Operation microscope with fixation device

The invention contemplates an operation microscope which incorporates an eye-fixation feature to enable a patient's eye (under microscope observation) to precisely maintain infinity focus and viewing alignment, either with the central axis of the microscope or at desired controllable offset therefrom. Embodiments are shown for incorporation of this feature both as part of the field-illumination optical system associated with the microscope, and otherwise, but nevertheless also utilizing part of the observational optical system of the microscope.

BACKGROUND OF THE INVENTION 
The present invention refers to an operation microscope, particularly for 
ophthalmological microsurgery. 
It is necessary in certain processes in ophthalmological microsurgery for 
the patient to bring the visual axis of his eye as closely as possible 
into the direction of observation (instrument central axis) of the 
operation microscope and to hold it there for a relatively long time. 
So-called fixation objects and fixation lights upon which the patient fixes 
to thereby bring the visual axis of his eye into a given direction are 
known in ophthalmological examination instruments. Generally, these aids 
are arranged at a slight distance from the eye of the patient so that, for 
persons with poor vision or for older persons, fixation is possible only 
poorly if at all, even for a short time. 
In fundus cameras, a fixation object is known which is arranged in the 
illumination-ray path in a plane which is imaged onto the retina of the 
patient, whereby the above-indicated difficulties in fixation are avoided. 
This fixation object consists of an opaque circular disk of small diameter 
which can be moved by the doctor in the plane indicated and which makes it 
possible for him, upon fixation by the patient, to direct the visual axis 
of the eye of the patient in any desired direction. 
As far as I am aware, fixation devices are not known in operation 
microscopes. 
BRIEF STATEMENT OF THE INVENTION 
The object of the present invention is to develop an operation microscope 
such that it becomes possible even for an older person or for a person 
with defective vision to direct the visual axis of his eye precisely in 
the direction of observation of the operation microscope and to keep it 
there, reliably, for a relatively long period of time. 
The invention achieves this object in a fixation device for aligning the 
visual axis of the eye of the patient, by providing the device with a 
fixation mark and an objective to focus the mark at infinity, 
substantially in the direction of microscope observation. The microscope 
incorporating the invention may illustratively be, but is not necessarily, 
a binocular stereo microscope, having a single main objective which serves 
both observation-ray paths of the stereo system. 
In one advantageous embodiment, a separate ray path is used for the 
fixation device. The separate ray path may be precisely coaxial with the 
instrument axis and, in the case of a binocular stereo microscope, may use 
the single main objective which serves both observation-ray paths of the 
stereo system, the fixation-ray path exiting from the instrument between 
the two observation-ray paths thereof. However, such precise symmetry is 
not necessary, since slight deviations can be compensated by displacing 
the fixation mark transverse to the ray path. In a second embodiment, the 
fixation-ray path is deflected via a beam splitter into one of the two 
stereo observation-ray paths. 
To compensate for the effect of the main operation-microscope objective on 
the ray path for the fixation mark and to correct for any possible defect 
in vision of the patient, one or more lenses are advisedly arranged 
swingably in front of the main objective. A turret mount is particularly 
advantageous for this purpose. 
In another embodiment, the fixation mark is brought into that plane of a 
coaxial or approximately coaxial illumination-ray path which is focused at 
infinity. In this case, only a limited correction for the defective vision 
of the patient can be effected with the lens turret described above, since 
this correction also affects the illumination-ray path. It is therefore 
particularly advantageous to effect the correction solely, or at least 
additionally, by displacement of the fixation mark in the direction of the 
optical axis, whereby the illumination-ray path is not affected. 
Other embodiments of the invention are described.

In FIG. 1, 1 designates the eye of the patient, 2 the lens of the eye, and 
3 the retina. An operation microscope 4 has two observation-ray paths 
which lie in front of and behind the plane of the drawing, and only one 
(5) of these ray paths is shown. A main objective 6 enables focus of both 
observation-ray paths upon the exterior surface of eye 1. Behind a 
magnification changer 7, a splitter cube 8 is arranged in each beam path; 
such cubes are customarily used for auxiliary access to the 
observation-ray paths, as for documentation or co-worker equipment. 
Finally, one of the two eyepieces is shown at 9. 
A fixation device of the invention consists of a fixation mark 11, which is 
illuminated by a lamp 12 and focused at infinity by an objective 13. An 
element 14 directs the fixation-ray path 15 through the main objective 6 
and onto the eye 1 of the patient. In order to compensate for the optical 
effect of the main objective 6, a swingable compensating lens 17 is 
arranged in the fixation-ray path 15 so that collimated light (i.e., a 
parallel bundle of light) strikes the eye 1, and an image of the fixation 
mark 11 is produced on the retina 3 by the eye lens 2, being thereby 
accommodated to infinity. 
For patients with defective vision, lenses of different refractive power 
can be brought into the ray path in place of the compensating lens 17. 
This is advisedly done by means of a rotatable turret 16. It will be 
understood that in the event of using a turret as at 16, its selectively 
available lenses may be designed to cooperate solely with the main 
objective 6 to project collimated light in the fixation-ray path to eye 
lens 2, thus eliminating lens 13 and enabling the fixation mark 11 and its 
illumination 12 to be arranged closer to the observation-ray path. 
It will also be understood that the fixation-ray path 15 can be arranged 
precisely in the instrument axis of the operation microscope and therefore 
between the two observation-ray paths. However, this is not necessary to 
achieve the object of the invention. In the case shown in FIG. 1, the 
fixation mark 11 need merely be so positioned in a plane perpendicular to 
the observation-ray paths that the center of its image strikes the retina 
exactly on the observation axis, i.e. on the central axis of the 
instrument; however, to achieve such centering of the image of the 
fixation mark at the retina, it will be appreciated that the fixation-ray 
path 15 need not necessarily pass through the main objective 6. 
In FIG. 2, as distinguished from FIG. 1, an operation microscope is shown 
with both of its observation-ray paths 5--5' in the plane of the drawing, 
i.e., viewed 90.degree. from the aspect of FIG. 1. In the embodiment of 
FIG. 2, the fixation-ray path 15, together with a fixation mark 11 focused 
at infinity by an objective 13, is deflected by a beam splitter 8' into 
one (5') of the two observation-ray paths, and the correction lens 17 
(needed for the target 11 to be observed by the patient) defocuses the 
doctor's observation on path 5'. The latter path therefore may not be 
available to the doctor for the time during which the patient directs the 
visual axis of his eye on the fixation mark 11. And if the doctor chooses 
to rely on monocular observation via path 5, without disturbance from the 
patient's use of path 5' to view the fixation mark 11, the observational 
use of path 5' can be selectively interrupted by a swingable beam shutter 
18. 
It will be understood that in the embodiments of both FIG. 1 and FIG. 2, 
the fixation mark 11 can alternatively be illuminated via a light guide or 
that it can also be self-illuminating. Further, the fixation mark 11 can 
be developed as a cross, circle or any other customary form. 
In the embodiment of FIG. 3, an approximately coaxial illumination-ray path 
is designated 25, the same providing illumination of the observation 
field. Projection on path 25 involves an incandescent bulb 21 whose 
filament is focused, by a condenser 22 and via a deflection prism 23, at 
the deflection surface of a prism 24. The deflection prism 24 is 
positioned close to the stereo observation-ray paths, so that illumination 
with the ray path 25 takes place practically coaxially. The 
deflection-prism (24) surface facing the main objective 6 is developed as 
a lens which, coactive with the main objective 6, focuses the plane of 
condenser 22 in the plane of eye lens 2. The fixation mark 11 is so 
arranged on ray path 15 between prisms 23 and 24 that mark 11 is focused 
at infinity by the deflection-prism (24) lens (coacting with the main 
objective 6), and so that an image of the fixation mark 11 is formed by 
the eye lens 2 on the retina 3. 
For eyes with defective vision, a turret 16 with correction lenses 17 can 
be arranged behind the main objective 6, in the same way as in the other 
embodiments. The correction range is, however, limited in this case by the 
fact that the lenses also act on the illumination-ray path 25. It is 
therefore better to effect the correction by displacing the fixation mark 
11 in the direction of the optical axis, which has no effect on the 
illumination-ray path 25; a double-headed arrow 11' will be understood to 
schematically indicate means for such selective displacement of mark 11. 
Of course, if desired, both possibilities of correction can be 
concurrently used. 
The fixation mark 11 for the FIG. 3 embodiment may illustratively be an 
opaque disk of small diameter or a colored transparent mark on a glass 
disk. Alternatively, mark 11 may comprise a small circle of greater 
brightness, produced as by a filter having greater light-transmittance at 
its center than on the rest of its surface. 
In the arrangement of FIG. 4, the complexity of FIG. 2 is reduced in a 
beam-splitting imposition of the fixation-ray path 15 on the 
observation-ray path 5'. The principal simplifying point of difference 
lies in the use of the main objective 6 alone as the means of imaging the 
fixation mark 11 on the retina 3, by positioning the mark 11 at the focal 
point of objective 6. It will be understood that use of the expression 
"beam splitter" in connection with element 8' in FIG. 4 is not intended to 
prescribe a 50:50 splitting of light intensity, but rather that the amount 
of reflected light passing via the mark-projection system 15 may be scaled 
to much less than 50 percent of the total light transmittance shared by 
the observation path 5' and by the mark-projection path 15; for example, 
the light reflected by element 8' along path 15 may be as little as 10 
percent of a perfect (or total) reflection. This being the case, the 
surgeon may choose to tolerate internal reflection of mark-projecting 
light, because the low level of its reflection into the path 5' does not 
spoil his depth perception via the focused stereo system; but if he 
chooses to avoid even this much reflection and to rely on monocular 
observation via path 5 alone, then shutter 18 is at his disposal for the 
purpose. What has been said as to less-than-50 percent reflection at 8' 
will be understood to apply to use of a small 45.degree. mirror at 8', 
wherein mirror area is a small fraction of the full effective area of the 
observation-ray bundle in path 5'. 
In all embodiments, it is advantageous not merely to make the fixation mark 
adjustable, as at 11' but also to make it selectively displaceable in a 
plane locally perpendicular to the fixation-ray path, as indicated by a 
double-headed arrow 11" in FIG. 3. Transverse adjustment, as by means 11", 
will be seen to enable the doctor to selectively direct the visual axis of 
the patient's eye 1 to desired offset from the instrument axis; and 
notched or detent action identified with one or more standardized offset 
adjustments of means 11", which may be two-component adjustments, will be 
understood to assure quick and precise shifting between standardized 
offsets.