Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Corneal implant
Patent
1991-02-14
1993-11-02
Beck, Shrive
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Corneal implant
427 2, 427164, 424429, 623 6, 623 4, 351159, 351160R, A61F 214
Patent
active
052580245
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
The United States Application stems from PCT International Application No. PCT/FR 90/00338 filed on May 11, 1990.
BACKGROUND OF THE INVENTION
The present invention relates to the techniques which make it possible to modify the optical properties of a transparent polymer, more particularly when it is sought to modulate the refractive index of a semifinished article of transparent organic material which has previously been polymerized and shaped, without substantially modifying its geometry or its state of surface.
Under these conditions, a preferred application of the invention relates to the manufacture of artificial optical lenses for correcting eyesight such as contact lenses and ocular implants in view of the fact that, in these examples, it is of great importance to preserve a predetermined geometrical shape as well as qualities of surface which ensure, on both faces of the lens, biological compatibility with the ocular medium and absence of irritation of the eye.
The distinctive feature of lenses of this type lies on the one hand in the fact that they have small dimensions and are intended to be employed in full aperture in contradistinction to spectacle lenses, and on the other hand in the fact that they must have a predetermined geometrical shape which will be adapted to the morphology of the wearer's eye in the case of contact lenses, for example, or which will provide basic accommodation power in the case of an implant for the replacement of the crystalline lens of the eye.
In this type of lens, the refractive index modulation contemplated by the invention may be intended in particular to produce a diffraction grating which endows a contact lens with bifocality or an implant for far-sighted persons. In the case of a contact lens, for example, this makes it possible to correct the user's near vision with a power which is determined by this element while correction of distant vision is achieved independently by the geometry of the lens.
It is at present known to construct contact lenses with diffraction elements by modulating the relief of the outer or inner face of the lens. This modulation can be obtained by a machining technique, by etching the lens material at the desired pitch in order to form the diffraction grating. This technique not only calls for the use of equipment involving high cost and delicate maintenance but has the additional disadvantage of being reserved for contact lenses of the rigid type. In regard to molding of the lens directly with the desired relief, this operation calls for preliminary construction of a mold which is just as costly and difficult to machine and is used for a short period of time.
In one case as in the other, the lenses obtained prove unsatisfactory. When the lens has been worn for a certain time, fouling of the diffraction element is observed. This phenomenon is particularly marked when the diffraction element is formed on the inner face of the lens. Moreover, in commercially available lenses of this type and for reasons of adaptation, the curvature of the inner face of the lens has been increased in order to minimize the contact surface between the etched face of the lens and the cornea, thereby increasing the thickness of the tear film and thus producing an additional lens effect having optical characteristics which are not fixed in time by reason of the instability of this tear film.
Another known method for forming diffraction-element contact lenses consists, as described in European patent No. 0,064,812, in applying on the lens a layer of gelatin which is light-sensitized by bichromate treatment and then exposed so as to form a diffraction grating thereon. It is proposed by way of alternative that the gelatin layer can be included within the lens as an intermediate layer in order to avoid any direct contact with the eye since bichromate is known as an irritant compound. It hardly seems possible, however, to adopt this solution in industrial practice.
In point of fact, when it is located on the outer face of t
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Baude Dominique
Chavel Pierre
Joyeux Denis
Lougnot Daniel
Meslard Jean-Claude
Beck Shrive
Dudash Diana L.
Essilor International (Compaigne Generale d'Optique)
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