WO1991011154A1

WO1991011154A1 - Method for producing an elastically flexible lens for correcting an ametropic eye

Info

Publication number: WO1991011154A1
Application number: PCT/FR1991/000068
Authority: WO
Inventors: Khalil Hanna
Original assignee: Khalil Hanna
Priority date: 1990-02-01
Filing date: 1991-02-01
Publication date: 1991-08-08
Also published as: FR2657698B1; FR2657698A1

Abstract

A method for producing an elastically flexible lens designed to correct an ametropic eye by contact with the front side of the Bowman's lamina of the cornea thereof, said contact involving the deformation of the lens in comparison with its state when unused. The topography of the front (3) of the cornea (4), and the refraction in the ametropic eye (1), are measured, and selected values are attributed to some of the mechanical, geometrical and optical features of a theoretical unused lens, while leaving unknown the value of another of said features which is determined by making a mathematical model of the ametropic eye (1), an emmetropic eye and the theoretical lens, and by simulating the contact between said theoretical lens and the front (3) or the Bowman's lamina, respectively, of the cornea (4) of the ametropic eye (1). Then, a real lens (2) is made or selected which when unused has the same selected values and the same value determined using the mathematical model concerning its mechanical, geometrical and optical features, and this real lens (2) is brought into contact with the front(3) or the Bowman's lamina, respectively, of the cornea (4) of the ametropic eye (1). Contact lenses (1) similar to epikeratophakia lenses can thereby be produced with sufficient accuracy to allow them to be held to the cornea by suction.

Description

PROCESS OF REAL I SAT I ON OF A SLOW I LLE ELAST 1 QUESTION FLEXIBLE DEST I BORN TO THE CORRECT I ON OF AN OE I L AMETROPE

The present invention relates to a method of producing an elastically flexible lens intended for the correction of an ametropic eye by attachment to the anterior face of the cornea thereof, said attachment involving a deformation of the lens in comparison with a state rest of it.

It can also be applied to the production of so-called "contact" lenses, intended to be temporarily retained by capillary action, with the possibility of limited displacement during blinking, on the anterior face of the cornea of the ametropic eye in order to be able to be removed and put in place at the option of the user, only when producing lenses for epikeratophakia, intended to be permanently attached to the Bowman's membrane of the cornea, by anchoring on the latter after localized debridement of the epithelium which then reconstitutes on the respective lens. Both have the function, by the vergence they add to that of the ametropic eye, of bringing as close as possible the refraction of the latter to the refraction of an emmetropic eye and are chosen for this purpose by a practitioner, after measuring the refraction of the ametropic eye and the topography of the cornea, in a range of lenses generally identified by the radius of curvature, in the state of rest, of their face intended to be turned towards the cornea or "posterior surface", by their diameter in the resting state and by their vergence in the resting state; in his choice, the practitioner must ensure that the shape of the lens is suitable in particular for ensuring self-centering of the latter on the anterior face of the cornea while allowing a displacement of an amplitude of the order of 0 , 5 mm on this rs of blinks, in the case of a contact lens, and to ensure close contact between the posterior surface of the lens and the Bowman's membrane in the case of an epikeratophakia lens. Now, in the techniques currently practiced, the measurement of the topography of the anterior surface of the cornea, also representative of the topography of the Bowman's membrane, is generally made only on the central or paracentral part of the cornea, it that is to say in the immediate vicinity of the visual axis whereas on the one hand it is known that the anterior surface of a cornea, even normal, is practically never axi-symmetrical, which is naturally also the case of the Bowman's membrane since the corneal epithelium is of uniform thickness, and that, on the other hand, the posterior surface of the lens, intended to extend widely beyond the part of the anterior surface of the cornea on which currently performs the topography measurement, is in turn axi-symmetrical in the case of currently known lenses, whether spherical or aspherical. As a result, when it is attached respectively to the anterior surface of the cornea or to the Bowman's membrane, the lens undergoes a deformation due to its flexibility and to the symmetry defects of the anterior surface of the cornea or of the membrane. of Bowman, respectively, that is to say takes a shape different from its shape at rest, before laying on the cornea.

Up to now, it has been considered impossible to take account of variations in curvature of the anterior surface of the cornea, that is to say also of the Bowman's membrane, according to the meridians and diameters, so that the deformations that the lens thus subjected to its installation on the cornea are hitherto unpredictable as to their value and as to their consequences on the one hand on the vergence of the lens and on the other hand on the way in which the posterior face of this ci cooperates mechanically with the anterior surface of the cornea or Bowman's membrane, so that, until now, only the experience of the practitioner leads the latter, after measuring the topography of the central or paracentral part of the anterior surface of the cornea, in the choice of a lens whose shape or curvature of the posterior surface, after deformation when it is attached to the anterior surface or, respectively, to the Bowman's membrane of the cornea of the ametropic eye, will be geometrically suitable and will bring the refraction of the lens - ametropic eye system satisfactorily closer to that of an emmetropic eye.

In the case of a contact lens, it is not uncommon for the lens chosen by the practitioner not to have the desired shape of its rear face, which requires successive tests of lenses having curvatures different from their face posterior; this is tedious and, even if one generally obtains the required correction of the ametropic eye concerned after a reduced number of tests, does not guarantee that the lens on which the choice ultimately stops is the best at the point of view form and dioptric power. Indeed, it is particularly difficult to take into account, by this empirical method, the geometry of the anterior face of the cornea of the ametropic eye to be corrected, if not to rule out in certain cases the use of contact lenses as a means of correction, for example in the case of an astigmastime or keratoconus; therefore, any significant difference between the geometry of the anterior surface of the cornea of the ametropic eye and a form close to axi-symmetry or any other irregularity even slight in the shape of the anterior surface of the cornea of the ametropic eye induces lens deformations which have hitherto been unpredictable, in particular as regards their consequences on the correction actually made by the lens and interferes with the attachment of the lens to the cornea by capillary action, which in practice leads to choosing lenses '' an excessively large diameter, offering an increased surface for securing by capillarity with the anterior face of the cornea, however with an often unsatisfactory aesthetic result, or to produce lenses which are increasingly fine in order to be able to be applied by their flexibility against the anterior surface of the cornea; Finally, the simultaneous treatment of several patients requires the practitioner to have a large stock of lenses, allowing him to perform the successive tests generally required on each of the patients.

In the case of lenses for epikeratophakia, there is the same difficulty in choosing the proper lens to provide the required correction; once the lens has been chosen and placed, traditionally by surgical intervention, the patient must be satisfied with the correction obtained unless accepting a new surgical intervention which may consist either of an ablation of the lens initially chosen, possibly followed by the placement of a new lens that is better chosen, a delicate and traumatic operation which it is naturally out of the question to repeat too often, either by remanufacturing, by laser, the lens initially chosen and fixed on the patient's eye, for example by the method described in "Laser adjustable synthetic epikeratoplasty" by Keith P. Thompson et al. (Refractive & Corneal Surgery, Vol 5, p. <+ 6 - + 8), which is delicate and tedious for the patient. Also in such a case, defects of the anterior surface of the cornea of the ametropic eye can oppose the fitting of a lens, however to a lesser extent than in the case of contact lenses since the contact lens epikeratophakia is generally secured to the cornea by anchoring therein when using traditional epikeratophakia techniques, or firmly attached to the surface of the cornea by bonding using a biological glue.

The object of the present invention is to remedy these drawbacks, by offering the possibility, from measurements practiced in a simple manner on the ametropic eye, of determining in an almost certain way the characteristics, at rest, of an elastically flexible lens. which, after having undergone a deformation following its attachment to the anterior surface or to the Bowman's membrane, respectively, of the cornea of the ametropic eye, either as a contact lens, or as epikeratophakia lens, will provide the ametropic eye with the correct correction to bring the refraction of the latter to the refraction of an emmetropic eye in a predetermined manner.

To this end, the present invention provides a method of producing an elastically flexible lens intended for the correction of an ametropic eye by attachment to the anterior face or to the Bowman's membrane of the cornea thereof, said attachment involving a deformation of the lens in comparison with a state of rest thereof, characterized by the succession of steps consisting in: a) measuring the topography of said anterior face and the refraction of said ametropic eye, b) assigning selected values to certain mechanical, geometric, optical characteristics of a theoretical lens in the resting state, keeping as unknown the value of at least one other of said mechanical, geometric, optical characteristics of said theoretical lens in the resting state , c) simulate by mathematical modeling said ametropic eye, an emmetropic eye and said theoretical lens and deduce therefrom a calculated value of l add another characteristic of said theoretical lens in the resting state, said calculated value being such that the joining, to said anterior face or to the Bowman's membrane, of a real lens having in said state of rest said selected values and said calculated value of said mechanical, geometrical, optical characteristics restores to the ametropic eye a refraction situated in a predetermined manner with respect to the refraction of an emmetropic eye, d) manufacturing or choosing an actual lens having said idle state selected values and said calculated value of said mechanical, geometric, optical characteristics. A person skilled in the art will easily understand that the recourse to a mathematical modeling of the ametropic eye, of the emmetropic eye and of a theoretical lens whose mechanical, geometrical, optical characteristics in the state of rest will have chosen values, the exception of one of these characteristics kept as unknown, will make it possible to determine the value of this last characteristic with a maximum of precision, and consequently to define with precision all the mechanical, geometrical, optical characteristics, with the state of rest, of a real lens which, after deformation, will bring to the ametropic eye considered the required correction, suitable for situating in a predetermined manner its refraction with respect to the refraction of an emmetropic eye.

A priori, one can choose as unknown the value of any one of the mechanical, geometrical, optical characteristics of the theoretical lens in the state of rest, among which one can quote: - as mechanical characteristics, the coefficients of elasticity of the theoretical lens,

- as geometrical characteristics, the diameter of the theoretical lens in the rest state and the respective geometries of the anterior and posterior faces of the theoretical lens in the rest state, in which case the term "value" chosen or calculated , respectively, a characteristic set of chosen or calculated values such as coordinates of points of these faces, respectively,

- As an optical characteristic, the refractive index of the theoretical lens. However, one preferably chooses as being said other characteristic, that is to say as being the characteristic of unknown value to be determined by the implementation of step c) of the method, a geometric characteristic of the theoretical lens to be the state of rest, namely preferably the geometry of the front face of this lens theoretical in the state of rest, which allows to freely choose the geometry of the posterior surface of the latter, according to the topography of the anterior surface of the cornea. Such a choice makes it possible, in the case of a contact lens, to adapt the geometry of the posterior face of the theoretical lens, and consequently of the real lens, exactly to the topography of the anterior face of the ametropic eye , which on the one hand makes it possible to guarantee both the retention of the lens on the cornea by simpie capillarity and the good mobility of the lens on the cornea and thus makes it possible to limit the diameter of the lens to what is strictly necessary, it that is to say to make the lens aesthetically more discreet, and on the other hand allows to consider the prescription of contact lenses manufactured specifically, according to said topography, even when the latter deviates strongly from a usual topography for example due to an astigmatism or a keratoconus or a strong lack of axi-symmetry, that is to say even in cases in which the prescription of contact lenses hitherto seemed excluded ; Indeed, a sufficiently precise mathematical modeling, of the field of the normal aptitudes of a mathematician, makes it possible to take into account all the irregularities of the anterior face of the cornea and to determine the characteristics, in particular geometric, even complex of the lens allowing 'bring to this cornea a desired correction, the machining of a lens having the particular geometrical characteristics required or its manufacture by molding falling within the normal aptitudes of a person skilled in the art in the field of micro-machining or molding. In the case of a lens for epikeratophakia, we find this possibility of rigorous adaptation of the shape of the posterior surface of the lens to the topography of the anterior surface of the cornea, or more precisely of the Bowman's membrane, and this possibility of prescription of a lens even when the anterior surface of the cornea is deformed to such an extent that epikeratophakia seemed hitherto excluded; naturally epikeratophakia can also be practiced in a traditional way, in particular as regards the anchoring of the lens on the cornea, but it also becomes possible to choose for the posterior face, always concave, of the lens a geometry having an accentuated curvature in a predetermined fashion in relation to a geometry which is strictly complementary to the topography of the anterior surface of the cornea, or more precisely of the Bowman's membrane, so that the positioning of the lens on the latter results in deformation of the lens and because of the elasticity of the latter, by a suction effect applied by the lens to the cornea via the Bowman's membrane with the result that the lens is anchored sufficiently effective so that may consider dispensing with completing this anchoring by other means such as engaging a peripheral edge of the lens in a annular incision of the cornea, which makes epikeratophakia much simpler, much less traumatic, and allows to consider it much more serenely.

In the case of a contact lens as in that of a lens for epikeratophakia, the risks of an incorrect choice of the lens are considerably reduced, which makes it possible, in the case of contact lenses, to avoid sessions successive clinical trials and to reduce the stock of lenses that a practitioner must have at his disposal to practice his trials simultaneously on several patients whereas, in the case of a lens for epikeratophakia, the risks that a new intervention is required after initial lens placement are reduced.

Preferably, to offer all the required precision, said mathematical modeling takes into account at least some of the following parameters:

- on-board conditions, including atmospheric pressure and palpebral pressure, - the capillary forces between the anterior surface of the cornea and the posterior surface of the lens,

- a law of behavior of the theoretical lens in elastic deformation from the state of rest. On the other hand, it is shown that, due to the intraocular pressure and a modulus of elasticity which, for the cornea, is much higher than that of the materials currently available for the manufacture of flexible lenses, such as co- collagen polymers, the deformations undergone by the eye due to the installation of the lens are negligible in front of the deformations of the latter, and which one can with a satisfactory approximation dispense with taking into account any law of behavior of the cornea in elastic deformation from a state of rest, corresponding to the absence of lens as well as intraocular pressure as an edge condition; the anterior surface of the cornea or the Bowman's membrane is then considered to be a non-deformable reference surface to which the lens is applied.

Said mathematical modeling can then be limited to the implementation of a mechanical model of the lens and of an optical model of the pair "lens attached to eye", that is to say of comparatively simple models.

According to a currently preferred embodiment of the present invention, the calculated value of said other characteristic of the theoretical lens in the state of

'rest, that is to say the value initially unknown, by implementing step c) by the succession of steps consisting in: e) assigning a chosen value also to said other characteristic of the theoretical lens state of rest, f) simulate by mathematical modeling the joining, to the anterior face or to the Bowman's membrane, respectively, of said ametropic eye, of said theoretical lens presenting in the state of rest said selected values of said mechanical, geometric characteristics , optical, g) to deduce therefrom a calculated refraction of the ametropic eye to the anterior face or to the Bowman's membrane, respectively, of the cornea of which a real deformed lens would be attached, having said chosen values of said mechanical, geometric characteristics in the rest state , optical, h) comparing said calculated refraction to the refraction of an emmetropic eye according to predetermined comparison criteria, and:

- Say that said chosen value assigned to said other characteristic of said theoretical lens in the rest state during sub-step e) is said calculated value of said other characteristic of said theoretical lens in the rest state if said criteria are satisfied and go to step d),

- repeat step c) if said comparison criteria are not satisfied, by assigning to said other characteristic of the theoretical lens in the rest state, during ia sub-step e), a chosen value which differs so predetermined of said chosen value.

Naturally, said comparison criteria are satisfied in a number that is all the more reduced in the implementation of step c) as the values chosen for said mechanical, geometric, optical characteristics of the theoretical lens in the rest state during step b) and sub-step e) are probable values for a lens meeting these criteria; the choice of these values is guided by the practitioner's experience in view of the measurements made during step a) and the mechanical and optical characteristics of the available materials, specific to the production of the lens or the mechanical, optical, geometric characteristics pre-existing lenses; the practitioner can however be helped in the implementation of step e) by using a method known as "ray-tracing", and more precisely by practicing the succession of steps consisting in: î) simulate by mathematical modeling the given images of a determined object, respectively by said ametropic eye and by an emmetropic eye, j) compare said images according to predetermined comparison criteria and deduce therefrom a correction to be made to said ametropic eye, k) calculating, as a function of said correction to be made to said ametropic eye, a value of said other characteristic of said theoretical lens in the state attached to said anterior face or to the Bowman's membrane, respectively, and deformed,

1) deduce therefrom a probable value of said calculated value of said other characteristic of said theoretical lens in the rest state, to make this probable value said chosen value of said other characteristic of said theoretical lens in the rest state during from step a).

Between steps c) and d), the practitioner can verify that a real lens having said selected values and said calculated value of said mechanical, geometric, optical characteristics in the idle state will effectively be suitable by simulating the images by mathematical modeling. given by a determined object, respectively by said ametropic eye to said anterior face or to the Bowman's membrane, respectively, of which said real lens would be attached and by an emmetropic eye and by observing an exact coincidence, or approached within admissible limits, of these two images. Other characteristics and advantages of the method according to the invention will emerge from the description below, relating to the aforementioned preferred embodiment of step c), as well as from the appended drawings which form an integral part of this description.

- Figure 1 shows a front view of an ametropic eye, hyperopic and astigmatic in practice, corrected by means of a lens produced by the method according to the present invention. FIGS. 2 and 3 show views of the cornea of this eye and of the lens in section through the two astigmatism planes, marked respectively II— II and III-III in FIG. 1.

- Figure * + shows a front view of an ametropic eye, in practice hyperopic and astigmatic, corrected by means of a lens for epikeratophakia produced according to the method according to the invention.

- Figures 5 and 6 show a view of the cornea of this eye and the lens in section through the astigmatism planes, marked respectively V-V and VI-VI in Figure •. - Figure 7 illustrates the respective decompositions, in finite elements, on the one hand of a simulated theoretical lens, namely a contact lens, in the rest state and on the other hand of the cornea of an ametropic eye simulated, with a view to simulating the attachment, to the anterior surface of the cornea of the ametropic eye, of the posterior surface of a real lens which, in the state of rest, would reproduce the mechanical, geometric characteristics, optics of the theoretical lens in the rest state.

- Figure 8 illustrates, analogously to that of Figure 7, these same decompositions into finite elements in the case of a theoretical lens for epikeratophakia in the resting state, that is to say before simulated joining to the Bowman's membrane of the cornea of the simulated ametropic eye.

- Figure 9 illustrates, analogously to that of Figure 8, these same decompositions in finite elements in the case of the theoretical lens for epikeratophakia after simulated joining to the membrane of

Bowman of the simulated ametropic eye cornea.

Reference will firstly be made to FIGS. 1 to 3 where the implementation of the present invention has been illustrated for the correction of an ametropic eye 1 by means of a contact lens 2 placed side by side in the deformed state, conventionally, on the anterior face 3 of the cornea k of this eye 1; in the example illustrated, the eye 1 is hyperopic and astigmatic, so that the lens 2 is in particular a converging lens, but it is understood that the present invention as it will be described in reference to FIGS. 1 to 3 could apply to the correction of any type of ametropia falling within the prescription of a contact lens.

When it is placed and retained in contact with the anterior face 3 of the cornea * +, the lens 2 has a conformation illustrated in solid lines in FIGS. 2 and 3, namely a conformation in which it has, with reference to an axis 5 more or less approximately coincident with the visual axis of the eye 1, a periphery 6 approximately of revolution with a diameter varying between a maximum D. and a minimum D-, of respective values close to that of the non-referenced minimum diameter of the cornea although less than a few tenths of a millimeter from this latter value; in contact with the anterior face 3 of the cornea * +, by interposing a film of tears not referenced, allowing a slight relative movement during blinking, the lens 2 has a posterior face 7 whose topography reproduces almost identically that of the anterior face 3 of the cornea • + while opposite this face 7, the lens 2 has an anterior face 8, the topography of which is determined, as a function of that of the posterior face 7, so that that when it is thus joined to the anterior face 3 of the cornea by its posterior face 7, and taking into account the refractive index of the material constituting it, the lens 2 brings the vergence of the eye 1 thus corrected for the vergence of an emmetropic eye.

However, this form of lens 2 attached by its posterior face 7 to the anterior face 3 of the cornea * + of the ametropic eye 1 results from an elastic deformation of the lens 2, in a manner known in itself, from of a state of rest illustrated in dotted lines in FIGS. 2 and 3, state of rest in which the periphery 6 of the lens 2 has a symmetry of revolution about the axis 5, with a diameter D, of value different from that of diameter D. and D-, and in intermediate practice between these values in the nonlimiting example illustrated, and the faces 7 and 8 of the lens 2 may have an axi-symmetry with reference to the axis 5, the rear face 7 then generally having in this state the shape of a spherical cap of radius R. , although other geometries of the faces 1 *

7 and 8 become accessible by the implementation of the present invention.

Under these conditions, the positioning of the lens 2 on the anterior face 3 of the cornea is accompanied by an elastic deformation of the lens 2, this deformation taking place in the direction of a flattening, that is to say i.e. a reduction in the curvature of its posterior face 7 along the astigmatism plane 11— II in which the anterior face 3 of the cornea * + has the least accentuated curvature, while it is accompanied by 'A deformation of the lens 2 in the direction of an accentuation of the concavity of its rear face 7, that is to say of a reduction of the radius R. of the latter, in the astigmastime plane II I— II I according to which the anterior face 3 of the cornea * + has its most accentuated curvature, as shown in FIGS. 2 and 3 respectively.

Naturally, the choice of a lens 2 intended to provide a determined correction to an ametropic eye 1 is made as a function of the radius R. or more generally of the geometry of its rear face 7, of the diameter D, of its periphery 6 and of its vergence while it is in the state of rest and the deformation which it then undergoes when it is applied to the anterior surface 3 of the cornea influences not only its geometrical characteristics but also its optical characteristics, that is to say its vergence, and causes the appearance of constraints tending to bring it back to its state of rest and having to remain compatible with the maintenance of its posterior face 7 on the anterior face 3 of the cornea.

Up to now, as said above, these variations in the geometrical and optical characteristics of the lens during its deformation with a view to applying its posterior face 7 to the anterior face 3 of the cornea. ametropic eye 1, as well as the internal stresses in the lens 2 and resulting from this deformation must be anticipated by the practitioner according to his experience but, whatever it is, many successive tests are necessary, more to lead to a satisfactory choice, apparently duly, of the radius R. or more generally of the geometry of the lens in the rest state than at a satisfactory value of the vergence of this lens 2 in the rest state, a satisfactory result in this respect being generally quickly achieved. The implementation of the method according to the invention, which will now be described, makes it possible to choose without fail characteristics, at rest, of a lens which will give satisfaction after placement on the anterior face 3 of the cornea, that is to say after deformation, from a range of pre-existing lenses, or to allow the production, in a personalized manner, of a lens meeting the needs of a determined ametropic eye 1, depending in particular on the topography of the anterior face 3 of its cornea * + and of the optical correction to be made to this ametropic eye 1. For this purpose, in accordance with the present invention, one begins by measuring the topography of the anterior face 3 of the cornea * + of the ametropic eye 1 not only in the immediate vicinity of the supposed visual axis coincident with axis 5, but from this visual axis to the periphery 9 of the cornea * +, in the form of coordinates of a multitude of points of this anterior face e 3 in an orthonormal reference frame Oxyz assumed to be linked to the ametropic eye 1, the axis Oz being approximately coincident with the visual axis; the overall refraction of the ametropic eye 1 is also measured, for example by means of an auto-refractor, this example being in no way limiting. On the basis of his experience, and his knowledge of the existing ranges of contact lenses or of the materials usually used for the production of contact lenses, the practitioner assigns selected values, in the probable field, to certain of the characteristics mechanical, geometrical, optical following of a theoretical lens in the state of rest, which it supposes that it will be able to correspond to a real lens which, after deformation, will make it possible to obtain the correction sought under optimal conditions of cooperation with the anterior surface 3 of the cornea of the ametropic eye 1 considered:

- mechanical characteristics, namely elasticity coefficients, in particular elastic modulus and Poisson's ratio, of the theoretical lens,

- geometric characteristics, namely geometry or respective topographies of the posterior 7 and anterior S faces of the the

theoretical lens in the idle state, in which case "selected value" should be understood to mean sets of values constituted for example by the coordinates of a multitude of points on the faces 7 and 8 of the theoretical lens in the state not deformed in the same orthonormal reference ûxyz as when it is a question of determining the topography of the anterior face 3 of the cornea of the ametropic eye 1 considered, as well as diameter D, of the theoretical lens in the state of rest ,

- optical characteristics, namely the refractive index of the theoretical lens. However, the value of one of these characteristics is subsequently considered as an unknown variable.

Preferably, this value considered to be unknown is the geometry or topography of the anterior face 8 of the theoretical lens in the rest state, it being understood that it would not go beyond the ambit of the present invention to choose as value the unknown another of the characteristics previously cited.

The value of this characteristic considered as unknown is then refined by successive approximations, to determine the value that it must have in a real lens, in the non-deformed state, in such a way that this real lens, once deformed to be joined on the anterior surface 3 of the cornea, corrects the optical defects of the ametropic eye 1.

To reduce the number of successive approximations, the surgeon can help himself, in the choice of a probable value of the characteristic considered as unknown, in practice the geometry or topography of the anterior face of the theoretical lens in the state of rest if we refer to the preferred mode of implementation of the present invention invoked above, by a simulation, by mathematical modeling, of given images, of a determined object, respectively by said ametropic eye and by an eye emmetropic, by means of an optical model of the eye, in order to compare said images according to criteria of predetermined comparison and to deduce therefrom a correction to be made to said ametropic eye: this method, implementing an optical model of the eye, is known in itself under the name of "ray-tracing", the determined object the images of which are generally simulated being a grid; with regard to an optical model of the eye, reference will be made, for example, to the following publications:

- Lotmar.: Theoretical eye model with aspherics (3 Opt Soc Am. 1971; 61: 1522- 1 529),

- Gullstrand A .: Helmholtz's Treatise on Physiologicai Optics. (New York, NY: Optical Society of America; 192 * +; i).

Once this correction has been determined, the practitioner can calculate by computer a value which must have the characteristic, considered to be unknown, of the theoretical lens in the state delivered to the anterior face 3 of the cornea k of the ametropic eye, c ' that is to say in the deformed state; the practitioner can then deduce therefrom a probable value from the value that this characteristic of the theoretical lens will have to present for this purpose considered this time in the rest state, to choose this probable value as the value initially chosen, to initiate the process of successive approximations, for that of the characteristics of the theoretical lens in the resting state which is considered to be unknown.

To implement the process of successive approximations, in accordance with the present invention, one implements:

- firstly a computer program numerically solving linear or non-linear elasticity equations using a discretization method of the finite element method type; such a program is capable of determining the shape that an elastic body will take, a part of the surface of which is applied to a given reference surface, as a function of its shape at rest and its mechanical characteristics; in the context of the present invention, it can determine the shape of a lens of known initial geometry, which one attaches by deforming it to the anterior surface of the cornea considered as a non-deformable reference surface, with a good degree of approximation;

- on the other hand, an optical model making it possible, as a function of the respective geometries of the attached lens and of the anterior face of the cornea of the ametropic eye, as well as their optical characteristics, to determine whether the pair "attached lens - cornea of the ametropic eye "presents optical defects such as myopia, hyperopia, astigma¬ tism, and to quantify these defects with a view to their comparison with predetermined admissibility limits.

With regard to the optical model, applicable both to the single eye, ametropic or emmetropic, as well as to the pair "lens attached to one another - cornea of the ametropic eye", reference will be made for example to the two aforementioned documents; with regard to the mechanical modeling and the resolution of the equations of the linear or nonlinear elasticity thanks to a discretization method of the type finite element method, in the particular case of an application to an elastically deformable lens, one will refer for example to the following documents:

- Ciarlet PC: Three-dimensional elasticity. (New York, NY: Masson Publishers, USA Inc; 1986),

- Zienkiewicz OC: The Finite Element ethod. (New York, NY: McGraw-Hiil International Book Co 1977).

The mathematical modeling thus defined takes into account at least some of the following parameters: - the edge conditions, under which the lens evolves, namely in particular the atmospheric pressure and the palpebral pressure, while the intraocular pressure. can be neglected if, as can be admitted with a good approximation, the anterior surface 3 of the cornea h is considered as a non-deformable reference surface. the capillary forces between the anterior face 3 of the cornea - * •• and the posterior face 7 of the theoretical lens 2,

- a law of behavior of the theoretical lens 2 in elastic deformation from the state of rest, while any law of behavior of the cornea in elastic deformation from a state of rest, corresponding to the absence of lens , can be neglected if we consider the anterior surface of the cornea as a non-deformable reference surface.

This modeling makes it possible to determine the value of any one of the following characteristics, as soon as one has fixed the respective values of the others of these characteristics:

- elasticity coefficients of the theoretical lens,

- respective geometries of the front and rear faces of the theoretical lens in the rest state and diameter of the theoretical lens in the rest state,

- refractive index of the theoretical lens.

In the preferred embodiment of the present invention which is described, the unknown characteristic is the geometry of the anterior face of the theoretical lens in the rest state, the values of the other characteristics above being considered to be chosen definitely.

Once these values have been chosen for a theoretical lens in the resting state, the value chosen being provisional for that of these ^• characteristics which is considered to be unknown, namely in this example the geometry of the anterior face of the theoretical lens at l state of rest, mathematical modeling simulates the joining. on the anterior face 3 of the cornea * + of the ametropic eye 1, of the theoretical lens having these chosen values in the rest state, by numerically solving the linear or non-linear elasticity equations by discretization using a method of the finite element method type; FIG. 7, in which the same numerical references are found as in FIGS. 1 to 3, illustrates the respective decompositions in finite elements, for this purpose, of the simulated theoretical lens 2, in the rest state, and of the cornea of the simulated ametropic eye 1; from this simulation, thanks to the optical model, a calculated refraction is deduced from the ametropic eye 1 to the anterior face 3 of the cornea, of which a real, deformed lens would be attached, in the idle state the values chosen for said characteristics. mechanical, geometric, optical ticks; then, the program compares this calculated refraction to the refraction of an emmetropic eye according to predetermined comparison criteria, suitably memorized and:

- if, as a function of this comparison, the couple formed by the ametropic eye 1 and by a theoretical lens attached thereto but having in the rest state all of the values respectively chosen initially for all of the characteristics mechanical, geometrical, optical of the lens presents a vision which one can consider as normal, in terms of refraction, taking into account the predetermined admissibility limits, said chosen values are considered as those which will have to present, in the state of rest, a real lens giving a satisfactory result after the attachment of its posterior face 7 to the anterior face 3 of the cornea • of the ametropic eye 1 and a real lens is chosen having, in the state of rest, these characteristics if such a lens preexists, or is specifically machined, for example in a piloted manner

^• the computer, then it is attached by its posterior face 7 to the anterior face 3 of the cornea * + of the ametropic eye 1 with the usual precautions;

- if the comparison criteria are not satisfied, and taking into account the way in which the refraction calculated for the ametropic eye 1 on the anterior face 3 of the cornea - + of which would be attached the theoretical lens having the state of rest the set of values chosen respectively for these different mechanical, geometrical, optical characteristics, is situated in relation to the refraction of an emmetropic eye, we set for that of these characteristics which is considered to be unknown a new chosen value, which differs in a predetermined manner of the value initially chosen, while the values initially chosen for the other characteristics remain unchanged, and we resume the simulation of the attachment of the new theoretical lens thus defined to the anterior face 3 of the cornea of the ametropic eye 1, the calculation of a refraction of the assembly thus formed and the comparison of the refraction thus calculated with the refraction of an emmetropic eye according to the same comparison criteria, and this process is possibly repeated until that the comparison criteria are satisfied, in which case one chooses or realizes a real lens presenting for its characteristics istic mechanical, geometric, optical in the non-deformed state all of the respective values chosen for a theoretical lens in the rest state fulfilling the aforementioned comparison criteria, to finally attach this real lens to the anterior face 3 of the cornea • of the ametropic eye 1, in the traditional way.

Possibly, before choosing or manufacturing the real lens having at rest the values of these mechanical, geometrical, optical characteristics having made it possible to fulfill the comparison criteria, we verify by a new "ray-tracing" whether the simulated images, data of the same object respectively by an emmetropic eye and by the couple formed by the ametropic eye and this lens in the deformed state to be attached to the anterior face 3 of the cornea * + of this ametropic eye 1 coincide exactly or approximately, in pre-defined limits.

The programming of a computer with a view to the mode of implementation of the present invention which has just been described falls within the normal abilities of a person skilled in the art, in the light in particular of the aforementioned publications, and will therefore not be detailed. . By using the same mathematical modeling and taking into account the same parameters, it is not only possible to determine the value of one of the mechanical, geometric, optical characteristics of a contact lens capable of adapting to an ametropic eye. 1 determined to bring it a determined correction, by setting respective values of the other of these characteristics within the limits of the probable, but also do so for an epikeratophakia lens 10, intended to cooperate with the cornea - + of the eye ametrope 1 either under previously known conditions, that is to say by attachment to the Bowman's membrane after localized removal of the epithelium and peripheral insertion into an annular incision of the cornea * +, for example as described in French patent application No. 89 08377 of June 23, 1989, or by bonding to the Bowman membrane, either in a new way, which will be d written now and results from the possibility of fine adaptation of the notably geometrical characteristics of the lens 10 to the topography of the anterior surface 3 of the cornea (representative of the topography of the Bowman's membrane), offered by the implementation of the present invention. Although the figures in 6 relate more particularly to this new mode of cooperation of an epikeratophakia lens with the cornea •% of the ametropic eye 1, a person skilled in the art will readily understand that the mechanical, geometric, optical characteristics of a lens ^' intended to cooperate in a traditional way with this cornea could also be determined by the implementation of the method according to the invention, without departing from the scope of this invention; Likewise, a person skilled in the art will easily understand that, although FIGS. * + to 6 relate more particularly to the correction of a hyperopic and astigmatic eye, the present invention can also be implemented for the correction of other optical defects and in particular hyperopia without astigmatism and myopia with or without astigmatism. The figures in 6 show the numerical references 1, 3, - * -. 9 to designate respectively the ametropic eye to be corrected, the anterior face of the cornea thereof, this cornea itself and its periphery, as well as an orthonormal reference mark Oxyz assumed to be linked as well to the ametropic eye 1 as to lens 6 and whose axis Oz coincides approximately with the unreferenced visual axis of the ametropic eye 1.

In addition, 1 1, in FIGS. 5 and 6, has designated the surface of the Bowman's membrane after localized debridement of the epithelium not referenced, this surface being able to be considered with good approximation as confused with the anterior surface 3 of cornea 4 before removal of the epithelium in a localized area around the visual axis approximately coincident with the oz axis.

In FIGS. 5 and 6, the lens 10 is shown in dotted lines in an undeformed state, at rest, that is to say as it appears before being placed on the Bowman II membrane of the ametropic eye 1 while it is illustrated in full line in the conformation which it presents after its installation on the Bowman's membrane 1 1.

In the rest state, the lens 10 has a periphery 12 of revolution about an axis 5 assumed to coincide with the axis Oz. with a diameter D ^ substantially less than the minimum diameter not referenced from the periphery 9 of the cornea and for example of the order of half this diameter; this periphery 12 delimits, in the direction of a distance with respect to the axis 5, two faces 13 and 1 * + of the lens 10, which faces 1 3 and 14 may be axi-symmetrical with reference to the axis 5 as in the case of lenses for epikeratophakia of the prior art and may also have other forms, specifically produced as a function of the topography of the anterior surface 3 (or of the Bowman's membrane 11) of the cornea * + the ametropic eye 1 considered, in the Oxyz coordinate system, when implementing the present invention; by way of nonlimiting example and for the sole purpose of illustration, it will be assumed for example that the face 1 3, which is intended to abut onto the Bowman's membrane 1 1 and therefore constitutes the rear face of the lens 10, has the shape of a spherical cap of radius R_ before deformation of the lens 10 while the opposite face 14, or anterior face of the lens 10, has a shape determined as a function of the refractive characteristics which it is desired to communicate to the lens 10.

After joining the Bowman's membrane 11 by its posterior face 13, which implies its elastic deformation, the lens 10 generally loses any possible axi-symmetry, with reference to the axis 5; the geometry of its rear face 13 at rest here represented by the radius

R-, is chosen so that the posterior face 13 of the lens 10 initially has a more pronounced curvature than that of the Bowman's membrane 11 or of the anterior face 3 of the cornea 4 and therefore flattens more or less when it is attached to this Bowman's membrane 11, so that the periphery 12 of the lens

10 in the deformed state, with reference to the axis 5, of the diameters D, - greater than and D, * respectively, one and the other greater than the diameter D ^, respectively along the plane VV along which the anterior face 3 of the cornea 4 is comparatively flatter and according to yaws VI-VI according to which the anterior face 3 of the cornea 4 is comparatively more curved.

This phenomenon of elastic deformation of the lens 10 during the joining of the posterior surface 13 to the Bowman's membrane 1 1 ^is' searched regardless of the shape of the posterior face 13 of the lens 10 at rest, in order to contribute to the anchoring of this lens 10 on the cornea 4 by a suction effect applied to the Bowman's membrane 1 1 by the posterior face 13 of the lens 10 in traditional epikerato¬ phakic methods, in which this anchoring is essentially ensured either by insertion of the periphery 12 of the lens 10 in an annular notch of the anterior face 3 of the cornea 4, in a way not illustrated, or by gluing of the posterior face 13 of the lens 10 on the Bowman's membrane 1 1 , also not illustrated; when one implements ia present invention, authorizing the choice or the realization of a topography of the posterior face 13 of the lens 10 in the state of rest suitable to adapt best to the topography of the Bowman II membrane, shown by the topography of the front face 3 of the cornea 4, after deformation of the lens, this effect alone ensures the anchoring of the lens 10 on the Bowman's membrane 11, this anchoring then becoming firmer made of the progressive covering of the anterior face 14 of the lens 10 by the epithelium as is known in

However, this deformation has the disadvantage of causing a variation in the vergence of the lens 10 when it passes from its state of rest to its deformed state of acceleration by its posterior face 1 3 to the Bowman's membrane 1 1, and the implementation of the method according to the invention makes it possible to determine which value should be assigned to one of the mechanical, geometric, optical characteristics of the lens 10 in the rest state so that the latter, after its attachment by its posterior face 13 to the Bowman's membrane 1 1, on the one hand provides the ametropic eye 1 considered with a refractive correction capable of restoring vision considered normal, according to predetermined comparison criteria with an emmetropic eye, and on the other hand ensures the desired suction effect of the Bowman's membrane 11 by the rear face 13 of the lens 10 in the deformed state, in particular under conditions suitable for allowing dispense with any other means of anchoring the lens 10 to the cornea 4 according to a preferred embodiment of the present invention, and then either choose or specifically machine an actual lens 10 having the characteristics thus determined at rest.

The characteristics thus determined may be those which have been indicated with respect to the contact lens 2, and their determination is carried out by the method described with reference to this contact lens 2, namely by a method of successive approximations of the value of one of these characteristics of the lens in the resting state, for example the geometry or topography of its anterior face 14, while values have been definitively assigned to the other mechanical, geometric, optical characteristics thereof, taking into account a measurement of the topography of the anterior face 3 of the cornea 4 of the ametropic eye 1, that is to say also of the Bowman's membrane 1 1 thereof. in the Oxyz coordinate system and a measurement of the refraction of the ametropic eye l, and taking into account the parameters already mentioned with regard to the determination of the characteristics of a contact lens 2; this method of successive approximations also implements a decomposition, into finite elements, on the one hand of a simulated theoretical lens 10 and on the other hand of the cornea 4 of the simulated ametropic eye 1, as shown Figures 8 and 9 where we find the same reference numerals as in Figures 4 to 6 and which illustrate the theoretical lens 10 simulated respectively in the rest state, before simulated joining of its rear face

1 3 to the Bowman II membrane, and in the deformed state, after this simulated joining; therefore, the implementation of the method for the determination of the mechanical, geometric, optical characteristics of the epikeratophakia lens 10 in the rest state, suitable for giving satisfaction after joining by its posterior face 13 to the membrane of Bowman 1 1 of the ametropic eye 1, is carried out in a manner entirely similar to what has been described with reference to Figures 1 to 3, programming a computer for this purpose also falling within normal skills of a person skilled in the art, in particular in view of the aforementioned publications. Once the mechanical, geometric and optical characteristics of the lens 10 have been determined and the suitable lens 10 has been chosen or manufactured, the lens 10 is joined by the posterior face 1 3 to the Bowman membrane 1 1 of the ametropic eye 1 considered, after debridement localized epithelium, and is anchored on this Bowman's membrane 11 by suction effect and any appropriate treatment, known in itself, makes it possible to facilitate the reconstitution of the epithelium on its anterior face 14; if necessary, the anchoring of the lens 10 on the cornea 4 of the ametropic eye 1 can be improved by any of the methods, already known, of anchoring an epikeratophakia lens 10 on a cornea 4 , namely by insertion of the periphery 12 of the lens 10, then suitably shaped at the level of this periphery 12, in an annular incision of the cornea 4, for example under the conditions indicated in the aforementioned French patent application, or also by bonding of the rear face 13 of the lens 10 on the Bowman's membrane 11 by means of a biological glue, under conditions which are also known in themselves.

A person skilled in the art will readily understand that, although the example and correction of an hyperopic and astigmatic eye has been described and illustrated in FIGS. 4 to 6 by means of a lens produced in accordance with the present invention, any other form of ametropia falling under the prescription of an epikeratophakia could thus be corrected.

Naturally, the embodiments of the invention which have been described constitute only nonlimiting examples and, in particular, one could choose as unknown, to be determined by implementing this method, a characteristic other than the geometry. or topography of the anterior face 8 or 14 of the lens 2 or 10, respectively; in particular, the characteristic of initially unknown value, determined by the implementation of the method, could be the geometry or topography of the rear face 7 or 13 of this lens, respectively.

It is also possible to keep as unknown the respective values of several of the mechanical, geometric, optical characteristics of the lens 2 or 10 at rest, namely preferably geometric parameters on which one can act thanks to a lens machining system or else geometric parameters of a set of pre-machined lenses, such as for example the radii of curvature of the anterior 8 or 14 and posterior 7 or 13 faces of the lens 2 or 20 according to axis 5, as well as the thickness thereof along axis 5, and determine in accordance with the present invention said unknown values so that after laying on the anterior face 3 or the Bowman's membrane 11, respectively, of the cornea 4 of a determined ametropic eye and therefore elastic deformation, ia lens 2 or 10 having the values thus determined optimally corrects this ametropic eye.

The implementation of the method according to the invention can then be carried out as follows, by way of nonlimiting example.

During a first step, starting from the ametropic eye of the patient, it is determined, for example by conventional clinical examination, its optical power or refraction and the correction to be made. The topography of the anterior face 3 of the cornea 4, that is to say its geometrical characteristics, is also determined, for example by a computerized shape recognition system. We obtain a digitized image of this anterior surface or, with a good approximation, of the Bowman's membrane 11.

During a second step, a certain number N of variable parameters N for variable lens 2 or 10 are chosen as characteristics of value initially unknown, these variable parameters preferably being geometric parameters as indicated upper. These parameters are noted (p .... p-X).

Let Ω be lens 2 or 10 at rest (before deformation).

It can be considered that the deformation undergone by the lens 2 or 10 when it is applied to the anterior surface 3 of the cornea 4 or to the Bowman's membrane i l, respectively, is low enough for the linear elasticity to be usable; the principle of the method which will be described remains the same in non-linear elasticity, but the numerical resolution of the equations is then more expensive, and the theorem of existence and uniqueness is no longer verified. It is assumed that the eye remains fixed during the application of lens 2 or 10.

One seeks the strain ψ: Ω -> ψ ( ^~ ) which checks the following problem of pure displacement:

Where T denotes the portion of the boundary of the domain Ω subjected to the imposed deformation ψ, that is to say the posterior face 7 or 13 of the lens 2 or 10 (which is applied to the anterior face 3 of the cornea 4 or on the Bowman's membrane 1 1, respectively). σ is the tensor of the containers of linear elasticity.

For a homogeneous isotropic material, it is connected to the tensor of the linear strains ε = 1 (Vψ + ψ T) -Id by the behavior law called Hooke's law: σ = λ tr (ε) .Id + 2uε Where Id denotes l identity and where λ and μ are the mechanical constants of the material called Lamé coefficients, related to the Young's modulus E and to the Poisson's ratio v by:

μ (3λ + 2μ)

E = and v = "(λ + μ) 2 (λ + μ)

There is existence and uniqueness of the solution of this problem. The variable parameters defining the lens 2 or 10 at rest having been chosen, and if we note Ω (p .... p _M ) the lens 2 or 10 defined by the geometric parameters (p .... p.) It it is a question of finding (p .... p.,) ^~ RN such that ψ ((p ^' ... p ^)) causes the necessary correction, determined in the first step. So we have an inverse problem to solve.

This problem is advantageously solved numerically by a Newton method relating to geometric parameters (p .... p _N ).

To do this, use is made of 3 computer programs, the structure of which can vary to a large extent and is apparent from the normal abilities of a person skilled in the art, but which are linked together by the aforementioned method, namely: 1. A "mesh generator" used to mesh the domain Ω (p. ... p _N ).

2. A linear or non-linear elastic solver if we chose this option, solving the problem (P) by a finite element method. It is two-dimensional axisymmetric if we limit ourselves to ametropic eyes not presenting the defect of astigmatism, or three-dimensional for the opposite case, knowing that the two-dimensional version calculates infinitely more quickly and can therefore prove to be more advantageous in the optics of microcomputer use at the practitioner's.

3. A program determining the total optical power or total refraction of the paired eye-lens pair.

If we note: It. (p. ... p) = (power of the eye-lens couple) - (desired power), we are looking for

(p ^ ... pβ) such that 11 (p ^û .p -) = O Newton's method is then written as follows:

Let us note p? = (p .... p _N )

We give p an initial estimate of the variable parameters.

If | TMp) | <ε given, we stop; this is the solution sought. Otherwise, we have the following recurrence:

an The computation of partial derivatives - is done approximately x

We pose

with h "small" in front of 1.

This method converges quickly as soon as the initial estimate of the variable parameters is fairly close to the solution, which is legitimate to assume since this estimate can correspond to the lens 2 or 10 that the practitioner would have chosen, without the help of the method according to the invention. In total, for each iteration of the method, we must perform: (N + l) mailiage.

(N + 1) solving elasticity problems. (N + 1) dioptric power ratings.

It is therefore very advantageous to choose a fairly low number N of variable parameters, that is to say of mechanical, geometrical, optical characteristics, of value initially unknown, of the lens 2 or 10 at rest; as far as possible, this number is preferably equal to unity.

Claims

CLAIMS 1. Method for producing an elastically flexible lens intended for the correction of an ametropic eye by attachment to the anterior face or to the Bowman's membrane of the cornea thereof, said attachment involving a deformation of the lens in comparison with a state of rest thereof, characterized by the succession of steps consisting in: a) measuring the topography of said anterior face and the refraction of said ametropic eye, b) assigning selected values to some of the mechanical characteristics, geometric, optical of a theoretical lens in the rest state, keeping as unknown the value of at least one other of said mechanical characteristics, geometric, optical of said theoretical lens in the rest state, c) simulate by modeling mathematically said ametropic eye, an emmetropic eye and said theoretical lens and to deduce therefrom a calculated value of said other characteristic of said theoretical lens in the rest state, said calculated value being such that the joining, to said anterior face or to the respective Bowman's membrane, of a real lens having in said rest state said selected values and said calculated value of said mechanical, geometrical, optical characteristics restores to the ametropic eye a refraction situated in a predetermined manner with respect to the refraction of an emmetropic eye, d) to manufacture or choose an actual lens having in said state of rest said selected values and said calculated value of said mechanical, geometric, optical characteristics.

2. Method according to claim 1, characterized in that said other characteristic is a geometric characteristic of ia theoretical lens in the rest state.

3. Method according to claim 2, characterized in that said other characteristic is the geometry of the anterior face of the theoretical lens in the rest state.

4. Method according to any one of claims 1 to 3, characterized in that said mechanical, geometric, optical characteristics include at least some of the following characteristics, respectively: - elasticity coefficients of the theoretical lens,

- refractive index of the theoretical lens.

5. Method according to any one of claims 1 to 4, characterized in that said mathematical modeling takes into account at least some of the following parameters:

- edge conditions, including atmospheric pressure and palpebral pressure, - capillary forces between the anterior surface of the cornea and the posterior surface of the lens,

- a law of behavior of the theoretical lens in elastic deformation from the state of rest.

6. Method according to any one of claims 1 to 5, characterized in that step c) is implemented by the succession of steps consisting in: e) assigning a chosen value also to said other characteristic of the theoretical lens in the resting state, f) simulate by mathematical modeling the joining, to the anterior surface or to the Bowman's membrane, respectively, of the cornea of said ametropic eye, of said theoretical lens having in the resting state said selected values of said mechanical, geometrical, optical characteristics, g) to deduce therefrom a calculated refraction of the ametropic eye to the anterior face or to the Bowman's membrane, respectively, of the cornea of which a real deformed lens would be attached, presenting to the state of rest said selected values of said mechanical, geometric, optical characteristics, h) comparing said calculated refraction to the refraction of an emmetropic eye according to predetermined comparison criteria, and:

- repeat step c) if said comparison criteria are not satisfied, by assigning to said other characteristic of the theoretical lens in the rest state, during sub-step e), a chosen value which differs so predetermined of said chosen value.

7. Method according to claim 6, characterized in that step e) is implemented by the succession of steps consisting in: i) simulating by mathematical modeling the given images, of a determined object, respectively by said ametropic eye and by an emmetropic eye, j) comparing said images according to predetermined comparison criteria and deducing therefrom a correction to be made to said ametropic eye, k) calculating, as a function of said correction to be made to said ametropic eye, a value of said another characteristic of said theoretical lens in the state attached to said anterior face or to the Bowman's membrane, respectively, and deformed,

1) deduce therefrom a probable value of said calculated value of said other characteristic of said theoretical lens in the rest state, to make this probable value said chosen value of said other characteristic of the theoretical lens in the rest state during from step e).

8. Method according to any one of claims 1 to 7, characterized in that it is implemented for the production of a contact lens.

9. Method according to any one of claims 1 to 7, characterized in that it is implemented for the production of an epikeratophakia lens.