Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1991-03-18
1993-05-11
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
G02C 702
Patent
active
052105539
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a progressive ophthamic lens having positive distance power, in which at least one surface is designed as a progressive area and which has a distance portion intended for distant vision with practically constant distance power and a near portion intended for near vision with practically constant near power including a progression zone, in which the surface refractive power increases from the surface refractive power at the distant reference point along a curved or plane main meridian to the surface refractive power at the near reference point.
STATE OF THE ART
An opthalmic lens of this type is known, by way of illustration, from DE 37 16 201. Moreover, express reference is made to this publication as well as to the other literature mentioned in this publication for the explanation of all the terms not made more apparent therein.
Initially, two different construction principles were pursued in the development of progressive ophthamic lenses:
In one principle of construction the progression zone, i.e. the area in which the power of the ophthamic lens, respectively in viewing only the progressive surface in which the surface refractive power of this surface increases from the value in the distance portion to the value in the near portion, is selected as long as possible in order to maintain a relatively low increase in progression which facilitates the correction of aberrations in the lateral regions.
Typical surfaces of this principle of construction are described in DE-PS 1 145 820 and in FIGS. 1 to 4 of U.S. Pat. No. 2 878 721.
In the other principle of construction the point of departure is a spherical distance portion and a spherical near portion and an attempt is made to "join" the two as aberration-free as possible by means of a transition zone.
Subsequently the attempt was made to combine the advantages of both principles of construction through the selection of the a spherical distance and near portions and for the most part avoiding the disadvantages thereof, with special consideration being given to the course of the increase in progression: with regard to this reference, by way of illustration, is made to FIG. 1 of the survey by B. Maitenaz in "The ophthamic optician", Sep. 17, 1966.
From the commercially available progressive ophthamic lenses with a progressive surface and those proposed in the patent literature, a common principle of construction has crystallized for about 8 years, that the as large as possible progressive distance portion has largely constant surface refractive power and as small as possible surface astigmatism at least on the main meridian, respectively in the central viewing-through area. The near portion also has largely constant surface refractive power in the prior art progressive ophthamic lenses and as small as possible surface astigmatism in the region of the main meridian.
Under "largely constant surface refractive power" and "as small as possible surface astigmatism" is understood that the refractive power in the distance portion of the prior art progressive ophthamic lenses does not fluctuate more than.+-.0.3 to 0.5 dpt and the surface astigmatism on the main meridian in the region of the progression zone and in the lower region of the distance portion is less than typically 0.25 dpt. Similar values also are true for the near portion, whereby the just given limits may be minimally higher in most ophthamic lenses due to the design.
The length of the progression zone, i.e. the length of the region in which the surface refractive power on the main meridian increases is usually dependent on the respective company policy, but never exceeds a value of 28 mm in any of the presently available ophthamic lens.
The typical course of the increase in refractive power for various addition values is shown in FIG. 6 of U.S. Pat. No. 4,315,673. In this instance the radius of curvature runs a long the main meridian in the case of astigmatism-free main merdians (umbilicus line) in proportion to the course in FIG. 6 of U.S. Pat. No. 4
REFERENCES:
patent: 4778266 (1988-10-01), Maitenaz
Barth Rudolf
Wehmeyer Klaus
Optische Werke G. Rodenstock
Sugarman Scott J.
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