Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
1999-12-22
2001-05-15
Epps, Georgia (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S176000
Reexamination Certificate
active
06231182
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a monofocal ophthalmic lens having two aspherical surfaces.
STATE OF THE ART
An ophthalmic lens of this type is known from Example 7 of EP 0560 999 A1. The described ophthalmic lens has a rotationally symmetrical aspherical surface, thus a surface which has identical principle radii of curvature in the apex, as well as a so-called atoric surface, thus a surface which also has astigmatic power in addition to so-called spherical power. EP 0 560 999 A1 deals essentially with reducing the lens thickness of ophthalmic lenses having astigmatic power while at the same time reducing aberrations.
Although the influence of terms of a high order on the dependence of the radius of curvature of a meridian on the distance from the apex is discussed in connection to
FIG. 5
of this printed publication, this figure indicates that according to EP 0 560 999 A1, the terms of a higher order are selected in such a manner that they do not noticeably influence the actual ophthalmic lens surface.
Even if the ophthalmic lens is ground to fit currently “unmodern” drop-shaped frames, no distance on the ophthalmic lens exceeds 35 mm from the apex. However,
FIG. 5
of EP 0 560 999 A1 indicates that according to this printed publication the higher terms have no noticeable effect until over approximately 40 mm.
As an element of the present invention it was recognized that the maximum potential reduction in thickness and aberration is not exploited on the basis of the EP 0 560 999 A1 concept.
An aspherical ophthalmic lens having, solely, positive refractive power, in which the front surface is designed aspherically and the side facing the eye is designed spherically or torically in a conventional manner is known from EP 0 379 976 B1. This printed publication states that it is advantageous for reducing the center thickness while maintaining good optical imaging properties if the first derivation of the curvature after the distance from the apex first diminishes with increasing distance from the apex and then increases. However, this teaching overlooks that both the optical effect, i.e. the refractive power respectively the refracting power, and the aberration and, in particular, astigmatism and refractive errors are not determined by only one curvature but rather by both principle curvatures.
Therefore, fulfilling the condition for the course of the curvature of a meridian set forth in EP 0 379 976 B1 is not sufficient for constructing a surface according to the state of the art.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a monofocal ophthalmic lens having two aspherical surfaces (a front surface and a rear surface) of which at least one surface has the identical principle radii of curvature in the apex, in which there not only is a balance between the reduction of the critical thickness, i.e., of the center thickness in lenses with positive power and of the peripheral thickness in lenses with negative power, and the reduction of aberrations but the reduction of both values is as great as possible.
An element of the present invention is that it was understood that both the critical thickness and the aberrations, i.e., in particular the astigmatism and the refracting error can be reduced more greatly in a monofocal ophthalmic lens having two aspherical surfaces (a front surface and a rear surface) than as is known from the prior art, in that the average surface refracting power of at least one of the front and rear surfaces outside the respective apex is defined by the formula:
B
f
=(
n−
1)/2*(1
/R
1
+1
/R
2
)
wherein
n: is the refractive index of the lens medium,
R
1
: is the radius of principle curvature
1
in a point of at least one of the front and rear surfaces in a first principle plane, and
R
2
: is the radius of principle curvature
2
in the point of the at least one of the front and rear surfaces in a second principle plane, and wherein the average surface refracting power of the points on the at least one of the front and rear surfaces is the function of the distance h at a constant azimuthal angle of &OHgr; of each point from the apex, and this function comprises an extreme value and/or the value 0. It is preferable if both an extreme value and the value 0 occur on each meridian.
By means of this invented design it can be achieved that if the critical thickness is very small the astigmatism ast and the refractive error ref in a central region, i.e. in a region having a radius of approximately 20 mm about the apex, assume very small values, i.e. values under 0.1 dpt.
Even in the ring-shaped region adjacent thereto having a radius of up to 30 mm both aberrations only reach values that would still permit direct vision in this region. Even in the outer region, i.e. in the region in which the radius is larger than 30 mm, direct vision is still possible, indirect vision however has practically no limitations.
In ophthalmic lenses with a negative refractive power in which the peripheral thickness is the critical thickness, the latter can be reduced by up to 30% compared to conventional ophthalmic lenses with only an aspherical surface. Even in lenses with a positive refractive power in which the center thickness is already greatly reduced by using an aspherical surface compared to conventional spherical lenses, the center thickness can be further reduced by approximately 10%.
The invented concept is suited, as it was surprisingly discovered, both for ophthalmic lenses with a positive power and ophthalmic lenses with a negative power. The advantages of the present invention becomes especially evident in ophthalmic lenses whose overall power ranges between −10 dpt and +8 dpt.
In any event, it is preferred if the mentioned invented conditions are maintained for the average surface refracting power for points on both aspherical surfaces. It is further preferred if both an extremal value and a zero point of the average surface refracting power occur.
In the case of a purely spherical prescription, the invented ophthalmic lens can have two rotationally symmetrical surfaces. In the case of an additional cylindrical prescription, one surface can be an atoric surface, thus a surface which has different powers in different principle planes. The other surface can be a rotationally symmetrical surface or a surface which although it has the identical principle radii of curvature in the apex, its principle curvatures differ in the peripheral region.
In the invented ophthalmic lens, the difference Ad between the maximum and minimum thickness of the ophthalmic lens is a function f of the spherical power sph, of the astigmatic power cyl, of the refractive index n and of the lens diameter &phgr;, with the function f the following applies:
&Dgr;d=f(sph,cyl,n,&phgr;)≦a+b*(n−1.5)+c*(&phgr;−66 mm)
with
a=f′(sph,cyl)=a
1
+b
1
*|sph+0.5*cyl|
b=f″(sph,cyl)=a
2
+b
2
*|sph+0.5*cyl|
c=f′″(sph,cyl)=b
3
*|sph+0.5*cyl|
The different coefficients are selected according to the prescription:
For example for the following prescriptions applies sph+0.5*cyl≦−1.0 dpt, and a
1
≦−0, 3 mm and b
1
≦1.2 mm/dpt.
Particularly preferred is if for the coefficients are:
sph+0.5*cyl≦−1.0 dpt, and
a
1
=−0.4 mm and b
1
=1.1 mm/dpt.
For the prescriptions sph+0.5*cyl≧2 dpt in particular applies a
1
≦−0.05 mm and b
1
≦1.05 mm/dpt.
Particularly preferred is if a
1
=−0.2 mm and b
1
=1.05 mm/dpt.
In any event, for the other coefficients a
2
, b
2
and b
3
applies
a
2
=−2 mm
b
2
=−0.2 mm/dpt
b
3
=0.04 m.
In another embodiment of the present invention, the astigmatism ast and the refraction aberration ref have very small values in a central region about the apex having a radius of approximately 20 mm, in an adjacent region with a maximum radius of approxima
Altheimer Helmut
Esser Gregor
Guilino Gunther
Haimerl Walter
Pfeiffer Herbert
Antonelli Terry Stout & Kraus LLP
Epps Georgia
Optische Werke G. Rodenstock
Schwartz Jordan M.
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