Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1990-02-22
1992-09-15
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
351176, 359652, G02C 702
Patent
active
051482053
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an ophthalmic lens having two boundary surfaces and a changing refractive index, which contributes to the correction of aberrations.
DESCRIPTION OF THE PRIOR ART
Ophthalmic lenses having a changing refractive index have frequently been dealt with in the literature in the field. With regard thereto, reference is made, by way of illustration, to the survey "Gradient Index Optics" by W. N. Charman (The Ophthalmic Optician, 1981, pp. 73-84) including the literature cited therein or DE-OS 27 07 601.
Essentially, this literature discusses the substitution of an "index gradient" for aspherical surfaces or further improvement of the imaging properties of ophthalmic lenses with aspherical surfaces by means of an index gradient, with DE-OS 36 16 888 proposing for the first time the use of a changing refractive index to reduce the critical thickness substantially more than is possible with just the use of aspherical surfaces. (The critical thickness is the center thickness in ophthalmic lenses having positive refracting power and the peripheral thickness in ophthalmic lenses having negative refracting power.)
Express reference is made to the afore-mentioned publication with regard to all terms not explained in more detail herein and with regard to the calculation and optimization process.
In general, DE OS 36 16 888 considers the refractive indices changing rotationally symmetrically about the optical axis. The radially dependent gradient employed, in particular, in the preferred embodiments of DE-OS 36 16 888 is, however, relatively complicated to produce, by way of illustration, by means of "twisting" and subsequent thermal treatment of concentric cylinders, respectively hollow cylinders having differing refractive indices.
On the other hand, refractive index variations can be produced relatively easily by means of an ion exchanger bath, into which a glass block, respectively a plastic block, is immersed. The exchange of ions in the bath results in the development of a so-called "surface normal" gradient. However, a "normal" gradient, i.e. a perdendicular one, only has--as was understood in accordance with the present invention --little optical power. Although refractive indices with a radial course can theoretically be produced by means of "ion exchange" via the cylindrical surface of a very long glass cyclinder, in practice, for ophthalmic lenses, it is only possible with a few types of glass due to the usually very shallow penetration of the ion exchange effect.
SUMMARY
The object of the present invention is to provide an ophthalmic lens having a changing refractive index, the course of which is adapted to the respective problem and a process of fabricating the same, which permits flexible adaptation of the variation of the refractive index yielded by the selected process for producing the index gradient to the respective optical problem and, in particular, to the object of correction.
A solution to the aforegoing object and its further embodiments is set forth in the patent claims hereto.
The following root ideas form the basis for arriving at the aforegoing solution in accordance with the present invention:
An element of the present invention is that it was understood that a normal gradient for a surface, i.e., the front surface or the surface facing the eye of the "finished" opthalmic lens, thus e.g. a gradient course like the one yielded by an ion exchange process, only exercises minor influence on the correction of aberrations with penetration depths typical of these processes.
In particular, in an ophthalmic lens, whose more curved surface was selected without taking the correction of aberrations into consideration - like, by way of illustration, suggested in DE-OS 36 16 888, the aberrations cannot be corrected by means of a gradient, which is perpendicular to the surface facing the eye and/or the front surface of the ophthalmic lens.
On the other hand, a gradient according to the present invention, i.e. a refractive index variation, which depe
REFERENCES:
patent: 3486808 (1969-12-01), Hamblen
Altheimer Helmut
Guilino Gunther
Pfeiffer Herbert
Optische Werke G. Rodenstock
Sugarman Scott J.
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