Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-02-26
2002-02-05
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S177000
Reexamination Certificate
active
06343861
ABSTRACT:
The present invention relates to a progressive ophthalmic lens and in particular to a progressive ophthalmic lens designed to reduce the rate of juvenile myopia progression, and to a process for producing such lenses.
Myopia, or short-sightedness, is a condition of the eye in which parallel rays of light come to a focus in front of the retina. The condition is generally corrected utilising a diverging lens. In many countries, particularly those in the Asian region, the rate of myopia progression is significant, particularly in children, with a rate between −1.25 Dioptre (D)/yr to −2.00 D/yr. This results in a very high proportion of the population with high levels of myopia. Many countries have accordingly embarked on research programs to determine suitable methods of reducing the rate of myopia progression, but with limited success.
Numerous progressive lenses are known in the prior art. Progressive lenses have heretofore been designed on the basis that they have distance, near and intermediate viewing zones. The intermediate zone joins the near and distance zones in a cosmetically acceptable way, in the sense that no discontinuities in the lens should be visible to people observing the lens of the wearer. The design of the intermediate zone is based on a line called the “eye path” along which the optical power of the lens increases more or less uniformly. However, progressive lens designs, whilst in certain cases tailored for wearers suffering from myopia (see International Patent Application PCT/EP97/00105 to Applicants) have heretofore not been applied to juvenile wearers, nor to the problem of juvenile myopia progression.
Accordingly, it would be a significant advance in the art if the progressive lens could more closely relate to the requirements of the individual juvenile wearer. It would be a further significant advance if the lens could be so designed to encourage acceptance by juvenile wearers. For example, it would be a significant advance if the corridor could be tailored to a juvenile wearer and the overall lens design could be optimised for mounting in a relatively small frame.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties and deficiencies related to the prior art. These and other objects and features of the present invention will be clear from the following disclosure.
Accordingly, in a first aspect of the present invention, there is provided a progressive ophthalmic lens element including a lens surface having
an upper viewing zone having a surface to achieve a refracting power corresponding to distance vision,
a lower viewing zone having a greater surface power than the upper viewing zone to achieve a refracting power corresponding to near vision; and
an intermediate zone extending across the lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone and including a corridor of relatively low surface astigmatism,
the progressive ophthalmic lens element including progressive design elements selected to reduce myopia progression.
By the term “progressive design elements”, we mean a combination of surface properties of a progressive lens element including, but not limited to, corridor length, width of upper viewing zone and width of lower viewing zone.
The progressive ophthalmic lens element may be specifically designed for juvenile use. Accordingly, the upper or distance viewing zone of the progressive ophthalmic lens element may be designed to be used at relatively low plus and minus prescription powers. Base curve in the range of 0.50 D to 4.00 D may be used.
Accordingly, in a preferred aspect of the present invention, there is provided a progressive ophthalmic lens element including a lens surface having
an upper viewing zone having a relatively low surface power to achieve a refracting power corresponding to distance vision;
a lower viewing zone having a greater surface power than the upper viewing zone to achieve a refracting power corresponding to near vision; and
an intermediate zone extending across the lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone and including a corridor of relatively low surface astigmatism, the length of the corridor being selected to encourage use by the wearer.
By the term “low to medium addition powers”, we mean addition powers up to approximately 2.50 D.
By the term “corridor”, we mean an area of the intermediate zone of varying power bounded by nasal and temporal contours of tolerable aberration for foveal vision.
The corridor has a “corridor length” (L), which corresponds to the length of the segment of the visual fixation locus which extends from the vertical height of the fitting cross (FC) to the vertical height of the near zone measurement point. For example, in a typical lens element according to the present invention, the power progression begins at the fitting cross (FC) height.
By the term “width of upper viewing zone” (W
U
), we mean a horizontal dimension on the lens surface bounded by nasal and temporal isoastigmatism contours of a particular value, for example 0.50 D, at a predetermined y value, for example y=7 mm.
By the term “width of lower (near) viewing zone” (W
L
), we mean a horizontal dimension on the lens surface bounded by nasal and temporal isoastigmatism contours of a particular value, for example 1.00 D, at a predetermined y value, for example y=−9 mm.
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.
By the term “astigmatism or surface astigmatism”, we mean a measure of the degree to which the curvature of the lens varies among intersecting planes which are normal to the surface of the lens at a point on the surface.
The lower or near viewing zone of the progressive ophthalmic lens element may exhibit a low to medium range of addition powers for example between 1.25 D and 2.50 D, preferably between 1.50 D and 2.25 D.
The intermediate zone may exhibit a relatively short corridor length for example of approximately 15 mm or less, preferably approximately 14 mm or less, more preferably approximately 10 to 14 mm. It has been established a short corridor length reduces the amount of downward gaze, thereby increasing the likelihood of children utilising the required addition power for near tasks.
The progressive lens element according to the present invention may include a relatively wide upper viewing zone. The width of the distance viewing zone, measured from the temporal 0.50 D astigmatism contour to the nasal 0.50 D astigmatism contour, should preferably be not less than 34 mm at the vertical height of 7 mm above the geometric lens centre for addition powers of up to 2.00 D.
Preferably, the width of the upper viewing zone, measured from the temporal 0.50 D astigmatism contour to the nasal 0.50 D astigmatism contour is not less than approximately 25 mm at the vertical height of 7 mm above the geometric lens centre for addition powers of above approximately 2.00 D.
The distance boundary may rise slightly towards the periphery of the lens element. This does not cause a difficulty as the relatively small size of the finished juvenile lens means that this region is removed in practice. It will be understood that this design provides an increased ability to reduce peripheral astigmatism in the lower portion of the lens.
The distribution of astigmatism in the lower portion of the lens may accordingly be relatively soft.
For example, the width of the near viewing zone, measured from the temporal 1.00 D astigmatic contour to the nasal 1.00 D astigmatic contour sh
Edwards Simon John
Fisher Scott Warren
Kris Dimitrios Jack
Pavy Simon John
Varnas Saulius Raymond
Burns Doane Swecker & Mathis L.L.P.
Sola International Holdings Ltd.
Sugarman Scott J.
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