WO2009018956A1

WO2009018956A1 - Device and method for the automatic focusing of a non-mydriatic fundus camera

Info

Publication number: WO2009018956A1
Application number: PCT/EP2008/006296
Authority: WO
Inventors: Lydia Hellrung; Michael Trost; Detlef Biernat; Axel Doering
Original assignee: Carl Zeiss Meditec Ag
Priority date: 2007-08-03
Filing date: 2008-07-31
Publication date: 2009-02-12
Also published as: DE102007036683B4; DE102007036683A1

Abstract

The invention relates to a non-mydriatic fundus camera, consisting of a focusing mark unit (3) disposed in the illumination beam path (1), generating at least one focusing mark in the infrared spectral region, having a focusing aid adjusting unit (4) for projecting onto the fundus oculi (S), an IR sensitive imaging sensor (9) disposed in the imaging beam path, having an image processing unit (10) for observing and recording the fundus oculi, having an imprinted focusing mark, and a control and analysis unit, wherein actuating signals are generated by the control and analysis unit (12) both for the focusing aid actuating unit (4) and for the focusing actuating unit (11) during the analysis of the images of the fundus oculi with an imaged focusing mark that are recorded by the sensor (9) having an image processing unit (10), for balancing any refractive imaging errors of the main lens disposed in the imaging beam path.

Description

Device and method for automatic focusing of a non-mydriatic fundus camera

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

According to the known state of the art, the following two different procedures have been established for the examination of the ocular fundus with a fundus camera.

While it is necessary in the first method to enlarge the pupil of the patient with medication to examine the fundus, fundus cameras work according to the "non-mydriatic" principle with (invisible) infrared light, wherein in a darkened room an enlargement of the pupil without If the pupil is sufficiently dilated, the eye is briefly illuminated with white (visible) light and an image of the fundus of the eye is taken.

In order to compensate for defective vision of patients, it is necessary that fundus cameras can be focused on the ocular fundus accordingly. In order to produce a sharp, high-contrast image of the patient's fundus on the image recorder or in the eye of the observer, despite defective vision, internal optical assemblies of the fundus camera are displaced.

For fundus cameras that use the "non-mydriatic" principle, there are additional problems for focusing, since observation takes place in the case of infrared light and image acquisition in the case of white light For the different wavelengths due to the optical conditions different focal planes, so that in sharp images during observation with infrared light, the result image would be picked up in the presence of white light blurred. For this reason, focusing aids are used in "non-mydriatic" fundus cameras During observation, a test mark is projected onto the ocular fundus by means of this focusing aid, for example with infrared light, and correspondingly on the basis of the image on the imaging sensor and / or in the eyepiece Preferably, this is done by a coincidence method in which two half marks are overlapped, whereby the half marks are conventionally manually aligned by the operator, thus the setting is subjectively subject to the operator and constitutes a significant source of error.

According to the prior art, corresponding solutions are known which seek to eliminate this subjective source of error by automating the focusing.

Thus, WO 2006/106977 A1 describes an ophthalmological imaging system in which contrast information of an IR observation image is evaluated by decoupling by means of a beam splitter and imaging onto 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 solution described in US 4,436,388 A1 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.

The illumination of the mark takes place with light of a different wavelength than the observation light. For evaluation, the image of the marking is coupled out via selective mirrors and imaged onto the linear, position-dependent photosensor, from whose signal a corresponding control signal for the focusing is derived.

A disadvantage of this solution are the additionally required mechanical, optical and electronic components, whereby the arrangement is complicated and complicated in their operation.

US Pat. No. 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 a examined human eye, a detector device for determining the focus mark position and a control device for automatic focusing as a function of 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 it is necessary that the Image of the half-mark reflected by the fundus of the eye is decoupled by means of selective mirrors and imaged onto a position-dependent photosensor.

In this approach too, the additionally required mechanical, optical and electronic components have a disadvantageous effect, since the arrangement becomes more complicated and more complicated to operate.

The object of the present invention is to develop a solution for the automatic focusing of ophthalmological devices, preferably non-mydriatic fundus cameras, which overcomes the disadvantages of the known state of the art and, with simple operation, ensures precise focusing.

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.

In this case, the proposed device for automatically focusing a non-mydriatic fundus camera from a arranged in the illumination beam path, at least one Fokussiermarke generating in the infrared spectral Fokussiermarken unit with a Fokussierhilfe- actuator unit for projection on the ocular fundus, arranged in an imaging beam IR-sensitive, imaging sensor with image processing unit for observation and recording of the ocular fundus with imaged focus mark, as well as a control and evaluation unit. The control and evaluation unit generates evaluations of the images of the ocular fundus imaged by the sensor with image processing unit with the focusing mark imaged, as well as actuating signals for the focusing aid setting unit and for the focusing adjustment unit to compensate for refractive aberrations of the main objective arranged in the imaging beam path forwarded and executed, whereby the tax and evaluation unit further control signals are generated until the focus state is reached.

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 imaging.

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

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

Figure 2: the flow chart for the evaluation algorithm.

The device according to the invention for the automatic focusing of a non-mydriatic fundus camera comprises a focusing-mark unit which is arranged in the illumination beam path and generates at least one focusing mark in the infrared spectral range with a focusing aid positioning unit for projection onto the ocular fundus, an IR-sensitive imaging sensor arranged in the imaging beam path Image processing unit for observation and recording of the ocular fundus with imaged focusing mark, and a control and evaluation unit. According to the invention, the control and evaluation unit generates evaluations of the images of the ocular fundus imaged by the sensor with image processing unit with imaged focus mark, as well as control signals for the focusing aid setting unit and for the focusing adjustment unit to compensate for refractive aberrations of the main objective arranged in the imaging beam path forwarded and executed, whereby the tax and evaluation unit further control signals are generated until the focus state is reached.

The focusing assist actuator unit present for the projection of the focusing mark on the fundus must be calibrated before it is put into operation, for which purpose a model eye is usually used. Calibration is done in such a way that coincidence is achieved when the system is focused for white light photography.

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. It is only through the calibration that it is possible to ensure that the focus state is actually reached when the two parts of the focusing mark agree.

In a second advantageous embodiment, both the setting unit for compensating refractive aberrations of the main objective arranged in the imaging beam path and the focusing unit are designed as electrical actuators.

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

In the apparatus according to the invention for automatic focusing of a non-mydriatic fundus camera, in addition to the infrared light source 2 already present in the illumination beam path 1, a focussing mark unit 3 with a focusing aid setting unit 4 for generating at least one focussing mark in the infrared spectral range is arranged. The focusing mark is projected onto the ocular fundus 6 illuminated by the infrared light source 2 via different optical elements 5 arranged in the illumination beam path 1 and, after reflection at the ocular fundus 6, via different optical elements 5 arranged in the imaging beam path 7 and the main objective 8 onto an IR objective. sensitive, imaging sensor 9 with an image processing unit 10 for observation and evaluation of the ocular fundus 2 with mapped focus mark shown. To compensate for refractive aberrations arranged in the imaging beam 7 main objective 8 has a focusing actuator 11, with which the main objective 8 along the optical axis of the imaging beam path 7 can be moved.

The image processing unit 10 generates control signals for the control unit 12 in evaluation of the images of the fundus 6 recorded by the sensor 9 with image processing unit 10 with imaged focusing mark, which control signals for the focusing aid setting unit 4 as well as for the focusing setting unit 11 of the main objective 8 generated. The image processing unit 10 generates control signals until the image of the focus mark indicates the focus state (coincident).

In the method according to the invention for the automatic focusing of a non-mydriatic fundus camera, at least one focusing mark is produced in the infrared spectral range and projected onto the ocular fundus by a focusing mark unit with focusing aid positioning unit arranged in the illumination beam path and an image of the ocular fundus with imaged focus mark is arranged by one in the imaging beam path IR-sensitive imaging sensor with image processing unit recorded for observation and recording. From a control and evaluation unit, in evaluation of the images taken by the sensor with image processing unit of the ocular fundus with imaged Fokussiermarke, both control signals for the focusing assist actuator and for a focusing actuator to compensate for refractive aberrations of the imaging in the imaging beam path arranged main lenses are generated, forwarded to this and executed, which are generated by the control and evaluation further control signals until the focus state is reached.

In a first embodiment variant, the focusing-mark unit generates a two-part focusing mark in the infrared spectral range for a coincidence method. It is only through the calibration that it is possible to ensure that the focus state is actually reached when the two parts of the focusing mark agree.

In a second embodiment variant, both the setting unit for compensating refractive aberrations of the main objective arranged in the imaging beam path and the focusing unit are electrically operated.

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 of the ocular fundus imaged by the sensor with image processing unit with imaged focus mark according to the evaluation algorithm illustrated in FIG.

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 displacement are 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 focus aid setting unit and the focusing adjustment unit are generated for the compensation of refractive aberration, transmitted thereto and set the new positions.

A next pass of the algorithm shows whether the focus state has already been reached or whether further correction and the generation of further control signals are necessary. Achieving the focus state is iterative.

In an advantageous embodiment of step 1), the predefined image area is restricted on successful search for statistical image features of the focusing mark for the further steps 2) to 5). This has the advantage that the image files to be detected smaller and thus the focus state is achieved faster. The method according to the invention can be advantageously integrated into a fundus camera.

With the solution according to the invention, a device and a method for automatic focusing of a non-mydriatic fundus camera are proposed, which overcomes the disadvantages of the known prior art and ensures precise focusing with simple operation

In this case, it is advantageous that both the illumination of the fundus and the focusing mark projected onto the fundus of the eye take place at the same wavelength (in the infrared range), since optical components for wavelength selection can be dispensed with and the overall structure can thus be made simpler and more user-friendly. The dependent on the subjectivity of the operator focusing is now fully automatic, which could be eliminated a significant source of error for blurred fundus recordings.

Claims

claims

1. A device for automatic focusing of a non-mydriatic fundus camera, consisting of a in the illumination beam path (1) arranged, at least one focusing mark in the infrared spectral range generating Fokussiermarken unit (3) with a focusing aid Stell- unit (4) for projection onto the ocular fundus (6), an in the imaging beam path (7) arranged IR-sensitive, imaging sensor (9) with image processing unit (10) for observation and recording of the ocular fundus (6) with imaged focus mark, and a control and evaluation unit (12), characterized in which the control and evaluation unit (12) evaluates the images of the ocular fundus (6) recorded by the sensor (9) with the image processing unit (10) with the focussing mark imaged, both actuating signals for the focusing aid setting unit (4) and for the focusing actuator (11) for compensating refractive aberrations of the imaging beam gear (7) arranged main lenses (8) generated, forwarded to this and executed, being generated by the control and evaluation unit (12) actuating signals, forwarded and executed until the focus state is reached.

2. Apparatus according to claim 1, characterized in that for the projection of the focusing mark on the ocular fundus (6) existing focus kussierhilfe-adjusting unit (4) is calibrated.

3. A device according to claim 1, characterized in that of the Fokussiermarken unit (3) a two-part Fokussiermarke in the infrared spectral range is generated for a coincidence method.

4. Device according to claim 1 and 2, characterized in that both the focusing aid setting unit (4) and the focusing setting unit (11) to compensate for refractive aberrations of the imaging beam in the (7) arranged main objective (8) are designed as electrical actuators.

5. Apparatus according to claim 1 to 3, characterized in that the device is integrated in a fundus camera.

6. A method for automatic focusing of a non-mydriatic fundus camera, in which at least one focusing mark in the infrared spectral range is generated by a focusing mark unit arranged in the illumination beam path with the focusing unit and projected onto the ocular fundus and an image of the ocular fundus with imaged focus mark of one arranged in the imaging beam path IR-sensitive, imaging sensor is recorded with image processing unit for observation and recording, characterized in that by a control and evaluation in evaluation of the sensor with the image processing unit recorded images of the ocular fundus with imaged Fokussiermarke, both control signals for the focusing and for an actuating unit for compensating refractive aberrations, the main objective arranged in the imaging beam path is generated, passed on to it and executed, whereby the control unit and evaluation unit control signals generated, forwarded and executed until the focus state is reached.

7. The method according to claim 6, characterized in that the existing for projection of the focusing mark on the fundus focusing unit is calibrated.

8. The method according to claim 6, characterized in that the focusing-mark unit generates a two-part focusing mark in the infrared spectral range for a coincidence method.

, Method according to at least one of Claims 6 to 8, characterized in that the control signals are generated in the control and evaluation unit in such a way that both look for statistical images of the focusing mark in predefined image areas in the images of the ocular fundus taken by the sensor with image processing unit Parts of the Fokussiermarke be detected in order to determine their distance, to calculate the focus position for the refractive compensation to generate corresponding control signals and to transmit to the focusing unit and the one adjustment unit for compensating refractive aberrations.

10. The method according to at least one of claims 6 to 9, characterized in that in the control and evaluation unit, the generation of the control signals takes place such that the predefined image area containing the Fokussiermarke is limited for the further process steps to a smaller image area.

11. The method according to at least one of claims 6 to 10, characterized in that the method and the optical elements required for it are integrated into a fundus camera.