Prism system for a stereoscopic microscope

A prism system for a stereoscopic microscope in which both an image inversion and also an interchanging of the sides of the two beam paths can occur. In order to achieve a reliable simply constructed design of a small size, the prism system has four reflecting surfaces for each beam path, of which two surfaces are constructed as reflection surfaces and are arranged in planes parallel with respect to the optic longitudinal axis. The two other surfaces are constructed as inlet or rather outlet surfaces and are inclined at 45.degree. with respect to the optic longitudinal axis and at 90.degree. with respect to one another. The inventive prism system makes it possible with a distinctly low structural height to interchange beam paths which are parallel with one another, and to carry out an image inversion at the same time. The prism system according to the invention can be utilized in particular in stereoscopic microscopes to carry out surgeries, in particular eye surgeries.

FIELD OF THE INVENTION 
The invention relates to a prism system for a stereoscopic microscope 
comprising several reflecting surfaces deflecting a right and a left beam 
path each at 90.degree. and, more particularly, a stereoscopic microscope 
for use during surgeries comprising a lens device and two ocular 
arrangements. 
BACKGROUND OF THE INVENTION 
In surgeries using a stereoscopic microscope, for example in the field of 
ophthalmology, neurosurgery, otology, etc., usually microscopes with a 
weak magnification are used. They have separate beam paths in order to 
make possible a stereoscopic viewing of the surgery field by the surgeon. 
Ocular systems are thereby utilized, each of which include an ocular tube. 
Furthermore, one common lens is usually used for both beam paths, in which 
a common collective lens is provided in most cases. 
Diverging beams enter the lens in such a microscope, which beams are guided 
parallel through the lens systems and are directed to the magnification 
changer. The beams exit from the changer again in the form of parallel 
beams and are fed to the respective ocular system or ocular tube. 
In the case of common stereoscopic microscopes suited for surgical 
purposes, it may be necessary to provide additional optic elements between 
the lens and the magnification changer or between the magnification 
changer and the ocular system, for example, beam splitters for optic 
recording devices or for co-observer systems. The use of this additional 
element results in a considerable increase of the structural length of the 
microscope, which is undesired both for technical use reasons and also for 
optic reasons. The structural length of the microscope is limited in 
technical use respects since the surgeon must carry out the surgery and at 
the same time also must watch same through the microscope. With respect to 
optic reasons, it is always desirable to keep the size of an optic device 
as small as possible, since an increase of the structural length results 
in a limitation of the optic field of vision and in addition is negatived 
by the loss of light. 
The limitation of the field of vision is particularly disadvantageous for 
surgeries on the vitreous body of an eye or rather in the vitreous body 
area, since it is not possible or only possible under considerable 
difficulties to overlook the entire area subject to surgery. It is 
therefore desirable to expand the field of vision angle as much as 
possible, for example up to a value of 150.degree.. 
A further problem occurring in such stereoscopic microscopes results when 
the microscope is supposed to be used with an in-between image. An 
in-between image becomes necessary when, for example, the retina or the 
vitreous body area of the eye of the patient is supposed to be viewed. A 
collecting system in the form of a contact glass or a lens is in such a 
case usually applied onto or in front of the patient's eye. The optic 
system of the eye and the contact glass or the supplementary lens produce 
thereby a true image of the retina or of a plane of the vitreous body 
area. The true image is behind the contact glass or rather the 
supplementary lens and is used when the microscope is adjusted for 
focusing. Due to the optic relationships, this true image appears inverted 
and interchanged with respect to the sides. The interchanging of sides 
results in an inverse stereoscopic effect, which in turn causes the 
surgeon to recognize the foreground or the background of the stereoscopic 
image interchanged. 
In order to overcome this interchanging of the stereoscopic effect and in 
order to reproduce the image in a correct manner, it is necessary, aside 
from the image inversion, to also carry out a change of the beam paths, 
namely, an interchanging of the right and the left beam path in the area 
of the microscope European A1-193 818 (which corresponds to U.S. Pat. No. 
4,710,000) describes a stereomicroscope, in which the stereoscopic 
inversion and the image inversion is overcome by means of a prism 
arrangement or a prism system. However, this known prism system proves to 
be disadvantageous in some cases because of its size, with the size not 
only influencing the outside dimensions of the microscope, but also the 
length of the optic path. By extending the optic path, limitations of the 
field of vision and undesired light losses result in turn. 
German OS 36 15 842 (which corresponds to U.S. Pat. No. 4,723,842) also 
discloses a prismatic intermediate assembly which is relatively large and 
consequently has the disadvantages known from the above-mentioned 
EP-A1-193 818. 
The Book Naumann-Schroeder "Bauelemente der Optik", Hanser Verlag, 
discloses various prism systems for image inversion and for lateral 
shifting, which in general show the possibility for use of prisms. 
The basic purpose of the invention is to provide a prism system or rather a 
stereoscopic microscope of the above-mentioned type, which with a simple 
design, a small size and high performance can avoid the disadvantages of 
the state of the art and can be manufactured inexpensively. 
The invention provides a prism system, for a stereoscopic microscope having 
a plurality of deflecting surfaces each deflecting a right or left beam 
path by 90.degree., wherein four reflecting surfaces are provided in each 
beam path, wherein two of the surfaces in each beam path are each a 
reflection surface arranged in a plane parallel with respect to the optic 
longitudinal axis of the microscope, and wherein the two other surfaces 
are respectively inlet and outlet surfaces and are inclined at 45.degree. 
with respect to the optic longitudinal axis and at 90.degree. with respect 
to one another. 
The inventive prism system is distinguished by a number of considerable 
advantages. By using four reflecting surfaces in each beam path, it is 
possible to guide the individual beams of the right or left beam path 
independently from one another in an exact manner so that on the one hand 
the inverted stereoscopic effect is removed and on the other hand an image 
inversion is carried out. With the separation into reflection surfaces and 
inlet or outlet surfaces, it is possible to arrange the individual 
surfaces separately from one another so that as a whole a design is 
created which, with the smallest structural dimensions, assures the 
highest degree of optic efficiency. Since the inlet or outlet surfaces are 
each inclined at 45.degree. with respect to the optic longitudinal axis 
and define an angle of 90.degree. with respect to one another, it is 
possible, while maintaining the same optic direction of the entering and 
exiting light beams of the prism system, for a narrow spacial association 
of the inlet and outlet surfaces to occur. 
A particularly advantageous development of the invention provides that the 
surfaces arranged in planes parallel with respect to the optic 
longitudinal axis each define an angle of 90.degree. with respect to one 
another. Thus, it is possible to design the entire prism system with 
respect to its outside dimensions substantially square or rectangularly, 
with the base of the square or rectangle being able to be adjusted in a 
simple manner to the structural demands of the microscope. Since the right 
and the left beam path is guided parallel to the base of the rectangle or 
square, a definitely low structural height can be achieved, which proves 
to be particularly advantageous with respect to the entire construction of 
the microscope, since the entire length of the microscope must only be 
increased insignificantly in order to store the inventive prism system. 
The reflecting surfaces are in a further advantageous development of the 
invention each constructed as hypotenuse surfaces of a rectangular prism 
member. This development has the advantage that the reflection of the 
light beam occurs inside of the prism member and that the light beams are 
not again broken when entering or exiting the prism member. A further 
advantage of this development lies in both the manufacture and also the 
assembly operations of the prism system being able to be significantly 
simplified. 
Furthermore, it can be advantageous when the prism member includes an inlet 
surface of the one beam path on the prism member having the outlet surface 
of the other beam path, with both surfaces adjoining one another. Two 
prism members are in this development united to form a cube or 
cubical-shaped element, so that a particularly good utilization of the 
available spacial relationships is possible. A further advantage lies in 
the inlet or outlet surface being protected against damage, since these 
are covered by the respectively adjacent prism member. 
Furthermore, it can be advantageous to arrange the prism members having the 
reflection surfaces each resting against one another or designing these so 
that they rest on the adjoining prism members including the inlet surface 
or the outlet surface. Since these prism members, which have the 
reflection surfaces, are arranged such that the reflection surfaces are on 
the outer periphery of the prism system, it is possible to significantly 
minimize the dimensions of the entire arrangement. It can thereby be 
furthermore advantageous to construct two of the prism members in one 
piece in each beam path. Loss of light during the entry or exit into the 
prism member medium is avoided by this measure. Furthermore, it is also 
possible to construct these prism members in one piece with the adjoining 
prism members having the inlet or outlet surface, so that the entire prism 
arrangement of the inventive prism system can be built of only two 
individual members. Such a development is particularly advantageous also 
in view of possible disadjustments, since individual adjustment of the 
individual reflection surfaces during installation into the microscope is 
no longer needed. 
The reflecting surfaces can be either of the minor type with a reflecting 
coating, or, by selecting suitable materials of a total reflection type. 
Those of ordinary skill in the optic art are thoroughly familiar with 
conventional reflecting coatings and with conventional principles of 
material selection to effect total reflection, and thus those principles 
are not, in and of themselves, disclosed herein in detail. The specific 
materials selected to effect total reflection would depend on the 
wavelengths to be used, the structural dimensions, and the required optic 
qualities. 
The purpose is attained with respect to the stereoscopic microscope by 
providing a prism system in an area of the microscope which includes two 
parallel beam paths. This development of the microscope has the advantage 
that no additional measures are needed for deflecting the beam path, since 
the already provided parallel beam paths can be used directly for 
transmission through the prism system. 
The inventive prism system can be arranged in the inventive microscope 
between a collective lens, which is provided in the area of the lens 
device, and a magnification changer, which is provided in beam direction 
after the lens. However, it is also possible to provide the prism system 
between the ocular arrangement and the magnification changer. Thus, it is 
inventively particularly advantageous that the prism system can be 
inserted at any desired area of the microscope anywhere where parallel 
beam paths exist. Thus, it is possible to use the inventive prism system 
in connection with conventional microscope developments without requiring 
conversions or changes to the microscope. 
A particularly advantageous further development of the inventive microscope 
is that the prism system, while maintaining the normal function of the 
microscope, can be removed from the beam path of same. The prism system 
can be moved or tilted, such that its movement is effected in the X- or 
Y-direction with respect to the optic axis of the microscope. This 
microscope development permits a quick change between a normal viewing 
through the stereoscopic microscope and a viewing of the surgery field 
using the inventive inverting prism system. Since no conversions of the 
microscope are needed in the inventive microscope for removing the prism 
system, the change can also be carried out quickly and easily by an 
unschooled operator. Furthermore, it has proven to be advantageous that 
the inventive prism system is very small, so that both the space needed 
for the change of the viewing manner can be dimensioned very small and 
also the required forces can be minimized. The latter is particularly 
important when the microscope, during surgery, must be held vibration-free 
on the eye of a patient. A further advantage is that in the inventive 
microscope upon removal of the inventive prism system, the normal viewing 
manner remains uninfluenced by the microscope, since the parallel beam 
paths can, upon removal of the prism system, continue to be guided 
parallel unhindered.

DETAILED DESCRIPTION 
FIG. 1 schematically illustrates the inventive prism system, with the 
individual elements of the prism system being shown separately from one 
another in order to make understanding of the invention easier. 
Two parallel beam paths R.sub.1 and L.sub.1 are shown in FIG. 1 and, in a 
manner which will yet have to be described, are constructed in a 
stereoscopic microscope. The beam paths are, in the prism system shown in 
FIG. 1, diverted several times independently from one another and are 
again sent out in a parallel arrangement as beam paths R.sub.2 and 
L.sub.2. The inventive prism system is constructed such that both an 
interchanging of the sides of the beam paths, namely, a change from the 
right to the left beam path and vice versa occurs, and also an image 
inversion. 
The inventive prism system has two reflection surfaces 4, 5 for the right 
and the left beam path, which reflection surfaces are aligned parallel to 
an optic longitudinal axis A (see FIG. 4), with the optic longitudinal 
axis A being parallel to the beam paths 2, 3. The entering beam paths 2, 3 
are fed to the reflection surfaces 4, 5 through inlet surfaces 6. The 
deflection of the exiting light beams of the beam paths 2, 3 is done by 
the also reflecting outlet surfaces 7. As shown in FIG. 1, the inlet 
surfaces 6 or rather the outlet surfaces 7 are each arranged at an angle 
of 90.degree. to one another and form an angle of 45.degree. with respect 
to the optic longitudinal axis A or rather with respect to the inlet and 
outlet direction of the beam paths 2, 3. 
The operation of the inventive prism system will be described hereinafter 
in connection with the schematic illustration of FIG. 1. Since the 
inventive prism system is symmetrically designed with respect to the right 
and left beam path, only the right beam path (R.sub.1) will first be 
described. For simplicity reasons, only one beam is illustrated which has 
the reference numeral 2. The beam path 2 encounters the inlet surface 6 
parallel with respect to the optic longitudinal axis A of the microscope 1 
and is deflected at 90.degree. by the inlet surface, since the inlet 
surface 6 is arranged at an angle of 45.degree. with respect to optic 
longitudinal axis A. In the illustration according to FIG. 1, the beam 
path 2 is deflected to the left. The beam path 2 subsequently encounters 
the reflection surface 4 which effects another deflection at 90.degree., 
so that the light beam or beam path 2 is guided to the reflection surface 
5, which also effects a deflection at 90.degree.. The beam path 2 then 
encounters the outlet surface 7 which is also inclined at 45.degree. with 
respect to the direction of the optic longitudinal axis A and deflects the 
beam path 2 again at 90.degree.. The exiting beam path 2 (R.sub.2) is thus 
parallel to the entering beam path 2 (R.sub.1), however, was laterally 
offset and subjected to an image inversion. 
The left beam path (L.sub.1) identified by the reference numeral 3 
encounters, parallel aligned with respect to the optic longitudinal axis A 
or rather to the beam path 2 (R.sub.1), the other inlet surface 6, is 
deflected at 90.degree. by the inlet surface, encounters the reflection 
surface 4, is again deflected at 90.degree. and guided to the reflection 
surface 5, which directs the beam path 3 again to the outlet surface 7 
which effects a further 90.degree. deflection. The deflection of the left 
beam path 3 occurs, so far, symmetrically with respect to the deflection 
of the right beam path 2. 
FIG. 1 illustrates that the entering right beam path R.sub.1 is aligned 
with the exiting left beam path L.sub.2, while the entering left beam path 
L.sub.1 is arranged coaxially with respect to the exiting right beam path 
R.sub.2. Thus, a reversal of sides or an interchanging of sides of the 
right and left beam paths occurs by means of the inventive prism system. 
The inventive prism system includes several prism members 8 to 15, each of 
which is a rectangular prism member having a hypotenuse surface 
functioning as a reflection surface. According to the above-described 
arrangement and operation, the respective beam paths 2, 3 first encounter 
the inlet prism members 8 and 9 and are guided by the prism members 
through the following prism members 10, 11 or 12, 13 prior to reaching the 
outlet prism members 14 or 15. The inlet prism members 8, 9 and the outlet 
prism members 14, 15 are each arranged in pairs with one another such that 
an outlet surface 7 is associated with the respective inlet surface 6. The 
prism members 9, 14 and 8, 15 respectively thus each form a cube or 
quadrangular prism, with the reflection surfaces 6 and 7 being inner 
surfaces of the quadrangular prism. According to the invention, the 
respective prism members 8, 15 and 9, 14 can be secured relative one 
another, for example by adhesives, cementing or the like. Since the prism 
members 10 to 13 are constructed and arranged such that their reflecting 
hypotenuse surfaces point outwardly, it is possible to adjust the distance 
d and b between the prism members 8 to 15 to meet requirements of a 
particular application. The distances b and d are reduced to zero in the 
exemplary embodiment illustrated in FIGS. 2 and 3, so that the inventive 
prism system is embodied by a single member having a minimum overall 
volume. The dimensions of the distances d and b depend on the respective 
structural requirements, with the distances between the right and left 
beam paths having to be considered in a suitable manner. 
Thus, with the aid of the inventive prism system both an image inversion 
and also a beam inversion or lateral interchanging of the right with the 
left beam path takes place. The parallelism of the beam paths or rather 
their coaxial arrangement is thereby maintained unchanged. 
FIG. 2 illustrates a side view of the inventive prism system according to 
FIG. 1 assembled ready for use, with the distances b and d, as already 
mentioned, being reduced to zero. FIG. 3 is a top view of the prism system 
shown in FIG. 2. FIGS. 2 and 3 do not show the beam paths 2 and 3 in order 
to have a clearer illustration. 
FIG. 4 schematically illustrates an inventive stereoscopic microscope which 
is provided with the inventive prism system. The microscope 1 includes, in 
the usual manner, a housing shown only schematically, on which an ocular 
arrangement 18 is arranged, which in the usual manner can be constructed 
in the form of a telescope ocular tube. A diaphragm 21 can be provided 
following the ocular arrangement, through which diaphragm the beam paths 
2, 3 are guided to a deflecting prism arrangement 20. The prism 
arrangement 20 can be constructed in the usual manner. Lenses 22 are 
provided following the prism arrangement 20, which lenses effect a 
parallel alignment of the beam paths 2 and 3. The inventive prism 
arrangement 19 is arranged in the parallel beam path, which prism 
arrangement is only schematically illustrated in FIG. 4 and has the design 
illustrated in FIGS. 1 to 3. Lenses 23 and 24 are each provided following 
the prism arrangement or the prism system 19, which lenses 23 and 24 can 
divert or again parallel align the beam paths 2, 3. A magnification 
changer 17 is provided following the lens 24, which changer 17 can be 
designed in the usual manner and makes possible a change of the 
magnification relationships. Thus, a detailed description of the 
magnification changer 17 is not needed. The magnification changer 17 is 
followed by collective lenses 16, by means of which the beam paths 
starting out from an image plane 25 can be focussed. An eye 26 of a 
patient is shown below the image plane 25. The eye 26 is thereby only 
schematically illustrated. 
Thus, in the inventive microscope the light exiting in the area of the eye 
26 of the patient or rather the image produced in the image plane 25 is 
guided through the collective lenses 16, the magnification changer 17, the 
lenses 24 and 23 to the inventive prism system 19, is inverted and 
laterally interchanged therein and is guided through the lenses 22 to the 
deflecting prism arrangement 20 effecting a lateral shifting of the beam 
paths 2, 3 in order to permit an adjustment to the interocular distance of 
the observer. The beam paths 2, 3 are thereafter guided through the 
diaphragm 21 to the ocular arrangement 18. 
The inventive prism system 19 has a very small thickness, for example 18 
mm, and thus facilitates a use with a common microscope without special 
changes or structural reconstructions. 
As illustrated by the arrow B in FIG. 4, it is possible without interfering 
with the operation of the microscope to remove the prism arrangement 19 or 
rather the inventive prism system out of the beam path by a lateral 
shifting or pivoting thereof in order to be able to use the microscope in 
the usual manner. 
FIG. 5 illustrates an alternate embodiment, which is substantially 
identical to the embodiment of FIG. 4 except for the following 
differences. First, the prism arrangement 19 has been relocated so that it 
is disposed between the collective lenses 16 and the magnification changer 
17. Second, a prism moving mechanism 35 is depicted, and moves the prism 
arrangement 19 in the direction of arrows B between the illustrated 
position in which it is disposed in the beam path of the microscope and a 
further position in which it is not disposed in the beam path. The 
mechanism 35 is conventional, and is not in and of itself the subject of 
the present invention. 
The invention is not to be limited to the illustrated exemplary embodiment, 
rather many possibilities for modifications exist in particular with 
respect to the dimensioning of the prism system and the association of the 
reflection surfaces. 
It is also easily possible to use reflecting surfaces, for example mirrors, 
in the place of the prisms, which mirrors are arranged at the areas of the 
reflecting surfaces of the prisms.