Abstract:
The invention relates to a laser treatment unit for performing eye surgery, comprising a contact glass ( 23 ), which can be placed onto the eye ( 21 ) and via which a treatment laser beam ( 2 ) passes. A safety mechanism ( 24, 25 ) is provided that displaceably holds the contact glass ( 23 ) in such a manner that the contact glass retreats when the contact glass ( 23 ) is subjected to the action of a force contrary to the direction of incidence of the laser beam. The safety mechanism ( 24, 25 ) enables this retreating when a force is greater than a force limit value (Fmin) and holds the contact glass ( 23 ) in a fixed manner when the force is less than the force limit value.

Description:
FIELD OF THE INVENTION 
     The invention relates to a laser treatment apparatus for ophthalmic surgery, said apparatus comprising a contact glass, which can be placed on the eye and through which a treatment laser beam is incident, and a safety mechanism holding the contact glass movable such that it retracts when a force is directed onto the contact glass counter to the direction of incidence of the laser beam. The invention further relates to a laser treatment apparatus for ophthalmic surgery comprising a beam-deflecting unit which variably deflects a treatment laser beam about at least one axis; focusing optics arranged following the beam-deflecting unit and focusing the laser beam into or onto the eye along an optical axis; a contact glass which can be placed on the eye and is arranged following the focusing optics, and a safety mechanism holding the contact glass movable such that it retracts when a force is directed onto the contact glass counter to the direction of incidence of the laser beam. 
     BACKGROUND OF THE INVENTION 
     Such laser treatment apparatuses are used for laser-surgical methods on the eye. In doing so, the treatment laser radiation is focused such that an optical breakthrough causes changes to the tissue. The treatment laser radiation acts, for example, by photo-disruption or photo-ablation. A particularly advantageous application of these effects is found in correction of visual deficiency in ophthalmology. Visual deficiencies of the eye often result from the fact that the diffractive properties of the cornea and of the lens do not cause proper focusing on the retina. In the case of near-sightedness (also referred to as myopia), the focus of the relaxed eye is located in front of the retina, whereas in the case of far-sightedness (also referred to as hyperopia) the focus is located behind the retina. A visual deficiency can also be present in the form of an astigmatism if focusing is not effected in a focal point but with linear distortion. 
     For correction of visual deficiencies, it is known to suitably influence the diffractive properties of the cornea by means of treatment laser beams. Such methods are described, for example, in U.S. Pat. No. 5,984,916 and U.S. Pat. No. 6,110,166. In this case, a multiplicity of optical breakthroughs are sequentially arranged such that a partial volume is isolated within the cornea of the eye. This isolated partial volume, which is thus separated from the remaining corneal tissue, is then extracted from the cornea through a laterally opening cut. The shape of the partial volume is selected such that the diffractive properties of the cornea after removal of the partial volume are modified so that the desired correction of visual deficiencies is achieved. 
     In order to form the cut by sequential arrangement of optical breakthroughs, it is, of course, indispensable to generate the optical breakthroughs at exactly predetermined locations. This requires exact positioning of the laser beam in the cornea of the eye. Therefore, displacement of the eye relative to the laser treatment apparatus must be avoided or compensated for as far as possible. U.S. Pat. No. 6,373,571 and WO 0/002008A1, therefore, propose contact lenses which are placed on the cornea of the eye as adapters and immobilize the eye relative to the laser treatment apparatus. The eye is usually secured to the adapter by suction using a vacuum. Such adapter, also referred to as contact glass, performs two functions: on the one hand, it deforms the eye in accordance with the adapter&#39;s predetermined surface shape. Thus, a defined surface shape is present in the beam path of the laser treatment apparatus. On the other hand, the contact glass fixes the eye and thereby prevents displacement of the eye during therapeutic intervention. 
     In order to hold the contact glass securely to the eye even when the patient moves, U.S. Pat. No. 5,336,215 proposes a device of the above mentioned type, wherein the lens focusing the laser radiation is seated in a frame together with a contact glass, which frame is in turn resiliently suspended. The lens and the contact glass are thus displaceable together along the optical axis of incidence of the treatment laser radiation. Any movement by the patient will thus automatically lead to a displacement of the contact glass and of the focusing optics in the beam path. Such movement of the optics has meanwhile turned out to be disadvantageous in terms of the quality with which the treatment laser beam can be focused. 
     As a remedy, it might be conceivable to mount the contact glass and the focusing optics permanently and irremovably to the laser treatment apparatus. However, this approach involves the risk of the eye being damaged by by bruising when the patient moves. Such movement could either be caused by a physical movement of the patient or could occur when placing the eye in contact with the contact glass. 
     Therefore, it is an object of the invention to improve a laser treatment apparatus of the above-mentioned type such that the safety mechanism can reliably avoid squeezing of the eye without adversely affecting the optical quality of the laser treatment apparatus. 
     This object is achieved in a laser treatment apparatus for ophthalmic surgery, said apparatus comprising a contact glass which can be placed on the eye and through which a treatment laser beam is incident, with a safety mechanism being provided which holds the contact glass movable on the housing such that the contact glass retracts when a force is directed onto the contact glass in a direction opposed to the direction of incidence of the laser beam, the safety mechanism enabling such retraction only in case of a force which exceeds a limit value of force and holding the contact glass fixed at a force which is below the limit value of force. 
     According to the invention, the object is further achieved by a laser treatment apparatus for ophthalmic surgery, said apparatus comprising a beam deflecting unit which variably deflects a treatment laser beam about at least one axis; focusing optics arranged following the beam-deflecting unit and focusing the laser beam along an optical axis into or onto the eye; a contact glass which is arranged following the focusing optics and can be placed on the eye, and a safety mechanism holding the contact glass movable in such a manner that it retracts when a force is directed onto the contact glass counter to the direction of incidence of the laser beam, wherein the beam-deflecting unit is arranged in the entrance pupil of the focusing optics, with respect to a deflecting element being effective for said one axis of deflection, and the safety mechanism couples the contact glass, the focusing optics and the deflecting element such that, during retraction, the deflecting element remains in the entrance pupil and the length of the light path between the deflecting element and the contact glass is constant. 
     According to the invention, the object is also achieved by a laser treatment apparatus for ophthalmic surgery, said apparatus comprising a contact glass which can be placed on the eye and through which a treatment laser beam is incident, and a safety mechanism holding the contact glass movable in such a manner that it retracts, when a force is directed onto the contact glass counter to the direction of incidence of the laser beam, wherein the safety mechanism comprises a detecting unit, which monitors retraction of the contact glass and which interrupts laser treatment operations of the laser treatment apparatus in case of a contact glass movement exceeding a threshold value. 
     Thus, the invention fundamentally deviates from the concept pursued by the prior art, which consists in compensating for any eye movements by a resilient support of the contact glass, and provides a contact glass which is rigid under certain basic conditions. In a first version of the invention, this rigidity is embodied such that the contact glass is movable only above a limit value of force. Thus, optimal optical conditions are ensured during irradiation of the eye with the treatment laser beam, and at the same time, compression of the eye is prevented, because the limit value of force causes a sort of panic release mechanism. 
     In another version of the invention, the rigidity of the contact glass does not relate to the eye, but to the mutual position of the contact glass, the focusing optics and the deflecting element. The coupling of the safety mechanism having this effect now allows movement of the contact glass due to eye or head movements of the patient, but now these movements have no effect on the optical properties of the focusing of the treatment laser beam. 
     In a third version of the invention, the rigidity of the contact glass provided for according to the concept of the invention is achieved in a functional manner. Laser treatment operation is interrupted if the contact glass is moved beyond a certain maximum amount. 
     Thus, the above-mentioned solutions provided by the invention realize different variants of the same inventive concept, namely to cause rigidity of the contact glass by means of a safety mechanism, said rigidity preventing unwanted defocusing or faulty positioning of the treatment laser radiation by eye movements or head movements. As mentioned above, said rigidity can be realized either structurally, with respect to the eye or the optics of the laser treatment apparatus, or functionally. These three approaches will be referred to hereinafter as the first variant (retraction of the contact glass above a limit value of force), the second variant (coupling of the contact glass, the focusing optics and the deflecting element) and the third variant (abortion of laser treatment if a movement of the contact glass exceeds a threshold value), respectively. 
     All three variants have in common that they prevent bruising of the eye. If there is danger of bruising, the contact glass and the patient are moved apart. This fact is referred to herein as retraction. This means, on the one hand, that the contact glass as well as possibly further parts of the laser treatment apparatus are moved away from the desired position of the patient. On the other hand, this term, of course, also covers a kinematically reversed approach, wherein the patient is moved away from the contact glass. From the patient&#39;s view, this is also a retraction of the contact glass, which justifies the generalization made herein. 
     Of course, the variants of the invention can also be combined with each other. This also applies to any embodiments and improvements. 
     In the first variant of the invention, an increase in the pressure which the patient exerts on the laser treatment apparatus, for example by his eye, only leads to a retraction of the contact glass if the limit value of force has been exceeded. Bruising of the eye is excluded if a suitable limit value of force is selected, and at the same time optimal operation is achieved under normal conditions. 
     In a particularly simple construction, the limit value of force is caused by an elastic force or weight force. One possibility of achieving this, is, for example, an elastic support for the patient on a bed, which support is selected such that the patient&#39;s bed retracts upon an apparent increase in the patient&#39;s weight. An increased pressure of the eye on the contact glass manifests itself in such apparent increase in the patient&#39;s weight so that the desired retraction then occurs. The laser treatment apparatus or the optical component of this apparatus can remain spatially fixed. Instead of the described possibility of mechanical compensation, a corresponding closed-loop control can also be effected, of course, e.g. in the form of electronic closed-loop control. 
     In a kinematically reversed construction, which is comparatively more simple in mechanical terms, it is advantageous to mount the contact glass to a holding element, which is pressed against a stop of the housing by a force defining the limit value of force. In case of a contact pressure force exceeding the limit value of force, the contact glass can then be displaced relative to the housing so that the desired safety features are achieved. Retraction is then effected by the contact glass; the bed need not be moved for this purpose. 
     This can also be combined by mounting a force sensor to the holding element but effecting retraction through movement of the bed. 
     In an advantageous further embodiment of the invention, laser treatment can be continued even if the contact glass retracts, as long as certain basic conditions are complied with. For this purpose, retraction not only of the contact glass, but also of the relevant components of the optics by which the treatment laser beam is focused into or onto the eye is convenient. Therefore, the holding element which is mounted to the contact glass may also carry focusing optics which focus the treatment laser beam into or onto the eye. When retracting, the contact glass and the focusing optics then move together. 
     The limit value of force is conveniently set such that bruising of the eye is definitely prevented. A suitable value for this purpose is approximately 1N. 
     The first variant of the invention is suitable not only to prevent damage caused by a patient&#39;s fault, but apparatus malfunction can also be checked thereby. During laser treatment, the patient is usually supported on a bed. A height adjustment unit allows adjustment of the distance between the laser treatment apparatus or the contact glass, respectively, and the patient. The safety mechanism according to the invention reliably prevents malfunction of this height adjustment mechanism resulting in bruising of the eye. If, for example, the height adjustment mechanism moves the patient too far towards the contact glass, the safety mechanism automatically causes retraction of the contact glass before there is a risk of the eye being squashed. 
     The second variant of the invention ensures that retraction of the contact glass has as little effect as possible on the optical quality with which the treatment laser radiation is introduced into the eye. Since in a laser treatment apparatus the laser treatment beam is guided to a great diversity of points (e.g. during the above-mentioned correction of visual deficiencies), three-dimensional shifting of the focus of the laser beam is usually required. This regularly requires deflecting elements in the form of two scanners, for example galvanometer scanners, for lateral movement of the laser focus. 
     In a simple construction, optical errors which occur during retraction of the contact glass can be minimized by rigidly connecting the contact glass and the focusing optics which focus the treatment laser beams into the eye such that they retract together. If a beam path section which is insensitive to changes in the length of the optical path, for example a parallel or near parallel beam path, is additionally arranged preceding the focusing optics, the optical errors occurring during retraction of the unit consisting of the focusing optics and the contact glass are automatically small. 
     In order to minimize errors induced by retraction of the contact glass, it is generally advantageous if the length of the light path following the deflecting element remains unchanged even during retraction. Otherwise, the distance in a projecting lens would change, which would be equal to a change in the effective focal length of the entire system. In particular, curved contact glasses, which have a concave curvature on the side facing towards the patient and which thus only add little to the internal pressure of the eye, would be difficult to use. Instead, contact glasses would have to be used, which flatten the front surface of the eye and are, therefore, disadvantageous with a view to keeping the internal pressure of the eye as constant as possible. Therefore, further minimizing is achieved if the contact glass, the focusing optics and at least one of the deflecting elements of the beam-deflecting unit are connected to form one single unit, and the safety mechanism causes longitudinal guiding of this unit. 
     The second variant of the invention then keeps the distance between the deflecting unit and the focus of the treatment laser radiation constant. If the axial position of the laser focus were shifted, unpredictable side effects could appear in the patient&#39;s cornea. In the worst case, a laser effect could even damage the epithelium or the endothelium. 
     The deflecting elements, e.g. AOD or scanners, are favourably arranged in pupil planes of the optics. In most cases, they effect beam deflection about two mutually perpendicular axes. However, other approaches, e.g. using a tumbling mirror, are also possible, if they effect 2-dimensional beam deflection. Common scanners operate by reflection at surfaces which are variable with respect to their clearance angle relative to the beam path. This has the effect that the entire beam path is folded at an angle at the scanners. In doing so, folding angles of approximately 90° are preferably realized. It is advantageous to design one of said bends such that part of the optical system is supported there rotatable about an axis. Retraction of the contact glass can then be achieved by rotating the optical system about said bend, so that the subsequent beam path is only pivoted, in principal, but otherwise does not change. If another deflection of the beam path, e.g. by 90°, is provided at this bend, retraction of the contact glass is realized as a pivoting movement about the axis of rotation located in the first bend. This enables pivoting of the subsequently arranged optics about the bend and, thus, a retraction of the contact glass without any changes appearing in the beam path. 
     Therefore, it is preferred that the light path of the laser beam be deflected at least once following the entrance pupil of the focusing optics and that the safety mechanism cause a joint rotary or pivoting movement of the contact glass, the focusing optics and the deflecting element during retraction. A particularly convenient construction is one in which the contact glass, the focusing optics and the deflecting element are rigidly connected to form an arm and the safety mechanism comprises a rotary support for the arm with the axis of rotation in the plane of the deflecting element. The arrangement of the axis of rotation at the deflecting element has the advantage that, during rotation or pivoting, no disadjustments are generated with respect to deflection. 
     However, a weight compensation may be necessary, because the rotary or pivoting movement requires the entire optical unit to be raised from the contact glass up to the pupil with the deflecting element. Therefore, it is favourable for this embodiment to provide corresponding balancing weights, reducing the force required to raise the arm and thus to retract the contact glass. 
     This embodiment is a variant of a generally preferable safety mechanism comprising a weight force compensation unit, in particular in the form of a counterweight or a spring element. If it is desired to combine the advantages of the first or second variants, the weight force compensation unit can conveniently set the limit value of force. In particular, it is possible for the arm to be supported by the housing of the laser treatment apparatus at the limit value of force. 
     Another approach involves placing the axis of rotation in the beam path at the location of the weight center of gravity, because, in doing so, a balanced structure and, consequently, a low force for the retraction of the contact glass is automatically achieved. 
     In the third variant of the invention, a detecting unit is provided for functional rigidity of the contact glass, which unit blocks the laser treatment operation upon a contact glass movement exceeding a threshold value. In this case, the threshold value can be selected according to different criteria. Depending on the design of the laser treatment apparatus, the threshold value can be selected in the sense of an emergency deactivation, which deactivates just before an inadmissibly great load on the eye, or may serve as a quality-ensuring feature and may consider the optical errors caused by said movement. 
     If the threshold value is selected such that it should prevent an inadmissibly high eye pressure, deactivation is effected before retraction of the contact glass reaches a mechanically determined end of said movement. Even after the threshold value has been exceeded, counter measures can still be initiated without the contact glass abutting at the end of its movement. For example, a height adjustment mechanism of the patient&#39;s bed can be deactivated or the patient&#39;s bed can be quickly lowered. 
     Thus, one of the counter measures consists in actively moving the contact glass and the eye apart. Therefore, it is preferred that the safety mechanism comprise a drive for active retraction of the contact glass and that a control unit control the drive to actively retract the contact glass in case of a force exceeding the limit value of force or a contact glass movement exceeding the threshold value, respectively. 
     In the case of the above-mentioned rotatable or pivotable optical arrangement of the second variant, the drive will usually initiate a pivoting or rotary movement, in particular rotating the arm mentioned above with respect to the second variant. 
     The detecting unit may use a light barrier located near a mechanical stop for the path of movement of the contact glass. Of course, a multi-level stepwise response detecting unit or continuous monitoring of the position of the contact glass is also possible according to the invention. 
     One possibility of additionally detecting that a desired maximum movement is exceeded consists in sensing at the mounting mechanism by which the eye is fixed to the contact glass. For this purpose, a vacuum is conventionally used. The detecting unit may then sense the pressure in the vacuum system and thus determine an inadmissible movement of the eye relative to the contact glass. 
     Due to the human physiognomy an eye movement directed towards the contact glass automatically involves a movement of the head. Therefore, it is possible to sense the force directed towards the contact glass not only at the eye, but also at the patient&#39;s body, preferably at the head. This procedure gives further protection to the eye. Therefore, it is convenient for all the above mentioned variants if a supporting unit is provided comprising a support that can be applied to the patient&#39;s body and is coupled to the safety mechanism such that a certain force on the support opposed to the direction of incidence of the laser beam also causes retraction of the contact glass. In the third variant, the detecting unit may detect pressure on the support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below, by way of example and with reference to the drawings, wherein: 
         FIG. 1  shows a schematic perspective view of a laser treatment apparatus for treatment of a patient lying on a patient&#39;s bed; 
         FIG. 2  shows a schematic partial view of the beam path of the laser treatment apparatus of  FIG. 1 , viewed against the patient&#39;s viewing direction; 
         FIG. 3  shows a representation of the beam path of  FIG. 2  in a plane rotated by 90°, i.e. as seen by a surgeon sitting behind the patient; 
         FIGS. 4 and 5  show representations of a laser treatment apparatus similar to that of  FIG. 3  in a similar view as in  FIG. 3 ; 
         FIGS. 6 and 7  show representations of a further modified laser treatment apparatus in a view similar to those of  FIGS. 4 and 5 ; 
         FIG. 8  shows a schematic representation of the laser treatment apparatus of  FIG. 1  with a modified construction in a view similar to that of  FIG. 3 ; 
         FIG. 9  shows a weight balancing mechanism provided in the laser treatment apparatus of  FIG. 1 ; 
         FIG. 10  shows a schematic representation of a laser treatment apparatus similar to that of  FIG. 1 , but in lateral reversal, comprising an additional safety mechanism in order to protect a patient against bruises; 
         FIG. 11  shows an enlarged detail of  FIG. 10 ; 
         FIG. 12  shows a diagram illustrating the forces appearing at the eye during operation of a laser treatment apparatus according to  FIG. 1 , and 
         FIG. 13  shows a schematic representation of a circuit diagram for the laser treatment apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a laser treatment apparatus in the form of a laser-surgical treatment station  1 . It comprises a bed  2  on which a patient (not shown) is made to lie down during treatment. A laser unit  3  comprising a treatment head  4  is arranged beside and above the bed. The distance between the bed  2  or the patient lying thereon, respectively, and the treatment head  4  can be adjusted by a height adjustment unit  5  provided at the bed  2 . The treatment head  4  is arranged on a cantilever  6  of the laser unit  3  such that it protrudes beyond a patient&#39;s head. 
     A surgeon can survey the progress of treatment through a microscope eyepiece  7  provided at the cantilever  6 . A keyboard  8  as well as a monitor  9  serve to adjust parameters of the laser treatment method. The laser-surgical treatment station  1  is controlled by a computer C and is intended for ophthalmic correction of visual deficiencies. 
     The treatment head  4  has a nozzle  10 , at which a treatment laser beam exits, and which nozzle contacts the eye for treatment. As will be explained below, the treatment head  4  comprising the nozzle  10  is movably supported within the cantilever  6  so that further space for movement exists between the nozzle  10  and a patient lying on the bed  2 , or his eye respectively, in addition to the adjustability moved by the height adjustment unit  5 . 
       FIG. 2  shows a detail of the treatment beam path  11 , which is used by the laser-surgical treatment station  1  in order to focus treatment laser radiation L in the eye of the patient, to thereby generate optical breakthroughs and to ultimately effect correction of visual deficiency. The laser unit  3  comprises a laser emitting the treatment laser radiation L and expansion optics expanding the treatment laser radiation L. 
     These two elements are of no further relevance to the safety function of the laser-surgical treatment statement  1 , which function is to be explained herein, and are therefore not shown in the Figures. The expansion optics include axially displaceable elements so that the laser focus can be shifted in an axial direction with the cornea. 
     Following the expansion optics, a first scanner is arranged comprising a scanning mirror  12 , which is driven by a motor  13  to be pivotable about a first deflecting axis S 1 . The first scanning mirror  12  is located in a pupil of an optical system which will be explained later. Following the first scanning mirror  12 , the pupil is imaged at elements  14  to ensure that the first scanning mirror  12  is located in a pupil of the optical system. In a further pupil lies a second scanning mirror  15 , which is also driven by a motor  16 . The axis of rotation of the second scanning mirror  15  is perpendicular to the deflecting axis S 1  of the first scanning mirror  12 . The second mirror  15  rotates about a second deflecting axis S 2 , shown in broken lines in  FIG. 3 . The deflecting axes S 1  and S 2  of the two scanning mirrors  12  and  15  are at right angles to each other. 
     Arranged following the second scanning mirror  15  are scanning optics  17 , in whose pupil the second scanning mirror  15  is located and whose beam path is deflected into the nozzle  10  by a beam splitter  18 . The nozzle  10  contains focusing optics  20  which focus the laser radiation L via a contact glass  23  into the cornea  21  of the patient&#39;s eye  22 . The beam splitter  18  couples in an observation beam path  19  for the microscope eyepiece  7 . At the same time, it deflects the beam path after the second scanning mirror  15  by 90°. 
     The scanning optics  17 , the beam splitter  18 , the focusing optics  20  and the contact glass  23  form an arm  24 . The arm  24  is mounted to a rotary joint  25  together with the motor  16  and the scanning mirror  15 . As a result, the arm  24  is pivotable about the rotary joint. The pivoting axis is located in the pupil, in which also the scanning mirror  15  is arranged, and extends perpendicular to the deflecting axis S 2 . Pivoting of the arm  24  consequently moves the contact glass  23  away from the cornea  21 . 
     The scanning optics of the embodiment according to  FIGS. 2 and 3  is mounted to a support  26  and is thus combined to the arm  24 . This arm is connected to the rotary joint  25  in the form of a ball bearing. The axis of the ball bearing—for the sake of stability, a plurality of bearings can also be used on a common axis—is identical with the optical axis of the preceding pupil imagery  14 . For example, a very large ball bearing having a large diameter can be used and placed directly on the mount of the pupil imagery  14 . Thus, simple centering of the rotary joint  25  relative to the optical axis of the pupil imagery  14  is achieved, and the pivoting axis is located exactly in the pupil plane. The mounting of the second scanner  15  to the rotary joint provided here, which mounting, of course, is understood to be optional, ensures that the deflecting axes S 1 , S 2  of the two scanners  12 ,  15  remain perpendicular to each other even when the arm  24  is raised and the beam reflected by the second scanning mirror  15  nevertheless always passes through the scanning optics  17  in a predetermined direction even when the arm  24  is pivoted. 
     Of course, it is alternatively possible to also have the pupil imaging elements  14  rotate together with the scanning optics  17 , i.e. with the arm  24 . This allows to realize a great length of guidance for the axis of rotation, thus achieving greater accuracy in guiding. In a further embodiment of this approach the entire optical unit, including laser(s), rotates. Such embodiment is favorable in terms of stability of the entire optical arrangement, but the forces of inertia which have to be overcome in order to initiate retraction of the contact glass increase with the mass of the supported unit. 
     In a further embodiment fiber coupling between the laser and its expansion optics is used. In this case all remaining elements of the optics are mounted on the pivotable supporting unit. Advantageously a chirp caused by the fiber is compensated for by a compressor unit either before entering the fiber or thereafter. The compressor unit is preferably arranged preceding the fiber, because the peak performance in the fiber is reduced thereby and light intensity-dependent damage to the fiber is avoided. At the same time self-phase modulation is reduced. 
     The construction of  FIGS. 2 and 3  in the laser-surgical treatment station  1  of  FIG. 1  allows the patient to push away the contact glass  23 , which is being mounted to his eye by means of a vacuum, for example. The contact glass  23  can move away from the eye together with the focusing optics  20  and the scanning optics  17  and relieve the eye in order to avoid bruises. However, due to the mass of the elements to be moved initiation of said movement may require a force which cannot be applied via the patient&#39;s eye alone without auxiliary means. 
     Therefore, in the case of bulky optical structures, an embodiment as shown in  FIGS. 4 and 5  is provided. In this case the arm  24  is stiffened by the support  26  to which the scanning optics  17 , including the beam splitter  18  and the nozzle  10 , are mounted. Further, a spring suspension  27  reducing the static forces is effective at the free end of the support  26 . The arm  24  or the support  26 , respectively, is further supported by the cantilever  6  such that it contacts the latter with a defined force. This bearing load is set by the suspension  27 . 
     Thus, by exerting pressure on the contact glass  23 , the patient can push the arm  24  on the support  26  away from himself using comparatively little force, so that the arm reaches the raised position shown in  FIG. 5 . It is merely required to overcome the bearing load. The force required to do so is set such that bruising of the eye is avoided. For instance, said force is 1N. 
       FIG. 5  further clearly shows that the scanning mirror  15  rotates along with the pivoting of the arm  24 . Thus, the coupling of the laser radiation from the scanning mirror  15  into the scanning optics  17  remains unchanged even if the support  26  is deflected and the contact glass  23  is thus raised. 
     However, the construction of  FIGS. 4 and 5  can not compensate for dynamic forces which are required in order to initiate rotation of the arm. Such dynamic forces appear as forces of inertia, when the patient moves towards the contact glass, because the bed  2  is being moved upwards. For acceleration of the arm  24  which is required for the contact glass  23  to retract, an additional force is required which can lead to at least temporary squeezing of the eye. In order to avoid this effect, which becomes relatively large from a certain moment of inertia of the arm  24  mounted to the rotary joint  25 , it is favorable to provide a mechanism which actively retracts the contact glass  23 , i.e. which assists the eye during acceleration of the contact glass  23  on the arm  24 . For this purpose, it is necessary for the construction described herein to actively raise the arm  24 . 
       FIGS. 5 and 6  show an exemplary embodiment of such mechanism operating here by means of a vacuum. A vacuum cell is mounted to the rotatable end of the arm  24  at the support  26 . If there is negative pressure in the vacuum cell, it contracts and raises the support  26  at its free end. This condition is shown in  FIG. 7 . By means of a sensor  29 , which is provided here as a mechanical feeler  30  actuating a switch  31 , a control unit  32  is switched on as soon as the patient raises the arm  24  by a certain minimum amount from the arm&#39;s lower position. The control unit  23  then activates the negative pressure drive  28  which raises the support  26  with the arm  24  and, thus, pulls the contact glass  23  away from the eye. A small movement of the scanning optics, thus, leads to actuation of the negative pressure drive. 
     In a modified form only a part of the scanning optics or an additional part mounted to different optics may be mounted axially moveable with the rest of the scanning optics. If this component is moved upwards by the pressure of the eye, a corresponding signal for the control unit  32  is derived, which in turn activates the negative pressure drive  28 . In doing so, the valve actuation required for this purpose can also be effected directly by mechanical means or even electrically. Of course, sensing of the scanning optics&#39; movement can also be effected contact-free, e.g. by light barriers or a capacitive distance sensors. 
     As an alternative to the negative pressure drive described here, any suitable drive is conceivable, of course, for example also one comprising electrically driven servo motors. 
     Instead of or in addition to actively driving the arm  24 , support by way of a mechanical spacer can be used as shown in  FIG. 8 . The spacer comprises a stem  34 , which can be placed in contact with the patient&#39;s head  33  and contacts the patents&#39; forehead  35  when the contact glass  23  is in place. In doing so, the stem  34  is set such by a locking mechanism that it contacts the forehead  35  directly. The stem extends parallel to the direction of irradiation along which the laser treatment radiation L is incident in the contact glass  23  and the cornea  21  through the nozzle  10 . As soon as the cornea  21  contacts the contact glass  23 , the stem is displaced downwards, e.g. moved by the force of its own weight, such that it contacts the patient&#39;s forehead. In this position, it locks automatically or is externally locked. If the patient&#39;s eye  22  moves upwards now, the arm  24  is automatically raised by the stem  34 . 
     In addition or as an alternative to the stem  34 , support may also be effected directly at the patient&#39;s bed  2 . Thus, inadvertent actuation of the height adjustment unit  5  is immediately converted to retraction of the contact glass  23  by pivoting of the arm  24 . 
     It is also possible to cause actuation of the negative pressure drive  28  by purely pneumatic means. The feeler  30  then actuates a switch  31 , which is provided as a valve and is located in a vacuum duct between a vacuum source, which corresponds to the control unit  32  in the drawing, and the negative pressure drive  28 . The valve is opened when the feeler  30  has moved upwards, as is the case during a slight movement of the support  26  with the arm  24 . When the valve is open, the negative pressure drive  28  is evacuated, contracts and thereby tilts the support  26  with the arm  24  upwards. 
     If the optics accommodated in the arm  24  have a suitable design, the suspension  27  is sufficient to avoid bruising of the patient&#39;s eye. Assuming a length of the arm of half a meter and realizing a moment of inertia of the arm  24  of 2 kg·m 2 , an eye movement at 6 mm per second towards the contact glass  23 , at a radius of curvature of 7.8 mm and a radius of curvature of the contact glass of 2 cm leads to a force of 0.3N, if the eye is pushed in by 0.77 mm during acceleration of the contact glass  23 . The contact glass  23  with the entire arm  24  is then accelerated to the speed of movement of the eye within a third of a second. Thus, it is evident that an external drive is not stringently required if the arm  24  is skillfully designed. 
       FIG. 9  shows a possible design of a spring mechanism serving the function of the suspension  27 . It is a supporting mechanism  37  which supports the arm  24  from below. The arm  24  is supported on a roll  38  which is connected to a spring  41  via a lever  40 , said spring pushing the roll  38  upwards. The weight force of the arm  24  acting in the direction of the arrow  39  can be compensated for as desired, except for a residual bearing load, by suitably selecting or positioning the spring  41 . 
     It is of absolutely no importance in the constructions described above whether the actuating movement is caused by the patient or by a movement of the bed  2 . The arm  24  is always raised. 
       FIG. 10  shows a further detailed view of an extension  6  of a laser-surgical treatment station similar to the construction shown in  FIG. 1 , although the representation in  FIG. 10  is mirror-inverted relative to that chosen in  FIG. 1 . It is evident again that the arm  24  with the nozzle  10  is provided in the extension  6 , of which merely some components of a housing B are shown. The arm  24  is pivotable with the support  26  relative to the extension  6  about a pivot point located to the left in  FIG. 10 , but not shown. In this pivotal movement, the nozzle  10  is raised relative to the housing B such that it retreats into the housing B. The arm  24  or the support  26 , respectively, contacts the extension  6  at a support not illustrated. LRaising the extension  6  can be effected by a force acting on the nozzle  10  (via the contact glass  23 ). 
     In the construction of  FIG. 10 , a safety mechanism is additionally provided which also protects the patient&#39;s body from bruises caused by the arm  24 . For this purpose, a baffle plate  42  is mounted to the housing B by means of a joint  43 , which may be designed, for example, as a bendable attachment in the form of a steel plate. The baffle plate  42  is supported on the arm  24  or its support  26  by a ridge  45 . A force acting on the baffle plate  42  in the direction of the arrow  44  thereby exerts an upward pressure on the arm  24 . A position sensor  46  detects raising of the arm  24 . A possible embodiment of this position sensor  46 , which senses the displacement of the arm  24  relative to the housing B or the extension  6 , respectively, is shown by way of example in  FIG. 11 . 
     As is evident from  FIG. 11 , light barriers  48  and  49  comprising slits  50  and  51  are mounted to a mounting surface  47  of the extension  6  on the housing side. Through these slits a position mark  42  can pass which is attached to the support  26  or to the arm  24 , respectively. Thus, when the arm  24  is raised, the position mark  52  moves into the slot  50  and, if raised further, also into the slot  51 . If the position mark  52  is located in the slot  50  or  51 , respectively, of the light barrier  48  or  49 , it generates a corresponding signal which is transmitted to a control unit (not shown), for example the computer C of the laser-surgical treatment station  1  (cf.  FIG. 1 ). The computer C then controls a corresponding reaction of the system, for example deactivating the treatment laser radiation L or lowering of the patient&#39;s bed  2 . 
       FIG. 12  schematically shows an exemplary relationship between the position P of the arm  24  or of the nozzle  10 , respectively, of the laser-surgical treatment station  1  and the force F on the eye of the patient, each as a function of the eye&#39;s position x, which is given for a patient lying on the bed  2  by the position of the height adjustment unit  5 . When a patient is being prepared for treatment, a new, sterile contact glass  23  is first attached to the nozzle  10 . Then, the patient is placed on the bed  2  whose height adjustment unit  5  is controlled by the surgeon at the laser-surgical treatment station  1 . For this purpose, the computer C comprises a suitable input device, for example a joy stick, and controls the height adjustment unit  5  accordingly. At the beginning the height adjustment unit  5  is moved downwards, resulting in the location x 0 . At the same time, the nozzle  10  is located at its lowermost position P 0 , because the arm  24  contacts the extension  6  at the lower stop. The surgeon then moves the patient upwards by means of the height adjustment unit  5  until the patient&#39;s eye contacts the contact glass  23  at the location x 1 . The surgeon now slowly moves the patient further up, until the eye fully contacts the contact glass  23 . This is the case at the location x 2 , which is characterized in that the vacuum for fixing the contact glass  23  to the cornea  21  can be applied. 
     In order for the cornea  21  to contact the internal surface of the contact glass  23  as completely as possible, the eye  23  presses against the contact glass  23  with a certain force. However, since this force is still weaker than the force Fmin, by which the arm  24  is raised, the arm  24  continues to rest in this case. 
     Upon activating the vacuum, the computer C automatically raises the height adjustment unit  5  slightly, so that the bed  2  is still raised slightly above the location x 2 , in order to ensure secure fixation of the contact glass  23  to the cornea  21  by means of a vacuum. The height adjustment unit  5  or the patient&#39;s head, respectively, is thus located between the locations x 2  and x 3 . The eye presses against the contact glass  23  with a force below the minimum force Fmin, so that the arm  24  still remains in the position P 0 , i.e. is not raised. The eye is fixed to the contact glass, and treatment can be started. 
     If the patient&#39;s head moves upwards during treatment, for example because the patient is moving his head, or due to an involuntary actuation of the height adjustment unit  5 , the force on the arm  24  will not be equal to the minimum force Fmin with which the arm  24  contacts the cantilever  6 , until the location x 3  is reached. Upon a further upward movement of the head, the cantilever  24  will be raised. This case corresponds to the rising of graph  53  (shown as a solid line) in  FIG. 12 , and the arm  24  leaves its resting position P 0 . If the cantilever has reached the position P 1 , because the patients head, or in the case of a malfunction or faulty operation, the height adjustment unit  5  has reached the location x 4 , the first light barrier  48  will output a switching signal. Because the arm  24  can be lifted through the set force Fmin, the force exerted on the eye, and, thus, the pressure on the eye does not increase any further. 
     The switching signal reached at position P 1  causes the computer C to switch the laser beam L such that no treatment is effected anymore. For example, the laser can be switched off or the laser beam energy can be reduced such that no optical breakthroughs are generated anymore. Moreover, it is possible to output an alert to the surgeon, for example in the form of a corresponding display on the monitor  9 . 
     Finally, a switching mechanism can be provided in the computer C, which mechanism automatically moves the height adjustment unit  5  downwards, i.e. to lower x-values, upon reaching position P 1 , in order to lead the eye back into the normal treatment region between x 2  and x 3 . Once this has been achieved, the switching signal from the light barrier  48  changes back to the resting condition, normal treatment operation is resumed and the alert is deactivated. If the relative movement of the eye and the contact glass is caused only by moving the bed, the switching mechanism can be adapted to the x-values such that, for example, movement is effected upon reaching x 3 . 
     However, if the arm  24  moves further up due to a malfunction or a corresponding action by the patient and reaches position P 2 , the second light barrier  49  will respond and the computer C will then initiate an emergency shutdown, which deactivates the height adjustment unit  5  and moves it down, on the one hand, as well as deactivating the laser-surgical treatment station  1 , except for the control, on the other hand. This happens in order to prevent that beyond the location x 5  the location x 6  is reached, where the arm  24  arrives at its maximum deflection at position Pmax, at which no further retraction is possible. If the raising movement of the head still continued, the force on the cornea  21  or on the eye  22  would suddenly increase from the location x 6  onwards, as clearly shown by the curve of force  24  of  FIG. 12 . At the location x 7 , the maximum admissible force Fmax on the eye  22  would be reached and there would be danger of bruising. 
     Due to the emergency shutdown of the laser-surgical treatment station  1  effected at the location x 5  or the position P 2 , bruising of the eye  22  is avoided even if the patient panics. 
     Since the baffle plate  42  is located below the cantilever  6  in the embodiment according to  FIG. 10 , bruising of the patients body is also avoided, which may occur if the height adjustment unit pushes the patient against the cantilever  6 . 
       FIG. 13  shows a circuit which may be realized for example by the computer C in order to carry out the method of protection described with reference to  FIG. 12 .  FIG. 13  shows the exemplary light barriers  48  and  49  of  FIG. 11  generally as sensors sensing whether the arm  24  has reached positions P 1  or P 2 , respectively.  FIG. 13  further schematically illustrates a suction pressure sensor  55 , which monitors whether the vacuum used for suction of the contact glass  23  is in a range of values in which reliable suction of the eye  22  to the contact glass  22  is given. The sensors as well as the vacuum sensor  55  act on a drive  56  of the height adjustment unit  5  in a manner yet to be described. The drive  56  is supplied by a d. c. source  57 , which feeds a power supply  58  of the drive  56 . The current source  57  is connected to the power supply  58  by two lines. Two emergency switches  59  and  60  are switched into a feed line, which open upon actuation and which are closed in their deactivated condition. 
     The emergency switch  59  is controlled by the second light barrier  49 , and the emergency switch  60  serves as a mechanical emergency switch for the surgeon, so that the connection between the current source  57  and the power supply  58  of the drive  56  can be interrupted at any time, and thus, the drive  56  can be deactivated. 
     The drive  56  further comprises a blocking mechanism  61  whose actuation deactivates the drive  56 . Such blocking occurs if a vacuum sensor  62  indicates that the suction of the eye  22  to the contact glass  23  is switched on and also if the vacuum sensor  55  indicates suction of the eye. In this condition the blocking mechanism  61  prevents any further action of the height adjustment unit  5  by the drive  56  because a shift in the height adjustment unit  5  may not be required and may even cause damage when the eye is subject to suction. 
     The drive  56  is further provided with a blocking mechanism  63 , which is controlled by the first light barrier  48  and, in parallel with the locking mechanism  61 , prevents any activity of the drive  56  when the first light barrier  58  indicates that the arm  24  has reached position P 1 . This prevents the height adjustment unit  5  inadvertently being actuated and raising the patient, which would be possible if the vacuum were cut by a movement of the patient and the vacuum sensor  55  thus no longer signaled that the eye is subject to the correct suction. Thus, for example when the patient moves sideways or upwards, operation of the drive  56  and, consequently, action of the height adjustment unit  5  is also prevented. 
     The parallel provision of the locking mechanism  61  as well as the blocking mechanism  63  thus allows to effect closed-loop control by means of the height adjustment unit  5 , said control guaranteeing secure suction of the eye. 
     The second light barrier  49 , which emits a signal when the arm is in position P 2 , is connected to the emergency switch  59  via a relay  64 . If the second light barrier  49  emits a signal indicating position P 2 , the emergency switch  59  will be opened and the drive  56  will be de-energized. Depending on the design of the drive  56 , the bed  2  then remains at the presently set height or smoothly glides downwards. 
     The described system according to the invention avoids bruising of the eye in a laser-surgical treatment station, due to the component which contacts the eye automatically executing a deflecting movement, if the patient is lifted or raises his head. At the same time, the deflecting movement is advantageously realized such that the optical quality of the treatment during such deflection remains unchanged, if possible. Moreover, it is ensured by corresponding sensors and control mechanisms that a movement leading to bruising of the eye cannot occur.