WO2013057176A1

WO2013057176A1 - Ophthalmic laser system and method for laser-surgical treatment of the cornea

Info

Publication number: WO2013057176A1
Application number: PCT/EP2012/070631
Authority: WO
Inventors: Dieter Grebner; Matthias Reich
Original assignee: Carl Zeiss Meditec Ag
Priority date: 2011-10-20
Filing date: 2012-10-18
Publication date: 2013-04-25
Also published as: DE102011116760A1

Abstract

2.1 The known ophthalmic laser systems (1) with a detection beam path (D), which contains an optoelectronic detector (12) for detecting light and a treatment beam path (B) having an ultra-short pulse laser (4), achieve only limited accuracy in the treatment of the cornea. 2.2. The accuracy can be increased with a detector (12) for detecting light of exactly one variably adjustable polarisation state and a respective adjustable beam deflection unit (7/7') in the two beam paths, by recording scattered light intensities of different polarisation states from the same direction before the treatment of the cornea, adjusting a model of a cornea thereto in order to determine the cutting geometry to be generated and adapting said geometry to a predicted deformation based on the model. This ensures highly accurate surgical treatment of the cornea because the biomechanical state of the cornea, including its internal mechanical stresses during the cutting procedure, is considered. 2.3. Correcting ametropia

Description

Ophthalmic laser system and method for the laser surgical treatment of the cornea

The invention relates to an ophthalmic laser system with a

Treatment beam path, which includes a pulse laser, and a

Detection beam path comprising an optoelectronic detector, and a method for laser surgical treatment of the cornea, in particular for the purpose of a refractive correction.

The cornea of the human eye has internal mechanical stresses. This tension structure can co-determine the shape of the cornea and thus cause, for example, defective vision.

From WO 2009/127921 A2 a system and a method is known, with which the shape of the cornea is changed by changing a voltage distribution of the cornea by cutting the tissue, wherein first the topography of the cornea is measured. However, this way of altering the shape of the cornea has limited accuracy.

Optically, tension in the cornea due to birefringence

from falling light. It has been suggested that these stresses in a refractive correction by means of an excimer laser in the calculation of the

Ablation profile (Alexander Bösecke: "In vivo optical

Stress analysis of the human cornea ", diploma thesis TU Ilmenau, 2007) .This approach has only a limited accuracy.

DE 10 2006 016 968 A1 specifies a reflection polariscope which evaluates the light scattered back from the iris. However, this does not permit a depth-resolved analysis of birefringence in the cornea and is problematic for the pupil, as there is no backscattering of light.

The invention has for its object to provide an ophthalmic laser system of the type mentioned, which is a laser surgery treatment of Cornea with high accuracy allows, especially taking into account internal mechanical stresses of the cornea.

The object is achieved by an ophthalmic laser system having the features specified in claim 1, and by a method having the features specified in claim 12.

Advantageous embodiments of the invention are specified in the subclaims.

According to the invention, an ophthalmic laser system is provided with a detection beam path which comprises an optoelectronic detector for (depth-selective) detection of light of precisely a variably adjustable polarization state, a first variably adjustable beam deflection unit and a transfer optic, and a treatment beam path comprising an ultrashort laser second variably adjustable beam deflection unit and a focusing optics, as well as a control unit, a calculation unit and an evaluation unit, wherein

- the evaluation unit is set up to carry out the following steps:

1 . Setting the detector to a first polarization state and determining at least a first scattered light intensity by means of the detector,

2. Setting the detector to a second polarization state, which is different from the first polarization state, and determining at least a second scattered light intensity by means of the detector in identical position of the first

Deflector

3. Determining a mathematical model of a cornea, which describes a topography and internal mechanical stresses, and adapting to the determined scattered light intensities using different light propagation velocities for the two polarization states,

- the calculation unit is set up to carry out the following steps:

1 . Determine a cut geometry to be created in the cornea and adjust by predicting a corneal deformation based on the fitted model and

2. Determine control data for a laser cut based on the adjusted

Cutting geometry and - The control unit for controlling the laser, the first deflecting unit and the focusing optics is set up based on the control data.

Conveniently, first and second scattered light intensities

determined different directions of the cornea by the first deflection unit is set differently and for each position first and second

Scattered light intensities are determined with different polarization states. As a result, a three-dimensional model can be determined and adapted, which allows a higher accuracy.

For the purposes of the invention, an ultrashort pulse laser is a laser capable of emitting radiation pulses with a duration in the fs or ps range. Mechanical stresses are preferably internal stresses in the corneal tissue.

Accordingly, it is provided for the method according to the invention for laser-surgical processing of a cornea by means of an ultrashort pulse laser to carry out the following steps:

1 . depth-selectively determining at least a first scattered light intensity having a first polarization state from a first direction of the cornea,

2. depth-selective determination of at least one second scattered light intensity having a second polarization state, which is different from the first polarization state, from the same direction,

4. Determine a cut geometry to be created in the cornea and adjust by predicting a corneal deformation based on the fitted model and

5. Determine control data for a laser cut using the adapted

Cutting geometry and

6. Controlling the laser, the first deflection unit and the focusing optics based on the control data. A determination of scattered light intensities is highly selective in the sense of the invention if scattered light intensities from different depths of the cornea can be recorded with depth resolution either simultaneously or sequentially.

The invention allows the surgical treatment of the cornea with high

Accuracy by taking into account the biomechanical state of the cornea including its internal mechanical stresses in the incision. As a result, both the spatial control parameters (position of the irradiated target volumes) and energetic control parameters (pulse intensities) can be determined with high accuracy. The evaluation unit, the calculation unit or the control unit can output the voltages determined on the basis of the model such that they can be visually perceived by an operator. In particular, the unit in question may receive instructions from the operator to modify the model.

The mechanical model can be composed, for example, according to US 2009/0187386 A1 of finite elements, their position and mechanical

Voltages starting from a cornea standard model by a

Adjustment to the topography data of the concretely measured cornea and the intensities of diffraction light diffracted differently by birefringence.

The direction from the cornea, from which the scattered light intensities are determined, defines from which location in the cornea the detected scattered light is recorded. Thus, at least one first scattered light intensity, which (exclusively) has the first polarization state, and at least one second scattered light intensity, which (exclusively) has the second polarization state, is determined from a location. Preferably, first and second scattered light intensities can be determined from a plurality of different locations of the cornea. For this purpose, the direction of the cornea, from which the

Scattered light intensities are determined, for example, be adjusted by means of an adjustable beam deflection unit. In turn, first and second scattered light intensities can then be recorded by the new location. By measuring multiple locations, a three-dimensional model can be identified and adjusted which allows higher accuracy. In addition, third and further scattered light intensities can be determined for additional polarization states and used in the adaptation.

In an advantageous embodiment, the evaluation unit determines a topography of the cornea from which to adapt the model to the light intensities

Scattered light intensities. This improves the accuracy of the model and eliminates the need to separately survey the topography.

In an alternative embodiment, the laser system comprises a

Topographiemessvorrichtung, wherein the evaluation unit is set up, the model before the adaptation to the light intensities by means of a

Topographiemessvorrichtung determined or predetermined topography data of the cornea adapt. Also in this way the accuracy of the model can be improved.

Appropriately, in the detection beam path

Illumination beam path to be coupled with a light source and the

Evaluation unit be set up to carry out the following steps before determining the first scattered light intensity:

Illuminating a cornea arranged in an examination area by means of the light source and

- Focusing the detection beam path on the cornea.

Thereby, the accuracy of the measurement of the scattered light intensities can be improved, in particular by a confocal illumination.

Embodiments in which the detection beam path has optics which directs light of the light source which is directed onto the cornea by means of the first deflection unit are directed perpendicularly to the cornea independently of a position of the first deflection unit, in particular with the arrangement of FIGS Optics on a side of the transfer optics facing away from the laser. Such

Attachment optics may be, for example, a diffractive or refractive element and consist of a lens or a lens combination. Their focal length preferably corresponds to their distance from the cornea plus about 8 mm, so for example 20 mm. The vertical incidence of the illumination light and the vertical detection at each location of the cornea simplify the adaptation of the model, since the

Birefringence so only occurs along a minimum path length through the cornea.

The control unit is expediently designed to carry out the following steps:

- Activating a fixation device on the cornea before controlling the laser and

Deactivate the fixing device after controlling the laser.

Thus, the risk of mistreatment by eye movements can be minimized.

Particularly advantageous embodiments are those in which the evaluation unit

is set up to carry out the following steps:

- Activating a deforming fixing device in contact with the cornea before determining the scattered light intensities and

Deactivate the fixing device after determining the scattered light intensities. Thereby, the stress states of the cornea can be measured in a defined deformed state of the cornea. The deformation may be, for example, a applanation through a plane contact glass. Advantageously, a

Measurement of light intensities with different polarization states without external deformation and before or after a corresponding measurement with external deformation are performed and the light intensities from both measurements are used in the adaptation of the model. For this purpose, for example, the same defined deformation can be simulated in the model. By taking into account a defined deformation, the strength of the cornea can be determined with higher accuracy.

The invention includes embodiments in which

the adaptation of the mathematical model to the determined scattered light intensities is carried out by the calculation unit or the control unit and / or

- The determination and adjustment of the cutting geometry is performed by the evaluation unit or the control unit. Preferably, the detector is an optical coherence tomograph (OCT) or designed to confocal with the second focusing optic detection. These detectors allow depth discrimination with high axial resolution. A system with a confocal detector, for example, according to FIG. 3 of the

WO 2010/07020 A2 be formed with other programming of the local control unit, the disclosure of which is incorporated herein in its entirety. A system with an OCT as a detector, for example, according to FIG. 5 or FIG. 6 of WO 2009/0331 1 1 A2 with other programming of the local

Be designed control units.

The evaluation unit can advantageously based on the determined

Scattered light intensities determine a length of the eye and a thickness of the lens. Based on these data, a cataract operation can be performed in the same treatment, for example in the form of an anterior or posterior capsulorhexis by means of the ultra-short pulse laser, the destruction of the biological lens or irradiation of the epithelial cells arranged equatorially in the capsular bag.

The invention includes embodiments in which

the evaluation unit, the calculation unit and the control unit are the same unit and / or

the first and second deflection units are the same deflection unit and / or

- The transfer optics and the focusing optics are the same look.

The invention also includes an OCT that detects a topography of the cornea, either by means of an integrated topography measuring device

(For example, using Placidoringen) measured topography data or determined from the measured OCT intensities topography data. In embodiments with or without topography determination, a

Inventive OCT determine the voltages within a cornea based on scattered light intensities of different polarization states. Such an OCT can be used in particular in the abovementioned applications in preliminary and / or follow-up examinations. In addition, the invention comprises an ophthalmological measuring device for receiving scattered light from a cornea, having an illumination beam path which comprises a light source, and a detection beam path coupled to the illumination beam path, which has an optoelectronic detector for (depth-selective) detection of light of precisely one variably adjustable light

Polarization state, a variably adjustable beam deflecting unit and a transfer optics, wherein the common behind the coupling point beam path is characterized by an optic, which light of the light source, which is directed by means of the deflection on the cornea, regardless of a position of the

Deflection unit perpendicular to the cornea directs, in particular with arrangement of the optics between the coupling point and a closing element to the outside, for example, a cover glass.

The invention can be used in particular in the following applications:

- For biomechanical treatments of the cornea, in particular

within a cataract operation (for limbal relaxation incisions or transparent corneal incisions).

- In the extraction of a refractive lenticle (ReLEx) to improve the accuracy of treatment (avoiding differences in the correction of higher orders of aberrations by different

Stress states between fixed and unfixed state of the cornea) and efficiency, and also in advance for patient selection, in particular by determining a fitness value based on the determined mechanical stresses or other biomechanical properties.

- For treatment planning in a keratoplasty, for example for

Definition of the keratoplasty zone.

- For refractive treatments such as femtosecond LASIK or cataract surgery (for limbal relaxation incisions, transparent corneal incisions and / or to reduce corneal astigmatism).

- To prevent or treat keratoconus.

- ICR implantation: to select the ICR and / or optimize the ICR position.

The invention will be explained in more detail by means of exemplary embodiments. In the drawings show:

Fig. 1 shows a first laser system consisting of a measuring device, a

Calculating device and an irradiation device,

Fig. 2 shows a second laser system in which the three devices are combined in one and

3 shows a flowchart of a method for the laser surgical treatment of the cornea.

In all drawings, like parts bear like reference numerals.

Fig. 1 shows a schematic representation of an ophthalmic laser system 1, the separate devices, namely a measuring device 1 .1, a

Computing device 1 .2 and an irradiation device 1 .3, which are interconnected via interfaces for data transmission. They can also stay connected permanently. To carry out the method according to the invention, the patient's eye 2 is first placed in the examination area in front of the measuring device 1 .1 for measuring the cornea 3, and later in the treatment area in front of the irradiation device 1 .3 for irradiation.

The measuring device 1 .1 comprises a detector 12, for example a

Spectral space OCT (engl., "Spectral-domain OCT"), in conjunction with a polarization beam splitter 5 and a defined for example motor defined about the optical axis of the system 1 rotatable λ / 2 plate 15 adjustable

is polarization-discriminating, a scanning optics 6, an x-y deflection unit 7 ("scanner unit"), an example z-focusable transfer optics 8 and a

End glass 9, which together form a detection beam D, which leads to the examination area. In the detection beam D is by means of

Beam splitter 5 a lighting beam C coupled, in which a

Light source 10 is arranged, which emits unpolarized IR light. Between the laser system 1 and the eye 2, an optical attachment 13 is arranged all on the Cornea 3 focused rays regardless of their angle of incidence perpendicular to the cornea 3 directs. The detector 12 accordingly receives in the reverse direction scattered light from the cornea 3 and converts its intensity into a digital quantity, which is output to the evaluation unit 1 1 .1. By means of the deflection unit 7 and the transfer optics 8, the evaluation unit 1 1 .1 set the direction from which light is picked up by the cornea 3. It may also be the light source 10 with respect to the emitted intensity and the wave plate 15 with respect to the single polarization state transmitted to the detector 12 (here: the

Direction of polarization).

As soon as the practitioner has triggered the measurement, the evaluation unit 1 1 .1 switches on the light source 10 and sets the detector 12 to a first one

Polarization state by correspondingly rotates the wave plate 15 and sets by the deflection unit 7, a first direction of incidence of light from the cornea 3. Then, it simultaneously detects first intensities of illuminating light backscattered at different depths in the cornea from the first direction. In

In alternative embodiments, for example with a confocal detector or with time-domain OCT as the detector, the determination can be carried out sequentially from different depths, and then places the deflection unit 7 back in a different direction of incidence from that of the cornea 3 Then, it simultaneously detects further first intensities of illumination light backscattered at different depths in the cornea from the second direction.This scanning operation is repeated for a plurality of directions of incidence.For the retina, no stray light is scattered into the detection beam path D because it is outside of the retina Coherence range of the OCT

Embodiments (not shown) with confocal detection, the retina is outside the confocal area.

Then the evaluation unit 1 1 .1 sets the detector 12 to a second one

Polarization state, which is different from the first polarization state, by rotating the wave plate 15 in another position, for example by 90 °, and sets the deflection unit 7, for example, in the first (incidence) direction. It then simultaneously detects second intensities of illumination light backscattered at different depths in the cornea from the first direction of the cornea. Subsequently, it adjusts the deflection unit 7, for example, to the second direction of incidence of the cornea 3. Then it simultaneously detects further second intensities of backscattered at different depths in the cornea

Illuminating light from the second direction. This scanning process will

for example, repeated for all previously set directions of incidence.

If all first and second scattered light intensities are determined, determine the

Evaluation unit 1 1 .1 a mathematical (standard) model of a cornea 3, which describes a topography and mechanical stresses,

for example, by taking it from the computing unit 1 1 .2. It adjusts the model to the detected scattered light intensities using different light propagation velocities for the two polarization states. For this purpose, for example, it can simulate the birefringence of light under the measured incident directions by means of ray tracing (English, "ray tracing") and carry out a compensation calculation with ray tracing parameters.

The calculation device 1 .2 is, for example, a commercial computer with a central processing unit, a calculation unit 1 1 .2

Main memory and a display which is connected via two interfaces on the one hand to the evaluation unit 1 1 .1 and on the other hand to the control unit 1 1 .3. The calculation unit 1 1 .2 can for example provide the evaluation unit 1 1 .1 with data for adapting the patient-customized model of the cornea 3, for example an intraocular pressure and general mechanical properties of the cornea 3. This data can be provided by the calculation unit 1 1 Receive treatment via an input device or read from a database.

From the evaluation unit 1 1 .1 takes the calculation unit 1 1 .2 the

patient-customized model contrary. It first determines a cut geometry to be generated in the cornea, for example by receiving it from the practitioner or a database, and iteratively adapts it based on this model by predicting a deformation of the cornea on the basis of the customized model of the cornea 3 to a predetermined target criterion, for example one predetermined refractive effect or a given Topography, is reached. Subsequently, the calculation unit 1 determines 1 .2

Control data for a laser cut on the basis of the previously adapted cutting geometry and outputs this to the control unit 1 1 .3.

The irradiation device 1 .3 comprises in addition to the control unit 1 1 .3 a

Ultrashort pulse laser 4, for example a Yb fiber laser, a scanning optics 6, a second xy deflection unit 7 '("scanner unit"), a z-focusing optics 8' and a cover glass 9, which together form a treatment beam path B, which belongs to A fixing device 14 with a contact lens for the eye 2 is arranged between the laser system 1 and the eye 2. On its side facing the eye 2, the contact lens can be spherical, plane, eye-curved or one For example, there is a spherical curvature, in which the cornea 3 is fixed in the fixed (eg.

aspirated) state is applanated.

The control unit 1 1 .3 receives the control data from the calculation unit 1 1 .2, fixed on a signal of the practitioner out the eye 2 in the

Fixing device 14 and controls the laser 4, the deflection unit 7 'and the

Focusing optics 8 'based on this control data so that the adapted laser cut is generated in the cornea 3. Finally, it releases the fixing device 14. Finally, the practitioner removes the tissue separated by means of the radiation pulses.

Any other adjustable polarization-selective element may be used in place of the polarization beam splitter 5 and waveplate 15 combination. So it is possible, for example, the first scattered light intensities in a linear

Polarization state and the second scattered light intensities a circular

Determine polarization state. In alternative embodiments (not shown), the detection beam path can be designed fiber-optically. The setting of the respectively to be detected polarization state can then be done for example via variable fiber optic elements. In alternative embodiments (not shown), the optical attachment 13 can be arranged within the measuring device 1 .1, for example between the

Transfer optics 8 and the cover glass 9.

In Fig. 2, an alternative laser system 1 is shown schematically, in which all three devices are combined in one. However, the operation corresponds to that described for Fig. 1 as far as nothing else is described below. The detection beam D is by means of the polarization beam splitter 5 in the

Treatment beam path B coupled, the same time as

Illumination beam C is used by a beam attenuator 17 in the

Treatment beam B can be pivoted. In the pivoted state, the laser 4 can serve as a light source 10, in the swung-out state it is used to process the cornea 3. The control unit 1 1 is simultaneously evaluation,

Calculation unit. This can for example be realized by appropriate software modules that interact with each other via interfaces.

Fig. 3 shows the sequence of a method according to the invention in the form of a

Flowchart. It is divided into the individual units 1 1 .1, 1 1 .2 and 1 1 .3 executed, but can for example also be carried out by the combined control unit 1 1.

First, the first and second scattered light intensities are determined for different polarization states and by means of the deflection unit 7 from different directions from the cornea, that is, from different locations of the cornea. Optionally, in alternative embodiments (not shown) by means of a

Topographiemessvorrichtung, for example, is coupled into the detection beam path, the topography of the cornea measured and in the form of

Topographiedaten be provided. Alternatively, topographical data can be determined, for example, from the scattered light intensities determined by means of the detector 12. Conveniently, a thickness of the cornea 3 (pachymetry) is determined in this way.

A given mechanical model of a general cornea is determined according to the thickness of the cornea and topographical data from the topography data and adjusted based on the determined scattered light intensities due to birefringence to the mechanical stresses patient-specific, for example by means of a finite element method (FEM) and a simulation of

Ray tracing in the model with different

Light propagation velocities for the two polarization states. to

Adaptation of the model, for example, a given intraocular pressure and predetermined general mechanical properties are used.

The FEM model comprising the topography and the mechanical stresses is then used to iteratively optimize a given cutting geometry by means of a compensation calculation: for this purpose, the cut is made in the

Simulated patient model adapted model and simulated deformation of the model according to the determined mechanical stresses. Then one will

Deviation of the model from a given target criterion (refractive effect or topography) determined. If the deviation is greater than a predetermined one

Threshold, the cut geometry is modified and in the original

simulated patient-customized model and determines a deformation. These iterations continue until the threshold is exceeded. If this goal is not achieved, the procedure is aborted.

If it was possible to determine an optimized cutting geometry, corresponding control data are determined which include spatial control data for a deflection unit 7 'and a focusing unit 8' in order, for example, to generate gas bubble fields as cut surfaces by means of optical breakthroughs. The patient then has to place his eye 2 in the treatment area. By means of an ultrashort pulse laser 4 and the

Deflection unit 7 'and the focusing unit 8' are radiation pulses in

Target volumes V registered, which cause the precalculated optical breakthroughs in the target volumes V. LIST OF REFERENCES

1 Ophthalmic laser system

1 .1 measuring device

1 .2 calculation device

1 .3 irradiation device

2 eye

3 cornea

4 ultrashort pulse laser

5 polarization beam splitters

6 scan optics

7 () scanning unit

8 transfer optics

8 'focusing optics

9 cover glass

10 light source

1 1 evaluation, calculation and control unit

1 1 .1 evaluation unit

1 1 .2 calculation unit

1 1 .3 control unit

12 detector

13 attachment optics

14 fixing device

15 λ / 2 plate with drive

16 Optical delay element

17 beam attenuator with drive

B treatment beam path

C illumination beam path

D detection beam path

R OCT reference beam path

V target volume

Claims

Patent claims

1 . Ophthalmological laser system (1) with a detection beam path (D), which comprises an optoelectronic detector (12) for detecting light of precisely a variably adjustable polarization state, a first variably adjustable beam deflection unit (7) and a transfer optics (8), and one

Treatment beam path (B), which includes an ultra-short pulse laser (4), a second variably adjustable beam deflection unit (7') and focusing optics (8'), as well as a control unit (1 1 [.3]), a calculation unit (1 1 [.2]) and an evaluation unit (1 1 [.1 ]), where

- the evaluation unit (1 1 [.1]) is set up to carry out the following steps:

1 . Setting the detector (12) to a first polarization state and determining at least a first scattered light intensity using the detector (12),

2. Setting the detector (12) to a second polarization state that is different from the first polarization state and determining at least a second scattered light intensity using the detector (12) and

3. Determine a mathematical model of a cornea that has a

Topography and mechanical stresses are described, and adaptation to the determined scattered light intensities using different

Light propagation speeds for the two polarization states,

- the calculation unit (1 1 [.2]) is set up to carry out the following steps:

1 . Determining a cutting geometry to be created in the cornea and adapting by predicting a deformation of the cornea based on the adapted model and

2. Determining control data for a laser cut based on the adapted cutting geometry and

- the control unit (1 1 [.3]) for controlling the laser (4), the second

Deflection unit (7') and the focusing optics (8') based on the control data

is set up.

2. Laser system (1) according to claim 1, wherein the evaluation unit (1 1 [.1]) for

Adapting the model to the light intensities determines a topography of the cornea from the scattered light intensities.

3. Laser system (1) according to claim 1, comprising a topography measuring device, wherein the evaluation unit (1 1 [.1]) is set up to adapt the model to topography data of the cornea (3) determined or specified by means of a topography measuring device before adapting to the light intensities .

4. Laser system (1) according to one of the preceding claims, wherein in the

Detection beam path (D) an illumination beam path (C) with a

Light source (10) is coupled in and the evaluation unit (1 1 [.1 ]) is set up to carry out the following steps before determining the first

Scattered light intensity:

- Illuminating a cornea (3) arranged in an examination area using the light source (10) and

- Focusing the detection beam path (D) on the cornea (3).

5. Laser system (1) according to the preceding claim, wherein the

Detection beam path (D) has optics (13) which light the

Light source (10), which is directed onto the cornea (3) by means of the first deflection unit (7), is directed perpendicularly onto the cornea (3), regardless of a position of the first deflection unit (7), in particular with the optics arranged on one of the Laser (4) facing away from the transfer optics (8).

6. Laser system (1) according to one of the preceding claims, wherein the

Control unit (1 1 [.3]) is set up to carry out the following steps:

- Activating a fixation device (14) on the cornea before controlling the laser (4) and

- Deactivating the fixing device (14) after controlling the laser (4).

7. Laser system (1) according to one of the preceding claims, wherein the

Evaluation unit (1 1 [.1 ]) is set up to carry out the following steps:

- Activating a deforming fixation device (14) in contact with the cornea before determining the scattered light intensities and

- Deactivate the fixing device (14) after determining the

Scattered light intensities.

8. Laser system (1) according to one of the preceding claims, wherein

- adapting the mathematical model to the determined ones

Scattered light intensities from the calculation unit (1 1 .2) or the

Control unit (1 1 .3) is carried out and/or

- determining and adjusting the cutting geometry of the

Evaluation unit (1 1 .1) or the control unit (1 1 .3) is carried out.

9. Laser system (1) according to one of the preceding claims, wherein the

Detector (12) is an optical coherence tomograph or for use with the

Focusing optics (8 ') is designed for confocal detection.

10. Laser system (1) according to one of the preceding claims, wherein the

Evaluation unit (1 1 [.3]) uses the determined scattered light intensities to determine a depth of an anterior chamber of the eye (2), a length of the eye (2) and a thickness of the lens of the eye (2).

1 1 . Laser system (1) according to one of the preceding claims, wherein the

Evaluation unit (1 1 .1), the calculation unit (1 1 .2) and the

Control unit (1 1 .3) are the same unit (1 1) and/or wherein the first and second deflection units (7, 7') are the same deflection unit (7) and/or wherein the transfer optics (8) and the focusing optics (8' ) are the same optics (8).

12. Method for laser-surgical processing of a cornea, in particular for the purpose of refractive correction, using an ultra-short pulse laser, comprising the following steps:

1 . depth-selective determination of at least a first scattered light intensity with a first polarization state from a first direction of the cornea,

2. depth-selective determination of at least a second scattered light intensity with a second polarization state, which is different from the first polarization state, from the same direction,

3. Determine a mathematical model of a cornea that has a

Topography and mechanical stresses are described, and adaptation to the determined scattered light intensities using different Light propagation speeds for the two polarization states,

4. Determine a cutting geometry to be created in the cornea and adapt by predicting a deformation of the cornea based on the adapted model and

5. Determining control data for a laser cut based on the adapted cutting geometry and

6. Controlling the laser (4), the first deflection unit (9) and the focusing optics (8) is set up based on the control data.

13. The method according to the preceding claim, wherein

- to adapt the model to the light intensities, a topography of the cornea is determined from the scattered light intensities or

- Before adapting the model to the light intensities, the model is determined to predetermined or using a topography measuring device

Topography data of the cornea (3) is adjusted.

14. The method according to one of the preceding method claims, wherein the

Cornea (3) before determining the scattered light intensities using a

Fixing device (14) is deformed, in particular with additional determination of first and second scattered light intensities before the deformation of the cornea and / or after an end of the deformation.