Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1997-01-17
1999-02-02
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
G02C 706
Patent
active
058672460
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a progressive ophthalmic lens and in particular an ophthalmic progressive lens exhibiting improved optical performance in the near viewing region. It is a feature of the present invention to provide spectacles designed specifically for near and intermediate vision and providing improved flexibility providing the wearer with an improved range of vision and improved fitting.
Numerous progressive lenses are known in the prior art. A progressive lens in general exhibits a distance, near and intermediate viewing zone in which 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 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 near 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, the design of progressive lenses in the prior art has concentrated on maximising the optical quality in the distance viewing zone. To achieve this the distance viewing zone has been specified to have a precise optical power and a large size. This has meant a limited area of vision which can be covered within the near vision zone through vertical and horizontal movement of the eyes alone.
In practice the optical power of the near viewing zone has been determined indirectly from the power of the distance zone through the addition of an add power to the optical power of the distance viewing zone. A disadvantage of prior art progressive lenses is that they are difficult to fit. Such lenses must be fitted to a carefully measured pupillary height relative to the lower frame edge, and to a carefully measured pupillary distance relative to the nasal frame edge. Errors of as little as 1 or 2 mm in either measurement can cause significant reductions in lens utility.
In other aspects of prior art, single vision lenses have been used to assist presbyopic patients with near viewing tasks. Such lenses provide a very wide near viewing area which is relatively free of optical aberrations. However, a disadvantage of such lenses is that they restrict the range of viewing distances available to the wearer since objects beyond a certain distance (typically beyond about 0.3 to 1 meter) will be out of focus due to the extra convergent power required in the lens to replace the accommodative deficit of the patient. However, single vision reading lenses have the advantage of easy fitting. Horizontal fitting is normally accomplished by using the near pupillary distance of the wearer. Vertical fitting is accomplished by placing the lens optical centre at the vertical frame midpoint (the so-called "frame datum"). Thus, no special fitting procedures, such as are used with progressive lenses, are required with single vision reading lenses.
Moreover, in the prior art, in order to provide a range of distance and near zone optical powers which permit optimum fitting of the lens to most presbyopic patients, a large family of progressive lens blanks with different distance and near 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 near 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 near viewing zones results in large power and aberration gradients 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 pup
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Barkan Eric
Edwards Simon John
Kris Dimitrios Jack
Sklar David Howard
Thyssen Mark
Sola International Holdings Ltd.
Sugarman Scott J.
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