FR2700024A1 - Gas-permeable rigid contact lens for irregularly deformed cornea - Google Patents

Abstract

The lens (L) for contact with the cornea (C) has an inner radius of curvature (R1) of its peripheral portion which is shorter than the radius (R2) of the adjacent inner face and that (Ro) of its centre.The inner peripheral portion is in the shape of a portion of a torus. Such a lens can be made to measure from the results of kerato-analysis esp. when the corneal deformation cannot be compensated fully by other means.

Description

EYE CONTACT LENS
The present invention relates to an eye contact lens intended to be applied to an irregular cornea.

 We know that contact lenses provide an elegant solution to certain vision impairments by avoiding the wearing of exacting glasses which, moreover, limit the visual field. But it is necessary that the lens is exactly adapted to the cornea with the interposition of a thin layer of tear fluid.

Soft hydrated lenses (LSH) are in common use and their flexibility allows them to exactly fit the shape of the cornea. However, it must have a certain regularity to obtain a correct optical correction (small or medium astigmatism) and good stability of this lens on the eye.

We also know rigid lenses permeable to gases. The purpose of this permeability is to allow oxygenation of the surface of the cornea and, consequently, to avoid corneal anoxia. The posterior faces of known rigid contact lenses are drawn from portions of spheres or aspherical surfaces which are variously assembled in order to best match the numerous corneal surfaces existing in nature.

But there are corneas deformed by trauma, pathology or as a result of insufficient results in refractive surgery, resulting, for example, in a corneal deformation "on a plateau" which cannot allow good optical correction.

To date, these corneas cannot receive contact lenses. In addition, vision cannot, in some of these cases, be improved by wearing glasses.

The object of the present invention is to overcome this drawback and to obtain increased precision in the adaptation of the internal face of rigid contact lenses to the anterior face of the cornea in order to establish the best possible alignment.
For the geometry of the lens itself, it calls upon the data of keratoanalysis. Briefly, this consists in projecting on the cornea disks equidistant from each other known under the name of "PLAClDO" disks, which define contour lines, then to photograph them. The representation in space offers a real molding of the cornea.

Recent commercially available photokeratoscopes such as that manufactured under the name TMS by the American company COMPUTED
ANATOMY Inc. or the EYESYS of the American company EYESYS
LABORATORIES allow obtaining several thousand points and mapping according to concentric zones with virtual colors and the development of the corneal surface. For all corneas, including deformed or difficult to fit corneas, the digital corneal topography offers instant molding. Comparative maps allow to follow the evolution of a pathology or its appearance.

According to the present invention, a rigid gas-permeable lens is characterized in that the internal radius of curvature of the rear part of the lens is less than the radius of curvature of the adjacent internal face.

That is to say that while all the known lenses flare, their posterior internal radius, constituting the edge of the lens, being greater than the radius of the adjacent zone, the lenses according to the invention shrink at the periphery by giving a reverse clearance, the radius of curvature of the outer edge of the rear face being less than the central radius of curvature.

They sort of align with the distorted corneal plateau. Thanks to this measurement, it has been found that the contact lenses adhere perfectly to the most irregular corneas. The clearance can be simply spherical or toric.

Other characteristics and advantages of the invention will appear during the description which follows, of particular embodiments given by way of nonlimiting examples, with reference to the figures which represent: - Figure 1, a view of a keratoscopy obtained with an apparatus of the type mentioned above of known type; - Figure 2, another keratoscopy; - Figure 3, a sectional view of a lens of the prior art placed on a regular cornea; - Figure 4, a sectional view of a lens according to the invention placed on a plateau deformation cornea.

In Figure 1 we see a cartographic representation of a cornea which is practically in color, each color being associated with a point value of the refraction expressed in diopters as it appears on the attached legend.

Another representation is shown in FIG. 2 in which the numerical values of diffraction at the different points are inscribed with the conventional colors defined by the legend. From this planar projection, it is relatively easy to define a correction lens.

FIG. 3 represents a conventional lens placed on a regular cornea.

We see that the lens exactly matches the surface of the cornea, the radius of curvature of the peripheral part Rt being greater than the radius of curvature of the adjacent zone R2 and, a fortiori that of the central region RO in which the optical axis.

On the other hand, in FIG. 4, a lens according to the invention is shown in position on a deformed cornea "in plateau", that is to say plane in its central region. With a very large central radius R0. The radius R1 of the peripheral zone is less than the radius R2 of the adjacent zone so that a narrowing of this peripheral zone occurs which allows good support on the eye by the tear film.

Example 1:
The eye of a patient operated for a keratoconus resulting from a keratoplasty sixty and whose graft is affected by an irregular astigmatism not equipable neither in glasses nor in conventional lens. Following the installation of a lens according to the invention, this eye has recovered a visual acuity of 10/10 P2.

The characteristics of the lens used are as follows:
Material: FLUOPERM 92
Optical zone: Diameter 6 mm.

Total diameter of the lens: 10 mm.

 R0: 750mm.

A1: 63Omm.

Power: - 5 diopters
Example 2:
A patient having been operated on by radial keratotomy requires an additional correction of (0-0.5) - 0.5 on the right eye and of (165-0.5) - 0.5 on the left eye, I ' absence of a correction causing visual fatigue.

The equipment with two lenses according to the invention makes it 10/10 P2. the characteristics of the two lenses according to the invention are as follows
Right eye
Material: FLUOPERM 92 Optical zone: 6 mm.

 e total of the lens: 9.5 mm.

 RO: 810 mm.

R1: 760 mm.

Power: - 0.5 diopter
Left eye
Material: FLUOPERM 92
Optical area: e 6 mm.

 e total of the lens: 9.5 mm.

R0: 800 mm.

A1: 7SOmm.

Power: - 0.5 diopter
Kerato-analysis thus makes it possible to produce "tailor-made" lenses, in particular when the corneal deformation in plateau cannot allow good optical correction. The lenses according to the invention are called upon to render services which are indicated when the surgery has reached its limits or when the patient or the surgeon abandons the operative route.

 It goes without saying that many variants can be made, in particular by substitution of technically equivalent means, without departing from the scope of the invention.

Claims (2)

 1 "Rigid gas permeable ocular lens, characterized in that the internal radius of curvature R1 of the rear part of the lens is less than the radius of curvature R2 of the adjacent internal face and the radius of curvature RO of the central zone.  2 "Rigid gas-permeable ocular lens according to claim 1, characterized in that the internal peripheral zone is toric.