WO1992013507A1

WO1992013507A1 - Process and device for modelling or correcting optical lenses

Info

Publication number: WO1992013507A1
Application number: PCT/EP1992/000093
Authority: WO
Inventors: Joachim Fiedler; Eckard Schröder
Original assignee: Aesculap Ag
Priority date: 1991-02-06
Filing date: 1992-01-18
Publication date: 1992-08-20
Also published as: DE4103493C1

Abstract

In order also to facilitate the correction of astigmatism by means of a process and device for modelling or correcting optical lenses, especially the cornea (5) of the eye (6) using a pulsed laser (1), the radiation pulses of which are directed on the surface of the lens to be modelled via optical imaging means and at least one diaphragm (3), where the diaphragm passes over different regions of the surface of the lens in successive steps and after each movement of the diaphragm the laser is struck at least once, it is proposed that the diaphragm be moved perpendicularly to the optical axis of the lens along a substantially straight path, that the diaphragm aperture have a greater extension in the direction in which its centre is moved, that the step length of the diaphragm movement be smaller than the extension of its aperture and the starting and finishing points of the diaphragm movement be such that the entire area of the diaphragm aperture covers the area of the lens to be modelled.

Description

METHOD AND DEVICE FOR MODELING OR CORRECTING OPTICAL LENSES

The invention relates to a method for modeling or correcting optical lenses, in particular the cornea of the eye, with a pulse laser, the radiation pulses of which are directed via optical imaging means and at least one diaphragm onto the surface of the lens to be modeled, the diaphragm being successively different Covered areas of the lens surface and the laser is fired at least once after each shift of the diaphragm.

The invention also relates to a device for carrying out this method.

Known methods for correcting the refractive power of optical lenses, for example contact lenses or also the cornea of the eye, remove the lens material at different depths in concentric circular ring surfaces, so that a desired cross-sectional shape of the lens can be achieved in this way. Very narrow circular ring faces are directly adjacent to one another (US Pat. No. 4,718,418; DE-OS 36 15 042), In order to be able to model the surface of the lens with concentric circles in the manner described, it has also been proposed to use an aperture which can be rotated about the optical axis and which has apertures of different lengths at different radial distances from the axis of rotation. Such a step-by-step diaphragm is acted upon by at least one laser pulse after each turning step, so that very precise rotationally symmetrical modeling of the lens surface is possible in this way (PCT / EP90 / 01101).

However, all of the methods described are only suitable for modeling the lens surface, in which it is removed in a circular region arranged concentrically to one another in a rotationally symmetrical manner with respect to the optical axis. With this, only corrections can be achieved which change the refractive power of the lens in all directions in the same way. Corrections of astigmatism are not possible with these known methods.

It is the object of the invention to design a generic method and a generic device such that astigmatism corrections and modeling are also possible with it.

This object is achieved according to the invention in a method of the type described in the introduction in that the diaphragm steps perpendicular to the optical axis along an essentially straight displacement path of the lens. is shifted wise that the aperture opening has a greater extent in the middle in the direction of displacement than at the edge, that the step width of the aperture displacement is smaller than the extent of the aperture opening in the direction of displacement and that the start and end point of the aperture displacement are chosen in this way are that the entire aperture of the aperture covers the surface of the lens to be modeled.

These measures make it possible to remove the lens surface in the form of an elongated trough which is deepest in the middle and rises on all four sides as seen from this deepest point. The length of the trough parallel to the direction of displacement results from the displacement path and can thus be varied, the width of the trough transverse to the direction of displacement is determined by the expansion of the aperture opening transverse to the direction of displacement and can be chosen according to the choice of aperture can be varied. The same applies to the boundary line of the trough at the two ends running transversely to the direction of displacement, the boundary lines at the ends running parallel to the direction of displacement is a straight line which extends parallel to the direction of displacement.

The use of such a diaphragm, the gradual advancement and the application of laser diaphragm to the diaphragm after the end of the respective displacement has the effect that the one released through the diaphragm opening in each case Surface of the lens is removed with each pulse. These released areas of the lens surface overlap, the overlap in the middle area of the aperture opening being greater than in the edge areas, since the extent of the aperture in the middle area is greater than in the edge areas. The greater the overlap, the more frequently the central areas of the treated lens surface are acted upon by laser pulses, ie the areas are removed the deeper.

It is advantageous if the step size is only a fraction of the greatest extent of the aperture parallel to the direction of displacement. In this way, the waste from the untreated lens surface to the deepest area of the trough-shaped recess is broken down into many individual stages, so that a very constant transition is obtained, both at the ends running transversely to the direction of displacement and at the ends parallel to the direction of displacement extending sides, provided the differences in expansion of the aperture in the direction of displacement are large in the central region and in the edge region.

The displacement path of the diaphragm opening center preferably leads through the optical axis of the lens. Of course, the displacement path can be rotated about the optical axis if this appears necessary due to the lens surface to be modeled or corrected.

The expansion of the diaphragm opening parallel to the direction of displacement can decrease in stages from the center to the edge. Se steps can also be smoothed, so that there is a continuous course of the edge.

It is expedient if the step size of the displacement movement is equal to or smaller than the smallest extension of the diaphragm opening parallel to the displacement opening. This ensures that even in the edge area, where the aperture generally has the smallest dimension, there are no "frayed" edges, but a clear transition between the modeled surface and the non-modeled surface.

In particular, the aperture opening can be delimited by two curved pieces that bulge in the opposite direction and meet at an angle; the direction of displacement is perpendicular to the connecting line between the two points of contact of the arc pieces.

According to the invention, an apparatus for carrying out the described method has the features of the characterizing parts of claims 7 to 12, these features largely correspond to the features corresponding to the method carried out.

The following description of preferred embodiments of the invention serves in conjunction with the drawing for a more detailed explanation. Show it: 1: a schematic side view of a treatment device for modeling or correcting a lens surface;

Fig. 2 to

Fig. 4: a top view of a very simplified

Example of an aperture in different, successive positions;

5: a partial view of a lens surface provided with a trough-shaped recess and

6: a plan view of a part of an aperture with an aperture opening delimited by curved edge lines.

Methods and devices for correcting or modeling a lens are described below using the example of correcting the cornea; However, it goes without saying that this method and this device can also be used for correcting different types of lenses, for example in the case of contact lenses which consist of material which can be removed by laser radiation.

In Fig. 1 the device used is shown very schematically. A laser 1, for example an excimer laser, generates radiation pulses of a certain duration, which are symbolized in Fig. 1 by an arrow. The radiation is directed onto the cornea 5 of the eyeball 6 via a mirror 2. Between the mirror 2 and the cornea 5 there is a mask-shaped diaphragm 3 with a diaphragm opening 4, the more precise shape of which is explained in more detail below. The diaphragm 3 is mounted on a holder 7 on a drive 8 which gradually moves the diaphragm 3 in a direction arranged perpendicular to the optical axis of the eyeball 6 along an essentially straight displacement path. The drive 8 is actuated by a controller 9 which, at the same time, ignites the laser 1 only when the drive 8 is at rest; one or more pulses can be emitted for each position of the diaphragm.

The aperture 4 is always shaped so that its expansion parallel to the direction of displacement is greater in the middle than at the two edges. 2 to 4 show a very simplified embodiment of such a diaphragm opening, this diaphragm opening comprises three regions of the same width, namely a central region 10, an edge region 12 and an intermediate region 11, each of which lies between the middle region 10 and between the two edge regions 12. These areas are delimited by edge lines 13 running transversely to the direction of displacement, the middle area is five times as long as the edge area, the intermediate areas are three times as long as the edge area. The A- individual areas merge into one another in stages, ie the border lines form stages. With regard to a center line running transversely to the direction of displacement, the diaphragm opening is mirror-symmetrical.

The aperture shown in FIGS. 2, 3 and 4 is shown there in different positions during the modeling process. In FIG. 2, the diaphragm opening occupies a lowermost position, in FIG. 3 it is shifted upwards by a distance which corresponds to the extent of the edge region 12 parallel to the direction of displacement, in FIG. 4 it is again by such an increment moved further up.

When modeling the lens surface, laser radiation is sent to the lens surface in each of the positions shown.

It can be clearly seen from the comparison of FIGS. 2 to 4 that in the described configuration of the diaphragm opening, the lens surface parts released by the edge regions 12 of the diaphragm opening directly adjoin one another, while those of the intermediate regions 11 and the central region 10 released surface parts of the lens partially overlap at the different positions of the aperture. In the lens surface parts swept by the edge regions 12, they are only hit by radiation at one position of the diaphragm opening, which is from the In contrast, the middle region and the surface parts swept over the edge region several times, and more frequently, the longer the extension of the diaphragm opening in the direction of displacement. This has the result that the surface of the lens is little removed in the side parts covered by the edge regions 12 and that the removal becomes stronger towards the center. A trench running parallel to the direction of displacement is thus modeled in the lens surface.

In the starting position, the aperture is completely above the surface of the lens to be treated, as is the end position. This also results in a constant decrease in the modeling depth at the two ends of the trench described. In the starting position (eg FIG. 2), the parts of the lens surface released by the aperture at its lower edge are only hit when laser beams are first applied, and these lowest parts are already covered when the aperture is moved for the first time. Multiple exposure also occurs in the middle area and in the intermediate area only in the parts at the top at the start of modeling. The full depth of the trench is only reached in the part of the lens surface which is arranged on the upper edge of the aperture opening at the beginning of the modeling. Over a region which results from the expansion of the aperture opening in the direction of displacement, a constant increase in the depth of ablation or, in the vicinity of the end position of the aperture, a decrease in the depth of ablation is obtained. Such a trench is shown in a simplified form in FIG. 5, the trough-shaped recess in the lens surface treated in this way being produced by the described increase or decrease in the modeling depth on the sides arranged transversely to the direction of displacement. Width and length can be different and adapted to the astigmatism to be corrected.

The diaphragm opening described in FIGS. 2 to 4 consists of only three areas of different dimensions in the direction of displacement, so that the trough-shaped recess (FIG. 5) that is produced only has to be composed of three layers with different depths. This results in very rough gradations. In practice, the number of stages is increased significantly. H. a much finer gradation will be carried out, if necessary the gradation can also be chosen so fine that a continuous edge line of the aperture opening is used.

An example of such an aperture is shown in FIG. 6. This aperture has on its front edge and on its rear edge an arcuate boundary line 14 and 15, which meet at an angle in two points of impact 16 and 17, respectively. A straight line passing through the two points of impact is arranged perpendicular to the direction of displacement; the direction of displacement is indicated by arrow A in FIG. The aperture shown in FIG. 6 is used in the same way as has been explained with reference to FIGS. 2 to 4. The step size of the feed can be selected to be very small, for example it can be 1/100 of the longest dimension of the diaphragm opening in the displacement direction, so that the steps of adjacent ablation layers are very close together in the trough-shaped recess in the lens surface and the height differences are small stay. In this way, an almost constant drop is obtained from the untreated lens surface to the deepest area of the trough-shaped recess.

The step size when advancing the diaphragm opening does not necessarily have to correspond to a step, even in the case of a step-shaped diaphragm opening, in fact the displacement path by a whole step of adjacent areas is normally the greatest possible displacement path between two irradiations. In practice, the step size will be selected to be smaller, so that even with a step aperture, a smooth transition as possible is possible between the untreated lens surface and the bottom of the trough-shaped recess.

Claims

P A T E N T A N S P R Ü C H E

Method for modeling or correcting optical lenses, in particular the cornea of the eye, using a pulse laser, the radiation pulses of which are directed via optical imaging means and at least one aperture onto the surface of the lens to be modeled, the aperture successively different areas of the Sweeps the lens surface and the laser is ignited at least once after each shifting of the diaphragm,

characterized ,

that the diaphragm is displaced step by step perpendicular to the optical axis along a substantially straight-line displacement path of the lens, that the aperture opening has a larger extension in the middle in the direction of displacement than at the edge, that the step width of the aperture displacement is smaller than the extent of the aperture opening in Verschiebe¬ Direction and that the start and end point of the diaphragm displacement are selected so that the diaphragm opening covers the entire surface of the lens surface to be modeled. A method according to claim 1, characterized in that the step size is only a fraction of the greatest extent of the aperture parallel to the displacement direction.

A method according to claim 1 or 2, characterized gekenn¬ characterized in that the displacement path of the center of the aperture leads through the optical axis of the lens.

4. The method according to any one of the preceding claims, characterized in that the expansion of the aperture opening decreases in stages parallel to the direction of displacement from the center to the edge.

5. The method according to claim 4, characterized in that the step size is equal to or smaller than the smallest dimension of the aperture parallel to the direction of displacement.

Method according to one of the preceding claims, characterized in that the aperture opening is delimited by two curved pieces which are bulged in the opposite direction and meet at an angle, and that the direction of displacement is perpendicular to the connecting line of the two points of contact of the curved pieces. Device for modeling or correcting optical lenses, in particular the cornea of the eye, with a pulse laser, the radiation pulses of which are directed via optical imaging means and at least one aperture onto the surface of the lens to be modeled, the aperture successively different areas of the Linsenober¬ surface sweeps and after each shift of the diaphragm the laser is fired at least once, characterized in that the diaphragm (3) perpendicular to the optical axis along a substantially straight-line displacement path of the lens (5) is gradually shifted that the aperture (4) in the direction of displacement in its middle (10) has a greater extent than at the edge, that the step width of the aperture displacement is smaller than the extent of the aperture (4) in the direction of displacement and that the start and end point of the apertures ¬ displacement sq__ are chosen that the aperture (4) covers the entire surface of the lens surface (5) to be modeled.

8. The device according to claim 7, characterized in that the step size is only a fraction of the largest dimension of the aperture (4) parallel to the direction of displacement. Apparatus according to claim 7 and 8, characterized gekenn¬ characterized in that the displacement path of the center of the aperture leads through the optical axis of the lens (5).

10. Device according to one of claims 7 to 9, da¬ characterized in that the expansion of the aperture opening (4) decreases in stages parallel to the direction of displacement from the center (10) to the edge (12).

11. The device according to claim 10, characterized gekennzeich¬ net that the step size is equal to or smaller than the smallest dimension of the aperture (4) parallel to the direction of displacement.

12. The device according to one of claims 7 to 11, characterized in that the aperture (4) is delimited by two curved pieces (14, 15) bulging in the opposite direction, which meet at an angle, and that the ver sliding direction perpendicular to the connecting line of the two points of impact (16, 17) of the arc pieces (14 and 15).