it is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a dear understanding of the present invention , while eliminating , for purposes of clarity , many other elements which are conventional in this art . those of ordinary skill in the art will recognize that other elements are desirable for implementing the present invention . however , because such elements are well known in the art , and because they do not facilitate a better understanding of the present invention , a discussion of such elements is not provided herein . the present invention will now be described in detail on the basis of exemplary embodiments . fig1 shows an exemplary ophthalmic laser device 1 which is suitable for clarifying the combined possibility of laser - surgical cutting and stabilizing cornea 2 of an eye 3 in keratoconus . further , it is configured to identify and locate existing cuts in the cornea 2 with respect to the shape and position thereof in order to crosslink the cornea 2 in the region of such cuts and thus to at least partially close the cuts again . for these purposes , the laser device 1 comprises a laser 4 , a polarizing beamsplitter 5 , scan optics 6 , a deflection unit 7 ( also referred to as scanner unit ), focusing optics 8 , and an exit window 9 which , together with a switchable beam attenuator 15 and a power modulator 16 , form an illumination beam path b , and a deflecting mirror 10 , a confocal aperture stop 11 , and a detector 12 which form a coupled - out detection beam path d . apart from this , the laser system 1 comprises an amplifier 13 for the detector 12 and a control unit 14 . a contact glass 17 with a device for immobilizing the eye 3 is arranged between the laser system 1 and the eye 3 ; the treatment area q lies behind this contact glass 17 . other embodiment forms ( not illustrated ) for realizing the solution according to the invention are possible . the scanner unit 7 comprises , for example , a quantity of galvanometric mirrors for deflecting the focus volume of the laser radiation in x and y direction over the cornea 2 . the focusing of the laser radiation in z direction along the optical axis is accomplished , for example , through a movable lens or lens group within the scan optics 6 or focusing optics 8 or , alternatively , through a movable tube lens ( not illustrated ). the detector 12 is configured , for example , as photomultiplier ( pmt ) or as avalanche photodiode ( apd ) because the light intensities to be received are low due to the transparency of the cornea 2 . the amplifier 13 is configured as a lock - in amplifier and is connected to both detector 12 and laser 4 . the laser 4 is a pulsed ti : sa infrared laser , for example , with a pulse length between 100 fs and 1000 fs . it emits laser radiation at a radiation power suitable for surgical incision . the pulsed ir laser radiation exits from the laser 4 and passes through the polarizing beamsplitter 5 , initially without alteration , in the “ surgical therapy radiation treatment ” switch position . the modulator 16 serves for fine adjustment of the radiation power delivered to the cornea 2 . the laser beam is subsequently focused in a target volume in the cornea 2 via the scan optics 3 , scanner unit 7 and focusing optics 8 . the target volume can be displaced in x , y and z direction relative to the cornea 2 by means of the scanner unit 7 and a movable lens or lens group inside the scan optics 6 or focusing optics 8 . in the “ illumination radiation power ” switch position , the attenuator 15 limits the radiation output so as to rule out alteration of eye tissue through the laser radiation . dispersion and / or reflection of the ir radiation is then brought about at the interfaces and in the interior of the cornea 2 , and the radiation is partially depolarized . backscattered and / or reflected light also falls in the illumination beam path b , where it retraces its path to the polarizing beamsplitter 5 . the portions of radiation with unchanged polarization state fall through the polarizing beamsplitter 5 on the laser 4 . this applies particularly to reflections originating from the scan optics 6 or focusing optics 8 . radiation components of this kind which have a changed polarization state due to depolarization in the eye 3 in the cornea 2 are deflected by the polarizing beamsplitter 5 as detection light into the detection beam path d to the detector 12 . the detection light falls on the detector 12 via a deflecting mirror 10 through the confocal pinhole diaphragm 11 . in an alternative embodiment form ( not illustrated ), the deflecting mirror 10 can be omitted or can be replaced by other beam guiding units . the confocal diaphragm 11 acts as a discriminator in z direction so that only backscattered light from a small focus volume is detected in a spatially resolved manner . the control unit 14 can irradiate selected scan points inside the cornea 2 with illumination light by deflecting the illumination light in x and y direction by means of the deflection unit 7 and changing the focusing in z direction by means of the focusing optics 8 and can determine the strength of the backscattering at these points by way of the intensity of the associated detection light . since the signals recorded at the detector 12 have a very low intensity , the electronic amplifier is adapted for an optimized signal - to - noise ratio . in a particularly advantageous embodiment form , the lock - in amplifier is temporally synchronized with pulse generation or with the repetition rate of the laser 2 . other embodiment forms use , e . g ., so - called boxcar techniques or sampling techniques with summing or averaging for noise suppression . the entire amplifier system of the detector signal advantageously has a nonlinear characteristic . a peak detector and / or a sample - and - hold circuit can also be used to achieve improved signals . in the “ photochemical radiation power ” switch position of the attenuator 15 , an optical output reaching the cornea 2 at most triggers a chemical reaction so that exclusively photochemical interactions with the tissue take place , namely particularly multiphoton absorptions in uv - absorbing π electron bonds of amino acids of the collagen fibers of the cornea 2 and subsequently , by intermediate excitation of an excitation level below the ionizing energy , the ionization of collagen fibers and crosslinking of the resulting radicals . in other embodiment forms ( not illustrated ), the laser device can be configured exclusively for stabilizing the cornea so that the laser 4 and / or attenuator 15 are permanently configured for a photochemical radiation power , for example . in this case , the detection beam path d can be omitted . however , other embodiment forms ( not illustrated ) are also possible in which only the detection of cuts and other lesions of the cornea is combined with stabilization of the cornea and the cutting capability is omitted . the excitation level of amino acids of the collagen fibers which can be used for crosslinking are shown ( not to scale ) in fig2 in jablonski term diagrams . fig2 a shows monochromatic excitation through single photon absorption ; fig2 b shows bichromatic excitation . fig2 c shows monochromatic excitation with multiphoton absorption over a virtual intermediate level v . fig2 d shows bichromatic excitation with multiphoton absorption from the ground state ( s 0 → s 1 ) over a virtual intermediate level . the radiated laser light always has a photon energy that is less than the ionizing energy ig . the wavelength range ( s ) radiated on the cornea ( s ) is / are preferably adjusted to fit amino acids such as tryptophan , tyrosine , phenylalanine , proline or hydroxyproline . for the first step , i . e ., resonant excitation s 0 → s 1 , a wavelength λ 1 between 260 and 290 nm ( preferably between 275 nm and 185 nm to minimize dna damage ) is necessary . for the second step , s 1 → s n , a photon must be radiated with an energy causing ionization of the amino acid proceeding from the excited level . the following condition must be met : to meet this condition , it is possible to use uv photons , but wavelengths in the visible region are also sufficient . in bichromatic crosslinking , uv radiation is preferably used only for the s 0 → s 1 excitation . accordingly , it is possible to use relatively low uv radiation powers . further , the singlet path is strongly favored through the subsequent application of a second laser pulse so that there is an extreme reduction in the tissue damage rate . there are various possibilities for crosslinking through ionization of collagen fibers over real intermediate levels : 1 . resonant excitation s 0 → s 1 → sn or s 0 → s 1 → t 1 → tn it is possible to generate crosslinking via the singlet path as well as the triplet path . as a result of the more improbable transitions isc between singlet systems and triplet systems in terms of quantum mechanics , singlet excitation is more efficient when using femtosecond pulses . after ionization , the transformation takes place — under suitable positioning of the secondary , tertiary and quaternary structures of the collagen fibers — from weak bonds formed with the intermediary of hydrogen bridges to strong covalent bonds . in addition , the excitation wavelengths radiated on the cornea 2 must satisfy the following conditions : λ 1 = wavelength [ nm ] h = planck constant ( 6 . 62510 − 34 js ) δe ( s 1 - s 0 )= energy of the photon for the excitation of s 0 → s 1 [ j ] λ 2 = wavelength [ nm ] e ionization − e ( s 1 )= energy of the photon for the excitation of s 1 → s n [ j ]. for the monochromatic case , λ 1 = λ 2 and equation ( 1 ) applies . 2 . resonant excitation s 0 → s 1 → sn or s 0 → s 1 → t 1 → tn ( multiphoton excitation ) for crosslinking through multiphoton excitation over one or more virtual levels , the excitation wavelengths radiated on the cornea 2 must satisfy the following conditions : for the monochromatic case , λ 1 = λ 2 and equation ( 3 ) applies . by means of infrared femtosecond laser radiation , as is shown by way of example in fig1 , multiphoton processes are induced in the molecules of the collagen fibers which finally lead to ionization of the molecule over at least one real intermediate excitation level . the radiation power must be high enough to trigger multiphoton absorptions , but no photodisruption ( optical breakdown ) or ablation may be induced . the control unit 14 carries out , for example , the operating method shown in fig3 , wherein step s 1 , framed in dashed lines , is typically carried out manually by the operator but only when a crosslinking agent is to be used . in so doing , the laser 4 is used for illumination during the detection phase as well as for the crosslinking of collagen fibers of the cornea 2 during the immediately following treatment phase . in case treatment is to be performed exclusively , steps s 2 and s 3 , framed in dashed lines , and sub - step s 5 , framed in dashed lines , are not executed . first , the patient &# 39 ; s eye 3 is immobilized , for example , suctioned by means of negative pressure at a contact glass device ( step s 2 ). the head of the patient may be immobilized in addition . the gaze of the patient can be kept as constant as possible by means of a suitable target . the illumination light is guided over the cornea 2 along an adjustable , continuous , three - dimensional scanning curve or scanning pattern at illumination laser power with a variable pulse frequency and detection light is received ( step s 3 ). in so doing , the pulse frequency is adjusted as a function of the speed of the scanning movement in such a way that a pulse frequency during a slower scanning movement is lower than during a faster scanning movement . the backscattered detection light is associated segment by segment or point by point with individual points of the scanning curve . successive scanning points in all spatial coordinates are distinguished through the continuity of the scanning curve . in an advantageous manner , respective darkfield values which are determined in a separate calibration pass are subtracted from the detected signal values . existing cuts are identified from the intensities associated with the scanning points and the shape and position thereof are reconstructed ( step s 4 ). to this end , for example , scanning points whose intensity exceeds an intensity threshold which is predefined or predefinable by the operator are determined as reference points of the cut . an assumed model of the cut , or one that is known from a previous treatment , is fitted to the three - dimensional coordinates of the determined reference points of the old cut by a best - fit calculation in order to make all of the coordinates of the old cut available as a basis for the crosslinking of the cut . subsequently , irradiation control data are determined ( step s 5 ). the irradiation control data include , for example , control signals for the axes of the scanner unit 7 or for the internal z focusing and for the laser beam source and power modulator 16 . the irradiation control data are determined , for example , from defaults which are queried from a database via a software interface or by the operator via a graphical user interface . in particular , topographical data , wavefront data , data of an ultrasound measurement or oct measurements of the cornea 2 to be treated , the spatial information concerning a keratoconus , existing cuts and / or other areas to be crosslinked are taken into account when determining the irradiation control data . insofar as existing cuts are identified , the data obtained in so doing can likewise be used in determining the irradiation control data in order to determine the sites at which crosslinking is to be carried out . for example , the sites to be irradiated along the cut can be calculated . immediately afterwards , the irradiation is carried out ( step s 6 ) based on the irradiation control data at a laser power having exclusively a photochemical effect . in so doing , the control unit 14 adjusts the beam attenuator 15 to the switch position for radiation power having at most a photochemical effect and moves the deflection units 7 and 8 in accordance with the irradiation data . at every site to be irradiated , it controls the power modulator 16 according to the irradiation control data so as to introduce the determined radiation energy into the cornea 2 . on the basis of the infrared radiation of the laser 4 , monochromatic crosslinking , for example , is carried out by multiphoton absorption corresponding to fig2 c . finally , the immobilization of the eye 3 is canceled ( step s 7 ). through use of adapted scanning curves ( scanning patterns ), for example , in the form of spatially extended lissajous figures , i . e ., two overlapped , particularly harmonic oscillations such as spatially offset figure - eights , it is possible to measure existing cuts in a short time , for example , within at most 30 seconds , which reduces movement inaccuracies on the one hand and leads to a higher acceptance on the part of the patient on the other hand . other exemplary scanning shapes ( not illustrated ) may include : two crossed rectangles in space ; two cylinder surfaces ; a cylindrical body with cross section in the shape of an eight or a four ; a plurality of scans along one - dimensional lines . it is also possible to raster scan the volume of a cylinder or cube . the volumes or surfaces can be scanned continuously or only partially , i . e ., with gaps between the individual scanning points . accordingly , greater distances may occur between individual lines . it is possible to make allowances for particulars of the patient &# 39 ; s eye 3 , for example , the sites to be crosslinked or the required crosslinking efficiency , etc ., by adapting the scanning curves , varying the distances between sites ( spots ), varying the pulse energy and varying the pulse frequency , among others . another laser device i for bichromatic crosslinking is shown schematically in fig4 . in a frequency multiplier 18 , for example , a quadruplet ( fhg ), the infrared beam ( first harmonic h 1 ) of the pulsed femtosecond solid state laser 1 is split spatially and spectrally into two beams : into the second or third harmonic h 2 / 3 in a green or blue wavelength region on one hand and into the fourth harmonic h 4 in the ultraviolet wavelength region on the other hand . beam h 2 / 3 with the longer - wave green / blue wavelength range is guided along a delay line 19 and recombined with the other beam h 4 at a beam recombiner 20 . both beams are then guided together in the same focus volume in the cornea 2 . the delay line 18 can be adjusted to different delays between 0 ps and 10 ps , for example , by mirrors which are displaceable along the optical axis . the green or blue pulses reach the cornea 2 later than the ultraviolet pulse by this amount of delay . instead of a delay line 19 , a coaxial - dispersive element can be used . in all of the embodiment forms , a device for tracking movements of the eye ( eye tracker ) can be used in order to carry out corrections in the irradiation control data . nanosecond pulses or picosecond pulses , for example , can be used instead of light pulses of femtosecond lasers . insofar as crosslinking agents are used , other light sources and , in particular , continuous wave irradiation ( cw ) are also possible during the scanning of different sites of the cornea 2 . while this invention has been described in conjunction with the specific embodiments outlined above , it is evident that many alternatives , modifications , and variations will be apparent to those skilled in the art . accordingly , the preferred embodiments of the invention as set forth above are intended to be illustrative , not limiting . various changes may be made without departing from the spirit and scope of the inventions as defined in the following claims .