, conical or even parabolic, spherical or the like curved shape.

This shows the 1 the basic structure of a distance-compensated measuring device with a flat surface radiator. The distance-compensated measuring device 1 for topographical and keratometric measurements on the eye 2 consists of a flat surface radiator 3 for the illumination of the eye 2 with structured patterns and one in a detection beam path 4 arranged imaging optics 5 and an image pickup device 6 , as well as a (not shown) control and evaluation. In the detection beam path 4 between the imaging optics 5 and the image pickup device 6 is additionally an aperture stop 7 arranged.

Furthermore, the shows 1 the entrance pupil 8th of the detection beam path 4 , as well as the distance D between the entrance pupil 8th and surface radiators 3 and the distance d of the surface radiator 3 to the eye 2 at the operating point of the distance-compensated measuring device 1 ,

In comparison, the show 2 the basic structure of a distance-compensated measuring device 1 with a conical surface radiator 3 ' , the 3 the basic structure of a distance-compensated measuring device 1 with a parabolic curved surface radiator 3 '' and the 4 the basic structure of a distance-compensated measuring device 1 with a spherically curved surface radiator 3 ''' , All other reference numerals correspond to those in FIG 1 , wherein for the distance D and the distance d in each case the average distances are to be set.

According to the invention, the surface radiator can vary not only in its shape (plan, conical or curved), but also in the type of structured pattern with which the eye is to be illuminated. As is known, the structured patterns can be based on points, lines, rings, bars or the like.

According to a further advantageous embodiment, the surface radiator can be designed so that the eye is illuminated for keratometric measurements with at least 2, preferably with 4 and particularly preferably with 6 rays (points).

In contrast, for topographical measurements, the eye must be illuminated by the surface radiator with 18 or more beams or with a ring or grid structure.

The surface radiator is preferably designed so that the existing points, lines, rings, beams or the like can be activated independently of one another and variably combined with one another to form a dynamic, structured illumination.

In the case of conventional distance-dependent measuring keratometers or topographs, the image size of the pattern in the imaging plane of the imaging optics changes as a function of the distance between the device and the eye due to the distance dependence.

This shows the 5 Diagrams illustrating the dependence of the image size M 'on the distance d between the measuring device and the eye for different measuring devices.

The upper diagram, which applies to a distance-dependent measuring device, shows a linear dependence of the image size M ', which becomes smaller as the distance d increases.

In contrast, the middle diagram applies to the measuring device according to the invention, which has no dependence of the image size M 'on the distance d at the operating point. Outside the operating point, however, deviations occur which have a quadratic dependence of the image size M 'on the distance d. This is shown in the lower diagram. The ordinate has a considerably finer scaling than the middle diagram.

The operating point is at the location of the minimum of the curve shown. This coincides with the optimum sharpness adjustment of the image of the surface radiator. This means that, for example, in punctiform structures of a typical 6-point keratometer, each of the detected spots has a minimum diameter. When varying the device distance to the eye, the spot diameter increases, no matter whether the device is moved towards the eye or away from it. The spot size can therefore be used to deduce the deviation of the device spacing from the operating point, but not its direction.

As according to the lower diagram of 5 the measurement error also depends only on the amount of deviation of the device spacing, but not on its sign, can be determined from the knowledge of the spot diameter of the measurement errors and thus corrected.

According to the invention, in a further preferred embodiment, the distance-compensated measuring device includes a device for determining spot sizes during the measurement and deriving therefrom correction values for the measurement results.

In this case, the spot sizes are detected in detail and a correction with respect to the detected spot size is made in the evaluation of the keratometry or topography data. The size or function for this correction can be determined experimentally with the aid of test objects or theoretically with suitable optical calculations.

Similar deviations occur in lateral shifts between eye and device with respect to the operating point.

This shows the 6 a diagram with enlarged ordinate scaling, to illustrate the dependence of the image size M 'of the decentering ΔZ of the eye for a distance-compensated measuring device. The deviations also have a quadratic dependence, wherein the minimum of the illustrated curve indicates the operating point in which the eye is exactly centered with respect to the optical device arrangement. The decentration can be easily determined from the measurement image by comparing the center of the imaged pattern with the center of the camera chip. Again, a correction of the resulting measurement error with knowledge of the size of the decentering is possible.

According to the invention, it is therefore provided in a further preferred embodiment to detect the decentering of the eye and to carry out a correction in relation to this value in the evaluation of the keratometry or topography data. The size or function for this correction can in turn be determined experimentally with the aid of test objects or theoretically with suitable optical calculations.

With the present invention, a measuring device is provided, with which even with the use of surface radiators distance-independent, topographic and keratometric measurements on the eye are possible. The measuring device is characterized by a simple structure and easy handling.

The distance-independent approach has established itself as the "gold standard" for the calculation of intraocular lenses (IOL). However, only 6 individual points are detected so far, since the projection principle requires a high technical complexity and prevents detection of the deviations of the corneal surface of a toric form.

The range-dependent measuring device allows projection of many points, circles or other suitable patterns, thereby enabling easy determination of a detailed topography of the cornea.

The present solution makes it possible to perform topographical and keratometric measurements at the operating point of the ophthalmological device regardless of distance. The solution thus combines the advantages of keratometric and topographic measurements on the eye with little technical effort. In this case, the present invention is suitable for various ophthalmic devices while maintaining the defined condition.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4685140 A [0005]
• US 5110200 A [0006]
• US 5194882 A [0006]
• US 5684562 A [0006]
• US 6116738 A [0006]
• US 5864383 A [0006]
• US 6575573 B2 [0007]
• US 6692126 B1 [0007]
• US 6048065 A [0009]
• US 6070981 A [0009]
• WO 2000/33729 A2 [0013]
• US 4660946 A [0014]
• WO 2012/160049 A1 [0015]

Claims (10)

Distance-compensated measuring device for topographical and keratometric measurements on the eye, comprising a surface radiator for illuminating the eye with structured patterns and an imaging optical system arranged in a detection beam path and an image recording device, and a control and evaluation, characterized in that for limiting the beam in the detection beam path between the imaging optics and the image recording device is arranged an aperture diaphragm, Distance-compensated measuring device according to claim 1, characterized in that the position of the aperture diaphragm is to be selected such that the image of the aperture forms the entrance pupil of the detection beam path, wherein the distance D between entrance pupil and surface radiator D = 2 · d + R (1) results in the d correspond to the distance of the surface radiator to the eye at the operating point of the device and R the mean radius of curvature of the cornea. Distance-compensated measuring device according to claims 1 and 2, characterized in that the distance D between entrance pupil and surface radiator at least approximately corresponds to that calculated with equation (1), wherein the deviation does not exceed ± 15%, preferably ± 10% and more preferably ± 5% , Distance-compensated measuring device according to claim 1, characterized in that the surface radiator has a plane, conical or else parabolic, spherical or curved shape. Distance-compensated measuring device according to claim 4, characterized in that the surface radiator is formed so that structured patterns in the form of points, lines, rings, beams or the like are used for illuminating the eye. Distance-compensated measuring device according to claim 5, characterized in that the surface radiator is formed so that the eye is illuminated for keratometric measurements with at least 2, preferably with 4 and more preferably with 6 rays. Distance-compensated measuring device according to claim 5, characterized in that the surface radiator is formed so that the eye is illuminated for topographic measurements with 18 or more beams or with a ring or grid structure. Distance-compensated measuring device according to claims 5 to 7, characterized in that the surface radiator is formed so that the existing points, lines, rings, beams o. Ä. Independently activated and can be variably combined with each other to a dynamic, structured illumination. Distance-compensated measuring device according to claim 1, characterized in that a device is provided to determine spot sizes during the measurement and to derive therefrom correction values for the measurement results. Distance-compensated measuring device according to claim 1, characterized in that a device is provided to determine the decentering of the eye during the measurement and to derive therefrom correction values for the measurement results.

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