UV-LASER-BASED SYSTEM FOR CORRECTING VISION DISORDERS

Abstract

A focusing optical system for a UVL-LVC system with a UV laser source and a scanning system that focuses a laser in a focal field and a lens assembly with a convergent focal field. The invention further includes a planning unit that generates planning data for a UVL-LNC system with a UV laser source, a scanning system, a focusing optical system, and a control unit for controlling the UVL-LVC system while taking into consideration planning data, wherein the planning unit takes into consideration geometry losses, Fresnel losses, and/or a spatial extension of laser radiation on a working surface while calculating the planning data, and the planning unit has an interface that provides the planning data. Finally, the invention includes a UVL-LVC system with a UV laser source, a scanning system, a focusing optical system according to the invention, a planning unit according to the invention, and a control unit.

Claims

1.-13. (canceled)

14. A focusing optical unit for a UV laser-based system for vision correction (UVL-LVC system), the UVL-LVC system having a UV laser source that provides laser radiation; and a scanning system that laterally scans the laser radiation in x- and y-directions: wherein the focusing optical unit is configured to focus the laser radiation in a focal field; and wherein the focusing optical unit comprises a first lens arrangement which is configured to provide a convergent focal field.

15. The focusing optical unit as claimed in claim 14, wherein the scanning system that laterally scans the laser radiation in the x- and y-directions also scans the laser radiation in a z-direction.

16. The focusing optical unit as claimed in claim 14, wherein the convergent focal field has a focal field diameter selected from a group consisting of at least 6 mm, at least 8 mm and at least 10 mm.

17. The focusing optical unit as claimed in claim 14, wherein each location in the convergent focal field has a local center of curvature on a side facing away from the focusing optical unit.

18. The focusing optical unit as claimed in claim 17, wherein each location in the focal field has a focal field curvature selected from a group consisting of a radius RS ranging from 8 mm to 50 mm, from 10 mm to 30 mm and from 12 mm to 20 mm.

19. A focusing optical unit for a UV laser-based system for vision correction (UVL-LVC system), the focusing optical unit comprising: a UV laser source that provides laser radiation; and a scanning system that laterally scans the laser radiation in x- and y-directions; wherein the focusing optical unit comprises a lens arrangement that provides perpendicular incidence of laser radiation on a curved surface, wherein each location on the curved surface has a local center of curvature on a side facing away from the focusing optical unit.

20. The focusing optical unit as claimed in claim 19, wherein the curved surface has a diameter selected from a group consisting of at least 6 mm, at least 8 mm and at least 10 mm.

21. The focusing optical unit as claimed in claim 19, wherein the curved surface has a surface curvature with a radius R.sub.F selected from a group consisting of a range from 8 mm to 50 mm, a range from 10 mm to 30 mm and a range from12 mm to 20 mm.

22. The focusing optical unit as claimed in claim 14, configured to have a working distance (Δ) in a range from 20 mm to 50 mm; an optical aperture selected from a group consisting of greater than 40 mm, greater than 50 mm, and greater than or equal to 60 mm, or a combination of the foregoing.

23. The focusing optical unit as claimed in claim 14, comprising a first lens which has a first lens material with a first refractive index and a first Abbe number and comprising a second lens which has a second lens material with a second refractive index and a second Abbe number, with the first refractive index differing from the second refractive index and the first Abbe number differing from the second Abbe number.

24. The focusing optical unit as claimed in claim 23, wherein the first lens has a negative optical power, the second lens has a positive optical power and the first refractive index is greater than the second refractive index.

25. The focusing optical unit as claimed in claim 14, wherein the focusing optical unit has at least two lens groups along a beam path with a non-imaging optical element being arranged therebetween.

26. A planning unit for generating planning data for a UV laser-based system for vision correction (UVL-LVC system), the UVL-LVC system comprising: a UV laser source that provides laser radiation; a scanning system that laterally scans the laser radiation in x- and y-directions; a focusing optical unit that directs the laser radiation to a work surface; and a control unit that controls the UVL-LVC system that is configured to take planning data into consideration; wherein the planning unit is configured to take account of: geometry losses, Fresnel losses, a spatial extent of the laser radiation in the work surface or a combination of the foregoing when calculating the planning data; and wherein the planning unit has an interface operably coupled to the control unit, by which the planning data can be made available to the control unit wherein the focusing optical unit: focuses the laser radiation in a focal field; and wherein the focusing optical unit further comprises a first lens arrangement which is configured to provide a convergent focal field; or wherein the focusing optical unit comprises a second lens arrangement that provides perpendicular incidence of laser radiation on a curved surface, wherein each location on the curved surface has a local center of curvature on a side facing away from the focusing optical unit.

27. (canceled)

28. The planning unit as claimed in claim 26, wherein the focusing optical unit includes the first lens arrangement configured to provide the convergent focal field; and wherein the convergent focal field has a focal field diameter selected from a group consisting of at least 6 mm, at least 8 mm and at least 10 mm; or wherein each location in the convergent focal field has a local center of curvature on a side facing away from the focusing optical unit; or wherein each location in the focal field has a focal field curvature selected from a group consisting of a radius RS ranging from 8 mm to 50 mm, from 10 mm to 30 mm and from 12 mm to 20 mm.

29. (canceled)

30. (canceled)

31. (canceled)

32. The planning unit as claimed in claim 26, wherein the focusing optical unit includes the second lens arrangement that provides perpendicular incidence of laser radiation on the curved surface; and wherein the curved surface has a diameter selected from a group consisting of at least 6 mm, at least 8 mm and at least 10 mm; or wherein the curved surface has a surface curvature with a radius R.sub.F selected from a group consisting of a range from 8 mm to 50 mm, a range from 10 mm to 30 mm and a range from12 mm to 20 mm; or wherein the planning unit has a working distance (A) in a range from 20 mm to 50 mm, or wherein the planning unit has an optical aperture selected from a group consisting of greater than 40 mm, greater than 50 mm, and greater than or equal to 60 mm; or wherein the planning unit comprises a first lens which has a first lens material with a first refractive index and a first Abbe number and comprising a second lens which has a second lens material with a second refractive index and a second Abbe number, with the first refractive index differing from the second refractive index and the first Abbe number differing from the second Abbe number; or wherein the focusing optical unit has at least two lens groups along a beam path with a non-imaging optical element being arranged therebetween; or a combination of the foregoing.

33. (canceled)

34. (canceled)

35. (canceled)

36. (canceled)

37. (canceled)

38. A UV laser-based system for vision correction (UVL-LVC system), comprising a focusing optical unit for a UV laser-based system for vision correction (UVL-LVC system) as claimed in claim 14; and a planning unit for generating planning data for a UV laser-based system for vision correction (UVL-LVC system) comprising: a control unit that controls the UVL-LVC system that is configured to take planning data into consideration; wherein the planning unit is configured to take account of geometry losses, Fresnel losses, a spatial extent of the laser radiation in the work surface or a combination of the foregoing when calculating the planning data; and wherein the planning unit has an interface operably coupled to the control unit, by which the planning data can be made available to the control unit.

39. The focusing optical unit as claimed in claim 14, wherein the focusing optical unit is configured to produce round laser spots having a full width at half maximum (FWHM) in a range from 0.3 to 0.8 mm in the focal field with a deviation chosen from a group consisting of less than 20% and less than 10%.

40. The focusing optical unit as claimed in claim 14, wherein the first lens arrangement which is configured to provide a convergent focal field is further configured to take into account a difference radius of curvature (R.sub.Δ) which represents an effective corneal curvature having effective corneal curvature values ranging from RA of 15 mm to R.sub.Δ of 450 mm for focal field radii of curvature of between 8 mm and 16 mm thereby facilitating an improved fluence loss function.

41. The focusing optical unit as claimed in claim 19, wherein the lens arrangement that provides perpendicular incidence of laser radiation on the curved surface is further configured such that the incidence of the laser radiation on the curved surface has an angle with a normal to the curved surface at a location of incidence that is selected from a group consisting of no more than 10 degrees, no more than five degrees and no more than 2 degrees.

42. The focusing optical unit as claimed in claim 19, wherein the lens arrangement that provides perpendicular incidence of laser radiation on the curved surface is further configured such that the incidence of the laser radiation on the curved surface occurs at a spot size in a range selected from a group consisting of between 0.3 mm to 1.5 mm and between 0.5 mm to 1.0 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0107] The invention is explained in greater detail below for example with reference to the accompanying drawings, which also disclose features essential to the invention. In the drawing:

[0108] FIG. 1 is a schematic representation of the geometry on the eye when the patient fixates in a wrong direction;

[0109] FIGS. 2a, 2b and 2c are schematic representations of the ablation geometry for UVL-LVC systems according to the prior art (2a and 2b) and for a focusing optical unit according to the invention (2c);

[0110] FIG. 3 depicts an example embodiment of a focusing optical unit;

[0111] FIG. 4 is a schematic representation for determining an effective corneal radius;

[0112] FIG. 5 is a schematic representation for elucidating the alignment of the focusing optical unit according to the invention with respect to the eye;

[0113] FIG. 6 is a schematic representation of the principle of geometry losses;

[0114] FIG. 7 is a graphical representation of normalized fluence losses for a system according to the prior art and for a focusing optical unit according to the invention;

[0115] FIG. 8 is a graphical representation of the percentage deviation of a normalized effective etch rate from a normalized target etch rate for different model approaches;

[0116] FIG. 9 depicts a basic arrangement of the optical beam path in an exemplary embodiment of a UVL-LVC system;

[0117] FIG. 10 depicts a basic arrangement of the optical beam path in a variant of a UVL-LVC system; and

[0118] FIG. 11 is a schematic representation of a UVL-LVC system.

DETAILED DESCRIPTION

[0119] FIG. 1 shows a schematic representation of the geometry on the eye 110 when the patient fixates in a “wrong” direction. In the example shown, the eye 110 of the patient is not gazing at the center of a fixation cloud 120. In this case, an ablation profile 150 is not applied correctly along the necessary treatment axis, for example along a visual axis 130. The visual axis 130 is defined by the ophthalmic pole OP and the fixation of the patient. Hence, the ablation profile 150 is not applied at right angles to the visual axis 130. The relationships are depicted with much exaggeration in FIG. 1. FIG. 1 furthermore shows a fovea 140 of the eye, a crystalline lens 145, a scanner 160 (rotatable, represented by the bent arrow) of the UVL-LVC system for the lateral deflection of laser radiation 170, an axis of symmetry 180 (e.g., optical axis) of the eye 110 and an optical axis 190 of the UVL-LVC system.

[0120] An ablation profile 150 is not applied at the correct angle (i.e., with the center not on the surface normal, that is to say perpendicular to the visual axis 130) as a result of the “wrong” fixation of the patient's eye 110. This may occur if the patient preferably fixates in a largely fixed, but “wrong” direction, that is to say for example permanently gazes in a fixed direction that does not correspond to the center of the “fixation cloud” 120. This may occur should the patient, depending on refraction deficit and treatment duration, no longer be able to see the fixation target in focus during the operation. A prismatic correction error (tip/tilt) arises on account of the wrong fixation.

[0121] FIGS. 2a and 2b represent ablation geometries for optical systems according to the prior art. In this case, FIG. 2a shows the ablation geometry for a first optical system of a UVL-LVC system according to the prior art, which is characterized in that there is telecentric focusing of the ablation pulses. Beams 250, 252, 254 for a central position in a work surface, for a first edge position and for a second edge position, respectively, are shown. In this case, the beams 250, 252, 254 of the laser radiation are incident on a lens 220 of the focusing optical unit according to the prior art and are focused at (or near to) the corresponding positions on the eye 210 by this lens 220. In this case, the eye 210 is at a working distance Δ from the lens 220. The focusing optical unit according to the prior art shown here is telecentric on the image side (on the side of the eye), that is to say the chief rays of the beams 250, 252, 254 run in parallel between lens 220 and eye 210.

[0122] FIG. 2b shows the ablation geometry for a second optical system of a UVL-LVC system according to the prior art, which is characterized in that there is divergent focusing of the ablation pulses. Convergent laser light incident on a scanner 230 is shown, said laser light—depending on the scanner position—being focused at different positions on (or near to) the eye 210. This is shown for three positions with beams 250, 252, 254 for a central position in the work surface, for a first edge position in the work surface and for a second edge position in the work surface, respectively. The beams 250, 252, 254 are aligned divergently with respect to one another (with respect to the UVL-LVC system) between scanner 230 and eye 210. The eye 210 is at a working distance Δ from the scanner 230.

[0123] FIG. 2c shows the principle of the ablation geometry for a first variant of the focusing optical unit according to the invention. The latter is characterized in that convergent focusing of the ablation pulses is provided. The beams 250, 252, 256 are incident on the first lens arrangement 240 of the focusing optical unit when diverging from one another; in the process, the individual beams 250, 252, 256 are intrinsically parallel. As a result of the first lens arrangement 240, the beams 250, 252, 256 are directed convergently to one another in the direction of the focal area 260 and are in each case focused there. In this case, beam 250 corresponds to a central position in the focal field 260, beam 252 corresponds to an edge position in the focal field 260 and beam 256 corresponds to a position in the focal field 260 that is between the central position and the edge position. The schematically shown lens arrangement 240 contains further imaging elements and is only represented by an individual lens for the purposes of clarifying the principle.

[0124] Furthermore, the focal area 260 has a radius of curvature R.sub.S in the example shown. This radius of curvature has the same sign as the corneal curvature with the radius of curvature R.sub.C (“scanning radius of curvature”). Additionally, the two radii of curvature R.sub.C and R.sub.S have almost the same magnitude such that the focal area 260 extends close to the cornea 215.

[0125] The focusing optical unit shown in FIG. 2c likewise corresponds to a second variant of the focusing optical unit according to the invention. Here, the curved surface is identical to the curved focal area 260 in this example; the radius R.sub.F of the surface curvature is identical in this case to the radius of the focal field curvature R.sub.S. The chief rays of the beams 250, 254, 256 are directed at an angle to the curved surface by the focusing optical unit, the angle being less than 10° in relation to the surface normal at the location of impingement by the laser radiation. This is realized by way of the second lens arrangement 240.

[0126] In FIG. 3, a lens section is depicted for an exemplary embodiment of a focusing optical unit 300 (in accordance with both variants), which is formed from spherical lenses. Laser radiation enters the focusing optical unit 300 from the side facing away from the eye 310. Plotted here are three (intrinsically approximately parallel) beams 350, 352, 356 for a central position on the eye 310, an edge position and a position between the central position and the edge position, respectively. These beams 350, 352, 356 are diverging from one another when incident on the focusing optical unit 300. In the example, the divergence is provided by way of a scanner (not plotted). The first lens arrangement 340 of the (first variant of the) focusing optical unit 300 provides the convergent focal field (not plotted) at a working distance Δ. In this exemplary embodiment, the focal field is curved (with a radius R.sub.S=R.sub.C=12 mm). In the example shown, the first lens arrangement 340 is identical to the second lens arrangement (according to the second variant) and the curved surface is also identical to the focal field (with R.sub.F=R.sub.S). The angle of incidence of the chief rays deviates by less than 10° from a perpendicular incidence on the curved surface for all beams 350, 352, 356.

[0127] The focusing optical unit shown here is particularly compact and has an installation size (length) of 54 mm in the case of an optical diameter of 56 mm, and provides a working distance of Δ=30 mm in the process.

[0128] FIG. 4 shows a schematic illustration for determining an effective corneal radius for a curved focal field. Shown is an eye 410 having a cornea 415 with a corneal radius of curvature R.sub.C. The focal field 460 provided by the focusing optical unit (according to the first variant; not depicted here) has a focal field radius of curvature R.sub.S (“scanning radius of curvature”), where R.sub.S>R.sub.C applies.

[0129] According to the sphere model, z(R,r)=r.sup.2/(R+√{square root over (R.sup.2−r.sup.2)}) applies. In this case, R describes the radius of a sphere, z describes the heights with respect to a tangent to this sphere, and r describes the distance along the tangent from the point of contact between circle and tangent.

[0130] The right-hand side of FIG. 4 shows the geometric conditions once again, in magnified fashion. For a difference height Δz, the following applies:

Δz(R.sub.C, R.sub.S, r)=z(R.sub.C, r)−z(R.sub.S, r)=z(R.sub.Δ, r)

[0131] In this case, z.sub.C:=z(R.sub.C, r) and z.sub.S:=z(R.sub.S, r). This difference height Δz is intended to be determined by a difference radius of curvature R.sub.Δ. This corresponds to an “effective” corneal curvature for light incident from the z-direction, for example like for solutions according to the prior art (see also FIG. 2a). As a result of the difference calculation, the cornea is “bent” upward—figuratively speaking—by the focal field radius of curvature, then allowing the calculation of the fluence loss to be carried out in a simplified manner, that is to say on the basis of an “effective” corneal curvature.

[0132] Using the aforementioned formula for a sphere model, the following arises from the equation for the difference height Δz:

[00001]$\frac{1}{R_{\Delta }+\sqrt{R_{\Delta }^2-r^2}}=\frac{1}{R_C+\sqrt{R_C^2-r^2}}-\frac{1}{R_S+\sqrt{R_S^2-r^2}}$

[0133] This relationship for determining R.sub.Δ applies to all r (in particular to r=0). This results in:

[00002]$\frac{1}{R_{\Delta }}=\frac{1}{R_C}-\frac{1}{R_S}$

[0134] Consequently, the following arises for the “effective” corneal radius of curvature:

[00003]$R_{\Delta }=\frac{R_C.Math.R_S}{R_S-R_C}$

[0135] Consequently, with a typical corneal radius of curvature of R.sub.C=7.86 mm, values of approximately R.sub.Δ≈450 mm to approximately R.sub.Δ≈15 mm arise for the effective corneal curvature for focal field radii of curvature with values between approximately 8 mm and approximately 16 mm. In these regions the advantage of an improved fluence loss function is particularly clear since these effective radii are significantly larger than the typical radius of curvature of the cornea, and so an impingement of the cornea with laser light is significantly closer to perpendicular incidence than in the prior art.

[0136] Even though the observations shown here were made for a first variant of the focusing optical unit, they also apply to a focusing optical unit according to the second variant. In this case, the curved surface is identical to the focal field 460 (with R.sub.F=R.sub.S).

[0137] FIG. 5 depicts a schematic illustration for clarifying the effect of decentrations of the focusing optical unit (according to the first variant) according to the invention with respect to the eye. To demonstrate this, a non-coaxial alignment of a patient when fixating a fixation target 520 is shown to the left in FIG. 5. Although the target 250 is fixated (it should be observed that a collimated beam 525 from the target 520 is used in this example), the patient is not aligned coaxially with the optical system. A correct centration according to the CSCLR condition would correspond to an alignment of the eye 510 with respect to the directed (collimated) beam 525 of the target 520 with Δ.sub.LS=0 mm (aligned with the “corneal vertex” CV). The example of FIG. 5 plots a shift of a system axis 505 (optical axis) of the focusing optical unit according to the invention of Δ.sub.LS=2 mm with respect to the directed laser beam 525 for a centration in accordance with the CSCLR condition. Furthermore, a focal field radius of curvature R.sub.S of 12 mm was assumed. In this example, the system axis 505 arises by way of a ray guided by the scanners of the UVL-LVC system (not plotted), for example by way of an alignment beam in the zero position of the scanners. The geometric considerations plotted to the right in FIG. 5 serve for the estimation of the angle of incidence α.sub.MB of a laser ray along the system axis 505 of the focusing optical unit on the cornea 515 for a focusing optical unit according to the invention, as a function of the pupil coordinate r.sub.MB≈r.sub.SdT, where r.sub.MB and r.sub.SdT describe the shift of the system axis 505 with respect to the centration in accordance with the CSCLR condition for a focusing optical unit according to the invention and a focusing optical unit according to the prior art, respectively. The following holds true:

[00004]$\gamma ={\sin }^{-1}\left(\frac{r_{MB}}{R_S}\right)\approx {\sin }^{-1}\left(\frac{r_{SdT}}{R_S}\right)$

[0138] In this case, γ is the angle between an incident laser ray for the focusing optical unit according to the invention with a convergent and curved focal field with respect to a focusing optical unit according to the prior art with telecentric focusing on a plane focal field. The following arises for the angle of incidence α.sub.SdT according to the prior art:

[00005]${\alpha }_{SdT}={\sin }^{-1}\left(\frac{r_{SdT}}{R_C}\right)$

[0139] By contrast, the following applies to the focusing optical unit according to the invention:

α.sub.MB≈α.sub.SdT−γ

[0140] Then, the angle of reflection 2α.sub.MB+γ arises for the reflected laser ray 590 in the case of a lateral displacement Δ.sub.LS. In this case, Δ.sub.LS is used in the calculation for the pupil coordinate r.sub.SdT(≈r.sub.MB). In this case, the ophthalmic pole (OP) and the corneal vertex (CV) are equated to one another WLOG. In this example, a reflection angle of approximately 2α.sub.MB+γ=20° arises for an offset of Δ.sub.LS=2 mm. This angle is detected without problems by the focusing optical unit and can be processed in the UVL-LVC system.

[0141] The axis of symmetry 580 of the eye 510 is also depicted in FIG. 5. Attention is drawn to the fact that the representation is simplified in relation to the corneal shape.

[0142] Even though the observations shown here were made for a first variant of the focusing optical unit, they also apply to a focusing optical unit according to the second variant. In this case, the curved surface is identical to the curved focal field (with R.sub.F=R.sub.S).

[0143] In the discussed configuration, the focusing optical unit (in both variants) is therefore particularly well suited to identify reflections such as the first Purkinje image and/or the vertex, and hence advantageously allows an improvement in the centration of the patient's eye with respect to the UVL-LVC system.

[0144] FIG. 6 shows a schematic representation of the principle of geometry losses. In this case, the geometry for the prior art is shown to the left in FIG. 6 (reference signs are marked by an asterisk “*”) while the right-hand side depicts the conditions for a focusing optical unit (according to both variants) according to the invention (with reference signs without an asterisk). The pulse ablation shape 620, 620* (corresponds to the ablation-effective fluence distribution of the radiated-in ablation laser pulse on a plane perpendicular to the direction of incidence) is deformed by the geometry of the irradiation on the cornea 615 to form the projected pulse ablation shape 630, 630* (pulse ablation footprint on cornea). For a geometry according to the prior art, this also changes the fluence distribution on the cornea 615 with respect to the radiated-in pulse ablation shape 620*. This is made clear by the hatching on the projected pulse ablation shape 630*. In this case, a constant fluence distribution was assumed for the pulse ablation shape 620, 620* for a better visualization. For the geometry in the case of the focusing optical unit according to the invention, the shape of the radiated-in pulse ablation shape 620 largely corresponds to the shape of the projected pulse ablation shape 630; as a result, the fluence distribution in the projected pulse ablation shape 630 remains largely constant. This is made possible by the convergent focal field according to the invention or by the perpendicular incidence according to the invention on the curved surface.

[0145] In UVL-LVC systems, laser pulses are typically designed approximately as low-order supergaussians, from which the pulse ablation shape 620, 620* can then be calculated. By way of example, the latter can be implemented from a given pulse shape with the aid of the blow-off model. The geometry loss is modeled as a cosine function for an infinitesimal surface element dA 625, 625*. The following applies: cos(α)=dA/dA′, with the angle of incidence a (angle of incidence with respect to the local surface normal on the cornea 615) and the projected infinitesimal surface element dA′635, 635*. In comparison with solutions according to the prior art (to the left in FIG. 6), the geometry losses are reduced for the focusing optical unit according to the invention (to the right in FIG. 6) on account of the small angle of incidence α. Moreover, the pulse ablation footprint on cornea 635 only deviates slightly from the radiated-in pulse ablation shape 625.

[0146] FIG. 7 shows normalized fluence losses for a system according to the prior art (left-hand side) according to an arrangement as depicted in FIG. 2b and for a focusing optical unit according to the invention (right-hand side, first variant). A focal field curvature with a radius R.sub.S of 12 mm and a working distance Δ of 40 mm was assumed for the focusing optical unit according to the invention. The plotted points mark typical work points during the ablation for a typical corneal curvature of R.sub.C=7.5 mm and in the case of a pupil radius of 4 mm (transition from the optical zone to the transition zone).

[0147] The two upper graphs in FIG. 7 show the normalized fluence losses (“Normalized effective Fluence”) as a function of a pupil radius (“Pupil Radius”) in millimeters for different radii of curvature of the cornea from R.sub.C=6 mm to 8.5 mm (in increments of 0.5 mm) on account of geometry losses (“geometry loss”). It is possible to identify that the geometry losses are significant for solutions according to the prior art. They are approximately 15% at the chosen work point. By contrast, the corresponding losses for the focusing optical unit according to the invention are only approximately 1%. Moreover, a clear dependence on the pupil coordinate (pupil radius) is evident in the prior art. The losses increase significantly in the outer regions of the pupil.

[0148] The two lower graphs in FIG. 7 show the normalized fluence losses (“Normalized effective Fluence”) as a function of a pupil radius (“Pupil Radius”) in millimeters on account of Fresnel losses (“Fresnel loss”). It is possible to identify that, apart from a constant component of approximately 4 percent, the Fresnel losses for unpolarized light are only a small component of a variation over the pupil (in the prior art, left) and have practically no influence in the solution according to the invention (right). However, there is a significant dependence on the pupil radius in the case of polarized light in the prior art. This disadvantage is overcome for the solution according to the prior art. The calculations were carried out using a refractive index of approximately 1.5 for the stroma; the calculations provide no fundamentally different results in the case of a more realistic value of n=1.377 for the stroma. The constant component would reduce to approximately 3% therewith.

[0149] Even though the observations shown here were made for a first variant of the focusing optical unit, they also apply to a focusing optical unit according to the second variant. In this case, the curved surface is identical to the curved focal field (with R.sub.F=R.sub.S).

[0150] FIG. 8 graphically depicts the percentage deviation of a normalized effective etch rate from the normalized target etch rate (target ablation, also referred to as “Deviation normalized etch rate”; specifications in percent) for a focusing optical unit according to the prior art (FO.sub.SdT) and a focusing optical unit according to the invention (FO, first variant) for different model approaches for a laser pulse fluence loss compensation function (FLC: fluence loss compensation) as a function of the (preoperative) radius of curvature of the cornea or of the stroma (“Corneal radius of curvature (mm)”). In this case, the shown calculations resort to the results of the explanations in relation to the geometry and Fresnel losses. The influence thereof and the differences in an energy correction for a solution according to the prior art (as shown in FIG. 2b) and a solution using the focusing optical unit according to the invention were examined on the basis of model calculations. An effective ablation rate was calculated on the basis of these calculations. The modeling is based on a simplified spherical corneal model, spherical corrections and the “blow-off” model, to simplify the understanding.

[0151] The calculations apply to the laser pulse maximum fluence (“peak fluence”). A spatial extent of the laser pulse (or of the laser radiation) was not taken into account for the calculation of the geometry and Fresnel losses. This is an approximation which improves as the pulse diameter decreases (ratio of pulse diameter to the diameter of the optical zone). Attention is drawn to the fact that taking account of the relationships shown below once again benefits the solution according to the invention. As representative values in all cases, 160 mJ/cm.sup.2 was taken for the “peak fluence” (F.sub.0) and 48 mJ/cm.sup.2 was taken for the stroma threshold ablation fluence (“threshold fluence”). The refractive index of the stroma was taken to be n=1.377.

[0152] FIG. 8 depicts the results of the modelings. The percentage deviation of the “etch rate” from the target etch rate as a function of the preoperative corneal radius of curvature (“Corneal radius of curvature”) is considered. The deviation of the target etch rate (Target “etch rate”) itself is naturally zero, which defines the zero line.

[0153] A spherical 5 D (dpt) correction in the case of a 4 mm pupil radius was considered as a case study. Attention is drawn to the fact that optical zones are usually located up to 6 mm, and often therebeyond, and, with transition zones of 1.5 mm, even lead to pupil radius coordinates closer to 4.5 mm (9 mm overall ablation diameter). Typically, hyperopic eyes (labeled as “more hyperopic like eyes”) exhibit on average larger corneal radii of curvature and require steepening, that is to say a reduction, of the corneal radii of curvature for correcting the visual defect (labeled by “hyperopia correction”). The opposite applies to myopic eyes (labeled “more myopic like eyes” and “myopia correction”).

[0154] The curves in the diagram of FIG. 8 arise as a result of the fact that the difference in the fluence loss-compensated etch rates from preoperative to postoperative is determined on the basis of the radii of curvature (given preoperatively, calculated postoperatively on the basis of the spherical correction). In this case, the actual fluence loss for the preoperative and postoperative states is initially calculated on the basis of the respective radii of curvature (“physically correctly”). Then the compensation of the loss is calculated. This is based on the preoperative radius of curvature (UVL-LVC system with a focusing optical unit according to the invention, labeled as “FO (with FLC)”) or on a fixed radius of curvature of 7.86 mm (labeled as “FO.sub.SdT (with FLC.sub.SdT)” for a UVL-LVC system with a focusing optical unit according to the prior art (FO.sub.SdT)).

[0155] The line labeled “FO.sub.SdT (with FLC.sub.SdT)” represents the deviation of the effective etch rate from the normalized target etch rate for a UVL-LVC system with a fluence loss compensation according to the prior art. This emerges from the calculated loss function and a typical compensation function according to the prior art, which does not consider the Fresnel losses but contains the cosine-dependent projection of the surface elements (cos(a) in FIG. 6) on the basis of a fixed corneal radius of curvature R.sub.C of 7.86 mm.

[0156] The line labeled “FO.sub.SdT (with FLC.sub.sdT+Fresnel)” represents the deviation for a system according to the prior art with a fluence loss compensation according to the prior art if the Fresnel losses are additionally considered. Essentially, it is possible to identify a shift of the function to the left, that is to say to smaller corneal radii of curvature (or “upward”, depending on the point of view). This is due to the fact that the Fresnel losses for unpolarized excimer laser pulses vary only slightly with the angle of incidence (cf. work point in FIG. 7).

[0157] The line labeled “FO (with FLC)” represents the deviation of the effective etch rate from the normalized target etch rate for a UVL-LVC system with a focusing optical unit according to the invention (FO) and a compensation according to the invention (FLC). The latter considers the optical geometry (in this case, focal field curvatures R.sub.S of 12 mm and a working distance Δ of 40 mm) of the focusing optical unit according to the invention for the compensation function. The curve once again arises from the calculated loss function and the compensation function according to the invention. The latter also considers the Fresnel losses in addition to the geometry losses (which are low in comparison with FO.sub.SdT) and uses the preoperative corneal radius of curvature for the compensation. The variation of this function over the corneal radii of curvature is significantly reduced in relation to a focusing optical unit according to the prior art. This leads to a significantly improved predictability or to a reduction in the variation of the refractive result, as will still be explained below.

[0158] The line labeled “FO (with FLC.sub.SdT)” represents the deviation of the effective etch rate from the normalized target etch rate for a UVL-LVC system with a focusing optical unit according to the invention (FO), which arises if use were to be made of the above-described compensation function according to the prior art (FLC.sub.SdT). Even in this case, the deviations of the effective etch rates for the arrangement according to the invention would still be approximately one order of magnitude smaller than in the case of the prior art. This is substantially based on the above-described “more good-natured” curve of the geometry losses over the pupil coordinates (see FIG. 7). An improved variant of this compensation (which would consider the accumulation points of the radii of curvature for hyperopic and myopic eyes) could for example be used by physicians who do not determine preoperative keratometry or do not use the latter.

[0159] Finally, the line labeled “FO.sub.SdT (with FLC)” represents the deviation of the effective etch rate from the normalized target etch rate for a UVL-LVC system with a focusing optical unit according to the prior art (FO.sub.SdT) if the compensation function according to the invention FLC were to be applied. The profile of the curve shows that the compensation function according to the invention FLC already leads to significant improvement in the predictability of the refractive result.

[0160] Even though the observations shown here were made for a first variant of the focusing optical unit, they also apply to a focusing optical unit according to the second variant. In this case, the curved surface is identical to the curved focal field (with R.sub.F=R.sub.S).

[0161] The intention is now to explain why the concept according to the invention is particularly advantageous in relation to an improved predictability of the refractive results.

[0162] The curve of the percentage deviations of the etch rates for a UVL-LVC system with a focusing optical unit according to the prior art, shown in FIG. 8, could for example be compensated by nomograms. As a rule, nomograms are created by a linear regression of the refractive correction results (attempted vs. achieved) in comparison with the correction target, and are intended to minimize these differences. As a result, the nomograms do not contain any dependence on the preoperative keratometry (“K-values”), and a mean keratometry value for which the nomogram correction is optimal arises. If there now is a treatment of a patient with a keratometry that deviates from this mean value, the obtained nomogram correction does not fit perfectly to the corresponding etch rate deviation (to be compensated by the nomogram). That is to say, a non-optimal compensation function is applied.

[0163] For prior art systems, the keratometry can now be taken into account in the nomogram as follows: Let the mean value of the keratometry in the considered hyperopia group for the nomogram correction be R.sub.C=8.25 mm. If a hyperopic patient with a keratometry deviating therefrom and assumed to be R.sub.C=7.25 mm is now treated, it is possible to read the difference in the ablation rate that would not be corrected from the diagram in FIG. 8, simply as the difference in the deviation (ordinate) in percent between these two radii of curvature. A miscorrection of approximately 5% (for a 5 diopter sphere correction in the case of a pupil radius of 4 mm) would arise for this case in solutions according to the prior art. Thus, the peripheral pupil regions of the correction ablation profile and the transition zone, in particular, would be represented incorrectly. In the case of assumed 14 μm (maximum etch depth) per diopter, this would correspond to approximately 3.5 μm. This deviation is presented both as a spherical aberration and a refractive miscorrection of approximately 0.25 dpt. Even though this case initially appears hypothetical, it nevertheless is not unrealistic and would become apparent as a deviation in the prediction in “attempted vs. achieved” diagrams.

[0164] The non-optimal energy compensation, which quite fundamentally is due to the ablation geometry of FIGS. 2a and 2b of laser systems according to the prior art, thus leads to a broader variation in the prediction of the refractive results, especially in conjunction with nomogram correction.

[0165] One could object that it is possible to apply an exact energy correction to UVL-LVC systems according to the prior art. This is fundamentally true but not implementable in practice. Ideally, the current corneal shape at the pupil position during the ablation would be determined for the next laser pulse. However, this cannot be done with current technology (processing speed, control speed), and would be accompanied by other limitations and problems. Alternatively, attempts could be made to take account of the current corneal shape during the pulse sorting process. This would represent a great advance and is categorically doable from the view of the sorting algorithms (sorting of the pulses for etch optimization). However, a subsequent and necessary thermal sort would then be impossible without undoing the previously considered improvement (resorting of the pulses). There is currently no prospect of a physical and mathematical method for combining sort and thermal sort (“simultaneously”). Therefore, the minimizing of the energy correction by the optical unit according to the invention and the consideration of the K-values offers an improvement of the predictability of the results, a reduction in the variation and, moreover, also an improvement of the nomograms as these have to correct smaller deviations per se.

[0166] A feature of the planning unit according to the invention is that the remaining aberrations and hence the spot variations in the focal field are measured or physically modeled for the calculation of the planning data and are made available to the sorting algorithm. These data can be used to determine the accurate ablation-effective fluence distribution of the pulses in the focal field as a function of the focal field position, and hence to take this into account when sorting the pulses (see FIG. 6).

[0167] FIG. 9 shows a basic arrangement of the optical beam path in an exemplary embodiment of a UVL-LVC system 705. Laser radiation 770 is provided by an excimer laser 720 as a UV laser source. The laser radiation 770 is attenuated by an (optional) optical attenuator 722, deflected by a deflector 740, is incident on a stop (or a pinhole) 724 and subsequently reaches a beam shaper 726. The latter serves to shape the beam of the raw excimer laser beam into a Gaussian or supergaussian pulse fluence distribution. By way of scanners 730, the laser beam 770 can be deflected laterally in the x- and y-directions (depicted by way of bent arrows). From here, the laser radiation 770 is guided in a first articulated arm. In the exemplary embodiment shown, the latter is movably connected to a base unit (not plotted) by way of a first rotary joint 760 (symbolized by an axis of rotation and a rotation arrow). The base unit comprises the laser source 720, the optical attenuator 722, the stop 724 (and the deflector 740 which is situated in the beam path between the optical attenuator 722 and the stop 724), the beam shaper 726 and the scanners 730. The first articulated arm is movably connected to a second articulated arm by way of a second rotary joint 762 (symbolized by an axis of rotation and a rotation arrow) on the side distant from the base unit. The laser radiation 770 is guided into the second articulated arm via two further deflectors 740 by way of the second rotary joint 762. From there, the laser radiation 770 is directed in the direction of the eye 710 by way of a further deflector 740. In this case, the laser radiation 770 is focused on the cornea 715 of the eye 710 by way of a focusing optical unit 700 according to the invention (in both variants). In this case, the focusing optical unit 700 has a two-part structure. A deflector 740 is situated in the beam path between the first lens group 701 and the second lens group 702. The required lenses of the two lens groups 701, 702 are only depicted schematically and not physically correctly.

[0168] Furthermore, the UVL-LVC system comprises what is known as an “alignment beam laser” 780. The latter serves to adjust the optical system and/or carry out an alignment with respect to the eye. The laser beam of the alignment beam laser follows the laser beams 770 of the excimer laser 720 on the cornea 715 and its focus. The “alignment beam laser” 780 is situated in the base unit of the UVL-LVC system 705.

[0169] Attention should be drawn to the fact that one or more deflectors 740 may also be embodied as beam splitters. This allows integration of other components, for example detectors for the detection of the collected corneal reflections or an observation camera. Various arrangements immediately evident to an expert but not plotted in FIG. 9 are possible to this end.

[0170] FIG. 10 shows a basic arrangement of the optical beam path in a variant of a UVL-LVC system. The laser radiation is shown here for three exemplary beams 850, 852, 854 from the beam shaper 826 and the scanner 830 (depicted together here for simplification purposes) to the cornea 815 via two articulated arms, which have deflectors 840 and are movably connected to the base unit (not depicted here) by a first rotary joint 860 and movably connected to one another by a second rotary joint 862, and via the focusing optical unit 800 (in both variants). In this case, the beams 850, 852, 854 correspond to three different locations on the cornea 815.

[0171] In contrast to the exemplary embodiment shown in FIG. 9, beam guidance is realized here by way of a relay optical unit. For simplification purposes, the relay optical unit is depicted here by way of a first relay lens 880 and a second relay lens 882. As a result, there is a larger beam diameter and an image inversion. Here, the option of lengthening the beam path is advantageous. Various other options arise for the imaging in the beam path (via the articulated arms). In this respect, the focusing optical unit 800 is uncritical.

[0172] FIG. 11 shows a schematic illustration of a UVL-LVC system 905. The UVL-LVC system 905 comprises a UV laser source 920, a scanner 930, a control unit S and a planning unit P. For data exchange between the control unit S and the UV laser source 920, the scanner 930 and the planning unit P, the control unit S has interfaces (represented by boxes on the control unit S), by application of which the data line can be transferred by way of cables. The planning unit P likewise comprises an interface (depicted as a box on the planning unit P) for data exchange with the control unit S. A wireless transfer is likewise possible. The planning unit P has a computing unit (not depicted here), by operation of which the planning data are calculated.

[0173] The aforementioned features of the invention, which are explained in various exemplary embodiments, can be used not only in the combinations specified in an exemplary manner but also in other combinations or on their own, without departing from the scope of the present invention.