Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1989-07-14
1991-08-27
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
359652, G02C 706
Patent
active
050429361
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a progressive ophthalmic lens having a distance portion, the refractive power of which being designed for distance vision, a reading portion, the refractive power of which being designed for near vision, and an intermediate portion, in which the refractive power along the main line of vision at least partially increases continuously from the refractive power of the distance portion to the reading portion.
2. State of the Art
The known progressive ophthalmic lenses as described above are made of a material having a uniform refractive index, attaining the increase in refractive power from the distant portion to the reading portion by means of appropriate design of one or both lens surfaces.
As the design of the surface of the state of the art ophthalmic lenses deviates very greatly from their spherical shape, their production and, in particular, the polishing of a surface cut "meridianwise" is difficult and often results in comparatively large discrepancies between the produced surface and the computed surface.
Furthermore, --at least in the case of a progressive surface --it is not possible to keep imaging errors and, in particular, astigmatism and distortion at a low level over the entire lens.
DESCRIPTION OF THE INVENTION
For this reason, the present invention proceeds from the concept to realize advantageous properties by means of a progressive ophthalmic lens having a changing refractive index. Ophthalmic lenses with a changing refractive index have been discussed numerous times in the literature in the field: reference hereto is made, by way of illustration, to the survey "Gradient Index Optics" by W. N. Charman (The Ophthalmic Optician, 1981, pp 72-84) as well as the literature cited therein.
As can be drawn from the aforecited article (p. 80, left column), hitherto ophthalmic lenses having a varying refractive index have been considered as a substitute for ophthalmic lenses having aspheric surfaces while possessing "similarly good" optical properties (p. 80, left column ff.). As yet there has been no known actual realization of a progressive ophthalmic lens having a changing refractive index.
This is probably due to the fact that progressive lens surfaces have a very complicated surface design. Thus, there seems to be a preconceived notion that a varying refractive index as an alternative for such a complicated surface design would result in a just as complicated refractive index function, which is technically not to be realized.
A key element of the present invention is that it was understood that it is possible to achieve such great advantages by using a varying refractive index in manufacturing lens surfaces with simplified production being the consequence thereof while maintaining overall comparable imaging properties.
Thus, the object of the present invention is to provide a progressive ophthalmic lens having a varying refractive index.
In accordance with the present invention it was understood that employing a varying refractive index yields the following possibilities:
The variation of the refractive index produces or enhances the increase in refractive power along a line following the curved line of vision or lying in a plane and being adjusted to the main line of vision.
Designated as main line of vision is that line on the front surface of the ophthalmic lens which connects the main points of peering through for vision in the distance and for reading and on which lie the points of penetration of the beams of vision for intermediate distances in the "straight ahead" direction. The main line of vision is an almost vertical line in the distance and reading portions and a sinous line in the intermediate section.
The utilization of a gradient medium corrects imaging errors lateral of the main meridian.
Assuming that the three effects "increase in refractive power along the main line of vision", "elimination of astigmatism along the main line of vision" and "lateral corrections" are chiefly partially or not borne by varyin
REFERENCES:
patent: 3610924 (1971-10-01), Sinai
patent: 4073579 (1978-02-01), Deeg et al.
Altheimer Helmut
Guilino Gunther
Pfeiffer Herbert
Optische Werke G. Rodenstock
Sugarman Scott J.
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