FR2685629A1 - Machining device, especially for a corneal lens - Google Patents

Abstract

The invention relates to a device for machining a corneal lens (10), through the stromal face (11). Photoablation radiation (8) produced by a laser (1) is focused by an optical lens (2). A lens (10) holder on which a lens (10) is mounted is driven in rotation by a lathe (5). The lens receives the radiation of the beam (8) at a given defocusing distance (D). An average effect of decreasing the light intensity in the beam (8) is thus obtained, which makes it possible to obtain the desired profile directly. A diaphragm makes it possible to vary the ellipticity of the beam (8).

Description

MACHINING DEVICE, IN PARTICULAR A CORNEEN LENTICLE
The present invention relates to a device for machining a corneal lenticle or a corneal graft by the stromal face.

 To date, there are numerous refractive surgery techniques aimed at surgically and definitively correcting the patient's ametropia by modifying the power of the corneal diopter.

 The dioptric apparatus of the eye which focuses the images on the retina has a power of 63 diopters (63 D) distributed between the lens (20 D) and the cornea (about 43 D).

 Let us first indicate the different types of corneal refractive surgery techniques.

 The most commonly used method is the radial keratotomy. It corrects weak myopia (less than 6 D) and consists of performing surgery on the cornea 4 to 16 incisions (usually 8), deep (80 to 100% of the corneal thickness), radially arranged respecting a central optical zone. The incisions cause a mechanical weakening of the peripheral cornea which flattens in its center. This results in a decrease in the dioptric power of the cornea.

This decrease depends on the depth of the incisions, their number and the diameter of the central optical zone.

 The functional results are satisfactory because the central zone around the optical axis is preserved. Side effects are low, complications extremely rare except long-term progressive progression to hyperopia which is a possible event for some authors.

 The correction of strong ametropia requires to modify more strongly the shape of the cornea by a true machining of it. Keratomileusis consists in taking, machining and then putting back a corneal lenticule on the patient's eye. The thickness of this lenticule is typically e = 200 u (whereas the cornea has a thickness of e = 500 u). We will describe further the various methods of sampling and machining. Note that the posterior stromal portion of the lenticule is planted and that Bowmann's membrane is respected.

 The epikeratoplasty consists of grafting on the patient's eye a corneal lenticule taken from a donor globe and machined. It is a sort of grafted contact lens. This technique has the advantage of being reversible.

 For about five years, different teams including ours (Dr. Aron-Rosa), study the use of the excimer laser in refractive surgery. This study is motivated by the particular character of the excimer laser-tissue interaction (see below). The excimer laser makes it possible to make cuts or abrasions (machining) with surface conditions of a very high quality, very smooth surfaces with a zone of necrosis of very small thickness (a few microns). Recall that this is a pulsed laser that emits W rays, whose repetition rate varies from one to several hundred Hertz (1 Hertz = 1 shot per second) and ablate typically 0.2 to 0.5 u per shot .

Two lines of research have been mainly explored.

 A first known technique is the excimer laser radial keratotomy.

The idea is to replace the diamond knife - which makes the radial incisions - with an excimer laser. The goal is to have a non-contact cutting technique (which avoids the problems of sterilization and maintenance of the knives, and which allows a better control of the operation). In fact, it has proved extremely difficult to perform - with the excimer laser - corneal incisions of determined depth. In addition, the safety of this technique will remain to be proven. This line of research has been abandoned by most teams. A description of such a technique using radial slits of a fixed mask placed near the eye in the article "An Ophthalmic" is described.
Excimer Laser for Corneal Surgery by E. Schroder et al, published in the American Journal of Ophthalmology, March 1977.

 Another known technique is myopic photorefractive keratoplasty.

 It involves laser machining the superficial and central portion of the cornea. The operation is done in a few tens of seconds, under anesthetic contact.

 This technique presents some technical difficulties and poses some medical problems.

 It involves machining the central part of the cornea by avoiding inducing astigmatisms. The laser beam must be of very good optical quality with a very uniform illumination and a good symmetry by rotation of the illumination. This condition is difficult to achieve technically because the radiation of an excimer laser is inhomogeneous and especially very asymmetrical, because of the transverse structure of the internal laser electric discharge (which prepares the excimer, namely the excited dimers and realizes the population inversion). The light beam from the laser is usually rectangular (typically 2.5 x 0.7 cm) with very different angular divergences in the horizontal and vertical directions. The search for a symmetrical and homogeneous illumination imposes the use of a heavy, expensive technology whose results are still imperfect. Optical systems are imperfect and expensive because the optical materials for excimer (MgF2, CaF2) are few and expensive.

Diaphragmming the light beam to take a more homogeneous part of it is always possible, but it costs to have to use an overpowering excimer laser.

In addition, machining the cornea on a waking patient, under contact anesthesia, requires a quick gesture (to prevent the patient from moving), with a high rate of fire (10 Hz). On the other hand, machining requires a complex optical system comprising a programmable progressive opening diaphragm as described for example in the patent application.
U.S. 4,903,695 (CRI.LP). This system loses light and requires the use of a laser powerful enough.

 Finally, a computerized control system of the laser imposes electrical shielding (because the internal laser discharge generates electrical noise incompatible with the operation of a computer), which explains why the excimer lasers currently on the market are complex, heavy and expensive (for example the one marketed by the company Summit weight 600 kg and cost 3 MF).

 The machining of the optical zone must be performed in the optical axis. This centering must be very precise to avoid any irregular astigmatism.

 In addition, the laser destroys an essential membrane: Bowmann's membrane, which can lead to more or less long-term complications.

Only myopia less than 10 D (which impose corneal thinning below 60 u) can be corrected by this technique.

 Excimer machining systems have been commercially available for about 2 years and lead to correct refractive results for myopia less than 6 diopters. In some cases, some opacification of the cornea appears, related to the destruction of Bowmann's membrane. This opacity, however, does not seem to cause a significant decrease in visual acuity.

 In cases where high refractive corrections (greater than 6 dioptres) are sought, a decrease in the refractive effect often occurs after 6 months to one year, due to epithelial hypertrophy with regard to the treated area.

It seems difficult to pronounce today on the correction of high myopia in photorefractive keratoplasty.

 Finally, it should be noted that, in cases of low myopia, radial keratotomy gives satisfactory, predictable results, that it has already fallen by 10 years and that it finally requires much less expensive equipment.

 Dr. Pouliquen's research team at the Hôtel Dieu, led by Dr. HANNA, experimented with an original method of machining corneas: the rotating lunge. This technique is described in the article by G. RENARD, K. HANNA et al.

entitled "Ultrastructural Appearance of the Excimer Laser on the Human Cornea" published in "Ophthalmology 1988 2: 185-7". The technique involves projecting a beam through the cornea through a feather-shaped diaphragm (or daisy petal). This diaphragm rotates and the axis of rotation is coincident with one of the ends of the pen. The image of this axis is centered on the patient's cornea.

 By the rotation of the diaphragm, it would theoretically be possible, by a judicious choice of the shape of the pen, to ablate on the surface of the cornea a symmetrical volume by rotation of any desired shape.

 If the method was tested on corpse globes, it was not used on patients. Some remarks can be made about this system: the central point of the cornea is singular. any defect in the shape of the pen at this point can significantly change the depth of the ablation. Moreover, this point, unlike all the others, is illuminated with all the shots (but very weakly). The other points are illuminated more strongly but only on part of the shots. There would be little problem if the depth of photoablation varied linearly with the fluence (light energy per unit area), but this is not the case.

 A second disadvantage is that the operation time is very long because the diaphragm only allows a few percent of the light emitted by the laser.

 A third drawback is that it is necessary to design as many rotary masks as it is necessary to types of incisions, and this poses problems in the design of these masks and their experimentation.

 Other photoablation techniques on the patient's eye have been implemented.

 European Patent Application EP-A-2 18427 masks the laser beam to a cylinder of circular section. According to this technique, it is necessary that the beam is made uniform to then achieve the desired profile on the cornea, and therefore, it necessarily implies the loss of a large part of the light energy provided by the laser.

 European Patent Application EP-2-80414 (TAUNTON TECHNOLOGIES INC) discloses a device in which the rectangular beam from the laser is first converted into a square-section beam by a cylindrical lens, then is rotated and homogenized by an optical filter to obtain a uniform flow profile. A drum provided with filters (as many filters as profiles to achieve) allows to give the beam previously "homogenized" a flow profile to achieve the desired machining, by a divergent light beam.

 The device is very complicated in terms of optics and extremely costly because the optical elements used in the radiation ranges useful in photoablation are expensive, and in addition the double filtering as well as the succession of the optical elements induce a significant loss of luminous flux. Such a disadvantage becomes prohibitive for the correction of strong ametropia.

 Thus, there is currently a need for a device for machining corneal lenticles or corneal grafts to correct strong ametropia and implementing photoablation machining. As will now be shown, the properties of the excimer-tissue laser interaction during photoablation make this kind of technique potentially very interesting (see in particular the article by D. Aron-Rosa, M.

Gross and B. Aron entitled "Use of short-wave ultraviolet lasers in ophthalmology" published in "Therapeutic and Clinical Year in Ophthalmology" vol.

XXXVIII, 1988).

The W photons emitted by the excimer laser have a very high energy (6.4 eV for the excimer argon fluorine laser emitting at 193 nm), higher than the energy associated with most chemical bonds. These photons are then likely to break the chemical bonds they encounter (because it is a photochemical process that is possible energetically) and are correlatively strongly absorbed by any material medium. It is thus difficult to find transparent optical materials at 193 nm (only the best quartz and some fluorinated crystals as
CaF2 or MgF2 are).

The 193 nm laser radiation then acts only on the surface, over a few microns thick (which is the depth of penetration of light into the corneal tissue). Correlatively to this strong absorption, the tissues subjected to the radiation are strongly modified. Macromolecular chains are broken by photons
W smaller fragments, therefore lighter and more volatile. These fragments volatilize in the ambient air and disappear. It is the phenomenon of photoablation which is a photochemical process (and not thermal as the Yag-tissue laser interaction).

 By photoablation, it is possible to machine a living tissue in an ideal manner with very low necrosis effects. The tissues that are subjected to the laser beam are volatilized leaving the underlying tissues intact, since they have not been exposed to laser radiation that has been absorbed by the destroyed tissues.

 Photoablation occurs only beyond a certain threshold fluence. This threshold, which depends on the material, is about 100 mJ / cm 2 (millijoule per square centimeter) on the cornea. The depth function ablated / fluence varies little when the fluence is around 300 mJ / cm2. We observed tissue necrosis and burns above 1000 mJ / cm2. Some authors recommend using a fluence exactly between 160 and 180 mJ / cm2 which alone, would prevent opacification of the cornea on the monkey.

We operate most often in the vicinity of this fluence, although this theory remains to be proved.

 Note that, although UV radiation is not visible directly, it is usually easy to "see" the impact of the laser, because all material media are fluorescent under the influence of the W radiation.

The device which is the object of the present invention aims to machine lenticules for epikeroplasties and keratomileusis. These lenticules have a diameter of 8 to 9 mm and a thickness before machining of 300 microns. These lenticules are taken either from donor corneas (epikeratoplasty) or from the patient himself (keratomileusis) during the procedure. The sample is taken using a microkeratome (planer). The lenticule is then machined by the stromal side so as to induce the desired refractive effect
- myopia: central photoblation
- hyperopia: peripheral photoablation.

 He is finally sutured on the patient's eye.

Note that the quality of this suture is very important because the suture often induces astigmatism as a side effect.

Surfacing lenticles is complicated by the fact that it is soft materials. The regularity of the surfacing of the optical zone is essential to obtain a satisfactory optical result. The techniques for machining lenticules by their stromal face currently used on patients are currently performing mechanical machining and are as follows
1) The tour of Barraquer
This is the oldest technique. The cornea is frozen on a lathe with liquid nitrogen. The frozen cornea, which is hard, is machined with a tool. This technique is now abandoned because freezing strongly damages the cornea which becomes edematous and then takes several weeks to clear.

2) The Microkeratome (refractive set ")
Barraquer-Krumeich
The parallel-faced corneal lamella obtained using a microkeratome from the cornea of a donor or patient is surface-free without freezing. The lamella is fixed on a mold whose radius of curvature determines the power of the obtained lenticule. The refractive section is made using the microkeratome. This section presents irregularities due to the oscillatory movement of the microkeratome blade, the variable speed displacement of the microkeratome during the cutting, and the compression of the lamella during resection.

 This results in obtaining an optical zone, certainly regular, but the scanning electron microscopy analysis showed some imperfections that may explain in some cases the decline in visual acuity postoperative.

 An experimental technique using an excimer laser was the subject of a communication in July 1991. The excimer laser systems indeed make it possible to machine corneal lenticles by placing the lenticule to machine stromal face exposed to the laser beam, and to program the laser system to modify, according to the ametropia of the patient, the refraction of the lenticule. The machining usually corresponds to one or two hundred shots. To correct myopia (the most common case), the treated area is circular with illumination as homogeneous as possible. The diameter of this zone varies during the machining operation (from 0 to 5 mm) so as to photoablate a volume having the shape of a lens: maximum ablation in the center (which receives all the laser shots), and weaker on the edges (which receives only a few).

However, the opening or the progressive closing of the diaphragm during the treatment, leads to irregularities in stairs, source of astigmatism.

 The present invention relates to a device for machining a corneal lenticle by the stromal face (rear face), implementing a photoablative laser light and which can be used without the disadvantages of known photoablative techniques.

 The basic idea of the invention consists in taking advantage of the decay of the center towards the periphery of the illumination of the light produced by a laser such as an excimer laser.

The invention thus relates to a device for machining a corneal lenticule by the stromal face. It comprises a laser capable of producing photoablation radiation, a lenticule holder adapted to receive a corneal lenticule, and a device for focusing said radiation. This system produces on the lens a spot whose dimensions correspond to those of the surface to be machined. I1 is characterized in that the focusing device is arranged to direct the whole of the elongated laser radiation beam from the laser onto the lenticule and in that it comprises
means for producing a relative rotation of the lens and the radiation beam around the axis of the lenticule,
a means for varying the focusing of the radiation, arranged to produce a controlled defocusing of radiation with respect to the lenticule, so that it is illuminated by a light spot of oval section whose edges are substantially blurred.

 This results in a decrease in illumination from the central region of maximum illumination to the edges, the fuzzy edges also allowing a transition between the periphery of the spot and the outside thereof.

 The relative rotation between the corneal lenticule and the radiation beam, preferably carried out by a lathe on which the portelenticule is placed, makes it possible to obtain an average effect of the decay of the illumination so as to obtain a regular decay. Defocusing also changes the shape of the light beam. A laser such as an excimer laser indeed generates an image of rectangular section, ovalized by defocusing.

It is this regular decay, which is used to directly obtain the desired machining profile shaped "bowl".

 The means for varying the focus of the radiation preferably has a translational member of the lenticule holder parallel to the axis of the lenticule. The most favorable defocusing values in practice are obtained by placing the lenticule at a distance from the focal plane of the focusing device of between 10 and 30% of the focal length of the focusing device.

 The device according to the invention advantageously has a translation device for translating the radiation beam perpendicularly to the axis of the lenticule. This makes it possible to obtain precise alignment to correct either myopia (when the axis of the radiation coincides with that of the lenticule) or hyperopia (when the two axes are different).

 According to a preferred embodiment, the device according to the invention comprises a variable aperture diaphragm arranged to allow to vary the length of the major axis of the light spot.

 This makes it possible to vary the ovalization of the light spot. By combining the defocusing and the action of the diaphragm, one can obtain both the ovality and the desired size. During a machining operation, the defocusing of the stain and the opening of the diaphragm remain constant. The device according to the invention may thus comprise a sequencing means arranged to produce a machining step during the opening of the diaphragm and the defocusing are each fixed to a predetermined value.

 The invention also relates to a method for implementing a device as defined above and comprising the steps of centering a corneal lenticule on the lenticule holder, setting the defocus to a determined value and performing a step of machining with relative rotation of the lenticule and the beam of radiation. According to a preferred embodiment, the method makes it possible to fix the opening of the diaphragm at a determined value.

Other features and advantages of the invention will appear better on reading the following description, given by way of non-limiting example, in connection with the drawings which represent
FIG. 1, a machining device according to a preferred embodiment of the invention,
FIGS. 2 and 3, two variants of a lenticular holder intended for a machining device according to the invention,
FIGS. 4a to 4d, the section of the light beam, respectively at its exit from an excimer laser (ech-2), after possible action of a diaphragm (ech-2), on the lenticule (ech-2) , and at the focal point F (echo-10),
FIGS. 5a to 5c, the steps of a keratomileusis carried out with a machining device according to the invention,
and FIG. 6, a curve representing the average light intensity seen from a point of the lenticule located at a distance 1 from the axis of the laser beam.

 The invention therefore relates to a machining device implementing an excimer laser and which is relatively simple and inexpensive.

 As has been shown above, the known machining devices use only a small proportion of the laser beam, which leads to the use of powerful and extremely expensive lasers both for the purchase and 'to maintenance.

 The basic idea of the invention is to take advantage of the decrease of the light energy of the laser beam and the average rotation, to obtain directly the desired machining profile, which allows to use all or almost all of the laser radiation and therefore use a much less powerful laser and much less expensive than in the prior art.

 A machining device according to the invention (see FIG. 1) comprises a photoablation laser 1 such as an excimer laser, a focussing lens 2, a total reflection prism for vertically reflecting the laser radiation 8 to focus it. F. A lenticule 10 is disposed on a lenticule holder 4, rotated by an axis 7 of a turn 5, for example a stepper motor, and controlled by an electronic microprocessor control device 30. F hearth is here located downstream of the lenticule 10 to produce a defocusing of the radiation 8 relative thereto. To vary the defocus distance D, the motor of the lathe 5 is displaced by vertical translation by a suitable device 50.

 This is in practice to rotate the lenticule 10 (keratomileusis or epikeroplasty) on its axis between each laser firing (there are typically one or several hundred) to make symmetrical laser ablation and to eliminate at least in large part by this effect of average illuminance inhomogeneities which, as indicated above, are very important in the horizontal and vertical directions, for lasers likely to produce a photoablation.

 According to the invention, the center of the lenticule is illuminated by imperfectly focusing the laser beam, the focal point of the laser being before or after the plane where the lens is located (see FIG. 1).

The rotation of the lenticule makes it possible to give the desired shape to the ablated volume. The illuminated area with "blurred edge" provides a smoother surface.

This technique can also be used in combination with a diaphragm which is progressively opened in a programmed manner during firing.

In this case, the diaphragm only serves to perfect the shape of the ablated volume.

Due to the defocusing, the area "illuminated" by the laser is oval in shape with maximum illumination in the center and regular decay of the illumination towards the periphery. By making the center of the illuminated area coincide
- with the center of the lenticule
- and with the axis of rotation of it,
a symmetrical volume is rotated by rotation of the laser beam, which produces an average luminous intensity I at a distance 1 from the axis of the laser beam, according to a regular decay curve (FIG. 6). The ablated volume has the shape of a lens (at least in the central part which is the part useful for the vision). All adjustments are made with precision using micrometric movements under the control of a biomicroscope. The variation of the diameter of the ablated volume is done by modifying the distance D between the point of focus
F of the laser beam and the lenticule 10. If the laser is focused with a lens 2 with a focal length of 10 cm, and if it is desired to ablate a volume with a maximum diameter of 4 mm, the distance D of defocusing is the order of the centimeter. the most useful defocusing range in practice corresponds to defocusing distances D of between 10 and 30% of the focal length of the focusing lens 2.

 From a practical point of view, the simplest solution is to keep fixed all the position parameters (lens focal length, defocus distance D), as well as the operating mode of the laser 1 (gas pressure, high voltage, power, shooting frequency), and to control the power of the lenticule 10 by varying the number of laser shots.

As a first approximation, the correction increases linearly with the number of shots. A brief experiment on some lenticules allows to determine the correction to bring to this linear law and to establish the abacus correlating the retractive correction and the number of laser shots corresponding to the position parameters and to the point of operation of the laser which one chose.

 As can be seen, the laser-tour does not require a powerful laser (almost all laser photons are useful), nor a high recurrence rate (because nothing forces to operate quickly on a lenticule) nor an elaborate optical system . It is a simple device that can be relatively inexpensive unlike currently distributed systems or the diaphragm systems as they are implemented generate a major energy loss.

 Note also that the implementation of a turn provides better results than a prism beam rotation device (see EP-280 414 for example). In fact, in a prism beam rotator, a rotation of a turn of the beam is obtained for a rotation of the prism of 180. . Even a slight decentering produces abnormalities in the vicinity of the axis of the lenticule.

 With the machining device according to the invention, the desired shape of the ablated volume is obtained by defocusing the laser beam. If a diaphragm is used, it is preferable that its opening remains fixed during machining. A progressive opening diaphragm can be implemented, to correct the second order the ablated profile. Since the accuracy obtained is good in the optically useful zone and the use of a progressive opening diaphragm complicates the process, the implementation of a progressive opening diaphragm is of little practical interest. Tower 5 consists of a stepper motor, 200 steps per lap, driven by a computer. <set "of Krumeich), to maintain the lenticule by suction.The holder of the microkeratome, which is of cylindrical shape, is then fixed on the motor (figure 3) But here, as the force to be exerted is very weak for maintain the lenticule 10, a very tenuous suction (support 18, tube 19 connected to a primary vacuum pump) and which does not hurt the cornea, is sufficient.The computer programming of the rotational movement is such that between each shot, the angle of rotation is large (the lenticule makes a turn in a few laser shots only) and not commensurable with the unit (the lenticule does not return to the same position after a few shots) An angle of 137.5 degrees is a good number.

The programming of the rotation movement can also allow, if desired,
to rotate at a constant, slow rate, but corresponding to an integer number of revolutions during the operation,
- Rotate so that, from one shot to another, or from a series of shots to another, the position of the object varies randomly.

 In the case where the holding of the object is by suction, a small hose 19 binds the support of the lenticule to a small pump. To avoid bending this pipe too strongly, the rotation of the turn is made so that the angle of rotation never exceeds one revolution. The angle of rotation between laser shots is constant (137.5 degrees for example), but at the end of each turn, instead of going forward (137.5 degrees), the motor goes back (-222, 5 degrees = 137.5 360 degrees).

 The excimer laser 1 works with an Argon Fluorine mixture. It emits ultraviolet (UV) light at 193 nm. The mixtures can also be used but they are less suitable for machining corneas because the effects of necrosis are greater. The firing frequency of the laser is 2 to 5 Hz, the energy emitted is conventionally 80 millijoules (but 50 mJ are sufficient). The light beam is emitted horizontally, it is rectangular (0.7 cm high h and 2 cm wide L typically) (see Figure 4a). The total reflection prism 3 of 2 x 2 cm returns the laser beam 8 vertically downward. This ray is focused by the lens 10 with a focal length of 10 cm placed just before the prism 3. The laser beam touches the lenticule 1 to 3 cm before the point of focus of the lens (distance D between 1 and 3 cm).

If we remove the lenticule 10 (and the motor), we observe the focal spot of the laser which is elongated in shape of dimensions 0.4 x 0.1 mm (Figure 4d). At the level of the lenticule 10, the focusing being imperfect, the focal spot is larger, for example 2 mm × 4 mm (FIG. 4c) and increases when defocusing (when the lenticule is moved away from the focusing point). This adjustment in height (Z axis) of the position of the lenticule is done by moving the motor of the "tower" vertically using a micro-displacement table 50 for example.

 A diaphragm 25 (diameter 0.5 to 2 cm) is placed before the lens 2. By closing the diaphragm 25 the laser beam 8 takes a width L '<L and keeps its height h, and thus the laser spot on the lenticule 10 becomes smaller and more "round". By adjusting the diameter of the diaphragm 25 and the position of the lenticule 10, the laser spot on the lenticule 10 can be given suitable dimensions and ovality. An "oval" of 4 mm x 2 mm is a good compromise (Figure 4c).

 Two micro-displacement tables 41 and 42 make it possible to move the motor of the "tower" and thus the lenticule 10, along the horizontal axes X and Y, in order to make the center of the laser "spot" coincide (the cornea fluoresces slightly and the laser "spot" is visualized by small blue flashes).

 By shifting the laser axis parallel to the axis of rotation of the motor, a crown can be machined to correct hyperopia. This axial offset can be performed by the microdisplacement tables 41 and 42.

 Alternatively, the micro-displacement tables 41 and 42 are arranged to move the portelenticule.

 Before operating, we measure the power of the laser at the level of the lenticule. This power is adjusted (by varying the high voltage of the internal excimer laser discharge) so as to reach the value that has been set beforehand (and which corresponds to the abacus that has been established) . A firing energy of 10.2 mJ seems satisfactory and corresponds, for a used area of 2 x 3 mm, to the fluence of 170 mJ / cm2, which seems to be the one to use.

 To perform a keratomileusis operation, a lenticule 10 is taken from the cornea 20 of a patient. In Figure 5a, there is shown in 21 the iris and in 22, the stroma. The lenticule 10 has a front face 12 covered by the Bowmann's membrane and a stromal rear face 11. The lenticule 10 is thrown so that the stromal face 11 becomes convex and is placed on the portelenticule 5 (FIG. 8. FIG. 5b shows the radiation 8 offset perpendicularly to the axis of rotation of the motor 5, that is to say to operate hyperopia. The radial section of the radiation 8 is in this case equal to the width of the crown to be operated.

 In Figure 5c, there is shown schematically in 15, the photo-ablation process.

Once the machining is finished, the lenticule 10 is again eversed and then surgically repositioned on the stroma 22 of the patient's cornea 20.

 The invention is not limited to the embodiments described and shown. In particular, the relative rotation of the laser beam and the lens could be obtained by rotating the laser beam by means of a known prism system.

Claims (9)

 1) Device for machining a corneal lenticle or a corneal graft by the stromal face using a laser capable of producing a photo-ablation radiation, and comprising an optical system and a door -Lenticule adapted to receive a corneal lenticule centered on its axis, and a device for focusing said radiation to produce on the lens a spot whose dimensions correspond to those of the section to be machined, characterized in that the focusing device ( 2) is arranged to direct the radiation beam (8) coming from the laser onto the lenticule (10), and in that it comprises  rotation means (5) for producing a relative rotation of the lenticule (10) and the radiation beam (8) about the axis of the lenticule holder (10)  means for varying the focusing of the radiation beam (8), arranged to produce a controlled defocus (D) of the radiation (8) with respect to the lenticule (10), so that the latter is illuminated by a stain oval light whose edges are substantially rounded.  2) Device according to claim 1, characterized in that the rotation means for producing a relative rotation of the lenticule and the radiation beam and a lathe (5) on which is disposed the lenticule holder (4).  3) Device according to one of claims 1 or 2, characterized in that it comprises a control device (30) of the rotation means arranged to produce between two laser shots a rotation of a non-commensurable angle with an angle of 360 ".  5) Device according to one of the preceding claims, characterized in that it comprises a translation device (41, 42) for inducing a relative translation of the radiation beam (8) and the axis of the lenticule holder (4) perpendicularly to the axis of the lenticule holder (4).  6) Device according to one of the preceding claims, characterized in that it comprises a diaphragm (25) with variable opening arranged to vary the width (L, L ') of the light spot.  7) Device according to claim 6, characterized in that it comprises a sequencing means (30) arranged to produce a machining step during which the opening of the diaphragm (25) and the defocusing distance (D) are each fixed at a predetermined value.  8) Device according to one of the preceding claims, characterized in that the means for varying the focusing of the radiation is adapted to arrange the lenticule (10) at a defocusing distance (D) of the focal plane of the focusing device (2), between 10 and 30% of the focal length F of said focusing means.  9) A method of implementing a device according to one of the preceding claims, characterized in that it comprises the steps of  - centering a corneal lenticule (10) on the lenticule holder (4)  - set the defocus to a determined value (D)  - Perform a machining step with relative rotation of the lenticule (10) and the radiation beam (8).  10) A method according to claim 9, characterized in that it comprises a step of fixing the opening of the diaphragm (25) to a determined value.