Method for determining data for treating a surface

A method for determining data for adapting a reflective surface to a desired surface, includes the steps of determining spatial co-ordinates of a multiple number of points of a surface and entering the determined spatial co-ordinates into a computer as a data record. Recorded in the computer are then shape and/or position of a desired surface, with the shape and/or position of the desired surface being variable. The computer calculates for the multiple number of points on the surface the spacing to the desired surface. The spatial co-ordinates and spacings of the multiple number of points are then outputted as a data record for adjusting the surface. By simulating the treatment process on the computer in advance, it is possible to select the optimal treatment process and to eliminate regional unevenness on the cornea.

BACKGROUND OF THE INVENTION
 The invention concerns a method for determining data for treating a
 surface, and in particular to a method for adapting a reflective surface
 to a desired surface.
 When treating the cornea of an eye, usually the refractive behavior of the
 cornea is determined in order to subsequently, in most cases by means of a
 laser method, subject the cornea to laser treatment so as to change the
 curvature and thus the refractive behavior of the cornea. In thus it is
 possible, by means of subjecting the cornea to a few targeted "exposures",
 to achieve a structural change of the cornea in certain regions of the
 remove parts of the cornea. In particular by radially different intensity
 of the laser treatment, the refractive behavior of the surface of the
 cornea is thus changed.
 It has however been shown that usually the refractive behavior of the
 cornea is not uniform across its entire surface and consequently the known
 procedures produce a good result only in the case of refractive behavior
 distributed at adequate similarity across the cornea. With the known
 treatment methods, smaller areas of the cornea of particularly high or
 particularly low curvature are not corrected at all or only inadequately
 corrected.
 U.S. Pat. Nos. 4,669,466 and 5,384,608 describe methods in which spatial
 co-ordinates of a multiple number of points on a surface are determined
 and entered as a data record in a computer in which also the form and
 shape of a desired surface is recorded. For the multiple number of points
 on the surface, the spacing to the desired surface is calculated, and the
 spatial co-ordinates and the spacings of the multiple number of points is
 outputted as a data record for adapting the surface.
 These known methods determine a desired surface and try to treat the
 surface in such a way as to eliminate the differences to the desired
 surface. It is however problematic that for a surface of any given form,
 it is impossible to unambiguously determine a desired surface. An optimal
 desired surface can only be determined if the spacings to the surface are
 known.
 SUMMARY OF THE INVENTION
 It is thus an object of the present invention to provide an improved method
 for determining data for treating a surface, in particular a cornea,
 obviating the afore-stated drawbacks.
 In particular, it is an object of the invention to propose an improved
 method for determining data for treating a surface, in particular a
 cornea, which method makes it possible, by treating locations of various
 curvature on a surface such as for example a cornea, to reduce such
 locations.
 It is still another object of the present invention to provide an improved
 method to reduce locations of the most varied curvature on a surface,
 using minimal intervention, in order to achieve a surface curvature
 suitable for the individual case.
 These objects, and others which will become apparent hereinafter, are
 attained in accordance with the present invention by determining the
 locations of a multiple number of points on the surface; entering these
 locations into a computer as a date record; entering the form and/or shape
 of a desired surface into the computer, with the shape and/or position of
 the desired surface being variable; calculating for the multiple number of
 points on the surface, the spacing to the desired surface; and outputting
 location and spacing of the multiple number of points as a data record for
 treating the surface.
 The method according to the present invention is based on the recognition
 that for a surface of any given form, it is impossible to unambiguously
 determine a desired surface. Only by repeated changing of the desired
 surface and respective determination of the necessary steps, is the
 surgeon in a position to determine a desired surface which serves as a
 basis for further treatment.
 The method according to the invention makes it possible not only to treat
 the surface as a whole but depending on the resolution, to determine the
 position of each individual point on the cornea in order to subsequently,
 by comparison with a predetermined desired surface, calculate the positive
 or negative spacing to the desired surface, and make it available for the
 actual treatment of the surface. In this way, local regional peaks can be
 treated more intensively while naturally existing troughs are treated to a
 lesser extent or not treated at all. The data record made available by the
 method thus makes possible a targeted treatment of even a relatively
 uneven cornea which is to comprise a regular curvature across its entire
 area as a result of the subsequent treatment method.
 Since the form and/or position of the desired surface is variable, it is
 possible to determine the desired surface on the computer in comparison
 with the surface of the cornea on the basis of clinical experience.
 Deviations between the desired surface and the cornea, which is calculated
 in an instant by the computer, assist the surgeon in correctly determining
 the desired surface.
 The method is above all suitable for reflective surfaces because these can
 be measured easily by means of topometry.
 A simple method for determining the locations of a multiple number of
 points on the surface consists of computing the locations of the surface
 of the multiple number of points topometrically in an iterative manner, as
 co-ordinates. An iterative method of computing the co-ordinates of
 individual locations on a reflective surface is described in
 PCT/DE95/01579, the full extent of which is referred to herewith.
 To facilitate work to the treating surgeon, it is advantageous if the
 locations of the multiple number of points are graphically represented. To
 do so, e.g. a grid representation is suitable which clearly shows the
 progression of the corneal shape or the deviation of the shape from a
 spherical surface.
 For better comparison it is advantageous if the shape and/or position of
 the desired surface too are/is graphically represented. To this effect the
 same methods can be used, with the surfaces to be represented either
 side-by side or in their relative arrangements to each other.
 A further embodiment of the invention provides for the spacings between the
 multiple number of points and the desired surface, too, to be graphically
 represented. This too can be made available to the treating surgeon as
 graphics in three-dimensional representations, projections or sectional
 representations.
 Particularly easy comprehension of the representation is achieved in that
 various spacings are represented by different colors. This makes it
 possible for the treating surgeon to recognize the areas of particularly
 extensive deviation from the desired curve, without necessitating
 expensive numeric comparison.
 As an alternative, or as a supplement to determining the desired surface
 according to clinical experience, the desired surface can also be
 determined by ray tracing. In this, a desired curve for the cornea is
 calculated on the basis of certain requirements of the course of the beams
 and in particular their intersection with the retina.
 A further embodiment of the invention provides for simulation of a surface
 treatment provides for simulation of a surface treatment method with the
 data record, for treating the surface and for the result to be displayed.
 To this effect additionally, the data for a special surface treatment
 method is entered, after which the computer displays the result achievable
 with this surface treatment method to the treating surgeon.
 If the surface treatment method is for example a laser treatment method,
 then the data of the change in shape of the cornea caused by a single
 exposure can be entered into the computer. The computer then calculates
 the location and number of the necessary exposures for approximating the
 surface of the cornea to the desired surface. If the result ins not
 satisfactory, either the surface treatment method can be changed, or the
 location or course of the desired surface I varied. The computer makes it
 possible within an instant to simulate various treatment methods and
 desired surface inputs right up to displaying the achievable result, so as
 to carry out the optimum treatment method on the patient.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 Throughout all the Figures, same or corresponding elements are generally
 indicated by same reference numerals.
 Turning now to the drawing, and in particular to FIG. 1, there is shown a
 sectional view of a cornea with exaggerated surface deformation. The
 surface of the cornea 1 is shown with highly exaggerated irregularities 2,
 3, 4, 5 and 6. As an example of the multiple number of points, point 7 is
 shown, the location of which can be determined by means of the
 co-ordinates of a co-ordinate system 8 with the randomly determined zero
 point 9. Thus for each point on the cornea 1 there is a co-ordinate
 reference which exactly determines the location of the point.
 In addition, in FIG. 1 a first desired surface 10 has been drawn in which
 can be varied to such an extent by the treating surgeon that the location
 and course match the clinical requirements. The variation gives rise to a
 second desired surface 11 which is positioned relative to the cornea by
 the surgeon according to his clinical experience.
 From the relative position of each pint 7 to the second desired surface 11,
 the computer calculates the spacing 12 for each individual point. This
 spacing serves as a basis for the subsequent treatment of the cornea 1.
 FIG. 2 is a top view showing possible curvatures of a cornea, represented
 by different hatching or crosshatching. Tight hatching 13, 14, 15
 indicates a stronger curvature while lighter hatching 16, 17 indicates a
 lesser curvature. Instead of hatching, the use of colors is advantageous
 in practical application.
 As an alternative to, or supplement to the curvatures, it is also possible
 to represent the locations of the surface of the cornea.
 The spacings 12 between the cornea 1 and the second desired surface 11 can
 also be represented analogously to FIG. 2 by hatching or colors, so as to
 highlight areas which require particularly strong treatment.
 FIG. 3 is a diagrammatic representation of treatment of the surface of a
 cornea according to FIG. 1 using a laser device. Based on the spacings
 between the cornea 1 and the second desired surface 11, the computer
 calculated the location and number of the exposures 18, 19, 20, 21.
 However, since the laser device only allows discontinuous settings, after
 treatment an actual surface 18 results which only approximates the second
 desired surface 11. At first the treatment is simulated on the computer to
 verify the result expected from carrying out treatment and if necessary
 for adjustment of the treatment method. Only after playing through various
 desired surfaces and or treatment methods does the treating surgeon
 finally determine a desired surface and a surface treatment method which
 most closely meet the intended result.
 While the invention has been illustrated and described as embodied in a
 method for determining data for treating a surface, it is not intended to
 be limited to the details shown since various modifications and structural
 changes may be made without departing in any way from the spirit of the
 present invention.
 What is claimed as new and desired to be protected by letters patent is set
 forth in the appended claims: