Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2000-01-20
2001-04-24
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
Reexamination Certificate
active
06220705
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to progressive multifocal ophthalmic lenses. Such lenses are well-known; they are suitable for correcting presbytic spectacle wearers, and consequently supply an optical power which is different between near vision and far vision, when mounted in a frame.
Progressive ophthalmic lenses conventionally comprise a far vision region, a near vision region, an intermediate vision region, and a main meridian of progression passing through these three regions. French Patent Application 2,699,294 to which reference can be made for more details, discusses, in its introduction, the various elements of a progressive multifocal ophthalmic lens, together with the work carried out by the applicant with an aim to improving comfort of wearers of such lenses. Briefly, the top portion of the lens is called the far vision region and is used by the spectacle wearer for distance vision. The lower portion of the lens is the near vision region which the spectacle wearer uses for close work, for example for reading. The region extending between these two latter regions is called the intermediate vision region.
In practice, progressive multifocal lenses frequently comprise an aspherical face, and a face which is spherical or toric, which is machined to adapt the lens to the wearer's prescription. It is consequently usual to characterize a progressive multifocal lens by surface parameters of the aspherical surface, specifically a mean sphere S and a cylinder, at each point thereof.
Mean sphere S is defined by the following formula:
S
=
n
-
1
2
(
1
R
1
+
1
R
2
)
in which R
1
and R
2
our minimum and maximum radii of curvature, expressed in meters, and n is the refractive index of the lens material.
Cylinder is given, using the same conventions, by the formula:
C
=
(
n
-
1
)
&LeftBracketingBar;
1
R
1
-
1
R
2
&RightBracketingBar;
We now call power addition the difference in mean sphere between a reference point in the far vision region and a reference point in the near vision region. These two reference points are usually chosen to be on the main meridian of progression.
The main meridian of progression is a line which is generally defined as being the intersection of the aspherical surface of the lens and the wearer's glance when the latter looks straight ahead, at various distances. The main meridian of progression is frequently an umbilical line, in other words one for which all points have zero cylinder.
The applicant has also proposed, in order to better satisfy the visual requirements of presbytic spectacle wearers and improve the comfort of progressive multifocal lenses, to adapt the shape of the main meridian of progression, as a function of power addition, and in this respect see French Patent Application 2,683,642.
Existing progressive multifocal lenses can be further improved, notably those having a high power addition. For such lenses, the values of cylinder reach high levels in view of the increase in lens power. This leads to disturbances to dynamic vision and a reduction in the width of the intermediate vision region and close vision region. This is all the more disturbing when one considers that, for prescriptions of power addition greater than 2.50, the wearer no longer disposes of objective accommodation. In such cases, it is consequently better to provide the spectacle wearer with the power addition he or she needs for sharp vision in close vision together with wide and accessible visual fields for near and intermediate vision.
Advantageously, the near vision region is also sufficiently high up to ensure the wearer enjoys optimal comfort.
In French Patent applications 2,683,642 and 2,683,643, the applicant has already proposed improvements consisting in varying the shape of the meridian as a function of power addition and, consequently, the age of the wearer. Lateral offset, at the nasal side, of the close vision reference point, takes account of the moving closer of the reading plane as the wearer's age advances.
Applicant has also proposed to vary the position of the close vision reference point not only as a function of power addition, but also as a function of ametropy, to take account of prismatic effects.
In French Patent application 2,753,805, applicant has disclosed another improvement for determining the meridian. A method employing ray tracing makes it possible to determine the meridian, by taking account of the moving closer of the reading plane as well as prismatic effects. Thus, for a given power addition, wearers suffering from different degrees of ametropia will perceive the same variations in power from the far vision region to the near vision region. Sphere and cylinder management ensure ample fields of vision.
SUMMARY OF THE INVENTION
The present invention sets out to improve lenses having a power addition greater than or equal to 2.50. The lenses obtained have wider near and intermediate vision regions, as well as a distribution of sphere and cylinder which is as homogeneous as possible over the complete surface. The invention particularly proposes to carefully master variations in cylinder in the region extending to both sides of the meridian, from the middle of the intermediate vision region to the top of the near vision region.
The present invention discloses a multifocal lens which overcomes the disadvantages of the prior art lenses and which also ensures the wearer benefits from a near vision region which extends high up along with a good binocular effect, not only in static vision, but in dynamic vision as well.
The invention provides a progressive multifocal ophthalmic lens, comprising an aspherical surface having at every point thereon a mean sphere and a cylinder, and comprising a far vision region with a reference point (CL), a near vision region with a reference point (CP), an intermediate vision region, a main meridian of progression passing through the said three regions, and a mounting center (CM), in which:
power addition A, defined as the difference in mean sphere between said near vision region reference point and said far vision region reference point is greater than or equal to 2.50 diopters,
a difference between mean sphere at said mounting center and mean sphere at said far vision region reference point is less than or equal to 0.25 diopters;
said far vision region includes at least one angular sector with its apex at said mounting center and a central angle of 110°, within which values of sphere and cylinder are less than or equal to 0.50 diopters;
in a region of said lens above said near vision reference point, and extending substantially up to the middle of said intermediate vision region:
differences between maximum cylinder values over a distance of 20 mm at both sides of said meridian have an absolute value less than or equal to 0.30 diopters; and
at each side of said meridian, an absolute value of difference between maximum and minimum values of cylinder is less than or equal to the product k*A obtained by multiplying power addition by a constant k having a value of 0.10.
Preferably, the above region of the lens above the near vision reference point extends over 7 mm, below a horizontal line located 11 mm below the mounting center.
Advantageously, the far vision region has a lower limit in the upper portion of the lens formed by A/6 isosphere lines, where A is power addition.
In one embodiment, the lens has a main length of progression less than or equal to 15 mm, length of progression being defined as a height difference between the mounting center and a point on said meridian having a value of sphere 85% of power addition greater than sphere at said far vision reference point.
Preferably, a norm of the gradient of sphere at each point on a surface thereof is less than or equal to the product k′*A resulting from multiplying power addition A by a constant k′ of value 0.1 mm−1.
Advantageously, an upper value of cylinder does not exceed power addition by more than 10%.
A norm of cylinder gradient on isocylinder lines representing half the va
Ahsbahs Francoise
Francois Sandrine
Essilor International
Fish & Richardson P.C.
Sugarman Scott J.
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