Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1998-12-15
2000-12-05
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
G02C 706
Patent
active
061556815
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a progressive ophthalmic lens and in particular an ophthalmic progressive lens exhibiting improved optical performance in the distance viewing region. It is a feature of the present invention to provide spectacles designed specifically for distance and intermediate vision and providing improved flexibility for the wearer, with an improved angular range of visual fields and greater tolerance to fitting variability.
Numerous progressive lenses are known in the prior art. A progressive lens in general exhibits a distance and intermediate viewing zone in which the intermediate zone joins the intermediate 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 intermediate zone should be optically acceptable in the sense that there should be a line or corridor called the eye path along which the line of vision moves while going between the distance and intermediate zones, and along which the optical power of the lens increases more or less uniformly. It is normal to select an eye path with a slant to accommodate the natural convergence of the eyes along the path.
However, in order to provide at least acceptable distance and intermediate viewing zones compromises may need to be made to any or all zones.
Moreover, in the prior art, in order to provide a range of distance and intermediate zone optical powers which permit optimum fitting of the lens to most patients, a large family of progressive lens blanks with different distance and intermediate zone powers have been necessary. It would be a significant advance in the art if an ophthalmic lens could be designed which requires a smaller family of individual lens types to satisfy the distance and intermediate viewing needs of a wide range of patients. This would be more nearly similar to the number of blanks in a single vision reading lens series.
In the prior art, the large power change between the distance and intermediate viewing zones results in large aberrations which greatly restrict the permissible fitting positions for the lens.
It would be a significant advance in the art if an ophthalmic lens could be designed with reduced sensitivity to horizontal fitting errors (such as errors in pupillary distance measurement of the wearer) and vertical fitting height errors ascribed to frame and face conformation measurement errors. This would make such lenses more similar in ease of fitting to single vision reading lenses.
SUMMARY OF THE INVENTION
It is accordingly 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.
Accordingly, in a first aspect of the present invention there is provided a progressive ophthalmic lens including a lens surface having an upper viewing zone providing good optical quality at a predetermined low surface power over a large area of vision; said predetermined power being determined by the viewer's distance prescription (R.sub.x) the horizontal fitting position normally being determined by the intermediate pupillary distance of the wearer, and the vertical fitting position normally being determined by the vertical frame midpoint; vision for intermediate or lesser viewing distances; and the contours of mean surface power and/or surface astigmatism within the upper viewing zone, lower viewing zone and corridor are generally symmetric about a vertical lens meridian.
In contrast to the prior art, it is a feature of the present invention to place emphasis on both distance and intermediate vision, with the aim of providing spectacles designed specifically for distance and intermediate vision. This results in a lens which is superior to conventional progressive lenses for distance and intermediate viewing and also superior to single vision distance lenses in providing an increased range of distances at which vision is sharp.
In order to do this the distance viewing zone has been speci
REFERENCES:
patent: 5867246 (1999-02-01), Edwards et al.
Edwards Simon John
Fisher Scott Warren
Kris Dimitrios Jack
Varnas Saulius Raymond
Sola International Holdings Ltd.
Sugarman Scott J.
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