Device, method, and control program for refractive surgery

Abstract

An apparatus and a method for refractive surgery, in particular LASIK, make provision whereby the apex of the cornea is taken as a basis, as the ablation center, for the refractive procedure. For this purpose, the dependence of the position of the apex on properties of the pupil is determined in the case of the eye to be treated and, from this dependence, measured properties of the pupil are used to calculate the position of the ablation center during the refractive surgery.

Claims

1. Apparatus for refractive surgery comprising the following: a laser-beam source; a camera .[.for recording the.]. .Iadd.configured to record an image of an .Iaddend.iris and .Iadd.a .Iaddend.pupil of .[.the.]. .Iadd.an .Iaddend.eye; a computer.[., comprising.]. .Iadd.storing .Iaddend.a control program .[.for controlling the said means.]. .Iadd.to control a laser beam emitted by the laser-beam source .Iaddend.according to an ablation profile.[.; wherein.]..Iadd., .Iaddend.the control program.[.: includes.]. .Iadd.including .Iaddend.a function .[.of the.]. .Iadd.relating a .Iaddend.position of .[.the.]. .Iadd.an .Iaddend.apex of .[.the.]. .Iadd.a .Iaddend.cornea of the eye .[.in dependence .]. .Iadd.depending .Iaddend.on at least one .Iadd.instantaneous .Iaddend.property of the pupil; .Iadd.the control program, when executed by the computer .Iaddend.during the refractive surgery.[.,.]..Iadd.: .Iaddend. records an instantaneous property of the pupil .[.by means of.]. .Iadd.based on the image recorded by .Iaddend.the .[.camera and.]. .Iadd.camera; .Iaddend. determines .[.therefrom, by means of the function,.]. the position of the apex of the cornea .Iadd.based on the instantaneous property of the pupil and the function.Iaddend.; and aligns the ablation profile to .Iadd.one of .Iaddend.the thus determined position of the apex .[.or of.]. .Iadd.and .Iaddend.a point of the corneal surface having a fixed distance from the apex.

2. Apparatus according to claim 1, wherein the .Iadd.instantaneous .Iaddend.property of the pupil is at least one or more of its dimensions.

3. Apparatus according to claim 1, wherein the .Iadd.instantaneous .Iaddend.property of the pupil is at least one of its shape and center.

4. Apparatus according to claim 1, wherein .[.the control program also determines, by means of a recorded property of the iris, an instantaneous position of at least one of the apex and a predefined point of the cornea having a fixed distance to the apex.]..Iadd.wherein: the function relates the position of the apex of the cornea of the eye to an instantaneous property of the iris; the control program, when executed by the computer during the refractive surgery: determines the instantaneous property of the iris based on the image recorded by the camera; and determines the position of the apex of the cornea based on the instantaneous property of the iris and the function.Iaddend..

.[.5. Apparatus for refractive surgery comprising the following: a laser-beam source; a camera for recording the iris and pupil of the eye; a computer which executes a control program for the purpose of controlling said means according to an ablation profile, wherein the control program: includes a function of the position of the apex of the cornea of the eye in dependence on at least one property of the pupil, during the refractive surgery, records the instantaneous property of the pupil by means of the camera and determines therefrom, by means of said function, the position of the apex of the cornea, and aligns the ablation profile to at least one of the thus determined position of the apex and a point on the corneal surface having a fixed distance from the apex..].

6. The apparatus of claim .[.5.]. .Iadd.1.Iaddend., wherein .[.the at least one property of the pupil upon which the position of the apex is dependent as set forth in.]. the function of the control program .[.includes a relationship of.]. .Iadd.sets forth a dependence of the position of the apex on the instantaneous property of the pupil in a relationship that relates .Iaddend.the position of the apex to a pupil width.

7. The apparatus of claim 6, wherein the relationship of the position of the apex to the pupil width is determined empirically for the eye to be treated.

8. The apparatus of claim 7, wherein empirically determining the dependency of the position of the apex to the pupil width is determined by altering incident visible light on the eye to be treated.

9. The apparatus of claim 8, wherein the incident visible light on the eye to be treated is altered in a stepwise manner.

10. The apparatus of claim .[.5.]. .Iadd.1.Iaddend., wherein .[.the at least one property of the pupil upon which the position of the apex is dependent as set forth in.]. the function of the control program .[.includes a relationship of.]. .Iadd.sets forth a dependence of the position of the apex on the instantaneous property of the pupil in a relationship that relates .Iaddend.the position of the apex to a pupil rotation.

11. The apparatus of claim 10, wherein the relationship of the position of the apex to the pupil rotation is determined empirically for the eye to be treated.

12. The apparatus of claim 11, wherein empirically determining the dependency of the position of the apex to the pupil rotation is determined by identifying variation of a position of an iris pattern.

.[.13. The apparatus of claim 1, wherein the at least one property of the pupil upon which the position of the apex is dependent as set forth in the function of the control program includes a relationship of the position of the apex to a pupil width..].

.[.14. The apparatus of claim 13, wherein the relationship of the position of the apex to the pupil width is determined empirically for the eye to be treated..].

.[.15. The apparatus of claim 14, wherein empirically determining the dependency of the position of the apex to the pupil width is determined by altering incident visible light on the eye to be treated..].

.[.16. The apparatus of claim 15, wherein the incident visible light on the eye to be treated is altered in a stepwise manner..].

.[.17. The apparatus of claim 13, wherein the at least one property of the pupil upon which the position of the apex is dependent as set forth in the function of the control program includes a relationship of the position of the apex to a pupil rotation..].

.[.18. The apparatus of claim 17, wherein the relationship of the position of the apex to the pupil rotation is determined empirically for the eye to be treated..].

.[.19. The apparatus of claim 18, wherein empirically determining the dependency of the position of the apex to the pupil rotation is determined by identifying variation of a position of an iris pattern..].

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are explained more fully in the following with reference to the drawings, wherein:

(2) FIG. 1 shows, schematically, a section through an eye, with the axes and points of intersection that are of particular interest in this case; and

(3) FIG. 2 shows, schematically, an apparatus for refractive surgery.

DETAILED DESCRIPTION

(4) The saggital section through an eye 10 according to FIG. 1 shows, schematically, a cornea 12, a lens 14, an anterior chamber 16, an iris 18, the edge 18a of which is bounded by a pupil 20, a fovea 22, a macula lutea 24, an optical axis 26 and a visual axis 28.

(5) The optical axis 26 intersects the front surface 12a of the cornea 12 at the location O. The visual axis 28 intersects the front surface 12a of the cornea at the location V.

(6) Regularly, as shown schematically in FIG. 1, the apex A of the cornea 12 is located neither at the location O nor at the location V, such that the point of intersection V of the visual axis is located between the apex A and the point of intersection O of the optical axis with the corneal surface. In this case, as a rule, V is located closer to A than to O. The invention exploits these anatomical regularities.

(7) FIG. 2 shows, schematically, an apparatus for refractive surgery, comprising a laser-beam source 34, which emits a laser beam 32 that, by means of devices 36 for beam shaping and guidance, is directed onto an eye 10 to be treated. A camera, for example an IR camera 38, is used to record, in particular, the pupil and the iris of the eye, and the digital image signal is input to a computer 40.

(8) The computer 40 controls all the components mentioned, thus, in particular, the laser-beam source 34 and the means 36 for beam shaping and guidance. The components described thus far are well known as such in the prior art, and are not explained more fully here.

(9) The ablation profile, explained above, is first determined, in a manner known per se, for an eye to be treated. This is effected through measurement of the eye, e.g. through wave-front analysis. The thus obtained ablation profile is stored in the computer 40. The computer 40 furthermore includes a control program for the purpose of controlling, in particular, the devices 36 for beam shaping and guidance in accordance with the ablation profile. This is likewise well known as such in the prior art.

(10) Firstly, the apex A of the cornea of the eye to be treated is determined, i.e. the spatial coordinates of the apex point A are measured. This can be performed, for example, by means of so-termed keratometer marks, i.e. one or more markings, which define the position of the apex A, are projected on the surface 12a of the cornea, close to the apex A. This measurement of the apex can be effected, for example, by means of a conventional topometer. Thereafter, the coordinates of the apex A can be assumed to be constant for the eye, and they serve as a reference point, i.e. as an ablation centre for a subsequently performed ablation, this reference point remaining invariable even in the case of changing pupil widths and, also, pupil rotation.

(11) In a further step, following the determination of the spatial coordinates of the apex A, the functional dependence of the position of the apex A on the individual pupil movement, thus the change in the pupil width and the in the pupil rotation, is determined for the eye to be treated.

(12) For this purpose, the dependence of the position of the centre on the pupil width is first determined. As explained above, as a general rule a widening of the pupil is not concentric, i.e., as a rule, the pupil centre will have shifted following a widening of the pupil. This dependence of the position of the pupil centre on the pupil width is determined in that differing pupil widths are produced in a stepwise manner, and the coordinates of the pupil centre are determined in relation to each pupil width, with the apex as the reference point. In this case, the variation of the pupil width is effected by altering the incident visible light, such that naturally occurring widening of the pupil is effected (a pharmacological widening of the pupil frequently differs from its natural movement). An infrared camera is then used to determine the respective position of the pupil centre for the various pupil widths, with the previously determined apex as the reference point.

(13) The dependence of the angle of the pupil rotation on the pupil width is determined analogously. In this case, in addition to identifying the pupil centre, the IR cameral also identifies the variation of the position of the iris pattern, which provides information concerning the pupil rotation.

(14) In this way, there is determined a function that represents the position of the apex A in dependence on instantaneously occurring properties of the pupil, such as, in particular, the pupil width and the rotational state of the pupil. This empirically measured dependence is stored, for the eye to be treated, in the computer 40, and is then used during the refractive surgery to be performed subsequently, thus, in particular, LASIK, in order to calculate the instantaneous ablation centre. Thus, in the case of this example, the ablation is centred on the apex A.

(15) This is effected, in the case of refractive surgery, in that the pupil 20 and iris 14 of the eye are recorded, by means of the IR camera 38, at a frequency that is sufficiently high to capture movements and pupil variations of the eye with such rapidity that the ablation is adjusted to such variations. The image processing programs stored in the computer 40 use the stored functions, described above, relating to the instantaneous pupil size and pupil position to calculate the coordinates of the apex A, and the computer 40 takes this instantaneous apex A, as the ablation centre, as a basis in the control of the devices 36 for beam guidance, i.e. the individual laser pulses are positioned in accordance with the ablation profile in which the instantaneously measured site of the apex A serves as the ablation centre. This is performed repeatedly, at the said high frequency, during the entire refractive surgical procedure, such that the instantaneous ablation centre always corresponds to the actual state of the eye. In parallel therewith, the eye tracking, known per se, is performed by means of the camera 38 and the computer 40 during the procedure.

(16) The centring of the ablation on the apex A, as described above, already provides an improved refractive-surgery result, i.e. an improvement of the visual correction.