DE102007036683A1 - Apparatus and method for automatically focusing a nonmydriatic fundus camera - Google Patents

Abstract

The present invention relates to a solution for the automatic focusing of ophthalmological devices, in particular of non-mydriatic fundus cameras. The proposed device consists of a arranged in the illumination beam path, at least one Fokussiermarke generating in the infrared spectral Fokussiermarken unit with a focusing assisting actuator for projection on the fundus, a arranged in the imaging beam IR-sensitive, imaging sensor with image processing unit for observation and recording of the fundus with mapped focus mark, as well as a control and evaluation unit, being refractive of the control and evaluation unit in evaluation of the sensor with image processing unit images of the ocular fundus with imaged Fokussiermarke, both control signals for the focusing aid setting unit and for the focusing actuator Abbildfehler, the arranged in the imaging beam main objective can be generated. Although the proposed solution is intended in particular for the automatic focusing of non-mydriatic fundus cameras, it can in principle also be used for other ophthalmological devices for examining the ocular fundus by means of an optical system and electronic sensors for image acquisition.

Description

The The present invention relates to an apparatus and a method for the automatic focusing of ophthalmological devices, preferably for Examination of the ocular fundus by means of an optical system and electronic sensors for image acquisition. Especially advantageous is the use for non-mydriatic fundus cameras.

To The prior art has become available for the investigation of the fundus with a fundus camera following two different ones Procedures established.

While It is necessary in the first procedure, the pupil of the patient expand with medication to examine the fundus Fundus cameras work according to the "non-mydriatic" principle with (invisible) infrared light, being in a darkened Space an enlargement of the pupil occurs without medication. If the pupil is sufficiently dilated, the eye will be present for a short time white (visible) light illuminates and a picture of the fundus added.

Around To compensate for defective vision of patients, It is necessary to have fundus cameras corresponding to the fundus can be focused. Thus, despite ametropia sharp, high-contrast image of the patient's fundus on the image sensor or in the eye of the observer internal optics modules of the fundus camera moved.

For Fundus cameras that work according to the "non-mydriatic" principle, arise for the focusing additional Problems, as the observation in infrared and image acquisition done in white light. Inevitably arise due to the different wavelengths the optical conditions different focal planes, so that with sharp pictures during the observation with infrared Light the result image with white light blurred would become. For this reason, in "Non-Mydriatic" fundus cameras Focusing helps used. During the observation will from this focusing aid, for example, with infrared light a test mark is projected onto the fundus and based on the representation observed accordingly on the imaging sensor and / or in the eyepiece and evaluated. Preferably, this is done by a coincidence method, in which two half marks are brought to cover. The semi-brands are traditionally manually by the Operator brought to cover. The attitude depends thus subjectively from the operator and represents a major source of error.

To the prior art, corresponding solutions are known who seek to eliminate this subjective source of error by the Focusing is automated.

So will in the WO 2006/106977 A1 an ophthalmological imaging system described in which contrast information of an IR observation image by decoupling by means of beam splitter and imaging are evaluated on a contrast sensor. The achieved sharpness of the image of a highlighter is used as a measure of the focus state. The light intensity, which is already limited by the fact that the light exposure of the eye to be examined is not too high, is additionally reduced by the necessary decoupling of part of the light reflected by the eye fundus. In addition, the overall arrangement becomes more complex and complicated in its application by additional electronic components required. From a technical point of view, it should be considered whether the contrast information is even sufficient to accurately estimate the focus state.

The in the US 4,436,388 A1 described solution relates to a fundus camera with an observation system and a photographic recording system. In addition to an ocular fundus illumination system, the solution has a projector for projecting markers on the background of the eye to be examined, which are used to focus the camera. While the marks projected on the fundus cover the camera when the camera is in focus, they diverge when the camera is out of focus. For detecting the marking, the arrangement has a linear photosensor and a control unit for focusing the camera by means of the output signal of the photosensor.

there the illumination of the mark takes place with light of a different wavelength as the observation light. For evaluation, the image of the marker over Selective mirror decoupled and on the linear, position-dependent Photosensor shown, from the signal of a corresponding control signal is derived for focusing.

adversely in this solution are the additional required mechanical, optical and electronic components, thereby the arrangement becomes more complex and complicated in its operation.

The US 4,412,728 A1 describes a fundus camera with automatic focus, with an optical projection device for projecting a focus mark on the ocular fundus of an examined human eye, a detector device for determining the focus mark position and a control device for automatic focusing in dependence on the output signal of the detector device. In each case only a part of the image of the focusing mark is selected and projected onto the fundus, wherein a different wavelength than that of the observation light is selected. Depending on the output signal of the detector device, a control signal for the focusing is derived by the control device and the automatic focusing is performed. For this purpose, it is necessary that the image of the half-mark reflected by the fundus is coupled out by means of selective mirrors and imaged onto a position-dependent photosensor.

Also in this approach, the additional effect required mechanical, optical and electronic components disadvantageous, since the arrangement thereby consuming and in their Operation becomes more complicated.

Of the present invention, the object is based on a solution for the automatic focusing of ophthalmic devices, preferably to develop non-mydriatic fundus cameras, the fixes the disadvantages of the known prior art and in a easy operation ensures precise focusing.

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

there is the proposed device for automatic focusing a non-mydriatic fundus camera from a in the illumination beam path arranged, at least one focusing mark in the infrared spectral range generating focussing unit with a focusing aid setting unit for projection onto the fundus, one in the imaging beam path arranged IR-sensitive, imaging sensor with image processing unit for observation and recording of the fundus with imaged focusing mark, as well as a control and evaluation unit. From the control and evaluation unit are in evaluation of the sensor with image processing unit recorded images of the fundus with imaged focusing mark, both actuating signals for the focusing aid setting unit as well as for the focusing actuator to compensate for refractive aberrations, generated in the imaging beam path arranged main objective, forwarded to this and executed, whereby by the tax and Evaluation unit further control signals are generated until the focus state is reached.

Even though the proposed solution, in particular for automatic Focusing non-mydriatic fundus cameras is provided in principle also for other ophthalmic devices Examination of the ocular fundus by means of an optical system and electronic sensors for image acquisition.

The Invention will be described below with reference to embodiments described in more detail. To show:

1 : the basic structure of the device according to the invention and

2 : the flow chart for the evaluation algorithm.

The Inventive device for automatic Focusing on a non-mydriatic fundus camera consists of a arranged in the illumination beam path, at least one focusing mark in the infrared spectral range generating Fokussiermarken unit with a focus aid actuator for projection on the fundus of the eye, a arranged in the imaging beam path IR-sensitive, imaging Sensor with image processing unit for observation and recording of the fundus with imaged focusing mark, as well as a Control and evaluation unit. According to the invention from the control and evaluation unit in evaluation of the sensor with Image processing unit taken pictures of the fundus with imaged focus mark, both control signals for the focus aid actuator as well as the focusing actuator for Compensation of refractive aberrations, in the imaging beam path arranged main lenses generated, forwarded to this and executed, wherein the control and evaluation unit additional control signals are generated until the focus state is reached is.

The for projecting the focus mark on the fundus Focusing aid setting unit to be calibrated before commissioning, what usually a model eye is used. The Calibration is done in such a way that coincidence is reached when the system focused for white light shooting is.

In a first advantageous embodiment, the focusing-mark unit generates a two-part focusing mark in the infrared spectral range for a coincidence method according to which both parts of the focusing mark are to be brought into coincidence. Only through the calibration can be ensured that if the two parts match Focusing the focus state is really achieved.

In In a second advantageous embodiment, both the setting unit to compensate for refractive aberrations of the imaging beam path arranged main lenses as well as the focusing unit, as formed electrical actuators.

In a further advantageous embodiment, the device according to the invention is integrated into a fundus camera. In addition shows 1 the basic structure of the inventive device for automatic focusing of a non-mydriatic fundus camera.

In the device according to the invention for the automatic focusing of a non-mydriatic fundus camera is in addition to that in the illumination beam path 1 already existing infrared light source 2 a focus mark unit 3 with a focus aid actuator 4 arranged for generating at least one focusing mark in the infrared spectral range.

The focus mark is on different, in the illumination beam path 1 arranged optical elements 5 on the, from the infrared light source 2 lighted eye background 6 projected and after reflection on the fundus 6 over different, in the imaging beam path 7 arranged optical elements 5 as well as the main lens 8th on an IR-sensitive, imaging sensor 9 with an image processing unit 10 for observation and evaluation of the fundus 2 imaged with mapped focus mark. To compensate for refractive aberrations this has in the imaging beam path 7 arranged main lens 8th via a focusing actuator 11 with which the main objective 8th along the optical axis of the imaging beam path 7 can be moved.

From the image processing unit 10 are being evaluated by the sensor 9 with image processing unit 10 taken pictures of the fundus 6 with focussing mark shown control signals for the control unit 12 which generates therefrom both actuating signals for the focusing aid setting unit 4 as well as for the focusing actuator 11 of the main objective 8th generated. The image processing unit 10 generates control signals until the image of the focus mark indicates the focus state (coincident).

at the inventive method for automatic Focusing of a non-mydriatic fundus camera is by a Focusing mark unit arranged in the illumination beam path with focusing aid actuator at least one focus mark in generated infrared spectral range and on the fundus projected and a picture of the fundus with imaged Focusing mark of a arranged in the imaging beam path IR-sensitive, imaging sensor with image processing unit recorded for observation and recording. From a tax and evaluation unit are in evaluation of the sensor with image processing unit recorded images of the fundus with imaged focusing mark, both actuating signals for the focusing aid setting unit as well as for a focusing actuator for compensation refractive aberration, the beam path arranged in the imaging Main lenses are generated, forwarded to them and executed be, with the control and evaluation unit further control signals are generated until the focus state is reached.

The for projecting the focus mark on the fundus Focusing aid setting unit to be calibrated before commissioning, what usually a model eye is used. The Calibration is done in such a way that coincidence is reached when the system focused for white light shooting is.

In a first embodiment variant is of the focussing unit a two-part focusing mark in the infrared spectral range for generates a coincidence method. Only through the calibration can be ensured that in case of agreement the two parts of the focus mark the focus state really is reached.

In A second embodiment variant, both the actuator to compensate for refractive aberrations of the imaging beam path arranged main lenses as well as the focusing unit electrically operated.

• 1) In einem vordefinierten Bildbereich wird nach statistischen Bildmerkmalen der Fokussiermarke gesucht. War die Suche erfolglos, wird in den anderen vordefinierten Bildbereichen gesucht bis die Suche erfolgreich ist.
• 2) In dem Bildbereich indem sich die Fokussiermarke mit hoher Wahrscheinlichkeit befindet werden beide Teile der Fokussiermarke mittels Verfahren der Mustersuche detektiert. Falls die Detektion doch erfolglos ist, wird zu Schritt 1) zurückgegangen.
• 3) In dem Bildbereich, der beide Teile der Fokussiermarke enthält, werden der Abstand zwischen beiden Teilen und die Richtung der Verschiebung bestimmt. Decken sich beide Teile der Fokussiermarke, ist der Fokuszustand erreicht.
• 4) Aus dem ermittelten Abstand der beiden Teile der Fokussiermarke und dem bekannten Zusammenhang zwischen Abstand der Teilmarken und Defokussierzustand wird die Fokusposition für den refraktiven Ausgleich errechnet.
• 5) Daraus werden die entsprechenden Steuersignale für die Fokussierhilfe-Stelleinheit und den Fokussier-Stelleinheit zum Ausgleich refraktiver Abbildungsfehlers generiert, an diese übermittelt und die neuen Positionen eingestellt.

In a further embodiment variant, the generation of actuating signals for the focusing unit as well as for the setting unit of the main objective takes place from the images taken by the sensor with image processing unit of the ocular fundus with imaged focusing mark according to the 2 illustrated evaluation algorithm.

• 1) Statistical image features of the focusing mark are searched in a predefined image area. If the search was unsuccessful, it will search in the other predefined image areas until the search is successful.
• 2) In the image area in which the focus mark is located with high probability, both parts of the focus mark are detected by pattern search methods. If the detection is unsuccessful, the procedure returns to step 1).
• 3) In the image area containing both parts of the focussing mark, the distance between both parts and the direction of the shift determined. If both parts of the focus mark coincide, the focus state is reached.
• 4) From the determined distance between the two parts of the focusing mark and the known relationship between the distance of the partial marks and Defokussierzustand the focus position for the refractive compensation is calculated.
• 5) From this, the corresponding control signals for the focusing assistance setting unit and the focusing adjustment unit for compensating refractive aberration are generated, transmitted to this and set the new positions.

One Next pass of the algorithm shows if the focus state already reached or whether another correction and the generation additional control signals are necessary. Achieving the focus state is iterative.

In an advantageous embodiment of step 1) is the predefined Image area on successful search for statistical image features of Focusing mark for the further steps 2) to 5) restricted. This has the advantage that the image files to be detected smaller and thereby the focus state is reached faster.

The inventive method can be advantageous integrate into a fundus camera.

With the solution according to the invention become a Device and method for automatically focusing a non-mydriatic fundus camera suggested that the disadvantages fixes the known prior art and a simple Operability ensures precise focusing It is advantageous that both the illumination of the fundus as well as the focusing mark projected onto the fundus at the same wavelength (in the infrared range), since waived optical components for wavelength selection can be and the overall structure easier and more user-friendly can be designed. The subjectivity of the operating staff dependent focusing is now fully automatic, which a major source of error for blurred fundus images could be eliminated.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - WO 2006/106977 A1 [0007]
• US 4436388 A1 [0008]
• US 4412728 A1 [0011]

Claims (11)

Device for the automatic focusing of a non-mydriatic fundus camera, comprising one in the illumination beam path ( 1 ), at least one Fokussiermarke generating in the infrared spectral range Fokussiermarken unit ( 3 ) with a focus aid actuator ( 4 ) for projection on the fundus ( 6 ), one in the imaging beam path ( 7 ) arranged IR-sensitive, imaging sensor ( 9 ) with image processing unit ( 10 ) for observation and recording of the fundus ( 6 ) with imaged focusing mark, as well as a control and evaluation unit ( 12 ), characterized by the control and evaluation unit ( 12 ) in evaluation of the sensor ( 9 ) with image processing unit ( 10 ) taken pictures of the fundus ( 6 ) with focussing mark imaged, both actuating signals for the focusing aid setting unit ( 4 ) as well as for the focusing actuator ( 11 ) to compensate for refractive aberrations, the in the imaging beam path ( 7 ) arranged main lenses ( 8th ) are generated, forwarded to them and executed, whereby the control and evaluation unit ( 12 ) Control signals are generated, forwarded and executed until the focus state is reached. Apparatus according to claim 1, characterized in that the projection of the focus mark on the fundus ( 6 ) existing focusing aid actuator ( 4 ) is calibrated. Apparatus according to claim 1, characterized in that of the focussing mark unit ( 3 ) a two-part focusing mark in the infrared spectral range is generated for a coincidence method. Device according to claim 1 and 2, characterized in that both the focusing aid setting unit ( 4 ) as well as the focusing actuator ( 11 ) to compensate for refractive aberrations, the in the imaging beam path ( 7 ) arranged main lenses ( 8th ) are formed as electrical actuators. Apparatus according to claim 1 to 3, characterized in that the device is integrated into a fundus camera. Method for automatically focusing a non-mydriatic Fundus camera, in which of a arranged in the illumination beam path Fokussiermarken unit with focusing unit at least one focusing mark in the infrared Spectral range generated and projected onto the fundus and an image of the fundus with imaged focus mark from an IR-sensitive, arranged in the imaging beam path, Imaging sensor with image processing unit for observation and recording is recorded, characterized in that from a control and evaluation unit in evaluation of the sensor images of the fundus taken with the image processing unit with imaged focus mark, both control signals for the focusing unit as well as an actuator for Compensation of refractive aberrations, arranged in the imaging beam path Main lenses are generated, forwarded to them and executed be, where generated by the control and evaluation control signals, forwarded and be executed until the focus state is reached. Method according to claim 6, characterized in that that to the projection of the focus mark on the fundus existing focusing unit is calibrated. Method according to Claim 6, characterized that of the focussing unit a two-part focussing mark in the infrared spectral range for a coincidence method is produced. Method according to at least one of the claims 6 to 8, characterized in that in the control and evaluation unit the generation of the control signals takes place in such a way that in the vom Sensor with image processing unit taken images of the fundus, in predefined image areas according to statistical image features the focus mark sought, both parts of the focus mark detected In order to determine their distance, the focus position to calculate for the refractive compensation, corresponding To generate actuating signals and to the focusing unit and the one actuator to compensate for compensating refractive aberrations. Method according to at least one of the claims 6 to 9, characterized in that in the control and evaluation unit the generation of the control signals takes place in such a way that the predefined Image area containing the focus mark for the further process steps to a smaller image area is restricted. Method according to at least one of the claims 6 to 10, characterized in that the method and the required optical elements integrated into a fundus camera become.