Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2000-05-18
2001-07-17
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S172000, C351S177000
Reexamination Certificate
active
06260967
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a progressive ophthalmic lens and in particular to the improvement of the progressive lens surface to compensate for cylinder correction applied to the non-progressive surface.
BACKGROUND OF INVENTION AND OBJECTS
Numerous progressive lenses are known in the prior art. Progressive lenses are typically designed to have distance, near and intermediate viewing zones where the intermediate zone joins the near and distance zones in a cosmetically acceptable way, such that no discontinuities in the lens are visible to people observing the wearer.
Significant advances in customising progressive lens design have been disclosed in international patent application PCT/EP97/00105. This application describes a series of lens elements where the progressive designs vary depending on whether the wearer is a myope (short-sighted), emmetrope (normal vision) or hyperope (long sighted), whilst maintaining substantially constant the optical field of vision in the near and/or distance zones.
Whilst these designs are a significant advance, they do not vary with the specific optical requirements of the individual wearer. For example, the designs do not vary when an astigmatic correction is introduced to the back surface of the lens.
It is an object of the present invention to provide a progressive ophthalmic lens that compensates for optical corrections introduced for individual wearers.
SUMMARY OF INVENTION
The present invention provides a progressive ophthalmic lens element having a front surface that includes an upper viewing zone having a surface power suitable for distance vision, a lower viewing zone having a surface power suitable for near vision, and a corridor of relatively low astigmatism connecting the upper and lower viewing zones, the corridor being a part of an intermediate viewing zone having a surface power varying from that of the upper viewing zone to that of the lower viewing zone. The progressive ophthalmic lens element also has a back surface. The present invention is then characterised by the front surface including at least one correction to improve optical performance of the lens element by at least partially compensating for a cylinder correction applied to, or to be applied to, the back surface.
In this respect, the present invention has identified that in order to satisfy the requirements of various wearers, including for example wearers requiring astigmatic correction, it is necessary to consider the effects of both front and back surfaces in optical performance, and to modify the front surface to improve optical performance in response to, or in anticipation of, the back surface design. By the term “astigmatic correction”, we mean the wearer's prescribed cylinder correction and the associated axis of this correction.
The improvement in optical performance is preferably an optimisation of the optical field of vision of the wearer in one or more of the upper, lower or intermediate viewing zones. This improvement, or optimisation, may be relative to an idealised lens element with zero cylinder, or may involve the creation of a new modified progressive lens surface.
By the term “optical field of vision” we mean a field defined by the boundary at which blur becomes apparent to the wearer. The optical field of vision is thus an area or object field viewed from the standpoint of the wearer, in which there is foveal vision with minimal loss of acuity. The size of the optical field of vision is influenced by the size of the lens zone, the net magnification in that zone, and the oblique aberration of the lens.
By the term “lens element” we mean all forms of individual refractive optical bodies employed in the ophthalmic arts, including, but not limited to, lenses, lens wafers and semi-finished lens blanks requiring further finishing to a particular patient's prescription. Also included are formers used in the manufacture of progressive glass lenses and moulds for the casting of progressive lenses in polymeric material such as the material sold under the trade designation CR39.
GENERAL DESCRIPTION OF THE INVENTION
In the ophthalmic lens element of the present invention, the progressive front surface may be created by taking any suitable conventional progressive surface and modifying it according to an optical optimisation process which considers the cylindrical correction applied to the rear surface. The resulting front surface may differ from conventional progressive designs in that the distance and/or near measurement points thereon may not be spherical.
The ophthalmic lens element may exhibit differing corrections in at least two regions of the progressive front surface, corresponding to the differing prescription requirements in the distance and near regions. In a preferred form, the front surface correction will at least partially compensate for a range of cylinder prescriptions. For example, the front surface correction may vary depending on the axis of the cylinder correction on the back surface. In particular, the front surface correction may cover a range of axis values, for example −20° to 20°, depending on the degree of optimisation required, or alternatively the design may involve a specific axis and cylinder.
Alternatively, or additionally, the front surface correction may vary depending on the distance prescription power, or may cover a range of distance prescription powers. Further still, the front surface correction may vary depending on the addition power.
There are a number of methods that may be used to achieve the front surface corrections referred to above. The most preferred of these is a general aspheric modification as it would allow for the modification to be applied to any existing progressive design. In this respect, by the term “general aspheric” we mean a non-rotationally symmetric aspheric surface that may or may not have one or two planes of symmetry.
For a general aspheric modification, a lens corresponding to the single vision prescription case is initially considered and an optimised front surface design created to produce optimal optical performance with a toric back surface. After the modification, the resulting surface may be a generally aspheric. This surface may then be used to replace the base curve of the progressive lens surface to produce a new modified surface, improving the optical performance of the lens for the complete prescription of the wearer
This method may be highly automated and utilised with any conventional progressive lens front surface to provide the corrections for a range of prescription, addition power, cylinder and axis orientation values.
As a further alternative, the progressive surface may be designed utilising optical optimisation methods from the initial stages of a progressive surface development. The optical optimisation methods consist of the minimisation of a blur measure, M, and applying any of the known finite element methods. This may be achieved by using an appropriate back surface for the prescription identified, and then designing a dedicated front surface. In this respect, the optical performance may be optimised for one or more of distance, intermediate, or near zone vision, depending on the prescription needs of the wearer.
By the term “blur measure M” we mean a value M defined by one of the following:
M
1
=
∑
θ
(
rms
blur
)
θ
2
M
2
=
∑
θ
(
(
mpe
)
2
+
(
cyl
error
)
2
)
θ
M
3
=
∑
θ
(
1
16
(
mpe
)
2
+
(
cyl
error
)
2
)
θ
M
4
=
∑
0
horizontal
(
ϵ
11
)
θ
2
+
∑
8
vertical
(
ϵ
22
)
θ
2
+
∑
θ
oblique
(
mpe
)
θ
2
M
5
=
∑
θ
(
(
mpe
)
2
+
1
16
(
cyl
error
)
2
)
θ
where summations are over a number of sample eye rotations &thgr;. In the case of M
4
, there are different blur measures used depending upon whether the sample point
0
represents a horizontal, vertical, or oblique rotation from the “straight ahead” pos
Edwards Simon John
Sklar David H.
Varnas Saulius Raymond
Burns Doane Swecker & Mathis L.L.P.
Sola International Holdings Ltd.
Sugarman Scott J.
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