Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-07-20
2003-03-18
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S161000, C351S177000, C623S006270
Reexamination Certificate
active
06533416
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to contact or intraocular lenses to correct the vision resulting from a possibly myopic or hyperopic and/or possibly presbyopic astigmatic eye.
It is known that myopia or hyperopia is generally corrected thanks to a spherical surface whose center of curvature must be on the optical axis of the lens, where the parameter that is usually used to define the correction to be made is the introduced spherical optical power, generally called “sphere value.”
It is also known that the correction of presbyopia is advantageously obtained thanks to a complex surface which procures a progressive simultaneous vision correction, that is a correction whose spherical optical power varies delicately (and not abruptly) between the center and the periphery of the correcting zone, so that several images are simultaneously formed on the retina, the useful image being selected as a result of sorting by the cortex.
It is also known that the correction of astigmatism is generally obtained thanks to a toric surface whose symmetrical plane must be oriented along a meridian plane of the eye to be corrected, that is along a plane which contains the optical axis of this eye, where the parameters that are usually used to define the correction to be made are, on the one hand, the angular separation between the meridian plane along which the toric surface must be oriented and the reference meridian plane, corresponding to the horizontal meridian plane when the wearer of the lens is standing, this angular difference usually referred to as “the axis” of the correction, and, on the other hand, by the cylindrical optical power introduced, usually called “cylinder value.”
For the toric surface of a contact lens to remain correctly positioned with regard to the eye, a means for the angular stabilization of the lens with respect to the eye must be provided, and, notably, a ballast prism which makes it possible to maintain the lens in position thanks to the weight, or bosses as described in French Patent No. 2,760,853, which use the dynamic effect produced by blinking the eyelids so that the lens remains permanently correctly positioned, or once again a progressive thinning or lightening at the top and bottom of the lens can be provided, along a direction which must correspond to the vertical direction of the eye, as described in U.S. Pat. No. 4,095,878, or a stabilization means which comprises a ballast and lightening at the top part of the lens, as described in U.S. Pat. No. 4,324,461. All these stabilization means, with the exception of the ballast prism, are located outside of the correcting portion of the contact lens, being located in the center of the lens at the level of the pupil of the eye to be corrected, for example, inside a circle having a radius of 4 mm centered about the optical axis of the lens.
Each one of these means for angular stabilization yields good results, the contact lens remaining, overall, correctly oriented. However, while the different orientations successfully assumed by the lens over time have a mean value which corresponds to the desired value, the amplitude of the variations in orientation around this mean value is such that at times the angular displacement produces a significant degradation of the optical performances.
Such a problem with angular stabilization does not arise with intraocular lenses, which are made in the form of an internal implant in the eye equipped with holding hooks which project radially but can nevertheless produce an angular displacement with regard to the nominal position during placement of the implant.
In order to correct the angular displacement, U.S. Pat. No. 5,570,143 proposes to apply to the toric lenses the techniques that are usually used to prevent spherical aberrations, techniques which have the effect of improving the depth of field where the proposed toric lens presents over at least one surface an optical topography which induces an effect of depth of field having a spherical power which would be sufficiently high to correct for the optical effect of the angular positioning separation.
U.S. Pat. No. 5,652,638 proposes a similar solution, except that the traditional techniques for improving depth of field are replaced by concentric rings.
U.S. Pat. No. 5,796,462 proposes to obtain the effect of depth of field thanks to a lens in which one of the surfaces is of the toric type, in which the meridians are not circles but curves belonging to the family of the classic cone shapes used to prevent spherical aberrations. The other face of the lens is spherical or has concentric rings.
SUMMARY OF THE INVENTION
The present invention is intended to reduce the effects of the angular displacement on toric contact or intraocular lenses by provision of a correcting portion characterized by one or more novel constructions. Per convention, the expression “optical path” designates the difference in optical path introduced by a lens on the rays originating from a point light source located at infinity on the optical axis.
In one embodiment, the lens may be constructed with a “smooth atoric” aspect where the optical path through the correcting portion of the lens corrects for both astigmatism and an axisymmetric aberration other than astigmatism, there being no sudden surface discontinuity (thus, “smooth”). In another embodiment, the lens may be constructed with so-called “sectors” circumferentially arranged around the optical axis such that an optical path through the correcting portion of the lens varies as a function of the angular separation from the reference meridian plane, and the correcting portion is divided into at least two sectors having different astigmatism correction axes. In either embodiment, the correcting surface may be provided on either or both of the anterior or posterior faces of the lens, and the optical performance of the lens in case of angular displacement (the “angular misalignment tolerance”) is increased. Specifically, the angular misalignment tolerance is increased by at least 30% over a standard toric lens of the same class and in the same conditions (i.e., the same cylinder and pupil diameter).
The contact or intraocular lenses of the present invention are best described by the desired optical path through the correcting portion, and it will be understood by those of skill in the art that there are a number of ways to construct the correcting portion so as to produce such an optical path. For example, definition of the particular shape of the lens enables a mold die of that shape to be formed. Lens machining tools may also be used. Whatever the method of manufacture, the present invention is intended to encompass lenses formed to have a particular optical path.
For this purpose, the present invention provides a contact or intraocular lens comprising a correcting portion to correct the vision of a possibly myopic or hyperopic and/or possibly presbyopic astigmatic eye, comprising an optical axis and a reference meridian; characterized in that it introduces, for correction of only the astigmatism, an optical path varying as a function of the distance with regard to the optical axis and as a function of the angular separation with regard to the reference meridian, at least when this distance is between 0.4 mm and 2.4 mm, according to the following equation:
&dgr;
A
(
h,&thgr;
)=&dgr;
toric
(
h,&thgr;
)+&dgr;
atoric
(
h,&thgr;
)
in which equation:
&dgr;
toric
(h,&thgr;) is a cylindrical optical path which satisfies, according to the parabolic approximation, the expression &dgr;
toric
(h,&thgr;)=C/2 h
2
sin
2
(&thgr;−&phgr;), where &phgr; is the axis required to correct the astigmatism of said eye expressed as an angular separation with regard to said reference meridian, and where C is the cylinder value required to correct the astigmatism of said eye; and
&dgr;
atoric
(h,&thgr;) is an optical path, such that, when h is a constant, it varies as a function of &thgr; with a 2&pgr; period, and differently from sin
2
(&thgr;−&phgr;) where this optical path in a
Chateau Nicolas
Fermigier Bruno
Legras Richard
Ocular Sciences, Inc.
Stout, Uxa Buyan & Mullins, LLP
Sugarman Scott J.
Uxa Frank J.
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