DE102013218416B4 - Non-reflecting ophthalmoscope lens - Google Patents

Abstract

Reflection-free ophthalmoscope lens, preferably for fundus cameras, with a substantially coaxial illumination and imaging beam path, consisting of a lens system of at least four lenses (1, 2, 3 and 4), which are tilted with respect to their optical axes against the illumination and imaging beam path, wherein the optical axes of two lenses are in one plane with the optical axis of the illumination and imaging beam path and these two planes essentially intersect along the optical axis of the illumination and imaging beam path and the at least four lenses (1, 2, 3 and 4) are arranged alternately tilted in the direction of the x and y axis in the illumination and imaging beam path such that, starting from the eye (5) to be examined, the first and third lenses (1 and 3) are arranged around the x axis and the second and fourth lenses ( 2 and 4) are tilted about the y-axis, characterized in that the tangent angle and diameter of the Vo r and rear surfaces of the four lenses (1, 2, 3 and 4) have values from the following value ranges, starting from the eye to be examined (5): surface tangent angle (in degrees) diameter (in mm) 1V5 to 1555 to 651R15 to 2570 to 802V -5 to 565 to 752R5 to 1565 to 753V-15 to -2580 to 903R-5 to -1580 to 904V-25 to -3545 to 554R-10 to -2040 to 50

Description

The present invention relates to a reflection-free ophthalmoscope lens, in particular for fundus cameras. With fundus cameras, which are used to image the fundus of the eye, there are generally reflections on the cornea, the lens and surfaces of the optical system, which have a disruptive effect on the image quality.

According to the known state of the art, the basic structure of a fundus camera has a multi-stage optical system in which an intermediate image of the retina of the eye to be examined is generated by an ophthalmoscope objective, which may also be designed as a single-lens system is imaged by a follow-up system in a further intermediate image or on an imaging unit in the form of a camera. The ophthalmoscope objective is thus both a component of the illumination system and of the observation or imaging system.

A particular problem when observing and recording the fundus are reflections that occur on the cornea, the lens and the surfaces of the optical system, especially the ophthalmoscope lens, since the light reflected by the retina, which carries the image information that is actually of interest, has a significantly lower Intensity than the light reflected before entering the eye.

Disturbing corneal reflections and reflections of the human lens are usually reduced by dividing the pupil of the eye. For this purpose, the ophthalmoscope lens forms an illumination ring in the pupil of the eye. The observation takes place exclusively over the area within the illumination ring. This ensures that only the light reflected by the retina is imaged on the camera, since the rays of illumination reflected by the cornea or lens miss the aperture of observation.

In contrast to this, essentially the following two concepts are known for suppressing the reflections on the surfaces of the optical system, in particular of the ophthalmoscope lens. According to a first concept, the light components produced by reflection on the surfaces of the optical system are hidden from the observation beam path.

This describes the DE 35 19 442 A1 an optical system in which such light components are hidden by means of so-called "black point plates" arranged at suitable points in the beam path. For this purpose, the "black point plates" are covered with light-absorbing layers in a defined way. The term "anti-reflection point" has become common for this type of reflection suppression.

A disadvantage of this concept is the required proximity of the antireflection point to the field diaphragm. The absorption of individual light components can become visible as uneven illumination of the fundus of the eye and thus hinder the evaluation by the ophthalmologist.

With the second concept, there is no blanking out of certain light components within the illumination optics. Instead, a multi-lens ophthalmoscope optics is used, the lenses of which are tilted against each other in such a way that the reflections at the optical interfaces do not reach the aperture of observation.

Such a solution with a multi-lens ophthalmoscope optics is in DE 103 16 416 A1 described. By tilting the lenses against each other, reflections occurring at the optical interfaces are prevented from entering the observation beam path. This solution requires considerable effort for the mechanical mounts and the associated exact adjustment of the lenses. Another disadvantage is that the lenses used have relatively large basic geometries, despite a very small proportion of the area used for the beam path, which makes this design relatively expensive. The associated measure of the relationship between surface curvature and lens diameter, referred to as the tangent angle, also leads to a high tolerance sensitivity to positional tolerances. The tangent angle given in degrees describes the angle between the y-axis of the coordinate system, the surface S and the tangent to the surface S at the height H. The surface can be spherical or aspherical.

In the DE 10 2008 040 944 A1 describes a lens for a dental camera, which includes at least two lenses in addition to a light source and an image sensor. The problem to be solved is to provide a lens whose aberrations are caused by directed reflections on surfaces of lenses of the objective is reduced. In particular, there are means for tilting each of the lenses to the illumination beam in such a way that an optical axis of each lens forms a tilting angle to the illumination beam that can be selected so large that the reflection beams can be reflected in a direction outside a pupil of the observation beam.

In addition, longitudinal and transverse chromatic aberrations are generated, which have to be laboriously compensated for in the following optical system, both in the observation and in the illumination beam path. For applications with very small beam diameters, such as laser applications, the high number of optical interfaces and the long glass path of the lens described have a disadvantageous effect.

In the DE 10 2010 008 629 A1 a reflection-free imaging optics for optical devices is described, which consists of at least two refractive, optical elements that are used both for illumination and for observation. The refractive, optical elements are approximately wedge-shaped and are tilted at any azimuth angle of at least 5° and/or arranged decentered in the beam path in order to hide single reflections of the illumination occurring on the optical system surfaces for observation. The proposed imaging optics are intended for optical devices, in particular in ophthalmology. At least two of the optical system surfaces of the refractive, optical elements are designed as free-form surfaces, while the remaining optical system surfaces have an aspherical, toric or else a spherical shape. A disadvantage of this solution is that free-form surfaces are difficult to produce because of their complexity, which makes their production very expensive.

Systems that use reflective elements instead of refractive elements work completely without unwanted reflections. Fundus cameras are known that use mirror elements instead of the ophthalmoscope lens. Relatively simple ophthalmoscope mirror lenses enable a small observation field with a viewing angle of <= 30°.

Mirror systems, such as in the U.S. 6,585,374 B2 described, use moving parts to expand the small observation field or illumination field through scanning principles. In addition to complex mechanics for precise movement, this also requires more extensive image processing technology.

Other mirror systems, as in U.S. 7,637,617 B2 described, very large observation fields with and without scanning principles can be realized with HMD-like approaches with a mirror.

U.S. 5,815,242 A uses a single aspheric mirror having the pupil of the eye at its first focus, the mirror preferably being elliptical. This means that the sine condition is not met and the spot diameter at the edge of the pupil is a multiple of the spot diameter in the center of the pupil (which is equal to 0). However, with the desired smallest possible installation space, neither the imaging quality that can be achieved nor the necessary working distance do not meet the requirements of a modern-day fundus camera.

Mirror systems, such as from U.S. 2009/0185135 A1 known, enable very large observation fields in the contact method. According to the requirements of today's fundus camera, a non-contact method combined with a large working distance is preferable in order to ensure universal applicability and operability.

Mirror-based ophthalmoscope lenses are also known that enable an observation field with a viewing angle of more than 30° without scanning principles and that meet the imaging properties and ergonomic requirements of today's fundus camera. Lenses of this type already largely solve the disadvantages of the previously mentioned concepts for suppressing reflections.

the DE 10 2006 061 933 A1 describes a lens which, by means of at least one free-form mirror, enables a well-corrected observation field with a viewing angle significantly greater than 30°. However, when the system is defocused, the curvature of the image shell changes to compensate for the patient's ametropia. This degrades the imaging quality with large defocusing.

the U.S. 7,275,826 B2 describes a lens which, with curved mirrors, takes on the task of a classic ophthalmoscope lens with a large viewing angle.

The one not released yet DE 10 2012 022 967.4 relates to a reflection-free, optical system for a fundus camera and is also used both for illumination and for observation and/or documentation. For this purpose, the reflection-free, optical system consists of optical mirror elements, with at least two of the existing optical mirror elements having a free-form surface in order to realize three reflections. Here, too, it is disadvantageous that free-form surfaces are difficult to produce because of their complexity and are accordingly very expensive.

With these mirror systems, however, it is not possible to meet the high demands placed on a high-quality, modular fundus camera. In particular, the desired high imaging quality over a very large defocus range, in particular for setting the fundus camera to ametropia of more than +/-15 dpt, cannot be achieved. Furthermore, such a fundus camera should preferably have an ophthalmoscope lens that largely maintains the rotational symmetry in the field image and in the pupil image and leaves enough space for coupling points in front of the next effective optics.

The object of the present invention is to develop a reflection-free ophthalmoscope objective which overcomes the disadvantages of the prior art solutions and which, with the smallest possible basic geometries of the lenses, achieves low sensitivity to positional tolerances, a large imaging scale and a large focal length. In addition to avoiding false light paths, artefacts or vignetting, the solution should also be free of color errors, so that high-resolution, color-corrected fundus images can be realized.

According to the invention, the object is achieved with the non-reflecting ophthalmoscope lens, which has an essentially coaxial illumination and imaging beam path, consisting of a lens system of at least four lenses, which are tilted with respect to their optical axes against the illumination and imaging beam path, the optical axes of two lenses each lie in one plane with the optical axis of the illumination and imaging beam path and these two planes essentially intersect along the optical axis of the illumination and imaging beam path, solved in that the at least four lenses are tilted alternately in the direction of the x and y axes are arranged in the illumination and imaging beam path.

Preferred developments and refinements are the subject matter of the dependent claims.

The proposed non-reflecting ophthalmoscope lens is preferably intended for fundus cameras. Irrespective of this, the proposed solution can in principle also be used for other optical units both in ophthalmology and in other areas in which reflection-free images are important.

• 1: eine dreidimensionale Ansicht des erfindungsgemäßen Ophthalmoskopobjektivs,
• 2: eine erste Schnittdarstellung des Ophthalmoskopobjektivs in der y-z-Ebene,
• 3: eine zweite Schnittdarstellung des Ophthalmoskopobjektivs in der x-z-Ebene und
• 4: eine tabellarische Auflistung der bevorzugten, besonders bevorzugten bzw. speziellen Tangentenwinkel und Durchmesser der Vorder- und Rückflächen der einzelnen Linsen des Ophthalmoskopobjektivs.

The invention is described in more detail below using an exemplary embodiment. The show:

• 1 : a three-dimensional view of the ophthalmoscope lens according to the invention,
• 2 : a first sectional view of the ophthalmoscope lens in the yz plane,
• 3 : a second sectional view of the ophthalmoscope lens in the xz plane and
• 4 : a tabular listing of the preferred, most preferred, and specific tangent angles and diameters of the front and back surfaces of the individual lenses of the ophthalmoscope objective.

The non-reflecting ophthalmoscope lens, preferably provided for fundus cameras, with a substantially coaxial illumination and imaging beam path, consists of a lens system of at least four lenses, which are tilted with respect to their optical axes against the illumination and imaging beam path, the optical axes of two lenses each having the optical axis of the illumination and imaging beam path lie in one plane and these two planes essentially intersect along the optical axis of the illumination and imaging beam path.

This shows the 1 a three-dimensional view of the ophthalmoscope lens according to the invention, which shows the illumination and imaging beam path starting from the eye to be examined 5 to the intermediate image 6. The four lenses are identified consecutively with the reference numerals 1 to 4. The intermediate image 6 usually represents the interface for a subsequent optical system.

According to the invention, the at least four lenses are tilted alternately in the direction of the x and y axes in the illumination and imaging beam path. In particular, starting from the eye to be examined, the first and third lenses are arranged tilted around the x-axis and the second and fourth lenses around the y-axis.

For this, the 2 and 3 Sectional representations of the ophthalmoscope lens according to the invention in the yz and xz planes. The representations of 2 and 3 it can be seen that, starting from the eye 5 to be examined, the lenses 1 and 3 are arranged tilted around the x-axis and the lenses 2 and 4 around the y-axis.

According to a first advantageous embodiment of the non-reflecting ophthalmoscope lens according to the invention, the tangent angles and diameters of the front and rear surfaces of the at least four lenses, starting from the eye to be examined, have values from the following value ranges, with the front and rear surfaces of the individual lenses being considered separately: Surface Tangent angle (in degrees) Diameter (in mm) 1V 5 to 15 55 to 65 1r 15 to 25 70 to 80 2V -5 to 5 65 to 75 2R 5 to 15 65 to 75 3V -15 to -25 80 to 90 3R -5 to -15 80 to 90 4V -25 to -35 45 to 55 4R -10 to 20 40 to 50

According to the 1 the front surfaces of the lens 1 are denoted by 1V and the rear surfaces thereof by 1R. The same applies to the other lenses 2 to 4.

According to a second advantageous embodiment of the non-reflecting ophthalmoscope lens according to the invention, the tangent angles and diameters of the front and rear surfaces of the at least four lenses, starting from the eye to be examined, have values from the following preferred value ranges: Surface Tangent angle (in degrees) Diameter (in mm) 1V 8 to 13 60 to 65 1r 15 to 20 75 to 80 2V -2 to 3 68 to 73 2R 8 to 13 65 to 70 3V -20 to -25 85 to 90 3R -8 to -13 83 to 88 4V -28 to -33 45 to 50 4R -15 to -20 42 to 47.

A particularly advantageous embodiment provides that the tangent angles and diameters of the front and rear surfaces of the four lenses have the following specific values, starting from the eye to be examined: Surface Tangent angle (in degrees) Diameter (in mm) 1V 10.62 62 1r 17:34 76 2V 0.09 70 2R 11.40 68 3V -23.59 86 3R -10.33 85 4V -30.21 48 4R -16.61 44

The use of these special values has the advantage that the illumination and imaging beam path of the non-reflecting ophthalmoscope lens has a high level of coaxiality. Specifically, the beam path is almost coaxial, with the beam direction at the exit of the ophthalmoscope objective deviating from its optical axis by less than 5°, preferably less than 3° and particularly preferably less than 1°.

This shows the 4 a tabular listing of the preferred, most preferred, and specific tangent angles and diameters of the front and back surfaces of the individual lenses of the ophthalmoscope objective. In addition to the special tangent angles and diameters, the last table contains an additional column that contains the transmitted surface areas (in %) of the front and back surfaces of the individual lenses of the ophthalmoscope objective.

With the arrangement according to the invention, a reflection-free ophthalmoscope objective is made available, preferably for fundus cameras, which has an essentially coaxial illumination and imaging beam path.

In addition, with the solution according to the invention, the area portion of each lens through which radiation passes could be increased by minimizing the displacement for each lens and improving its ratio between surface curvature and lens diameter (tangent angle).

This advantageously led to smaller basic geometries of the lenses, less wedge-shaped lens segments and thus to a lower sensitivity to positional tolerances and better coaxiality.

The proposed ophthalmoscope lens overcomes the disadvantages of the solutions of the prior art and, with the smallest possible basic geometries of the lenses, achieves low sensitivity to positional tolerances, a large imaging scale and a large focal length.

By avoiding false light paths, artefacts or vignetting, high-resolution, color-corrected fundus images can also be realized.

Claims (4)

Reflection-free ophthalmoscope lens, preferably for fundus cameras, with a substantially coaxial illumination and imaging beam path, consisting of a lens system of at least four lenses (1, 2, 3 and 4), which are tilted with respect to their optical axes against the illumination and imaging beam path, wherein the optical axes of two lenses are in one plane with the optical axis of the illumination and imaging beam path and these two planes essentially intersect along the optical axis of the illumination and imaging beam path and the at least four lenses (1, 2, 3 and 4) are arranged alternately tilted in the direction of the x and y axis in the illumination and imaging beam path such that, starting from the eye (5) to be examined, the first and third lenses (1 and 3) are arranged around the x axis and the second and fourth lenses ( 2 and 4) are tilted about the y-axis, characterized in that the tangent angles and diameters of the V Order and rear surfaces of the four lenses (1, 2, 3 and 4) starting from the eye to be examined (5) have values from the following value ranges: Surface Tangent angle (in degrees) Diameter (in mm) 1V 5 to 15 55 to 65 1r 15 to 25 70 to 80 2V -5 to 5 65 to 75 2R 5 to 15 65 to 75 3V -15 to -25 80 to 90 3R -5 to -15 80 to 90 4V -25 to -35 45 to 55 4R -10 to 20 40 to 50 Non-reflecting ophthalmoscope lens claim 1 , characterized in that the tangent angles and diameters of the front and rear surfaces of the four lenses (1, 2, 3 and 4), starting from the eye (5) to be examined, have values from the following preferred value ranges: Surface Tangent angle (in degrees) Diameter (in mm) 1V 8 to 13 60 to 65 1r 15 to 20 75 to 80 2V -2 to 3 68 to 73 2R 8 to 13 65 to 70 3V -20 to -25 85 to 90 3R -8 to -13 83 to 88 4V -28 to -33 45 to 50 4R -15 to -20 42 to 47. Non-reflecting ophthalmoscope lens according to one of Claims 1 or 2 , characterized in that the tangent angles and diameters of the front and rear surfaces of the four lenses (1, 2, 3 and 4), starting from the eye (5) to be examined, have the following specific values: Surface Tangent angle (in degrees) Diameter (in mm) 1V 10.62 62 1r 17:34 76 2V 0.09 70 2R 11.40 68 3V -23.59 86 3R -10.33 85 4V -30.21 48 4R -16.61 44 Non-reflecting ophthalmoscope lens claim 3 , characterized in that the beam path is almost coaxial, the beam direction at the exit of the ophthalmoscope objective deviating from its optical axis by less than 5°, preferably less than 3° and particularly preferably less than 1°.

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