FR2655837A1 - SURFACE TREATMENT MASK AND DEVICE FOR EYE SURGERY OR LASER OPTICAL LENS PRODUCTION. - Google Patents

Abstract

A mask and a system for surface treatment by exposure to laser radiation. Each mask consists of a plate (P) which is opaque at the wavelength of the laser radiation and includes a plurality of windows (F). The windows are transparent to the laser radiation and form a sieve-like mask. The density of windows on the mask is proportional to the law of rectification and the spatial distribution of the windows is random over a given portion of the surface. During treatment, the mask moves in a random translational manner in a plane perpendicular to the direction of the laser (FL) beam. The mask can be used during refractive eye surgery or for making optical lenses, implantable or otherwise.

Description

 The present invention relates to a surface treatment mask and to a device for treatment or refractive surgery of the cornea of the eye or of a determined surface.

 The purpose of these modifications to the shape of the cornea or of optical lenses is the correction of ametropia by correction of the dimensional optical characteristics of the cornea or of the optical lens and mainly of its radius of curvature. Until a recent past, these modifications, also called keratomileusis, were obtained by a real machining of a disc taken from the cornea, this disc being able either to be made rigid by freezing and machined according to the process of Barraquer, or to be applied on a template with a suitable radius of curvature and cut out using the Barraquer-Krumeich technique.

 This type of intervention has the major drawback of first requiring removal of the disc of corneal material and then treatment of the aforementioned disc, which must be re-implanted on the patient's eyeball after treatment.

 More recently, work has highlighted the very precise ablative properties of the radiation of an excimer laser when this radiation is applied to the corneal tissue. The radiation emitted by excimer lasers, of wavelength substantially equal to 193 nm, makes it possible to remove the corneal material by photodecomposition. Generally, a light spot, image of an appropriate mask and generally variable, temporally or spatially, illuminated by the laser beam, is formed on the cornea, the spot being substantially centered on the optical axis of the eyeball. The spot of substantially circular, annular or symmetrical shape substantially with respect to the optical axis of the eyeball can be moved, the exposure time of a determined area depending on the optical correction to be made.

 Such devices, if they can allow a direct intervention on the eyeball of the patient, allowing better centering, avoiding the aforementioned problem of cutting and reimplantation of a rectified corneal fragment, however do not allow the implementation work of a precise treatment method insofar as, if the exposure time, that is to say in fact the number of pulses, can be defined with good precision, the effects and in particular the thickness of the cornea subjected to photo-decomposition varies with the size of the light spot and the energy density of the laser beam used. In addition, the surface condition of the cornea after treatment (and its undesirable effects caused by thermal or shock wave) varies greatly depending on the level of energy delivered by pulse and the frequency of recurrence with which the same area is irradiated successively.

 In particular, other work relating to a device for surgery of the cornea of the eye by laser irradiation which has been the subject of a European patent application EP 88 401607.2 published under the number 0 296 982 relates to the implementation implementation of a device making it possible to conduct a process of ablation by successive discrete ablations, the total ablation resulting from the summation of numerous elementary or discrete ablations, while avoiding deteriorating the same zone by two or more strictly consecutive pulses and by limiting the surface irradiated by pulse.

 The device for refractive surgery of the eye by laser treatment of the cornea, described in the aforementioned document, comprises means for emitting a laser beam by pulses. This device comprises means making it possible to generate a treatment laser beam comprising at least one lobe of elongated section, means for focusing the image of the said lobe (s) of the treatment laser beam on the area of the eye to be corrected, means for synchronizing the displacement of the image of said lobe (s) of the processing laser beam, the total rectification or ablation being effected by summing a plurality of elementary discrete ablations.

 The aforementioned device gives all satisfaction with regard to the criterion of precision of ablation depth, and, ultimately, of precision of the rectified profile of the cornea thus treated.

 However, the aforementioned device, in particular, involves very high accuracy and stability of alignment of the slot (s) of the irradiation mask with the optical axis of the cornea and of the eye.

 In addition, due to the symmetry of the treatment with respect to the optical axis of the eye or of the cornea, it is essential that the eye and therefore the cornea are kept in a substantially fixed position relative to the direction of the eye. 'axis of symmetry of the mask or treatment, the uncontrolled micromovements of the eyeball and the cornea subjected to the treatment must imperatively be avoided as much as possible.

 The present invention aims to remedy the aforementioned drawbacks by the implementation of a system and a mask for surface treatment by laser irradiation, in particular refractive eye surgery, in which the stability of the alignment of the central axis or axis of symmetry of the treatment mask and the optical axis of the cornea, or of the axis of symmetry of the surface to be treated, is not decisive.

 Another object of the present invention is the implementation of a system and a mask for surface treatment by laser irradiation, in particular refractive eye surgery, in which the absence of uncontrolled micro-movements of the surface to be treated, such as the cornea of an eye, is not as critical.

 The mask for surface treatment by laser irradiation, object of the present invention, is remarkable in that it consists of a plate opaque to the wavelength of the laser radiation provided with a plurality of windows formed therein. . The windows are transparent to laser radiation and form a screen-like mask. The density of the windows on the mask d (h) is proportional to the law of rectification A (h): d (h) = ss.A (h) where h denotes the radial distance of a point of the mask with respect to a reference point and where ss is a proportionality coefficient determined by the number of windows per unit of area.

 The surface treatment system by laser irradiation, object of the present invention, comprises means for emitting a laser beam by pulses. It is remarkable in that it further comprises means making it possible to generate a treatment laser beam comprising a treatment mask by laser irradiation, as defined above, and means for displacement in two orthogonal directions of the treatment mask. area ; the aforementioned mask is, during the duration of the irradiation, continuously moved randomly in a plane orthogonal to the longitudinal axis of the treatment beam.

 The mask and the system of surface treatment by laser irradiation, objects of the present invention, find application in refractive surgery of the eye, for the correction of ametropia, and / or in the surface rectification of optical lenses, implantable or no.

A more detailed description of the mask and of the surface treatment system, objects of the present invention, will be given below with reference to the drawings in which, in addition to FIGS. 1 and 2a, 2b, relating to preliminary reminders with regard to the effects of irradiation by light of an excimer laser, at the wavelength of 193 nm, when this light is applied to the corneal tissue, and to the definition of an ablation profile for a substantially spherical surface such as the cornea of the eye or an optical lens,
- Figure 3a shows, schematically, the configuration of a mask according to the object of the present invention in which the windows or openings are of substantially circular or rectangular shape and distributed in annular zones, Figures 3a (1 ) and 3a (2) showing views of this mask in section along a plane marked in AA in FIG. 3a according to whether, respectively, this mask has the general shape of a flat plate or a spherical cap,
- Figure 3b shows, schematically, the configuration of a mask according to the object of the present invention in which the openings are constituted by annular windows, Figures 3b (l) and 3b (2) showing views of this mask in section along a plane marked in AA in FIG. 3b according to whether, respectively, this mask has the general shape of a flat plate or a spherical cap,
- Figure 3c shows, schematically, the configuration of a sieve type mask more particularly suitable, in accordance with the present invention, to a myopic keratomileusis
- Figure 3d shows, schematically, the configuration of a sieve type mask more particularly adapted, in accordance with the present invention, to a hyperopic type keratomileusis
FIG. 3e represents, schematically, the configuration of a mask of the sieve type adapted to a keratomileusis of the myopic type, but also allowing a reduction of the astigmatism of the cornea or of the optical spherical surface to be treated,
- Figures 4a and 4b show respectively, schematically, a sieve type mask according to the subject of the present invention for a keratomileusis myopic type and the corresponding ablation profile A (h) on the cornea or on the corresponding spherical optical surface
- Figures Sa and 5b show respectively, schematically, a sieve type mask according to the object of the present invention for a keratomileusis hypermetropic type and the corresponding ablation profile A (h) on the cornea or on the corresponding spherical optical surface,
- Figure 6a shows by way of nonlimiting example a model of sieve type mask actually produced for an intervention of keratomileusis type of myopic type
FIG. 6b represents, by way of nonlimiting example, a model of sieve type mask actually produced for the purpose of a hyperatomic type keratomileusis type intervention,
- Figure 7 shows a general view of a surface treatment system by laser irradiation according to the subject of the present invention
FIG. 8a represents an advantageous non-limiting embodiment of an element of the system, object of the present invention, as shown in FIG. 7,
- Figures 8a and 8b show elementary displacement laws in X and Y of the sieve type mask as shown for example in Figure 8a.

 - Figure 8c shows a block diagram of a random displacement control circuit in X, Y of the sieve type mask according to the invention.

 Preliminary reminders relating to the effects of irradiation by laser light, such as an excimer laser at the wavelength of 193 nm, when this light is for example applied to the corneal tissue, and to the definition of 'a corresponding ablation profile will first be given in connection with Figures 1 and 2a, 2b.

 It should be noted, however, that lasers with different wavelength emission can be used.

 FIG. 1 represents an ablation curve on which the values of the discrete elementary ablation depth are plotted on the ordinate axis, this axis being graduated in micrometers, as a function of the energy density per illumination pulse laser, the abscissa axis being graduated in millijoule / cm2.

 The discrete elementary ablation curve is characterized by the presence of a threshold, that is to say a value of the energy density below which no ablation occurs. In general, the previous curve has a great non-linearity and the depth of ablation increases only very slowly with the energy density. It will in fact be found that the depth of each discrete elementary ablation is small, between 0.25 to 0.5 μm.

Although the discrete elementary ablation caused by a laser illumination pulse has, with regard to the depth thereof as a function of the energy density, the aforementioned non-linearity is admitted, provided that the energy density is constant from one pulse to another, that the total ablation resulting at a fixed point of a number n of given consecutive pulses is equal to n times the average ablation corresponding to a single pulse. discrete elementary ablation corresponding to the above-mentioned mean ablation is noted
(1) a (e)
This average ablation corresponds substantially to a laser illumination pulse whose energy density is of the order of 200 millijoules / cm2 at an ablation depth corresponding to the level of the curve shown in FIG. 1, and in practice, to an ablation depth of between 0.5 and 0.8 ijm.

 A more detailed description of the operations to be carried out for the correction of ametropia by correction of the dimensional optical characteristics of the cornea and mainly of its radius of curvature, will be given in conjunction with FIGS. 2a and 2b. The main operations mentioned above will be limited, for the purpose of simplifying the description of the system which is the subject of the invention, to the operations of myopic keratomileusis, hypermetropic keratomileusis and myopic astigmatic keratomileusis, or their equivalent on implantable or non-implantable optical lenses.

 FIG. 2a represents a plan view of the eyeball of the eye designated by OE. The aforementioned plan view is observed in the direction of the optical axis of the eye designated by OZ, in FIG. 2a, the aforementioned optical axis being centered on the cornea designated by COR and the pupil of the iris not shown on this figure. In the description below, it will be considered that the optical axis and the visual axis of the eye are substantially combined. Reference directions are noted OX and OY, the OX coordinate system, OY forming an orthogonal coordinate system. We denote by h the distance of a given point from the corneal surface to the optical axis OZ.

 Figure 2b shows a section along the plane AA of Figure 2a. In FIG. 2b, rg denotes the radius of curvature of the cornea COR, before treatment, the cornea before treatment being shown in FIG. 2b in dotted lines, and by r denotes the radius of curvature of the cornea COR, after treatment with l using the device which is the subject of the invention.

 R denotes, in general, the radius on the cornea of the optical intervention and rectification zone thereof. Of course, the value of this parameter R and the area of the cornea on which the intervention will be performed is defined by the practitioner, following a clinical analysis carried out by the latter. Finally, denote by A (h) the ablation function, i.e. the thickness, in the direction OZ of the optical axis of the eye, to be removed by photodecomposition at a distance h from the axis OZ eye optics to bring the cornea from the initial radius of curvature rg to the final radius of curvature r, after the above-mentioned intervention.

 For a more precise definition of the ablation profiles A (h) in the case of a myopic keratomileusis, in the case of an astigmatic keratomileusis and in the case of a myopic astigmatic keratomileusis, reference may usefully be made to the request. of European patent 0 296 982 previously cited and incorporated in the present description for reference.

 It will also be noted that in the case of astigmatic, myopic or hypermetropic keratomileusis, the resulting ablations are not of revolution around the axis OZ. The ablation function A (h) can then be replaced by an ablation function A (x, y) where x, y represent the coordinates x, y in the plane ox, oy, with h2 = x2 + y2.

 A more detailed description of a mask for surface treatment by laser irradiation in accordance with the object of the present invention will now be given in conjunction with FIGS. 3a and 3b.

 According to the aforementioned figures, the mask for surface treatment by laser irradiation, object of the present invention, is constituted by a support P opaque to the wavelength of the aforementioned laser radiation.

 The support P includes a plurality of windows F formed therein.

 In FIGS. 3a and 3b, the windows F are represented by points in a nonlimiting manner. The windows F are transparent to laser radiation and form a screen-like mask.

The density of the windows F for a non-zero surface element d # on the mask, this density being noted d (h) is proportional to the law of rectification or ablation, previously noted A (h)
d (h) = # .A (h).

 In the previous relation, h denotes, as previously mentioned in relation to FIGS. 2a and 2b, the radial distance of a point of the mask with respect to a reference point, ss being a coefficient of proportionality determined by the number of windows F per unit area.

 It will be understood, in particular, that the radial distance h can be determined relative to a reference point, which corresponds substantially to the center of the sieve mask, shown in FIG. 3a or 3b.

In practice, for a surface element d of the mask located at the distance R from the center C of the mask, the number N (h) of windows or openings F on this surface element checks the relationship
N (h) =. A (h). da
According to an advantageous characteristic of the mask for surface treatment by laser irradiation, which is the subject of the invention, masks of the sieve type relate, on the one hand, to masks whose openings are of random distribution, in which the windows or openings F, as shown in Fig. 3c and 3d and 4a, Sa, are such that for the surface element d considered, the number of windows or openings F contained in the above-mentioned surface element is proportional, in the case of myopic keratomileusis, at 1- h2. A similar law, however favoring an annular domain, can be established in the case of hypermetropic keratomileusis, as will be further described later in the description.

 The sieve type masks which are the subject of the present invention relate, on the other hand, to masks in which the openings or windows form a plurality of concentric annular zones. In this second type of mask, the windows F on the support can admit as a center of symmetry the reference point at the center c of the mask, as shown in FIGS. 3a and 3b. It is of course possible for this second type of mask to envisage masks for myopic as well as hyperopic keratomileusis.

 As shown in FIG. 3a, in particular, the openings or windows F are of substantially rectangular or circular shape and distributed in concentric circles.

 According to another alternative embodiment as shown in FIG. 3b, the openings F are formed by annular windows or annular sectors. The annular windows or annular sectors are formed by slots. Thus for annular windows or annular sectors formed by slits of determined transverse dimension, the density of the rings or annular sectors is proportional to l-h2, in the case of a mask for myopic keratomileusis. The aforementioned density can then be reduced to a linear density of rings or annular sectors, that is to say the number of rings or annular sectors per unit of length for a radial excursion of the mask considered. As shown in FIGS. 3a and 3b, in the case of a mask for myopic keratomileusis, the density of the rings or sectors of rings increases from the periphery towards the center C of the mask, the totality of the rings or sectors of rings or slots having however shown in the central area of Figures 3a, 3b. It will further be understood that, provided that the window density laws F are similar, to the rings or sectors of rings, as shown in FIG. 3b, may be substituted rings with discrete, substantially point-like openings, as shown in FIG. 3a, the mask thus produced constituting in a way a mask with regular distribution of slots or openings.

 A more detailed description of masks of the random sieve type in accordance with the object of the present invention will be given in connection with FIGS. 3c and 3d.

 According to an advantageous characteristic of the mask of the sieve type for surface treatment by laser irradiation, object of the invention, the spatial distribution of the windows F is random on a given surface element of the support P constituting the mask.

 As has also been shown in Figures 3c and 3d, for the treatment of spherical or substantially spherical surfaces, such as optical lenses or surfaces such as the cornea of the eye, the treatment then consisting of a refractive eye surgery treatment by ablation on this cornea, the mask has a plurality of windows F contained in a substantially circular area, as shown in Figures 3c and 3d.

 As will be noted in FIGS. 3c and 3d, the windows F can be constituted by holes made in the mask or more particularly in the support P constituting the latter, these holes being contiguous or not.

 According to an advantageous characteristic of the mask which is the subject of the present invention, the support P can be constituted by a flat plate. It can also be constituted by a spherical cap, which makes it possible to be freed during the laser irradiation with a view to the treatment to be freed from the problems relating to the depth of field. The sectional views AA of FIGS. 3a and 3b show the constitution of the support P according to a flat plate or according to a spherical cap.

 As has also been shown in FIG. 3e, in order to allow the correction of astigmatisms of spherical optical surfaces, such as the cornea for example, the mask, object of the present invention, may also include blackout flaps , noted VO1 and V02 in the above-mentioned figure.

 Preferably, the blackout flaps VO1 and V02 are symmetrical with respect to a direction z of the plane of the plate P constituting the diameter of the above-mentioned substantially circular area.

 The blackout flaps VO1 and V02 each have a straight edge defining a slot materializing the direction of correction of astigmatism, the aforementioned direction z.

 According to an advantageous characteristic of the sieve type mask, object of the present invention, the width e of the slot, as shown in FIG. 3e, is adjustable.

 According to a nonlimiting embodiment, the plate or the spherical cap P opaque to the laser radiation used can be made of a metallic material, such as aluminum, nickel alloys for example. In this case, the windows F can be formed by perforations.

 In addition, the plate P opaque to laser radiation can be constituted by a glass or by a silica blade treated to ensure opacity to electromagnetic radiation, at the wavelength used, the windows being formed by untreated zones.

 In all cases, the windows F can be formed either by perforations or by untreated zones, the windows being substantially circular and having a diameter of between 10 μm and 50 μm for example. The windows or openings F of the same mask can have different dimensions. When the windows F consist of untreated zones, these can be obtained by photo-lithographic processes on a support P made of quartz for example.

In this case, the windows F may have the form of continuous concentric rings.

 Of course, it will be understood that in the drawings representing the screen masks, objects of the invention, these drawings correspond to models, which can, by reduction of optical magnification, give rise to screen masks, objects of the present invention.

 According to a nonlimiting embodiment, the slot Fe can be produced by the rectilinear edges of two blackout flaps VO1, V02, which can be sliding on the plate or spherical cap P constituting the sieve mask.

 The sliding of the blackout flaps VO1, V02 then makes it possible to adjust the width e of the aforementioned slot Fe.

 According to another nonlimiting embodiment, the blackout flaps VO1 and V02 can be produced by a single plate made of aluminum material for example, plate in which is formed a slot Fe with substantially rectilinear edges. Of course, in this case, the width e of the slot Fe can be adjusted by means of a set of plates constituting the blackout flaps VO1 and V02, each plate comprising a slot of determined width e.

 A plate from the aforementioned set of plates can then be used and placed superimposed on the sieve mask, object of the present invention, as shown previously in FIG. 3e.

 During use, the practitioner can thus be led to change a plate considered comprising a slot Fe of given width e to replace the latter by another plate of the same set comprising a slot Fe of width e 'different. If necessary, the blackout flaps or plates forming the Fe slot can be replaced by spherical cap parts.

 In addition to the aforementioned Fe slot, according to an advantageous aspect of the present invention, this can be replaced by an auxiliary mask replacing the sieve type mask as shown in FIG. 3a, 3b or 3c, 3d above. Such an auxiliary mask intended for obtaining the cylindrical ablations required for the correction of astigmatism has a law of distribution of the openings or windows F in the corresponding azimuth direction u, as shown in FIG. 2a, d (u) = K (l-u2), where u represents the abscissa in the abovementioned direction u. Such an auxiliary mask as shown in FIG. 3f has for example an alignment of openings or windows F, which, during irradiation for treatment, must be aligned in the aforementioned azimuth direction u.

The treatment operation then takes place in two stages - ablation of revolution using one of the sieve type masks such as
shown in Figures 3a to 3d for example, 4 - "cylindrical" ablation along the azimuth 4 required by means of the mask
auxiliary.

 Different details of embodiment of the sieve type masks, as shown in Figures 3c and 3d, will now be given in connection with Figures 4a, 4b and Sa, 5b.

 In order to carry out a treatment with myopic or hypermetropic keratomileusis, the sieve type masks, objects of the present invention, as shown in FIG. 4a in particular and 4b, or 5a, 5b, have a density of windows on the symmetry mask axial. The density of windows (d) h is substantially constant and with random spatial distribution for any surface element, denoted da, corresponding to a portion of circular crowns of width, denoted dh, at a radial distance h from the center of the mask, denoted C .

 In the case of treatment with myopic keratomileusis, the density d (h) of the windows on the mask, as shown in FIG. 4a and in FIG. 4b, is monotonically decreasing from the center C of the mask towards the periphery.

 It will be noted that in FIG. 4b, the ablation function A (h) has been shown in solid lines, this function as a function of the radius h relative to the center of the cornea being substantially parabolic, and in dashed lines the density of the windows. d (h), this density being proportional to the aforementioned ablation function to the nearest ss coefficient.

 As shown in FIG. Sa and in FIG. 5b, in the case of treatment with hypermetropic keratomileusis, the density d (h) of the windows on the mask is monotonically increasing from the center of the mask, center C, towards the periphery then decreasing for constitute a transition zone.

 In FIG. 5b, the ablation function A (h) has also been represented on the one hand, and in dashed lines, the density of the windows d (h), this density being proportional to a coefficient ss close to the aforementioned ablation function.

 FIGS. 6a and 6b show non-limiting embodiments of models of sieve type masks, in accordance with the subject of the present invention, on the one hand, in the case of a treatment of myopic keratomileusis type and, on the other hand, in the case of a hypermetropic keratomileusis type treatment.

 The aforementioned models are, of course, shown on an enlarged scale, as indicated above, and can be executed for example by means of software of the design software type assisted by the CAD computer.

 In FIGS. 6a and 6b, it will be noted that, preferably but not limited to and in order to ensure a rationalized execution of the aforementioned masks, the windows F or orifices can advantageously all have an identical surface of determined value.

 In addition, as can be seen in the aforementioned figures, none of the orifices or windows provided in the model is overlapped with a neighboring orifice or window.

 The two aforementioned characteristics make it possible to simplify the software for implementing the mask models described above, the configuration of the software intervening only in this case, in order to determine, as a function of the intervention to be carried out, the density d (h) of windows for a surface element da, as shown previously in FIGS. 3a and 3b.

 Without limitation and by way of example only, it will be considered that the distribution density of the windows d (h) is constant for surface elements da formed in concentric rings relative to the center C of the masks as shown in FIGS. 6a and 6b or their models, the width dh over which the density of windows is substantially constant can be equal, for example, to ten times the dimension of a window or orifice.

 Preferably but not limited to, the windows or orifices are then constituted by substantially circular windows or orifices.

 Preferably, for the masks or mask models as represented in FIGS. 6a and 6b, in accordance with the object of the present invention, and for safety purposes, the ratio of the sum of the surfaces of the windows F or orifices and of the total surface of the mask, that is to say ultimately of the zone substantially in the shape of a circumference, is determined by a coefficient intended to avoid the harmful side effects of laser irradiation, the duration of the intervention as well as , in the case of refractive eye surgery, the roughness which can be accepted for the surface of the cornea. For a small correction of the treated surface, small window masks will be used, in order to generate a smooth rectified surface. On the other hand, for a large correction, the windows may be of larger dimension, in order to shorten the duration of the intervention.

 A more detailed description of a surface treatment system by laser irradiation, in accordance with the object of the present invention, will now be given in connection with FIG. 7.

 In general, the system for surface treatment by laser irradiation, which is the subject of the present invention, comprises, in a similar manner to the system described in European patent application No. 0 296 982 and previously mentioned in the description, means, denoted 1, emission of a laser beam, noted FL, by pulses.

The system which is the subject of the invention also comprises means 2 making it possible to generate a processing laser beam, noted
FLT.

 As described previously in the aforementioned patent application, these processing means may comprise a group of lenses 20 making it possible to bring the laser beam FL to suitable dimensions relative to the dimensions of the mask, as described above.

 Thus, the means 2 for constituting a laser beam for processing FLT comprise a mask for surface treatment by laser irradiation, as described previously in the description, this mask being mounted for example on a support 21 shown in FIG. 2.

 The laser irradiation surface treatment system which is the subject of the present invention also comprises displacement means, denoted 4, in two orthogonal directions X, Y of the aforementioned surface treatment mask. The mask, on its support 21, is, during the period of irradiation, continuously moved randomly in a plane orthogonal to the longitudinal axis of the treatment beam FLT.

 It will of course be noted that, conventionally and as already described in the aforementioned patent application, the surface treatment system by laser irradiation, object of the present invention, also comprises focusing lenses 9, a prism or a deflection mirror 30 and an auxiliary alignment laser 6, such as a helium-neon laser, making it possible to ensure the alignment of the optics constituted by the deflection prism 30 and by a focusing lens 31 with the optical axis of the cornea and of the eye, denoted OE, in FIG. 7.

As has also been shown in Figure 7, the displacement means 4 in X, Y of the mask object of the invention comprise means for random displacement in translation in the first direction
X, these means being denoted 40, 41 in FIG. 7 and the means for random displacement in translation in the second direction Y, these means being denoted 42, 43 in FIG. 7.

A more detailed description of the means of travel in
X, Y randomly of the mask, in accordance with the system which is the subject of the invention as shown in FIG. 7, will be given in connection with FIG. 8a.

 According to the aforementioned figure, the displacement means in the two orthogonal directions X and Y comprise an external frame 44 forming a substantially square support frame and two guides, denoted 410, 430, mounted to slide on the uprights of the external support frame 44. The guides 410, 430 are substantially orthogonal and mechanically integral.

 An internal frame 47 is provided, making the two guides 410 and 430 integral and supporting the treatment mask.

 A first stepping motor, denoted 40, and a gear 41 make it possible to drive a first guide 410 in translation in the first direction X. Preferably, as will be described later in the description, this translation can consist of a displacement increment, positive or negative X with respect to a rest position.

 In the same way, a second stepping motor 42 and a gear 43 are provided so as to allow the second guide 430 to be driven in translation in the second direction Y. This translation can consist of a positive or negative displacement increment GY relative to a rest position.

 As shown in FIGS. 8b and 8c, the guides 410 and 430 are successively driven in translation in a random manner, the positions X, Y being represented for example in time in FIGS. 8b and 8c.

 It goes without saying that the instantaneous position of the internal frame 47 and of the mask supported by the latter then results from the composition of the two movements of the guides 410 and 430 in the directions X and Y mentioned above.

 In order to allow the movements or displacements to be carried out in the X and Y directions, as shown in FIGS. 8b and 8c, the displacement means in two orthogonal directions furthermore, as represented in FIGS. 7 and 8d, contained in means command 5, a first and a second generator of random numbers, denoted 51 and 52, making it possible from the aforementioned random numbers to generate a first and a second random series of displacement increments EX, A X.

 By way of nonlimiting example, the aforementioned control means 5 then make it possible to deliver to the stepping motors 40 and 41 the control signals SCDX and SCDY, which correspond to the displacement increments represented in FIGS. 8b and 8c.

 In order to generate the two random series of displacement increments a X and AY, each random number generator 51, 52 can be followed for example by a subtractor circuit 53, 54 making it possible to perform the subtraction of two successive random numbers , each subtractor circuit 53 and 54 being itself followed by a comparator 55, 56 making it possible to compare the value of the difference calculated between two successive random numbers generated by each generator 51, 52 with a plurality of three ranges of values of numbers , the comparison of the aforementioned difference with the previously mentioned ranges, and as a function of the belonging of this difference to one of the ranges, making it possible to generate by said comparator a positive, negative or zero signal, this positive, negative or null corresponding to signal SCDX or SCDY and representing, ultimately, the corresponding displacement increment AX or AY positive, negative or zero.

 It will be understood for example that for random numbers belonging to a range of values of numbers between 0 and 333333 for example, the three ranges of values can be constituted by a first range between 0 and 111111, 111112 and 222222 and 222223 and 333333 , the difference between two successive random numbers generated by one of the generators 51 or 52 of random numbers, these numbers being understood of course in the range of values 0, 333333, is then compared with the aforementioned ranges, the comparators 55 and 56 allowing then to deliver a positive, negative or zero signal depending on whether this difference belongs to one or the other range.

 Of course, any other embodiment of the control means 5 can be envisaged, in particular the random numbers can be drawn from a program residing in calculating means 8 represented in FIG. 7 and the difference between two successive random numbers can also be carried out from a corresponding program replacing the difference calculating circuits 53 and 54.

 In the same way, the comparison of this difference with the three ranges of values mentioned above can be carried out by software. In the latter case, the control means 5 then boil down to an interface circuit making it possible, from logic signals delivered by the calculating means 8 corresponding to the positive, negative or zero signals representative of the SCDX or SCDY signals, to generate excitation control signals, for example stepping motors, in order to apply to them the corresponding displacement increments t X or AY previously described. This type of interface circuit will not be described since it corresponds to interface circuits normally available on the market.

 As has also been shown in FIG. 8a and advantageously without limitation, the internal frame 47 can be provided with a drive system, denoted 470, the mask as previously described in the description then being mounted on its support 21, which is rotatably mounted relative to the internal frame 47.

 Thus, the mask can, in addition to the random translation movements in X and in Y previously described, be subjected to a rotational movement at an angular speed w for example. In addition, when using the blinds VO1 and V02 and the slit Fe, the rotary drive means 470 can then be used to orient the mean direction of the slit to correct the astigmatism mentioned above.

 It will thus be understood that the training, for example of the mask, according to random movements as previously described, composed with a rotational movement, makes it possible to avoid the continual ablation of the same points on the surface to be rectified, whether it is the cornea of the eye or that of an optical lens, which makes it possible to achieve regular ablation, which allows, for a corresponding distribution of the windows or orifices, to obtain a smoothing of the treated surface.

The means for random displacement in X, Y and in rotation of the mask, as shown in FIG. 8a to 8c in particular, can advantageously be implemented from a micrometric drive system in translation and rotation marketed in France, under the reference of commercial designation, catalog 1988 p. 104, 49, 79, MR8 and UT 10025 PP, UR 100 PP by the company MICRO-CONTROLE ZI de Saint Guénault - 7, rue Jean Mermoz - BP 144 - 91005 EVRY CEDEX
France -
Masks of the sieve type and a particularly efficient laser irradiation surface treatment system have thus been described since these practically overcome the imperatives of critical alignments of the optical axes of the devices of the prior art with respect to the he optical axis of the cornea or of the spherical surface constituting the optical lens to be treated, as well as practically erotic movements of the cornea of the eye during interventions by refractive surgery of the eye.

Claims (19)

 1. Mask for surface treatment by laser irradiation, characterized in that it consists of - a support (P) opaque to the wavelength of said laser radiation, - a plurality of windows or openings formed in this support,  said windows being transparent to said laser radiation, and forming  a sieve type mask, the density of the windows on the mask d (h) being  proportional to the law of rectification A (h): d (h) = ss .A (h) where h denotes  the radial distance of a point on the mask from a point of  reference and where ss is a proportionality coefficient determined by the  number of windows per unit area.  2. Mask according to claim 1, characterized in that the openings or windows form a plurality of concentric annular zones admitting for center the reference point or center of the mask.  3. Mask according to one of claims 1 or 2, characterized in that the openings or windows are of substantially circular or rectangular shape.  4. Mask according to claim 2, characterized in that the openings are constituted by annular windows.  5. Mask according to claim 3, characterized in that the spatial distribution of the windows is random on a surface element da of the given mask.  6. Mask according to one of claims 1 to 5, characterized in that, for the treatment of spherical surfaces such as lenses or refractive eye surgery, by rectification or ablation on the cornea, said mask has a plurality of windows contained in a substantially circular area.  7. Mask according to claim 6, characterized in that, in order to carry out a treatment with myopic or hypermetropic keratomileusis, said masks have a density of windows on the mask with axial symmetry, the density of windows being substantially constant and with distribution random spatial for any surface element da corresponding to a portion of circular crown of width dh at a radial distance h from the center of the mask.  8. Mask according to claim 7, characterized in that, in the case of a treatment with myopic keratomileusis, the density d (h) of the windows on the mask is monotonically decreasing from the center of the mask towards the periphery.  9. Mask according to claim 7, characterized in that, in the case of a treatment by hypermetropic keratomileusis, the density d (h) of the windows on the mask is monotonically increasing from the center of the mask towards the periphery, then decreasing to constitute a transition zone.  10. Mask according to one of claims 1 to 9, characterized in that, in order to allow the correction of astigmatisms of spherical optical surfaces, said mask further comprises blackout flaps (VOl, V02), the blackout flaps being symmetrical relative to a direction of the plane of the plate constituting the diameter of the substantially circular zone, the blackout flaps each having a rectilinear edge defining a slit (Fe) materializing the direction of correction of astigmatism.  11. Mask according to claim 10, characterized in that the width of the slot is adjustable.  12. Mask according to one of the preceding claims, characterized in that said support is constituted by a substantially flat plate or by a spherical cap.  13. Mask according to claim 13, characterized in that the opaque plate or the spherical cap is made of a metallic material such as aluminum, nickel alloys, said windows being formed by perforations.  14. Mask according to one of claims 1 to 12, characterized in that the opaque plate consists of a glass or a blade of silica treated to ensure opacity to said electromagnetic radiation, said windows being constituted by untreated areas.  15. Mask according to one of claims 13 or 14, characterized in that said windows formed either by the perforations, or by the untreated areas, are circular and have a diameter between 10 Cim and 50 pm.  16. Surface treatment system by laser irradiation comprising means for emitting a laser beam (FL) by pulses, characterized in that it comprises means (2) making it possible to generate a laser treatment beam (FLT ), said means (2) comprising a mask for surface treatment by laser irradiation according to one of  preceding claims 1 to 15, means of displacement in two orthogonal directions X, Y of said  surface treatment mask, said mask being, for the duration of  irradiation, continuously moved randomly in a plane  orthogonal to the longitudinal axis of the treatment beam.  17. System according to claim 16, characterized in that said means of displacement in X, Y of said mask comprise - means (40, 41) of random displacement in translation in the  first direction X, - means (42, 43) for random displacement in translation in the  second direction Y.  18. System according to claim 17, characterized in that said means of displacement in two orthogonal directions comprise - an external frame (44) substantially square support, - two guides (410, 430) mounted to slide on the uprights of said  external support frame, said guides being substantially orthogonal and  mechanically integral, - an internal frame (47) making the two guides (410, 430) integral and  supporting said processing mask, - a first stepping motor (40) making it possible to drive a first  guide in translation in the first direction X, said translation possibly consisting of a positive displacement increment # X, or negative relative to a rest position, - a second stepping motor (42) making it possible to drive the second  guide in translation in the second direction Y, said translation  can consist of a displacement increment, Y positive or negative  relative to a rest position, - a first and a second generator of random numbers allowing  from the aforementioned random numbers to generate a first and a  second random series of displacement increments t X, A Y.  19. System according to one of claims 17 or 18, characterized in that it further comprises means (470) for rotating said surface treatment mask.