DE19618883A1 - Device and method for the photorefractive correction of ametropia - Google Patents

Abstract

The invention relates to a device (2) for photo-refractive correction of defective vision which has a device (50) for detecting the present position of an eye (20). Said device (2) also has a device (8) which tracks a piercing point (16) of a reference axis (12) of a laser ablation beam (10) through the cornea (18) of an eye (20) during treatment at varying positions of the piercing point (26) of a visual field line (24) through the cornea (18). The device (8) may, for example, include a tilted mirror (38) suspended on gimbals and is controlled by a control unit (52). In the case of an excessively large difference between the position of the piercing point (16) and the position of the piercing point (26), the ray of the laser beam (100) can, preferably, be interrupted.

Description

The invention relates to an apparatus and a method for the photorefractive correction of ametropia according to the preambles of claim 1 and claim 14.

The surgical correction of ametropia is out carried out for various reasons. So z. B. on Visual acuity is particularly demanding in some professions uncommitted (e.g. for pilots, firefighters, Police officers, professional athletes). Also wearing one leads Spectacles for perspective patients for some patients stungen, whereby contact lenses not tolerated by everyone are. In these and other cases, the opera tive correction of ametropia using photorefractive Proof proven.

In a known device for photorefractive Correction of ametropia (keratome from Schwind) is using a pulsed laser beam with a wavelength of 193 nm the cornea usually in the range of The pupil is worn away on its surface in such a way that the then the refractive properties of the cornea changed Ametropia is corrected. So that the laser The cornea should only be removed at the intended locations the so-called facial line of the eye during treatment be properly aligned (the facial line is the line which from the place of best vision on the retina through the Center of the lens of the eye leads). If the patient the eye moves too far from the predetermined position, the corneal laser beam would be outside of the intended Remove the treatment zone. This condition is therefore in the  known device recognized and treatment immediately and automatically interrupted. When resuming the correct alignment, the removal is immediately automatic continued.

This known device has the disadvantage that the duration of treatment depends on the restlessness of the eye to be treated can lengthen significantly, as this Restlessness again and again to automatically caused breaks leads to laser treatment. A longer treatment duration increases on the one hand the treatment stress at Pa tients and on the other hand leads to a smaller host economy for the operator of the device.

The object of the invention is therefore a device for the photorefractive correction of ametropia create and specify a corresponding procedure, which by an avoidance or at least by a significant reduction in the number of automatically summoned during treatment breaks, the duration of treatment clearly shortened and so on the one hand the treatment stress when Patients diminished and on the other hand the economic Improved device usage.

The object is achieved by a pre direction for photorefractive correction of ametropia keiten with the features given in claim 1, and by a method with those given in claim 14 Characteristics.

The device according to the invention for photorefractive Correction of ametropia shows a radiation swell which emits a laser beam. This Laser beam is through a beam processing system guided. This can e.g. B. mean that the laser beam in  appropriate optics expanded and then in a so-called integrator is homogenized. In a optional conditioning device one Beam shaping system can then change the energy distribution about the cross section and the contour of the laser beam in be changed in a desired manner. So z. B. annular, elliptical or other cross-sectional shapes can be set. Then the laser beam hits one Tracking device, which serves the laser beam in the direction of the two axes, which are perpendicular to the beam are to be deflected so that the position of the through point of intersection of a reference axis of the laser beam the cornea of an eye to be treated within certain limits can be changed continuously. Between the tracking device and the eye can continue there are zoom optics to be assigned to the beam shaping system, which serves the size of the projection surface of the Infinitely variable laser beam on the eye.

The device according to the invention also has an on direction, which serves the current position of the eye to be treated continuously and a tax associated with this facility unit to control the tracking device so that the point of penetration of the reference axis of the ablation area beam through the cornea of a movement of the eye, d. H. a movement of the puncture point of the face field line through the cornea follows. So it is possible Movements of the eye during the operation by a Compensate panning of the ablation laser beam.

For aligning the eye before and during treatment and thus to align and define the face field line, the device further comprises a diode laser, which is to be fixed by the patient.  

Advantageous developments of the invention are in Unter claims reproduced.

The development according to claim 2 has a device on the generation of an ablation laser beam interrupts as soon as the deviation between the positions the penetration points on the one hand the reference axis of the Ablation laser beam and on the other hand the visual field line through the cornea of the eye Limit exceeded.

This avoids that when the tracking direction due to the mechanical and electronic System sluggishness of a movement of the eye is not quick can follow enough cornea outside of the desired one Digits is removed.

The development of the invention according to claim 3 a tracking device on which a gimbal includes movable deflecting mirror, which is designed is that it is pivotable about two axes and on this way the ablation laser beam in the desired Way can align.

This embodiment allows a particularly robust Structure of the device according to the invention.

In the development of the invention according to claim 4 the tracking device a first and a second Deflecting mirror, which are arranged so that, for. B. the first deflecting mirror follows the ablation laser beam deflects up or down and the second deflecting mirror then deflects the ablation laser beam laterally. Both deflecting mirrors are along the axis of each  incident ablation laser beam linearly displaceable executed.

This embodiment allows the angular alignment to maintain the reference axis of the ablation laser beam and the ablation laser beam by displacing the Deflecting mirror, so to speak, "parallel to itself" in Direction of the two spatial axes, which are perpendicular to the Beam axis are to be shifted. This will make the Distortion of the ablation laser beam is reduced, which on the one hand due to the non-perpendicular radiation of the Is effected by means of the zoom optics, and which on the other hand due to the oblique impact of the ablation laser beam on the deflected treatment area on the eye becomes.

In the development of the invention according to claim 5 include the means of moving the tracker-in cause electromagnetic motors, which each via gear and connecting rods of the deflection swivel or move mirror.

This embodiment allows an inexpensive and robust Manufacture of the device according to the invention.

The development of the invention according to claim 6 includes Means for the movement of the deflecting mirror, which linear position motors such as B. voice coil drives for Panning or include moving. Hereby the number of parts to be moved is reduced and one quick response achieved.

The development of the invention according to claim 7 includes Means for the movement of the deflecting mirror, which in the Bearings have built-in rotary actuators. Here  is also the number and weight of the moving parts reduced and thus a faster Responsiveness achieved.

The development of the invention according to claim 8 includes Sensor means which the current position of the Detect deflecting mirror and send corresponding signals to the Forward control unit. This makes one special enables exact positioning of the tracking device.

The development of the invention according to claim 9 includes Sensor means for the detection of the current Position of the deflecting mirror, which in the respective Drive are integrated. This will save space Execution guaranteed.

The development of the invention according to claim 10 a device for detecting the current position tion of the eye, which includes a video camera that appropriate signals to the control units directs.

The development of the invention according to claim 11 a tracking device which contains deflecting mirrors, which are semi-permeable, so that the device to detect the actual position of the eye and / or to fix the eye in the facial line behind the semi-transparent deflecting mirror (s) can be arranged.

The development of the invention according to claim 12 includes Fiber optic cables for the data line between eye posi tion detection device and control unit or between the tracking device and control unit. Hereby will be a fast, safe and above all disruptive  specially protected data transmission accomplishes.

In the subordinate claim 14 and this under ordered claim 15, a method is described as it with the front disclosed in claims 1 to 13 directions can be carried out.

The invention based on embodiment examples with reference to the drawing he purifies. In this show:

Figure 1 is a sectional side view of an eye illustrating the concept of visual field of an eye line and their Durchstoßungspunkts through the cornea.

Fig. 2 is a perspective view of the projection surface of the ablation laser beam on the eye to explain the term of the reference axis of the ablation laser beam and its penetration point through the cornea;

Fig. 3 is a schematic representation of a device for photorefractive correction of ametropia;

Fig. 4 is a schematic illustration of a gimbal-mounted mirror for beam tracking;

Fig. 5 is a schematic representation of two translationally movable mirrors for beam tracking;

Fig. 6 shows three positions of an eye at time points A, B and C and corresponding orientations of subtractive laser beam (angle exaggerated);

Fig. 7 is a graph showing the deviation of the positions of the piercing points over time;

Fig. 8 is a diagram in which the switching state of subtractive laser over time is shown.

The term “visual field line” is first defined in FIG. 1: an axis 24 leads from the location 22 of the best vision on the retina 21 of an eye 20 through the center of the lens 27 . This axis is called the "visual field line". It pierces the cornea 18 at a puncture point 26 . As shown below, this penetration point 26 of the visual field line 24 is the reference point for the alignment of the ablation laser beam.

The term “reference axis” is defined in FIG. 2: The figure shows a perspective view of a section of a cornea 18, which has just been shown for simplification. An ablation laser beam 10 , which, as shown in more detail below, can have any desired contour and energy distribution, strikes the cornea 18 and generates a projection surface 14 there corresponding to its contour and energy distribution. The ablation laser beam 10 has a "reference axis" 12 , which, for. B. in the case of a circular contour and energy distribution would coincide with the central axis of the circle. The reference axis 12 pierces the cornea 18 at a puncture point 16th

The ablation laser beam 10 is precisely aligned when the penetration point 26 of the visual field line 24 on the one hand and the penetration point 16 of the reference axis 12 of the ablation laser beam 10 on the other hand coincide.

FIG. 3 shows a device 2 for the photorefractive correction of ametropia, which, among other things, has a beam processing system 4 , a beam shaping system 6 and a tracking device 8 as main components.

The beam processing system 4 comprises a laser light source 28 , lenses 30 and a so-called integrator 32nd

The beam shaping system 6 comprises a shadow mask device 34 and a zoom lens 36 .

The tracking device 8 comprises a gimbal and semi-transparent mirror 38 , a first motor 40 , a second motor 42 and a position sensor 44 .

The operation of the device 2 is as follows:
The ablation laser beam 10 is generated by the laser light source 12 . It is expanded in the lenses 30 and homogenized over the cross section in the integrator 32 .

The cross section of the laser beam is now adjusted in size in the hole mask device 34 and receives the desired contour and energy distribution at the moment. The ablation laser beam 10 then strikes the deflection mirror 38 of the tracking device 8 , which is gimbal-mounted and pivotable about two mutually perpendicular axes and whose position is effected by the two motors 40 and 42 and is detected by the position sensor 44 . The deflection mirror 38 directs the ablation laser beam 10 through the zoom optics 36 of the beam shaping system 6 onto the eye 20 to be treated.

With the aid of the zoom optics 36 , the size of the laser projection surface 14 on the cornea 18 of the eye 20 can be continuously changed in conjunction with the shadow mask device 34 , as a result of which a uniform ablation of the cornea on the eye 20 can be achieved (see FIG. 1 and 2).

The instantaneous position of the eye 20 and thus the position of the penetration point 26 of the visual field line 24 through the cornea 18 on the eye 20 is determined by the video camera 50 , which continuously records an image of the eye 20 .

To immobilize the eye 20 on the one hand and to align the field of view line 24 on the other hand, a diode laser 46 is provided, the beam of which is directed in the direction of the eye 20 via a semi-transparent mirror 48 . For this purpose, the deflection mirror 38 is also made semi-transparent.

The motors 40 and 42 , the position sensor 44 and the video camera 50 are connected to a first control unit 52 . The position sensor 44 and the video camera 50 are also connected to a second control unit 54 , which is also connected to the laser light source 28 .

The control of the tracking device 8 is carried out as follows:
Via the video camera 50 , a signal corresponding to the current position of the penetration point 26 of the visual field line 24 is passed through the cornea 18 on the eye 20 to the control unit 52 . The control unit 52 also receives from the position sensor 44 a signal corresponding to the current position of the deflection mirror 38 , which is representative of the position of the penetration point 16 of the reference axis 12 of the ablation laser beam 10 through the cornea 18 . The control unit 52 processes these signals and controls the motors 42 and 44 in such a way that they continuously pivot the deflection mirror 38 in such a way that the penetration point 16 of the reference axis 12 of the ablation laser beam 10 through the cornea 18, whenever possible, at the desired location Eye 20 , namely at the point of penetration 26 of the visual field line 24 through the cornea 18 .

Due to the possible high speed of eye movements and the inertia of electronics and mechanics, deviations between the positions of the piercing points 16 and 26 are possible. The control unit 54 therefore continuously monitors the deviation of these two positions. If a predetermined limit value is exceeded, the control unit 54 switches off the laser light source 28 until the limit value is again fallen below.

FIG. 4 schematically shows a gimbal-mounted deflection mirror 38 as can be used in the device in FIG. 3. The deflection mirror 38 is preferably in its neutral position at an angle of 45 ° to the reference axis of an incident laser beam 10 a. The deflection mirror 38 is octagonal in order to save weight. The deflecting mirror 38 is pivotally mounted about a first axis 56 via two bearing pins 58 . The bearing pins 58 are fixed with their end facing away from the deflecting mirror 38 via a bearing 60 on a frame 62 . This frame 62 is on the one hand rigid and on the other hand designed to save weight. It is also pivotally mounted about a second axis 64 via bearing pins 66 . The second axis 64 is perpendicular to the first axis 56 . The bearing pins 66 are fastened with their end facing away from the frame 62 to a housing 70 via bearings 68 . The deflecting mirror 38 is moved via a rod 72 by a motor 40 (not shown). The frame 62 is moved over a rod 74 by a motor 42 (not shown).

By this articulating the mirror 22 may be the axis of the emergent ablative laser beam 10 b to the two spatial axes x and y are any which can pivot en.

In Fig. 5 another embodiment of the tracking device is shown schematically. An incident parallel to the x-axis of laser beam 110 a is incident on a first prior preferably at a fixed angle of 45 ° with respect to the yz plane employed deflecting mirror 138 a and is deflected upwardly therefrom parallel to the z-axis. It now meets a second deflecting mirror 138 b, which is preferably set at a fixed angle of 45 ° with respect to the xz plane so that it is deflected as a failing ablation laser beam 110 b parallel to the y axis.

The first deflecting mirror 138 a is parallel to the x-axis and the second deflecting mirror 138 b parallel to the y-axis ver sliding. The drives for these movements are not shown. A translational displacement of the first deflecting mirror 138 a along the x-axis leads to an axis-parallel displacement of the ablation laser beam 110 b in the x-direction. A translatory displacement of the second deflecting mirror 138 b along the y axis leads to an axially parallel displacement of the ablation ablation laser beam 138 b in the z direction.

This embodiment thus achieves a shift in the ablation laser beam 138 b without an associated change in the angle of a reference axis 112 (not shown) of the ablation laser beam 138 b.

In Fig. 6 three treatment situations at the points A, B and C are shown (the deflection angles are greatly exaggerated for better understanding). The ablation laser beam 10 is deflected by the deflecting mirror 38 of the tracking device 8 described in FIG. 3. At time A, the eye 20 is in its target rest position practiced by means of the diode laser 46 (cf. FIG. 3). The tracking device 8 controls the ablation laser beam 10 so that the penetration point 16 of the reference axis 12 of the ablation laser beam 10 through the cornea is arranged as precisely as possible above the penetration point 26 of the visual field line 24 .

At time B, the eye 20 is pivoted to the left, which causes the tracking device 8 to pivot the reference axis 12 of the ablation laser beam 10 so that the piercing point 16 is still as close as possible to the piercing point 26 .

At time C, the reference axis 12 of the ablation laser beam 10 did not immediately follow the eye 20 pivoted to the right due to the inertia of the electronics and mechanics. Thus, the puncture point 16 of the reference axis 12 of the ablation laser beam through the cornea 18 would be clearly distant from the puncture point 26 of the facial field line 24 through the cornea 18 . This is detected by the control unit 48 and leads to a shutdown of the laser light source 28 until the tracking A device 8 the ablative laser beam has 10 to which can pivot th eye 20 tracked so that the two puncture ungspunkte 16 and 26 again are sufficiently close together.

In Figs. 7 and 8 are diagrams are shown which on the one hand the deviation of the position of the Durchstoßungs point 16 of the reference axis 12 of the ablative laser beam 10 from the position of the penetration point 26 of the visual field line 24 on the eye 20 and on the other hand, the switching states of the laser light source 28 each represent as a function of time, in particular at the times A, B and C shown in FIG. 6.

It can be seen that the deviation is very small at time A and therefore the laser light source 28 is switched on. Shortly before time B is reached, the deviation is greater, which reflects the laser beam tracking process. At time B, when the beam is again aligned to the new eye position, the deviation is small again. The pulsed laser light source is switched on continuously. At time C, the deviation exceeded the permissible limit, because due to the inertia of the electronics and mechanics, the beam could not track the very rapid eye movement quickly enough. Therefore, the laser light source 28 is automatically switched off and only switched on again when the deviation is again less than the permissible limit.

This ensures that eye movements, which are unavoidable during an operation, are compensated for by the tracking device 8 up to a certain limit value. This improves the treatment result and shortens the time required for such an operation. In the event of the limit value being exceeded, the laser light source 28 can be switched off, as a result of which a deterioration in the treatment result by protruding the cornea outside the desired range is avoided.

Claims (15)

1. A device for photorefractive correction of ametropia, which comprises: a device for generating a laser ablation beam for ablation of cornea on an eye, a beam processing system, a device for detecting the instantaneous position of the eye, which corresponds to the position of a puncture ungspunkt corresponds to a visual field line through the cornea of the eye, and a device for fixing the eye; characterized in that the device ( 2 ) further comprises: a device ( 8 ) for continuously tracking a penetration point ( 16 ) of a reference axis ( 12 ) of the ablation laser beam ( 10 ; 110 ) through the cornea ( 18 ) to varying positions of the penetration point ( 26 ) of the visual field line ( 24 ) through the cornea ( 18 ), the tracking device ( 8 ) being coupled to the eye position detection device ( 50 ) via a first control unit ( 52 ) in such a way that deviations between the positions of the penetration points ( 16 ) and ( 26 ) are returned. 2. Device according to claim 1, characterized in that it has means ( 54 ) which interrupt the generation of the ablation laser beam ( 10 ; 110 ) as long as the difference between the position of the puncture point ( 26 ) of the visual field line ( 24 ) through the cornea ( 18 ) on the eye ( 20 ) and the position of the penetration point ( 16 ) of the reference axis ( 12 ) of the ablation laser beam ( 10 ) exceeds a predetermined limit value. 3. Device according to one of the preceding claims, characterized in that the tracking device ( 8 ) comprises a deflecting mirror ( 38 ) which is pivotally mounted about a first axis ( 56 ) in a frame ( 62 ), which itself again around a second axis ( 64 ) is pivotally mounted, which is at an angle to the first axis ( 56 ) so that the suspension of the deflecting mirror ( 38 ) corresponds to a gimbal. 4. Device according to one of the preceding claims, characterized in that the tracking device ( 8 ) comprises a first ( 138 a) and a second, to the first non-parallel, preferably oriented at an angle of 90 ° second deflecting mirror ( 138 b) , which are arranged so that the incident ablation laser beam ( 110 a) from the first ( 138 a) to the second deflecting mirror ( 138 b) and from this as an outgoing ablation laser beam ( 110 b) towards the eye ( 120 ) is forwarded, and the two deflecting mirrors ( 138 a, 138 b) are linearly displaceable while maintaining their position in space. 5. Device according to one of the preceding claims, characterized in that the means ( 40 , 42 ) which move the deflecting mirror ( 38 ; 138 a, 138 b) comprise electric motors which effect the movements via gears and / or rods. 6. Device according to one of the preceding claims, characterized in that the means ( 40 , 42 ) which move the deflecting mirror ( 38 ; 138 a, 138 b), linear actuators (z. B. moving coil drives) which comprise the Cause movements. 7. Device according to one of the preceding claims, characterized in that the means ( 40 , 42 ), which move the deflecting mirror ( 38 ; 138 a, 138 b), in the bearing built-in rotary actuators (stepper motors) which comprise the movements effect. 8. Device according to one of the preceding claims, characterized in that it comprises means ( 44 ) which detect the current position of the deflecting mirror ( 38 ; 138 a, 138 b) and forward corresponding signals to the control units ( 52 , 54 ). 9. Device according to one of the preceding claims, characterized in that the means ( 44 ), which detect the current position of the deflecting mirror ( 38 ; 138 a, 138 b), are integrated in the movement means ( 40 , 42 ). 10. Device according to one of the preceding claims, characterized in that the eye position detection device ( 50 ) comprises a video camera. 11. Device according to one of the preceding claims, characterized in that the deflecting mirror ( 38 ; 138 a, 138 b) are semi-transparent. 12. Device according to one of the preceding claims, characterized in that the data transmission between eye position detection device ( 50 ) and control units ( 52 , 54 ) and between the tracking device ( 8 ) and control unit ( 52 ) by means of fiber optic cables. 13. Device according to one of the preceding claims, characterized in that it comprises a beam shaping system ( 6 ) which can change the contour of the beam cross section and the energy distribution over the cross section. 14. A method for the photorefractive correction of ametropia, in which a preferably variable projection surface of an ablation laser beam on an eye causes ablation of the cornea on the eye and the position of the eye, which indicates the position of the point of penetration of the visual field line through the surface of the cornea corresponds to an eye, is continuously detected, characterized in that the position of the penetration point ( 16 ) of the reference axis ( 12 ) of the ablation laser beam ( 10 ; 110 ) through the surface of the cornea ( 18 ) of the eye ( 20 ) the position of the Through the point of impact ( 26 ) of the visual field line ( 24 ) through the cornea ( 18 ) of the eye ( 20 ) is tracked. 15. The method according to claim 14, characterized in that the generation of the ablation laser beam ( 10 ; 110 ) is interrupted as long as the difference between the position of the penetration point ( 16 ) of the reference axis ( 12 ) of the ablation laser beam ( 10 ; 110 ) and the position of the penetration point ( 26 ) of the visual field line ( 24 ) through the cornea ( 18 ) exceeds a predetermined value.