Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
1999-09-21
2001-06-05
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06241356
ABSTRACT:
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 achi
Neuhann Thomas
Von Wallfeld Herbert
Day Ursula B.
Feiereisen Henry M.
Manuel George
Technomed Gesellschaft für Med und Med.-Techn. Systeme mbH
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