Slit-lamp microscope spatial light modulator and low-pass filter

Abstract

The slit-lamp microscope comprises a microscope device (8) which projects an object plane (11) into an eyepiece (18) or a camera (16) and an illumination device (9) with a spatial light modulator (24). The illumination device includes a beam splitter (70) that acts as a low-pass filter to suppress the spatial frequencies of the pixels of the light modulator (24) and to generate more uniform illumination. In other embodiments, at least a portion of the illumination imaging optics (26) may be deflected using an actuator (90-98) to generate a low-pass filtered image of the spatial light modulator (24).

Description

Technical Field

[0001] The invention relates to a slit lamp microscope, ie to an ophthalmic microscope suitable for illuminating a patient's eye with a slit-shaped or otherwise structured illumination field and for viewing the eye through a microscope apparatus. The structured illumination is generated by means of an electronically controlled spatial light modulator. Background Art

[0002] Traditionally, the illumination apparatus of a slit lamp microscope comprises a slit aperture and illumination imaging optics adapted to project the slit aperture into the object plane.

[0003] WO 2021144000 describes a slit lamp microscope in which the slit aperture is replaced by a high-resolution spatial light modulator. This type of slit lamp microscope allows the eye to be illuminated using a slit-shaped illumination field or other types of structured light fields, and the structure of the illumination can be quickly and easily adjusted to the current requirements. Summary of the invention

[0004] The problem to be solved by the present invention is to further improve the illumination quality of this type of slit lamp microscope.

[0005] This problem is solved by a slit lamp microscope according to claim 1. Therefore, the slit lamp microscope comprises at least the following elements:

[0006] i) Microscope apparatus: This apparatus projects the object plane into the eyepiece and / or camera of a slit lamp microscope. In operation, the patient's eye is placed in the object plane so that it can be viewed through the microscope apparatus.

[0007] ii) Illumination device: This device is suitable for generating a structured, adjustable illumination field in the object plane. It comprises the following elements:

[0008] a) At least one light source: The light source generates radiation to be projected into the object plane.

[0009] b) Electronically controlled spatial light modulator: This modulator is suitable for spatially modulating light from a light source. It has an array of pixel modulators, such as a mirror array or a liquid crystal light valve. The array has a spatial frequency fx along a first dimension and a spatial frequency fy along a second dimension, wherein the two dimensions extend laterally, in particular perpendicular to each other.

[0010] c) Illumination imaging optics: These optics project an array of pixel modulators towards the object plane, thereby generating a structured light field in the object plane. The structure (e.g., boundaries) of this light field can be defined by setting the spatial light modulators to a desired pattern.

[0011] According to the invention, the imaging optics comprises a low-pass filter which attenuates at least one of the spatial frequencies fx and fy in the object plane.

[0012] In the absence of such a low-pass filter, the structure of the array of pixel modulators is at least to some extent projected into the image plane. As described below, this can generate a perceptible periodic modulation of light in bright areas of the object plane, with spatial frequencies corresponding to fx and fy, respectively. By providing a low-pass filter, i.e., reducing the transmission of the spatial frequencies of fx and / or fy into the object plane, this modulation can be reduced, which allows a more uniform illumination in bright areas of illumination.

[0013] In particular, the low-pass filter attenuates the modulation transfer function T between the spatial light modulator and the object plane much more strongly at the spatial frequency fx than at the spatial frequency fx / 10, i.e., if T1 is the modulation transfer function of the illumination imaging optics without the low-pass filter, and T2 is the modulation transfer function of the illumination imaging optics with the low-pass filter, then

[0014] T1(fx) / T2(fx) is at least 5 times greater, in particular at least 10 times greater, than T1(fx / 10) / T2(fx / 10).

[0015] Advantageously, the same applies to the dimension y, ie T1(fy) / T2(fy) is at least 5 times greater, in particular at least 10 times greater, than T1(fy / 10) / T2(fy / 10).

[0016] Advantageously, the low-pass filter is adapted to attenuate the transmission of spatial frequencies fx and / or fy into the object plane by at least a factor of 10, in particular by at least a factor of 20, compared to the transmission of one-tenth of the spatial frequencies fx / 10 and fy / 10, respectively. In other words, for example, for the first dimension x, if

[0017] - T2(fx) is the modulation transfer function of the illumination imaging optics at the spatial frequency fx,

[0018] -T2(fx / 10) is the modulation transfer function of the illumination imaging optics at the spatial frequency fx / 10,

[0019] In this case, the ratio T2(fx / 10) / T2(fx) is greater than 10, in particular greater than 20.

[0020] Advantageously, this attenuation by a factor of at least 10 is achieved for both spatial frequencies fx and fy.

[0021] The low pass filter can be based on various principles, such as imperfect imaging, temporal variation of imaging and / or beam splitting. These techniques can be used alone or in combination.

[0022] In one embodiment, the low pass filter is structured and adapted to generate at least two spatially offset images of the spatial light modulator at the object plane. Using two or more such offset images, it becomes possible to provide low pass filtering along at least one dimension of the array of the pixel modulator. In order to provide low pass filtering along both dimensions x, y of the array, the filter needs to generate at least three images that are offset from each other along at least two different (i.e., non-colinear) directions.

[0023] Advantageously, the low-pass filter generates at least four images of the spatial light modulator in the object plane, said at least four images having a mutual offset along at least two different (ie non-collinear) directions.

[0024] In a particularly simple embodiment, the low-pass filter comprises at least one beam splitter located in the illumination beam path after the spatial light modulator, i.e. between the spatial light modulator and the object plane. The beam splitter can be adapted to generate at least two, in particular at least four, mutually offset light fields, which can then be used to generate mutually offset images in the object plane.

[0025] Additionally or alternatively thereto, the low-pass filter may comprise an actuator adapted to move at least one optical element of the illumination imaging optics between at least a first position and a second position, thereby generating at least two spatially offset images at the object plane. Alternatively or additionally thereto, the actuator may be adapted to move the spatial light modulator between at least a first position and a second position, thereby generating at least two spatially offset images in the object plane. In both cases, the microscope comprises a control unit adapted to periodically operate the actuator.

[0026] Advantageously, the frequency of the periodic actuation is at least 40 Hz, in particular at least 100 Hz, in order to generate for a human observer the impression of a flicker-free, continuous superposition of the at least two images.

[0027] In yet another embodiment, the illumination optics has a Fourier plane corresponding to the Fourier transform of the spatial light modulator, and the low-pass filter comprises a spatial filter in the Fourier plane. The spatial filter blocks at least a region corresponding to the spatial frequencies fx and / or fy, and advantageously blocks harmonics thereof.

[0028] In another embodiment, the low pass filter may be implemented by illumination imaging optics that project the image of the spatial light modulator into an image plane that is offset by at least 500 μm from the object plane.

[0029] In another embodiment, the low-pass filter may comprise a diffuser, in particular a diffractive diffuser. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be better understood and other objects besides the above mentioned objects will become apparent when considering the following detailed description of the present invention. This description refers to the accompanying drawings, in which:

[0031] Figure 1 An embodiment of a slit lamp microscope is shown,

[0032] Figure 2 An embodiment of a component of a lighting device is shown,

[0033] Figure 3 shows a portion of a spatial light modulator,

[0034] Figure 4 Shows Figure 3 an idealized image at the object plane of the portion of the spatial light modulator for the mirror in a first position (where the dark areas represent illuminated regions),

[0035] Figure 5 The frequency transfer function of the illumination imaging optics with a low-pass filter is qualitatively shown,

[0036] Figure 6 A first embodiment of a low pass filter is shown,

[0037] Figure 7 Shown with Figure 4 but with the low-pass filter in place, and

[0038] Figure 8 and Fig. 9 Fourier filters optimized for two different wavelengths are shown. DETAILED DESCRIPTION

[0039] Overview

[0040] Figure 1 An embodiment of a slit lamp microscope is shown.

[0041] The microscope has a base 1 placed on, for example, a table, a translatable stage 2 mounted to the base 1 , a first arm 3 , and a second arm 4 .

[0042] The stage 2 can be linearly displaced relative to the base 1 along two horizontal directions.

[0043] Arms 3 and 4 are mounted to table 2 and pivot about a common vertical pivot axis 5 .

[0044] The device may further comprise a headrest 7 mounted to the base 1 for receiving the patient's head.

[0045] Arm 3 carries a microscope device 8 and arm 4 carries an illumination device 9, a so-called "slit lamp".

[0046] The microscope device 8 has an optical axis 12. It comprises microscope optics 14, 15, such as an objective 14 and zoom optics 15, which for example project an image of the eye 10 onto a camera 16 and / or into an eyepiece 18. A beam splitter 20 or a flip mirror may be provided to split the light between these components.

[0047] The illumination device 9 pivots about a pivot axis 5. It is adapted to project a structured light beam onto the eye 10 to be examined. It comprises a light source 22, a spatial light modulator 24 and an illumination imaging optics 26 comprising at least one lens 27.

[0048] The light source 22 may, for example, comprise several units emitting different wavelengths, for example wavelengths in the red, green, blue and infrared range of the spectrum. These units may be individually controlled in order to change the color of the light source 22.

[0049] Advantageously, the light source 22 comprises at least one LED and / or a semiconductor laser. This type of light source is advantageous because LEDs and semiconductor lasers can be pulsed quickly and precisely.

[0050] The illumination imaging optics 26 projects light from the modulator 24 onto, for example, the front surface of the eye 10, for example via a deflection mirror 28 mounted to the arm 4. The front surface of the eye 10 is assumed to be located at the object plane 11, which is the optical conjugate plane of the spatial light modulator 24 with respect to the illumination imaging optics 26. Note that, as described below in the "Defocus" section, in one embodiment, the object plane 11 is not exactly located in the optical conjugate plane of the spatial light modulator 24.

[0051] The pivot axis 5 is located in the object plane 11 so as to keep the center of the image in focus when one or both of the arms 3 , 4 are rotated.

[0052] The lighting device 9 can be arranged above or below the deflecting mirror 28 .

[0053] The control unit 32 controls the components of the microscope. In particular, it may for example comprise a microprocessor 34 and a memory 36. The microprocessor 34 is programmed to perform the steps of controlling the microscope, and the memory 36 contains data and / or instructions to do so.

[0054] Lighting

[0055] Figure 2A more detailed embodiment of the lighting device 9 is shown. It is designed to project an illumination field with a defined contour onto the eye 10. The illumination field may be circular, rectangular or slit-shaped, for example. Although the lighting device is referred to herein as a "slit lamp", the illumination field does not need to be slit-shaped at all. It may take any shape.

[0056] In the present embodiment, the lighting device 9 comprises four individual light sources 22a-22d having different spectral emission characteristics, which together form the "light source" 22 of the lighting device. For example, they may comprise an infrared light source, a red light source, a green light source and a blue light source. Advantageously, the light sources are LEDs. In particular, each light source may be a single LED.

[0057] The light from each light source is substantially collimated by means of collimating optics 40a-40d.

[0058] Three dichroic mirrors 42a, 42b, 42c are used to coaxially combine the light from the light sources 22a-22d.

[0059] The combined illumination light passes through homogenizing optics 44, such as a fly's eye lens array, for example as described in US6507434.

[0060] The two cylindrical lenses 46a, 46b, the further lens 46c and the homogenizing optics 44 may also together widen the light beam in one direction, e.g. giving it an elongated cross-section, e.g. with an aspect ratio of 16:9, to better match typical available form factors of spatial light modulators.

[0061] Mirror 48 deflects the light into an assembly of two prisms 50a, 50b with a gap 52 between them.

[0062] The light beam passes through the prism 50 a , the gap 52 , and the prism 50 b and reaches the spatial light modulator 24 .

[0063] In the illustrated embodiment, the spatial light modulator 24 is a DMD ("digital micromirror device") in which a two-dimensional array of individually pivotable micromirrors 60 acts as a pixel modulator. The control unit 32 is adapted to control the alignment of each micromirror 60 between at least a first position and a second position.

[0064] When the given mirror 60 is in the first position, light from the light source 22 is reflected by the given mirror (as shown by line 54), passes through the first surface 62a of the prism 50b, is completely reflected at the second surface 62b of the prism 50b (at the gap 52), and exits through the third surface 62c of the prism 50b in the direction shown by line 56.

[0065] However, when the given mirror 60 is in the second position, light from the light source is reflected by the given mirror and passes through the first surface 62a, but is not completely reflected at the second surface 62b. A portion of its light exits through the surface 62b. The reflected portion exits the prism 50b through another surface, but not in the direction 56, and, for example, it will not pass through the aperture of the illumination imaging optical device 26.

[0066] Therefore, the control unit 32 can individually set each pixel (each micromirror 60) of the spatial light modulator 24 to an on state and an off state, thereby defining the target 10 (at Figure 2 The outline and shape of the light field at the object plane 11 of the lighting device are shown in FIG.

[0067] The light from the pixels of the spatial light modulator 24 enters the illumination imaging optics 26, which may include one or more lenses. From there, it may pass through a deflection mirror 28 to the object plane 11.

[0068] The illumination imaging optics projects the spatial light modulator 24 onto the object 10 , ie the object 10 is located at an object plane 11 which is a conjugate plane of the plane 64 of the spatial light modulator 24 with respect to the illumination imaging optics 26 .

[0069] Figure 3 A sub-portion of 64 mirrors 60 of the spatial light modulator 24 is shown in a first position (i.e. in an open position). As can be seen, the mirrors 60 form a two-dimensional array extending along a first dimension x and a second dimension y. The pixel pitch along x is dx, and the pixel pitch along y is dy. The mirrors 60 have extensions ex and ey, respectively, which are generally smaller than dx and dy, i.e., there are gaps 61 between the mirrors 60 that do not reflect light.

[0070] Assumptions Figure 3 If all mirrors 60 of the modulator part of FIG. 1 are in their first position, the illumination pattern generated by these mirrors in the object plane 11 will look like Figure 4 As shown in , it is assumed that the imaging of the illumination imaging optics is essentially perfect. (Note: Figure 4 The dark areas in the figure represent the illuminated parts in the object plane 11. )

[0071] As can be seen, an array of illuminated areas 66 extending along directions x' and y' is created, having a spacing dx' along direction x', and a spacing dy' along direction y'.

[0072] Between the illuminated areas 66 there are non-illuminated areas 68 corresponding to the gaps 61 between the mirrors 60. Thus, the illumination is non-uniform.

[0073] Such non-uniform patterns in bright areas of the object plane 11 may become apparent when viewing the eye 10 with the aid of a high-power microscope device 8. This is particularly true for examinations that rely on specular reflection of light on the eye, for example when viewing the anterior or posterior surface of the cornea, for example to examine the endothelium, or when viewing the anterior or posterior side of the natural lens. Non-uniform illumination is also particularly apparent when using slit illumination to record cross-sections of the eye.

[0074] Although artifacts due to non-uniform illumination can be removed from the camera image by means of image processing, such processing can be difficult, particularly if the illumination structure interferes with the pixel structure of the camera, and is not possible when viewing the microscope image directly through the eyepiece. Furthermore, any such processing will likely reduce the resolution of the microscope device 8.

[0075] Low pass filter

[0076] To reduce artifacts due to non-uniform illumination, the illumination device is equipped with a low-pass filter, such as a beam splitter or other devices described in the following sections.

[0077] That is, the purpose of the low pass filter is to suppress (ie, attenuate) spatial frequencies fx=1 / dx and / or fy=1 / dy along x and y when imaging the spatial light modulator 24 into the object plane 11 .

[0078] In the coordinate system of the object plane 11 , the spatial frequencies fx and fy of the light modulator correspond to the spatial frequencies fx′=1 / dx′ and fy′=1 / dy′.

[0079] In the following, we define T as the modulation transfer function of the illumination imaging optics 26, which is a function of the spatial frequency f at the spatial light modulator 24 (see https: / / en.wikipedia.org / wiki / Optical_transfer_function). f is the spatial frequency of dimension x or y. (Note: for simplicity, we assume that dimensions x and y have the same modulation transfer function T. If not, then Tx(f) and Ty(f) can be used).

[0080] Figure 5 The modulation transfer function T1(f) is shown for illumination of the imaging optics 26 without a low pass filter. As can be seen, T1 decreases for larger frequencies, but at least at frequency fx a residual modulation transfer occurs.

[0081] Figure 5Also shown is the modulation transfer function T2(f) of the illumination imaging optics 26 when a low-pass filter is present. As can be seen, the low-pass filter generates a strong attenuation at fx, but a much smaller attenuation at lower spatial frequencies (e.g., fx / 10). Thus, for a given luminance of the illuminated region of the target in the object plane, the illumination non-uniformity at fx is suppressed.

[0082] As mentioned above, it is advantageous that the attenuation of the modulation transfer function at fx / 10 is at least a factor of 5 (in particular, at least a factor of 10) less than the attenuation at fx, i.e., T1(fx) / T2(fx) is at least 5 times larger, in particular at least 10 times larger, than T1(fx / 10) / T2(fx / 10).

[0083] This also advantageously applies to fy.

[0084] As can also be seen from Figure 5 the modulation transfer function T2(f) in the case of having a low-pass filter should be much smaller at fx than at lower frequencies (such as fx / 10) so that the illumination non-uniformity at fx is hardly visible. Thus, as mentioned above, the ratio T2(fx / 10) / T2(fx) is advantageously greater than 10, in particular greater than 20. This also advantageously applies to fy.

[0085] Figure 5 Another variant of the modulation transfer function in the presence of a low-pass filter is shown under T2'(f). In this variant, the modulation transfer function T2'(f) has a local minimum at fx and then rises again for higher frequencies (e.g., for 1.5.fx), which improves the imaging quality of the high-frequency components of the illumination pattern that are not caused by the repeating structure of the spatial light modulator. However, T2'(f) should advantageously decrease again towards the second harmonic frequency 2.fx.

[0086] Thus, more generally, the modulation transfer function T2(fx) at the frequency fx is advantageously less than the modulation transfer function T2(1.5.fx) at the frequency 1.5.fx by at least a factor of 2, i.e., T2(fx) < T2(1.5.fx) / 2. In particular, T2(1.5.fx) at the frequency 1.5.fx is advantageously greater than T2(2.fx) at the frequency 2.fx by at least a factor of 2, i.e., T2(2.fx) < T2(1.5.fx) / 2.

[0087] This frequency adjustment of the modulation transfer function is preferably achieved using the Fourier filtering technique described below.

[0088] There are various ways to implement such low-pass filtering, some of which will be described in the following sections.

[0089] Beam splitter

[0090] Figure 6 A first embodiment of the low pass filter is shown. In this embodiment, the low pass filter comprises a beam splitter 70. It is arranged in the path of the illumination light after the spatial light modulator 24 and before the object plane 11 and is adapted to generate at least two, in particular at least four mutually offset light fields.

[0091] In the illustrated embodiment, the beam splitter 70 includes a first birefringent plate 72 , a quarter-wave retarder 74 , and a second birefringent plate 76 , wherein the quarter-wave retarder 74 is disposed between the birefringent plates 72 , 76 .

[0092] The optical axis of the first birefringent plate 72 is advantageously arranged at 45° to its input surface so that the incoming light 78a is split into two light fields 78b, 78c of equal intensity. (Here, it is assumed that the incoming light 78a is unpolarized. If it is partially or fully polarized, one or more polarizers and / or wavelength retarder plates can be used to adjust the polarization so that the light fields 78b, 78c have the same intensity, as known to those skilled in the art).

[0093] Since the light fields 78b, 78c after the first birefringence plate 72 are linearly polarized, their polarizations are transformed into circular polarizations using the quarter-wave retarder 74.

[0094] The light fields 78b, 78c then enter the second birefringent plate 76. Again, the optical axis of the second birefringent plate 76 is arranged at 45° to its input surface to split the incoming light fields 78b, 78c again. The second birefringent plate 76 is in a different orientation than the first birefringent plate 72 to generate splitting into different directions. Therefore, at the output side of the beam splitter 70, the incoming light 78a has been split into four mutually offset light fields 80a, 80b, 80c and 80d.

[0095] Advantageously, the four light fields 80a - 80d are offset from one another along rectangular directions rx, ry, which correspond to the dimension x.

[0096] For reasons explained below, the offset between the light fields along rx and ry is approximately half the spacing dx and dy of the mirrors 80, respectively.

[0097] The beam splitter 70 can be arranged adjacent to the prism 50b, in particular adjacent to the first surface 62a or the third surface 62c. Advantageously, it is mounted to one of these surfaces, in particular glued there. It is particularly advantageous to arrange a transparent filler (such as glue) between 50b and the beam splitter 70 to prevent an air gap between the two parts, because it reduces the number of surfaces that the light needs to pass through.

[0098] exist Figure 2 In the embodiment of FIG. 6 , the beam splitter 70 is shown to be arranged on the third surface 62 c with a transparent filler 71 between the two parts.

[0099] As mentioned, the beam splitter 70 acts as a low-pass filter. In particular, if it is not arranged too close to the lens 27, it will block the image of the spatial light modulator 24 in the object plane 11 (e.g. Figure 4 As shown in FIG. , without a beam splitter) is basically split into Figure 7 The spatially offset image shown in .

[0100] To illustrate these four images, Figure 7 A single mirror 60 in each of the four images is shown at 82a-82d, outlined with different dashed lines.

[0101] By comparison Figure 4 and Figure 7 As you can see, Figure 7 Lighting pattern ratio Figure 4 The illumination pattern is more uniform, ie the mirror structure is less noticeable, which produces a better quality image.

[0102] The image is offset by mx' along the x' direction and by my' along the y' direction. The offset should be in the "blur" Figure 4 within the range of the non-illuminated area 68. Therefore, advantageously, mx'=dx' / 2 and my'=dy' / 2. However, if the gap between the mirrors 60 is not too large, the offset may deviate from these numbers. Along x', the offset mx' is advantageously between 0.2.dx'=0.2 / fx' and 0.8.dx'=0.8 / fx'. Similarly, along y', the offset my' is advantageously between 0.2.dy'=0.2 / fy' and 0.8.dy'=0.8 / fy'. Advantageously, mx' is between 0.4 / fx' and 0.6 / fx', and my' is between 0.4 / fy' and 0.6 / fy'.

[0103] Beam splitters based on birefringent plates are known to be used for a completely different purpose, namely as anti-aliasing filters arranged on camera chips, e.g. et al. in Dimensioning of Optical BirefringentAnti-Alias ​​Filters for Digital Cameras, Proc.of2010IEEE 17 thInternational Conference on Image Processing, September 26-29, Hong Kong. This document mentions stacks of M=2, M=3, M=4 or more mutually rotated birefringent plates, which can also be used in the present context.

[0104] Thus, more generally, the beam splitter 70 advantageously includes at least two differently oriented birefringent plates 72 , 76 and a quarter-wave retarder 74 disposed between each two birefringent plates 72 , 76 .

[0105] Instead of using a birefringent beam splitter, the present technology can also use other types of beam splitters to generate two or more mutually offset light fields. For example, a semi-transparent mirror can be used to split the light, and the resulting light fields can be redirected and directed by a mirror to be parallel and at a desired offset.

[0106] Actuator

[0107] In another class of embodiments, the low pass filter may include one or more actuators.

[0108] Figure 2 The dotted line shows such an actuator 90, which is to be arranged at the deflection mirror 28 of the illumination imaging optics 26. The actuator 90, which may for example comprise one or more piezoelectric elements, is adapted to change the tilt angle of the deflection mirror 28 and thereby shift the image of the spatial light modulator 24 in the object plane 11.

[0109] Advantageously, the actuator 90 is suitable for tilting the deflection mirror 28 about two transverse axes in order to generate an image in the object plane 11 that is shifted both along the directions x′ and y′.

[0110] The control unit 32 periodically operates the actuator 90 to rapidly shift the image. If this shift is sufficiently rapid, for example with a period of at least 40 Hz, advantageously at least 100 Hz, several spatially offset images are generated for a human observer on the object plane 11, which again blurs the image. Figure 4 The non-illuminated area 68 is reduced, thereby generating more uniform illumination.

[0111] Alternatively (or additionally) to moving the deflection mirror 28, other parts of the illumination imaging optics 26 may be moved by an actuator. Figure 2 Another actuator 92 is shown which is suitable for periodically moving the lens 27, and another actuator at 94 for moving the prism assemblies 50a, 50b or a portion thereof.

[0112] As a further variation, an actuator 96 may be provided to move the spatial light modulator 24 along the directions x and / or y.

[0113] In such Figure 1 In yet another embodiment shown in , an actuator 98 may be provided to move all of the lighting device 9 .

[0114] In order to assess whether a given actuator-based device is a low-pass filter in the sense of the present invention, the image of the spatial light modulator 24 at the object plane 11 is advantageously averaged over a period of time to obtain a "subjective image", i.e., the image perceived by a human observer. This averaging is performed while the actuator is operated periodically. The averaging advantageously extends over a period of at least 2.5 ms (corresponding to 40 Hz), in particular over a period of at least 5 ms (corresponding to 20 Hz). Low-pass filtering is then detected by testing whether specific frequencies fx' and / or fy' in the subjective image have been suppressed (e.g., as described above, by a factor of at least 2, in particular by a factor of at least 5).

[0115] Fourier filtering

[0116] In yet another embodiment, the filter 100 is placed in the back focal plane (Fourier plane) 102 of the lens 27 (see Figure 2 ). This plane holds the Fourier transform of the image of the spatial light modulator 24. The filter 100 is adapted to suppress the Fourier components corresponding to the spatial frequencies fx and fy, and advantageously their higher harmonics.

[0117] For narrowband illumination, the filter 100 may, for example, consist of a simple aperture that blocks spatial frequencies above a given threshold (eg, 0.8fx and 0.8fy).

[0118] If we only want to block fx and fy and their harmonics, such as Figure 5 As shown in the modulation transfer function T2' in FIG. 1 , the filter 100 can be configured, for example, according to the pattern generated by the spatial light modulator (ie, as shown in FIG. 1 ). Figure 4 It is calculated by Fourier transform of the pattern shown in ). Figure 8 Such a filter 100 is shown in , where the dark portions indicate portions that block light.

[0119] As known to those skilled in the art, the Fourier transform in the back focal plane 102 is scaled according to the wavelength of the light. Thus, if the light source 22 is a broadband light source, the filter 100 may, for example, comprise several superimposed color filters assigned to different wavelengths, wherein each color filter blocks the spatial frequency components fx, fy (and their harmonics) at a wavelength range centered around the wavelength to which it is assigned.

[0120] If Figure 2In the embodiment shown in FIG. 1 , there are several individual light sources 22a-22d centered at different wavelengths λi, then the filter 100 advantageously comprises several wavelength selective filters that block the spatial frequency fk of the wavelength λi and its harmonics. For example, Fig. 9 Shown with Figure 8 The same filter in , but scaled to approximately twice the wavelength. For example, Fig. 9 The filter (in the dark part) will absorb at the first (longer) wavelength λ1 (but will not absorb or will absorb much less than this at λ2), and Figure 8 A filter of (in the dark part) will absorb at the second (shorter) wavelength λ2 (but not absorb or absorb much less than this at λ1).

[0121] Thus, more generally, the filter 100 advantageously comprises several wavelength selective filters which suppress the spatial frequencies fk of several different wavelengths λi and advantageously suppress harmonics thereof, wherein the filters comprise light blocking structures whose size is scaled according to the different wavelengths λi. Advantageously, in this case, the lighting device 9 comprises several light sources with different emission spectra, wherein the maximum emission is at the wavelength λi.

[0122] Defocus

[0123] In another embodiment, the low pass filter can be implemented by intentionally defocusing the illumination of the imaging optics 26. For example, the dimensions of the lens 27 can be designed to project the image of the spatial light modulator into the image plane 104 instead of the object plane 11 (e.g., Figure 2 ), the image plane 104 is offset from the object plane 11 by an offset r of at least 500 μm.

[0124] As mentioned above, the illumination device 9 is pivoted about a vertical pivot axis 5, wherein the pivot axis 5 is located in the object plane 11. Such a defocusing therefore means that the image of the spatial light modulator 24 is located in front of or behind the pivot axis 5.

[0125] like Figure 2 As shown in , the object plane 11 is preferably arranged between the microscope apparatus 8 and the image plane 104, i.e., the image plane 104 is located behind the object plane 11 when viewed from the microscope apparatus 8. This is advantageous because when the microscope apparatus 8 is adjusted (as is usually the case) so that the user focuses his eyes to infinity to clearly see the objects in the object plane 11, it will be difficult for the user to focus on the image plane 104, i.e., it is less likely that the user will "accidentally" focus on the image plane 104.

[0126] In another embodiment, such defocusing may be achieved by introducing spherical aberration in lens 27 or other portions of imaging optics 26 .

[0127] Spherical aberration, also called higher order spherical aberration, is an aberration (such as defocus) that is independent of field position and rotation, and can be used to intentionally and uniformly blur the image of the spatial light modulator throughout the object plane, thereby forming a low pass filter. In a similar manner, other aberrations (such as astigmatism) act as low pass filters. Advantageously, a combination of classical aberrations and higher order aberrations can be used to create the desired low pass filter.

[0128] Diffuser

[0129] In yet another embodiment, a diffuser 106 arranged between the spatial light modulator 24 and the object plane 11 can be used as a low-pass filter. Such a diffuser can, for example, be arranged at the first surface 62a or the third surface 62c of the prism 50b, the same as the beam splitter 70. Alternatively, it can also be arranged, for example, in the Fourier plane.

[0130] Advantageously, the diffuser 106 is a diffractive diffuser, ie a diffuser that diffuses light using diffraction.

[0131] Notice

[0132] In the above-described embodiment, the low-pass filter is adapted to suppress the spatial frequencies fx and fy along x and y. Alternatively, the low-pass filter may also be designed to suppress only one of these spatial frequencies, in particular if the illumination device is designed such that, at the object plane 11, one of the corresponding frequencies fx' and fy' is much larger than the other. In this case, it may be necessary to suppress only the smaller frequencies, since the larger frequencies may exceed the resolution of the microscope device 8.

[0133] The various embodiments of the low-pass filters described above may also be combined, for example with a beam splitter for one direction x and an actuator for another direction y.

[0134] In the above described embodiments, the light source and the spatial light modulator are separate elements. Alternatively, they may also be formed by a single device having an array of light sources, each of which defines the illumination in one pixel.

[0135] While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the appended claims.

Claims

1. A slit lamp microscope, comprising i) a microscope device (8) that projects an object plane (11) into at least one of an eyepiece (18) or a camera (16), and ii) an illumination device (9) having a) at least one light source (22), b) an electronically controlled spatial light modulator (24) including an array of pixel modulators extending along a first dimension and a second dimension (x, y), wherein the pixel modulators have spatial frequencies fx and fy along the first dimension and the second dimension (x, y), and c) illumination imaging optics (26) that project the array towards the object plane (11), wherein the illumination device (9) includes a low - pass filter (70, 90 - 100, 106) that attenuates at least one of the spatial frequencies fx and fy in the object plane (11).

2. The microscope according to claim 1, wherein: If T1 is the modulation transfer function between the spatial light modulator (24) and the object plane (11) of the illumination imaging optics (26) without the low - pass filter (70, 90 - 100, 106), and T2 is the modulation transfer function between the spatial light modulator (24) and the object plane (11) of the illumination imaging optics (26) with the low - pass filter (70, 90 - 100, 106), then T1(fx) / T2(fx) is at least 5 times larger, particularly at least 10 times larger, than T1(fx / 10) / T2(fx / 10), and in particular, T1(fy) / T2(fy) is also at least 5 times larger, particularly at least 10 times larger, than T1(fy / 10) / T2(fy / 10).

3. A microscope as claimed in any one of the preceding claims, wherein: If T2 is the modulation transfer function between the spatial light modulator (24) and the object plane (11) of the illumination imaging optics (26) with the low - pass filter (70, 90 - 100, 106), then T2(fx / 10) / T2(fx) is greater than 10, particularly greater than 20.

4. The microscope according to claim 3, wherein T2(fx)<T2(1.5.fx) / 2, and in particular wherein T2(2.fx)<T2(1.5.fx) / 2.

5. The microscope according to any one of the preceding claims, wherein the low - pass filter (70, 90 - 96, 100, 106) is adapted to generate at least two spatially offset images (82a - 82d) of the spatial light modulator (24) at the object plane (11).

6. The microscope according to claim 5, wherein: At the object plane (11), the images (82a - 82d) of the spatial light modulator (24) have an offset mx' along a first dimension of imaging, which offset is between 0.2 / fx' and 0.8 / fx', particularly between 0.4 / fx' and 0.6 / fx', where fx' and fy' are the spatial frequencies of the array in the image in the image plane.

7. The microscope of any one of claims 5 or 6, wherein the low-pass filter (70, 90-100, 106) is adapted to generate at least four spatially offset images (82a-82d) of the spatial light modulator (24) at the object plane (11).

8. A microscope as described in any of the preceding claims, wherein the low-pass filter (70, 90-100, 106) includes at least one beam splitter (70) located after the spatial light modulator (24), wherein the beam splitter (70) is suitable for generating at least two mutually offset light fields (80a-80d).

9. The microscope as claimed in claim 8, wherein the beam splitter (70) is adapted to generate at least four mutually offset light fields (80a-80d).

10. The microscope of claim 9, wherein the beam splitter (70) comprises at least two differently oriented birefringent plates (72, 76) and a quarter-wave retarder (74) disposed between every two birefringent plates (72, 76).

11. The microscope as claimed in any one of claims 9 or 10, wherein the illumination device (9) comprises an array of individually pivotable mirrors (60), wherein each mirror (60) has a first position and a second position, A prism (50b) having a first surface, a second surface and a third surface (62a, 62b, 62c), wherein: For a given mirror (60) in a first position, light from a light source (22) is reflected by the given mirror (60), passes through a first surface (62a), is completely reflected at a second surface (62b), and exits through a third surface (62c), while for a given mirror (60) in a second position, light from a light source (22) is reflected by the given mirror (60), passes through a first surface (62a), and is not completely reflected at a second surface (62b), And wherein the beam splitter (70) is arranged adjacent to the prism (50b).

12. The microscope as claimed in claim 11, wherein a beam splitter (70) is arranged on the first surface or the third surface (62a, 62c), in particular on the third surface (62c).

13. The microscope as claimed in claim 12, wherein the beam splitter (70) is connected to the first surface or the third surface (62a, 62c) via a transparent filler (71).

14. The microscope according to any one of the preceding claims, wherein the low pass filter (70, 90-100, 106) comprises an actuator (90-100) adapted to move between at least a first position and a second position. at least one optical element of the illumination imaging optics (26) and / or the spatial light modulator (24), At least two aerial images (82a-82d) are thereby generated at the object plane (11), and wherein the microscope comprises a control unit (32) adapted to periodically operate the actuators (90-100).

15. A microscope as claimed in claim 14, wherein the illumination imaging optical device (26) includes at least one deflection mirror (28), which deflects light from the spatial light modulator (24) towards the object plane (11), and wherein the actuator (90) is suitable for changing at least one tilt angle of the deflection mirror (28).

16. A microscope as described in any of the preceding claims, wherein the illumination optical device has a Fourier plane (102) that maintains the Fourier transform of the spatial light modulator (24), and wherein the low-pass filter (100) suppresses the Fourier component of the image of the spatial light modulator (24) in the Fourier plane (102).

17. A microscope as claimed in claim 16, wherein the low-pass filter (100) comprises several wavelength selective filters which suppress the spatial frequencies fk of several different wavelengths λi and advantageously suppress their harmonics, wherein the filters comprise blocking structures scaled according to the different wavelengths λi.

18. Microscope according to claim 17, wherein the illumination device (9) comprises several light sources (22a-22d) with different emission spectra, wherein the maximum emission is at the wavelength λi.

19. A microscope as claimed in any one of the preceding claims. wherein the lighting device (9) is pivotable about a pivot axis (5) located in the object plane (11), and The low pass filter (70, 90-100, 106) is implemented by the illumination imaging optical device (26), which projects the image of the spatial light modulator (24) into an image plane (104) offset by at least 500 μm from the object plane (11).

20. The microscope as claimed in claim 19, wherein the object plane (11) is located between the microscope device (8) and the image plane (104).

21. The microscope as claimed in any of the preceding claims, wherein the low-pass filter (70, 90-100, 106) comprises a diffuser (106), in particular a diffractive diffuser.

Images