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Claims  |
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I claim:
1. An apparatus for producing images of an object, comprising an
illumination device, the light of which is focused on the object to be
imaged and which is provided with at least one laser; a scanning device
which produces a scanning motion of the light from said illumination
device on said object to be imaged; a detector device having at least one
detector which receives the light reflected from said object to be imaged;
and an assessment and synchronization unit which produces the image from a
time-sequential output signal from said detector device comprising
individual detectors arranged conjugate to one of different planes and to
different regions of a plane one of shutters and polarization filters
being arranged at selected detectors for selective reception of light
reflected from different planes, areal distribution of the intensity of
said light in a particular plane and a polarization state of said light.
2. An apparatus according to claim 1, wherein said illumination device
projects light of several wavelengths simultaneously onto said object to
be imaged (R), and for the light of each wavelength at least one a
wavelength-selective individual detector is provided.
3. An apparatus according to claim 2, wherein the entrance and/or exit
pupils of the light beams of differing wavelengths are different.
4. An apparatus according to claim 3, wherein the representations by said
light of differing wavelengths have differing depths of focus.
5. An apparatus according to claim 1, wherein said assessment unit presents
the output signals from said individual detectors on one or several
monitors.
6. An apparatus according to claim 1, wherein said assessment unit couples
said output signals from said individual detectors in real time and
presents the coupled signal on a monitor.
7. An apparatus according to claim 1, wherein said assessment unit feeds
said output signals from said individual detectors into an image memory
and couples the stored signals.
8. An apparatus according to claim 1, wherein said detector device receives
said light reflected from said object to be imaged via said scanning
device and, selective shutter devices are provided.
9. An apparatus according to claim 1, wherein a detector arrangement, which
determines the distribution of the intensity of said reflected light, is
provided in a plane conjugate to the pupil (P) of the eye for observing
the fundus of the eye.
10. An apparatus according to claim 9, wherein said assessment unit
determines from said output signals from said individual detectors
characteristic features of said distribution of intensity, including the
main point of said reflected light and directional asymmetries.
11. An apparatus according to claim 10, wherein said individual detectors
are sectors of a circle and are arranged in a circle.
12. An apparatus according to claim 1, wherein a detector arrangement is
provided in a plane conjugate to said object to be imaged, which
determines the distribution of intensity of said reflected light in said
plane.
13. An apparatus according to claim 12, wherein said assessment unit
determines from said output signals from said individual detectors the
characteristic features of said distribution of intensity including
transverse scattering within the retina.
14. An apparatus according to claim 1, wherein a number of individual
detectors, before which analyzers are provided in a plane conjugate to
said object to be imaged.
15. An apparatus according to claim 14, further comprising four individual
detectors, wherein no optically effective element is arranged before the
first individual detector, a first linear analyzer is arranged before the
second individual detector, a second linear analyzer turned 45.degree. to
said first analyzer is arranged before the third individual detector, and
a quarter-wave plate is arranged before the fourth individual detector,
and
said assessment unit determines the degree of polarization, the
polarization direction and the ellipicity from the output signals.
16. An apparatus according to claim 1,
wherein before said detector device are connected at least partially
structured filters and/or variable shutters.
17. An apparatus according to claim 16, wherein areal light modulators,
which can be triggered electronically, from said filters.
18. An apparatus according to claim 17, wherein said light modulators are
LCD elements having regions, which can be triggered separately.
19. An apparatus according to claim 16, wherein said filters can be shifted
or turned in a longitudinal direction and/or oblique to the detection beam
path.
20. An apparatus according to claim 1, wherein, in addition, markings can
be projected onto said fundus of the eye.
21. An apparatus according to claim 20, wherein said projection of said
markings occurs by modulation of said illumination light.
22. An apparatus according to claim 21, wherein at least one of an
additional source of light and an additional deflection unit is provided
for said projection of said markings.
23. An apparatus according to claim 22, wherein said deflection unit is
provided with one of an acousto-optical demodulator and a wobble unit.
24. An apparatus according to claim 20, wherein said projection of said
marks occurs for the purpose of fundus perimetry.
25. An apparatus according to claim 1, wherein said scanning device is an
x/y scanning device which is provided with a rotatable polygonal mirror
drum and a galvanometer mirror.
26. An apparatus according claim 1,
wherein for the illumination of the surrounding area an additional light
source is provided, the light (B) of which expansively illuminates said
object to be imaged.
27. An apparatus according to claim 1,
wherein the beam of an operational laser is additionally mirrored in.
28. An apparatus according to claim 1, wherein a control unit is configured
to redirect at least one of an observation beam path and an operational
laser beam and to selectively switch off the laser.
29. An apparatus according to claim 28, wherein said control unit
additionally permits setting the operational parameters including
treatment planning.
30. An apparatus according to claim 1,
wherein a field-of-view shutter, which produces a dark-field illumination
for at least one part of said individual detectors, is arranged before
said detector device.
31. An apparatus according to claim 1,
wherein at least one of a fundus angiograph and markings can be congruently
superimposed on the received image.
32. An apparatus according to claim 1,
wherein said control unit is provided with an image processing device for
processing the images received simultaneously or consecutively.
33. An apparatus according to claim 1,
wherein said illumination device, said scanning device and said detector
device form a confocal arrangement and said field-of-view shutters of at
least some of said individual detectors are substantially larger than the
diameter of the image point on said fundus of the eye.
34. An apparatus according to claim 1, wherein field-of-view-determining
shutters and their detectors are arranged spaced and stationary in planes
conjugate to said differing planes.
35. An apparatus according to claim 34, wherein light conducting means
connect said shutters and said detectors.
36. An apparatus for producing images of an object and for observing the
rear portions of the eye, comprising
an illumination device, the light of which is focused on the object to be
imaged and which is provided with at least one laser wherein said
illumination device projects light of several wavelengths simultaneously
onto said object to be imaged (R), and for the light of each wavelength at
least one and a wavelength-selective individual detector is provided;
a scanning device, which produces a scanning motion of the light from said
illumination device on said object to be imaged;
a detector device, having at least one detector, which receives the light
reflected from said object to be imaged; and
an assessment and synchronization unit which produces the image from the
time-sequential output signal from said detector device.
37. An apparatus according to claim 36, wherein before said detector device
are connected at least partially structured filters and/or variable
shutters.
38. An apparatus according to claim 36, wherein markings can be projected
onto said object to be imaged and onto said fundus of the eye.
39. An apparatus according to claim 36, wherein for the illumination of the
surrounding area an additional light source is provided, the light of
which expansively illuminates said object to be imaged and in particular
said fundus of the eye.
40. An apparatus according to claim 36, wherein the beam of an operation
coagulation laser is additionally mirrored in.
41. An apparatus according to claim 36, wherein a control unit is
configured to redirect at least one of an observation beam path and an
operational laser beam and to selectively switch off the laser.
42. An apparatus according to claim 36, wherein a field-of-view shutter is
arranged before said detector device to produce a dark-field illumination
for said individual detectors.
43. An apparatus according to claim 36, wherein a fundus angiograph and/or
markings can be congruently superimposed on the received image.
44. An apparatus according to claim 36, wherein said control unit is
provided with an image processing device for processing the images
received simultaneously or consecutively.
45. An apparatus for producing images of an object and for observing rear
portions of an eye, comprising:
an illumination device whose light is focused on an object to be imaged and
which is provided with at least one laser:
a scanning device operatively arranged to produce a scanning motion of the
light from said illumination device on the object to be imaged;
a detector device having at least one detector receiving light reflected
from the object to be imaged;
an assessment and synchronization unit producing the image from a
time-sequential output signal from said detector device; and
at least one of partially structured filters and variable shutters
connected before said detector device so as to detect intensity
distribution of the light reflected at the fundus of the eye.
46. An apparatus for producing images of an object and for observing rear
portions of an eye, comprising:
an illumination device whose light is focused on an object to be imaged and
which is provided with at least one laser;
a scanning device operatively arranged to produce a scanning motion of the
light from said illumination device on the object to be imaged;
a detector device having at least one detector receiving light reflected
from the object to be imaged;
an assessment and synchronization unit producing the image from a
time-sequential output signal from said detector device; and
an additional light source configured to illuminate a surrounding area,
such that the light of the additional light source expansively illuminates
a fundus of the eye for effecting fundus perimetry. |
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Claims |
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Description |
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BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an apparatus for producing images of an
object and in particular for observing the rear portions of the eye.
Apparatuses for producing images of an object for observing the rear
portions of the eye are well known in the art and are implemented with
various equipment for producing images. By way of illustration, a number
of laser-scanning cameras, laser-scanning microscopes and laser-scanning
ophthalmoscopes have been proposed in medical technology.
Apparatuses of the known type have proven to be particularly advantageous
when a comparatively large object has to be viewed through a small
aperture arranged before the object. For example, when observing the rear
portions of the eye, there arises the problem that the fundus must be
illuminated and observed through the pupil of the eye and frequently
through the not clear anterior media of the eye, where reflexes occur to
produce image defects. Similar circumstances have been encountered in
other cases of medical or technical application.
For this reason, fundus cameras have usually been employed in the past to
observe the rear portions of the eye, in which the entrance pupil and the
exit pupil were separated according to "GULLSTRAND" to suppress the
so-called corneal reflex i.e. the part of the pupil of the eye used for
the illumination surrounds ring-like the part used for observation.
Nonetheless, reflexes cannot be entirely suppressed when working with such
fundus cameras. Moreover, the attainable resolution of approx. 15 .mu.m is
often insufficient.
Therefore, it has repeatedly been proposed to employ apparatuses for
observing the fundus of the eye, which do not illuminate expansive areas
of the fundus of the eye, but rather scan as small as possible a spot with
a focused illuminating light and detect the reflected light in relation to
the scanning sequence. In this regard, reference is made, by way of
illustration, to "The Foundations of Ophthalmology", Vol. VII, pp.
307/308, Yr. 1962, U.S. Pat. No. 4,213,678, EP-A-0 145 563 as well as
Japanese patent publications 61-5730 and 50-138822.
The apparatuses described in the aforementioned references differ from one
another in the pupil separation. The Japanese patent publication 61-5730
proposes a "GULLSTRAND separation", U.S. Pat. No. 4,213,678 an inverted
"GULLSTRAND pupil," and the Japanese patent publication 50-138822 adjacent
pupils as illumination and observation light.
In the apparatus for observing the rear portions of the eye described in
EP-A-145 563, both the illumination light beam and the observation light
beam are directed via a scanning device. A "double scanning system" of
this type has the advantage that the reflected beam of light can be
determined by means of a stationary detector with a relatively small
surface.
The apparatuses mentioned in the preceding for observing the rear portions
of the eye with "scanning illumination" have in common that the resolution
of the received image is determined by the size of the "focus spot"
(approx. 8-12 .mu.m) on the fundus of the eye and that the reflected light
is received by a single detector with a more or less large field of view
aperture for building up the image of the rear portions of the eye.
Further analysis of the returned light has not previously been considered.
The present invention is based on the recognition of the fact that
apparatuses for producing images, in particular, due to special types of
illumination and/or the analysis of the light scattered back according to
most varied criteria permits gaining essential further ground-laying
information about the object of which an image is to be made, for example
the fundus of the eye, than is possible with any of the other known
apparatuses.
Therefore, a primary object of the present invention is to improve an
apparatus for producing images of an object hereto in such a fashion, that
it is possible, by means of special types of illumination and/or the
analysis of the light scattered back, to analyze the object to be imaged
proceding beyond a pure image production analysis.
By way of illustration, the apparatus of the present invention permits
making a spatial analysis and/or one of the polarization state of the
returned light. For this purpose, the apparatus is provided with several
individual detectors, which, in order to receive the light reflected from
different planes and/or to receive the patchlike distribution of the
intensity of the light and/or to determine the polarization state of the
light conjugate to different planes or assigned to different areas of a
plane or to which corresponding apertures or polarization filters are
connected in a series.
In this manner, apparatus permits measuring the spatial distribution of the
intensity and/or the polarization state of light reflected from the object
to be imaged, by for example the rear portions of the eye. Moreover, the
arrangement of the detectors in planes conjugate to the different planes
of the object to be imaged makes a depth analysis of the object possible.
It is expressly made clear at this point that when in the case of the
present invention it is said that the detectors have a specific form or
are arranged at a specific location, it is not necessary that the
detectors actually are designed accordingly; but rather it suffices if
apertures for determining the field of view are arranged at the
corresponding location and are connected with the detectors via
light-conducting means, for example relay optics or light conductors. Such
an arrangement of field-of-view-determining apertures instead of detectors
is a particular feature of the "scan process" used for image build-up, in
which no actual image is produced, but reflected or scattered light is
received and assessed time-sequentially to the image build-up at any time
in the entire space angle or the assessable space angle. Another primary
object of the present invention is that light of several wavelengths,
preferably the light from several lasers, is projected simultaneously onto
the location of the object to be imaged. By this means varied effects can
be achieved.
By way of illustration, it is possible to simulate a white light
illumination in a laser scanning ophthalmoscope and deliver the
ophthalmologist his "accustomed" picture of the fundus of the eye with a
"representation in real color".
Moreover, with an appropriate selection of the wavelengths it is possible,
by way of illustration, to determine the blood oxygen saturation level,
which indicates local circulatory disturbances and of the entire system,
avascular zones, etc. Furthermore, tumor analysis, visual pigment
analysis, etc. are possible.
In addition, the simultaneous reception of an angiofluorescent and a
"normal" image of the fundus of the eye is possible if an Ar.sup.+ -laser
or a HeNe laser and a laser with a different wavelength are employed
simultaneously.
Simultaneous implementation of light of several wavelengths, moreover,
makes other interesting possibility feasible.
The depth of focus of the illumination light depends on the entrance pupil,
i.e. on the size and form of the pupil for the illumination light. By way
of illustration, a great depth of focus is gained with an entrance pupil
designed as an inverted Gullstrand pupil as proposed in the U.S. Pat. No.
4,213,678 due to the small peripheral angle of the illumination light. On
the other hand, a small depth of focus is gained when a normal Gullstrand
pupil or the pupil used in EP-A-0 145 563 is employed due to the large
angle enclosed by the peripheral rays.
Normally, the entrance pupil is selected corresponding to the respective
intention, whereby the inverted Gullstrand pupil yields the best
resolution, because the optically poorer peripheral regions of the eye are
not used in it and thus the illumination light can be focused onto the
smallest spot diameter.
When several sources of light are employed yielding light of different
wavelengths, different entrance pupils can be used, whereby, it is
particularly preferable if for light of one wavelengthan entrance pupil
delivering a great depth of focus is employed and an entrance pupil
delivering a small depth of focus is used for light of another wavelength.
In this manner, it is possible to simultaneously receive a full overall
image with high resolution and great depth of focus and a second image,
which is "depth selective", whereby the selection of the different
entrance and, if required, exit pupils occurs, for example, by means of a
suitable wavelength selective coating of the so-called optical input
coupling element (divider mirror), i.e. of the mirror separating the
illumination and observation beam path. In this case, complementary pupils
are received for the different wavelengths. Naturally, a different
separation of the pupils by suitable means is also possible, such as by
employing several divider mirrors in such a fashion that other pupil
separations are also possible as complementary pupils.
The signals from the various detectors, e.g. an angiograph image and the
"normal" image can be superimposed on a monitor or presented on several
monitors.
In any case, the representation of both or several images in real time or
following storage can be coupled. By "coupling" it meant the known state
of the art operations in image processing, by way of illustration, very
revealing images are received by means of "real time superimposition" of
an angiograph image and a normal image. The individual direct images or
those received after processing can, of course, be presented and/or
received on several observation devices simultaneously, such as monitors.
In this case, it is particularly advantageous to design the apparatus of
the present invention in such a fashion that both the illumination light
and the reflected light are directed via the scanning device. With such an
apparatus, a simple detection light signal, which does not change its
position in space, is received in a simple manner behind the scanning
device.
As already explained in detail, in accordance with the present invention
the spatial distribution of the reflected light can be detected and
assessed. For this purpose, it is, in particular, possible to arrange
detectors or field-of-view determining shutters in planes which are not
conjugate to the actual plane of the object.
By way of illustration, a detector arrangement or field-of-view determining
shutter is provided in a plane conjugate to the pupil of the eye to detect
the distribution of the intensity of the reflected light in this plane. In
this case, the individual detectors or shutter elements preferably have
the shape of sectors of a circle so that the main point of the reflected
light or light scattered back, or directional symmetries etc. can be
determined, by means of which, by way of illustration, it is possible to
draw conclusions about the surface structures.
In a further embodiment, a detector arrangement or a shutter arrangement is
provided in a plane conjugate to the object to be imaged, thus, by way of
illustration, conjugate to the fundus of the eye, which determines the
intensity of the distribution of the reflected light in this plane.
By this exemplary means, it is possible to detect the portion of transverse
scattering in the retina by analyzing the distribution of the intensity in
an image plane conjugate to the retina and thereby gain information about
the structure of the retina.
In addition to the spatial analysis of the reflected light, another
embodiment makes it possible to analyze the polarization state of the
reflected light so that an improved representation of the
double-refracting nerve fiber layer of the retina is yielded compared to
that of the known apparatuses.
A further embodiment, moreover, permits determining the Stokes parameters
to describe the polarization characteristics by which local defects can be
detected, and anistropic, i.e. directional structures of the retina, such
as, for example, the nerve fiber layer can be made more prominent.
Moreover, with regard to the definition of Stokes parameters, reference is
made to the article "Polarization Imaging" in APPLIED OPTICS; Vol. 20, pp.
1537 ff.
Further features of the present invention make an optical structure
analysis or an optical image pre-processing of the reflected light
possible. The optical image pre-processing operates substantially faster
than available electronic image processing systems and thereby permits
making special structures of objects prominent in real time even in the
case of complex filtering.
Depending on the position of the analyzing filter or the shutter,
polarization states can be isolated, directional anisotropes can be
selected, aberrations can be compensated for, etc. It is particularly
advantageous if variable filters and/or shutters controlled by, by way of
illustration, a calculator exchangeable and/or rotatable shutters as well
as shutters having a gradual transmission (apodization) are provided. Such
shutters are generally not simple apertures, but rather formed
arrangements depending on the respective use, by way of illustration,
slits, rings, combinations of quadrants or a pattern of individually
controlled dots. Furthermore, the shutters may be partially mirrored glass
plates, perforated mirrors, wavelength-selectively vaporized mirrors or
semi-translucent mirrors. It is also possible to produce zones of
different optical effects by means of appropriate design of the divider
mirror.
The present invention provides a simply constructed light modulator,
namely, a liquid crystal element, which can be switched area-selectively
translucent or untranslucent.
Another preferred solution for accomplishing a primary object of the
present invention and, in particular, a design of an apparatus for
observing the rear portions of the eye, is distinguished by the fact that,
in addition, marks may be projected onto the object to be observed, by
such as the fundus of the eye. These marks can, by way of illustration,
serve to mark areas to be treated (coagulated) or to be examined, and are
produced by means of image processing in a representation which was
previously made. On this point, patent application P 36 07 721.6,
discusses in detail the use of image processing for treatment planning and
for producing markings.
These marks may, by way of illustration, be produced by "lightening" the
illumination light beam at the corresponding location. The lightening is
particularly preferred when the marks are to serve for orientation and/or
marking a specific area as, in any case, the spatial relationship between
the "scanning beam" and the mark remains constant.
However, it is also possible to employ a light source and in particular a
positioning unit to project the marks as, in that case, far as possible
independence of the individual systems of each other is ensured. This
construction is especially recommended if the additional beam is intended
for processing purposes, such as coagulating purposes.
This positioning system can, by for example, by an acousto-optical
deflector or a wobble optic shown in German patent application P 35 32
464.3, as the same is stable and easy to handle.
On the other hand, in accordance with the present invention, an x/y-scanner
with a polygonal mirror drum and a galvanometer mirror is preferably used
as the scanning device for a system of this type which operates
independently of wavelengths, and is particularly of advantage in the case
of the simultaneous implementation of light of several wavelengths.
Besides the possible applications of the additional mirrored-in markings
previously explained as a further possible application there is the fundus
perimetry. In this case the markings serve as so-called stimuli, which the
patient recognizes or in the event of field-of-view failures does not
recognize. It is particularly advantageous if an infrared laser is
employed as the source of the observation light as thereby the observation
light does not have an adverse effect on the recognition of the stimuli.
By means of this embodiment of an apparatus for observing the rear
portions of the eye, a fundus perimeter is yielded that makes
microperimetry possible under visual control and moreover also permits
training the eye to eliminate vision or fixation weaknesses.
In microperimetry it is also advantageous, however, not only when the
present invention is employed, if additional illumination of the
surrounding area is provided, which, by way of illustration, is coupled
via a semitranslucent mirror. This illumination of the surrounding area
permits, for example, perimetry of a "specific level of lightness", but,
of course, has other advantages.
In fundus perimetry, special search algorithms, scotoma detection, a
variable measuring point density, fundus tracking for automatic detection
of the position of the projected markings on the fundus can be realized
via a control unit. Furthermore, a positive and negative perimetry, color
differential examinations, etc. may be carried out.
A further improvement, in accordance with the present invention, of an
apparatus, which is particularly suited for the observation of the rear
portions of the eye, is provided with one or several detectors, before
which shutters are arranged in such a manner that the result a dark field
illumination of the detectors so that only the multiply scattered
components are recorded in the image of the object or the fundus. By this
means an intensified contrast representation of specific structures, e.g.
papillary tissue, is made possible, which is of utmost interest for
automatic determination of the edge of the papilla within the scope of
glaucoma diagnosis.
By providing several detectors it is, of course, also possible to receive
"dark-field" and "light-field" images simultaneously.
Furthermore, in accordance with the present invention it is advantageous if
earlier received images and/or markings are mirrored congruently into the
received and presented image in such a manner that the operating
personnel, by way of illustration, can compare images made according to a
different method, such as angiographs, or control an automatic laser beam
positioning. To this point, reference is again made to the German patent
application P 36 07 721.6. The "mirroring in" can occur by optical means,
preferably, however, by electronic means in the observation apparatus,
such as by means of a monitor.
The apparatus of the present invention is not only suited as an
image-producing or diagnostic device, but also as a processing or therapy
device and can be combined with many very different instruments, such as
processing or treatment lasers of different wavelengths.
In particular, however, it is advantageous if in addition the beam of a
coagulating laser, e.g. an Ar.sup.+ -laser or a dye laser, is mirrored in
preferably between the scanning device and the eyeball. However, "a short"
raising of the output of the observation laser is, of course, also
possible for coagulating as described in U.S. Pat. No. 4,213,678. The
joint implementation of the "scanning device" permits in this case in
particular treating large areas or several areas in one step.
An apparatus for observing the rear portions of the eye with a scanning
illumination is particularly useful as an image transmitter for a
so-called eye tracking unit due to its reflex-free and high resolution
presentation of the image. With regard to the principal
eye-tracing-concept-directing of the observation and/or treatment unit,
switching off the laser in the event of eye motion, etc. reference is
again made to the German patent application P 36 07 721.6, the content of
which, moreover, is expressly viewed as a disclosure of this application.
Furthermore, an apparatus for observing the rear portions of the eye with a
scanning illumination is especially suited as an image transmitter for
treatment planning due to its reflex-free and high resolution presentation
of the image as also already described in the German patent application P
36 07 721.6.
It is especially advantageous, however, to employ an apparatus with "double
scanning", in contrast to the apparatus known from EP-A-0 145 563, a
field-of-view shutter having a diameter from 80 to 150 .mu.m is used,
being thus substantially larger than the diameter of the point image on
the fundus of the eye which is typically between 8 and 12 .mu.m and at the
most, however, approx. 20 .mu.m. This selection of field-of-view shutter,
which differs from the selection in EP-A-0 145 563, particularly supports
the concept of the present invention of using several individual
detectors. The pupil separation in the pupil plane may be carried out in a
state of the art manner from the above-mentioned individual references.
BRIEF DESCRIPTION OF THE DRAWING
The present invention is made more apparent from the following detailed
description of preferred embodiments when taken in conjunction with the
accompanying drawings wherein:
FIG. 1 illustrates the general beam path of an apparatus in accordance with
the present invention,
FIG. 2 illustrates the beam path "before" the scanning device,
FIG. 3 illustrates a possible arrangement of detectors in a plane conjugate
to the object,
FIG. 4a-c illustrate possible arrangements of detectors in a plane
conjugate to the pupil,
FIG. 5 illustrates possible pupils for the illumination light and the
reflected light.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the general beam path of an apparatus of the present invention
using, for illustration purposes and without limiting the scope of the
invention, a laser scanning opthalmoscope. Light L of an illumination
device illustrated in more detail in FIG. 2 hits a polygonal mirror 1 of a
scanning device. The polygonal mirror 1 deflects light L in a horizontal
direction corresponding to its shift in the direction of an arrow 1'. A
concave mirror 2 and another concave mirror 3 reflect the image of the
horizontally deflected bundle of light onto a galvanometer mirror 4, which
swings in the direction of an arrow 4' and additionally deflects the
bundle of light in a vertical direction. The bundle of light deflected in
a horizontal direction (x) and in a vertical direction (y) is deflected by
a plane mirror 5 and focussed by a concave mirror 6 onto the fundus
(retina) R of an eyeball 7 in such a manner that the light beam scanning
in the x and y directions has a "waist" in the pupil plane P of the
eyeball 7. The refractive power of elements 2, 3, and 6, as well as the
optical paths between the elements, are measured in such a fashion that
the planes P' or P" of mirror 4 or 1 are planes conjugate to the pupil
plane P of eyeball 7.
The light N reflected or scattered from the fundus of the eye R is guided
back on the reverse path via mirrors 6, 5 4, 3 and 2 to the polygonal
mirror 1 and may, as illustrated in more detail in FIG. 2, be detected
"behind" the scanning device by a stationary arrangement of detectors.
Furthermore, an independent source of light 11, which preferably is a
laser, and a deflection unit 12, operating independently of deflection
device 1,4, are provided to deflect beam M of light source 11 and permit
positioning beam M on the retina. For this purpose, mirror 5 in the
illustrated embodiment is designed as a semitranslucent mirror.
Light source 11 may, by way of illustration, be a coagulation laser, thus
e.g. an Ar.sup.+ -laser, an image mark transmitter or the light source
permitting conducting a microfundus perimetry.
Deflection unit 12 may, of course, be any unit which permits positioning a
light beam on a surface of the object. Deflection unit 12 may be an
acousto-optical deflector or a wobble unit.
Moreover, another semitranslucent mirror 13, which permits expansive
mirroring in of light B from an additional source of illumination, which
is not depicted, is arranged in the beam path. The purpose of light B is
to illuminate the fundus of the eyeball R and may, particularly in the
case of microperimetry, serve to "set" a specific light level on which
subsequently the marks mirrored in with laser 11 must be recognized.
FIG. 2 shows the design of the illumination apparatus and the detector
device arranged "before" or "behind" the polygonal mirror 1 of the
scanning device.
In the depicted preferred embodiment the illumination device is provided
with two lasers 21 and 22, which emit light of different wavelengths, by
way of illustration in the UV and visible range or in the visible and
infrared range. The light paths of both lasers are united by means of a
semitranslucent or wavelength-selective mirror 23 and coupled by a divider
mirror 24 in the mutual light path of the illumination light L and the
detection light N.
The design of the divider mirror 24 determines the design of the entrance
pupil, i.e. of the part of the pupil of the eye passed through by the
illumination light L, and the exit pupil, i.e. the part of the pupil of
the eye passed through by the light N reflected or scattered from retina
R.
FIG. 5 depicts a possible pupil separation. By means of a
wavelength-selective coating of the divider mirror 24, it can be achieved
that the light from, for example a laser operating in the visible range is
only reflectd by the region surrounding the optical axis in such a manner
that the entrance pupil is the region 51.
The region 52 surrounding region 51 is then the exit pupil. If the mirror
layers of mirror 24 are selected in such a fashion that the layer
reflecting visible light is translucent to, by way of illustration, light
in the infrared range and reverse, the entrance pupil for light in the
infrared range is region 52 and region 51 is the exit pupil.
Due to the different angles of the peripheral beams, the light passing
region 51 is focused on retina R with a great depth of focus, whereas the
light entering through region 52 is focused with a small depth of focus.
In this manner images having great depth of focus and images having little
depth of focus in the range from 0.1 mm and under, which permit a depth
analysis, can be received simultaneously with two lasers 21 and 22,
whereby the simultaneously received image with great depth of focus makes
a full overall representation possible.
Furthermore, FIG. 5 indicates that the exit pupil 51 may be separated into
two regions 52' and 52". The difference between the signals received in
the regions 52' and 52" permit drawing conclusions about the directional
asymmetry of the transverse scattering.
Moreover, FIG. 2 shows, by way of example, a detector device employed in
accordance with the present invention. The detector device is provided
with four individual detectors 311, 312, 313 and 314, arranged in a plane
conjugate to the retina R and hit by the detection light N reflected from
the retina R.
Due to the "scan processing" employed for the image build-up, detecting all
the scattered or reflected light in the assessable space angle and using
it time-sequentially for building up the image, the detectors do not have
to actually be physically arranged in a plane conjugate to the retina, but
rather it suffices if field-of-view-determining shutters are arranged in
this plane (or in FIG. 4 in a plane conjugate to the pupil) and the light
passing through these shutters is directed by elements transmitting an
intermediate representation, by way of illustration a relay optic or light
conductor, to the spaced detectors. Whenever detectors are mentioned in
the following discussion, it is also meant that
field-of-the-view-determining shutters may be substituted instead.
Furthermore, according to FIG. 2, beam dividers 301, 302 and 303 may be
provided. There is element influencing the beam path arranged before
detector 311, whereas a 0> analyzer 322 is arranged before detector 312, a
45> analyzer 323 is arranged before detector 323 and a quarter-wave plate
324 is arranged before detector 314.
If the output signals of detectors 311 to 314 are designated A-D, the
Stokes parameter S.sub.i may be formed to analyze the polarization state
of the reflected light by means of a synchronizer (not shown) and
evaluation unit:
S.sub.o =A, S.sub.1 =B-A, S.sub.2 =C-A, S.sub.4 =D-A
Therefrom the following quantities may be derived to describe the
polarization characteristics:
##EQU1##
The determination of the polarization characteristics permits determining
and making anisotropic, e.g. directed structures of the retina prominent,
such as for example the nerve fiber layer.
The detector arrangement (shutter arrangement) illustrated in FIG. 2 is
merely an example of a detector arrangement implemented in accordance with
the present invention, in which several detectors arranged in a plane
conjugate to the object to be imaged, which in the present example of an
embodiment is the retina.
FIG. 3 shows another example of a detector arrangement (or arrangement of
field-of-view-determining shutters) having detectors 41 to 45 in a plane
conjugate to the plane of the retina. Detector 41 is a so-called
light-field detector, whereas detectors 42 to 45 are dark-field detectors.
If the ouput signals of detectors 41 to 45 are designated 41' to 45', the
quantity
(41'+43')-(44'+45')
indicates the directional characteristics of the reflexion.
Of course, it is also possible to arrange the detectors or
field-of-view-determining shutters not in planes conjugate to the object
plane R, but, by way of illustration in planes conjugate to pupil P.
Corresponding examples are shown in FIGS. 4a to 4c.
FIG. 4a depicts a detector arrangement having three detectors 41 to 43. The
output signal from detector 41 is proportional to the specular portion,
whereas the output signals 42' and 43' from detectors 42 and 43 represent
the scattering under large angles.
FIG. 4b depicts a detector arrangement having five individual detectors 41
to 45 arranged in a plane conjugate to pupil plane P in a confocal design.
Output signal 41' from detector 41 indicates again the specular portion,
whereas output signals represent
(42'-43') the diff. phase contrast
and output signals
(42'+43')-(44'+45') the scattering characteristics.
FIG. 4c shows a detector arrangement, having four circle sector-shaped
individual detectors 41 to 44, again arranged in a plane conjugate to
pupil P. The coupling
(41'+43')-(42'+44')
of the output signals from these detectors represents, by way of
illustration, the left-right asymmetry of the scattered light. Once more
it is pointed out that the aforegoing detector arrangement and arrangement
of field-of-view-determining shutters have been used synomymously.
The present invention has been described above using preferred embodiments
without the intention of limiting the scope of the overall inventive
concept--to gain essential ground-laying information about the object to
be imaged, e.g. the fundus of the eye by special types of illumination
and/or the analysis of the light scattered back according to most varied
criteria than is possible with any other known apparatus for producing
images.
Most varied modifications and alterations are, of course, possible within
the scope of this overall inventive concept.
The optical image pre-processing of the present invention may also be made
more sophisticated by specially designed exchangeable and/or variable
shutters, like LCD shutters before the detectors, instead of or in
addition to elements 322 to 324.
The apparatus may also operate without "double scanning, in particular with
the detector arrangements arranged in the pupil plane, which can forego
confocal detection.
Apparatus having only one detector, but correspondingly designed shutters
are also possible. Field-of-view-determining shutters, arranged in an
exchangeable manner in a specific plane may also be connected via light
conducting means to stationary detectors arranged in another plane.
The mirroring-in of a positionable additional beam and/or of the
surrounding illumination may also be carried out in another manner than as
previously described. Other pupil separations or strict confocal
arrangements may also be realized.
The preceding description of the present invention permits realizing the
assessment and synchronization unit, which couples and/or stores the
individual signals, e.g. a microcomputer, even without a detailed
description of an embodiment.
The preceding description of a laser-scanning opthalmoscope does not
restrict the basic concept of the present invention to opthalmoscopes,
although they, in particular, are especially advantageous for the
observation of the fundus of the eye due to the specific difficulties
resulting from the pupil of the eye. The basic inventive concepts may, of
course, be employed in other instruments, including those employed for the
observation of the cornea, designed for medical and technical use as
laser-scanning cameras or laser-scanning microscopes or in other
laser-scanning-image transmitters.
The preceding description is to be construed as an illustration and not a
restriction or renouncement of protection of elements of invented further
embodiments claimed in the individual claims hereto of state of the art
apparatuses.
* * * * *
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