Ophthalmic filter materials

Details Ophthalmic filter materials Ophthalmic filter materials

1998-09-29

1999-10-26

Spyrou, Cassandra

Optical: systems and elements

Absorption filter

351163, 351177, 65 37, G02B 522, G02C 710, G02C 706, C03B 1108

Patent

active

059738650

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The field is ophthalmic filter materials, in particular, lenses designed to protect the eye from the effects of strong sunlight.


BACKGROUND OF THE INVENTION

The present invention relates to ophthalmic filter materials. These materials selectively transmit radiation in the visual and near-visual regions of the spectrum. The present materials are primarily concerned with controlled transmission of sunlight through ophthalmic lenses.
The invention was developed employing photochromic glass lenses. However, for some purposes, photochromic glass is not suitable because of safety and/or weight. Fortunately, the invention is also applicable to tintable plastic materials as well. The invention may also find application in products other than glass and plastic, ophthalmic lenses, such as visors and shields.
The invention was developed using photochromic glass lenses, and is largely so described. However, as indicated, the invention is not so limited, and may also be practiced employing tintable plastic materials. Accordingly, that practice is also described.
All of the commercially important photochromic glasses contain a precipitated, microcrystalline, silver halide phase. It is this phase which is considered to cause the reversible darkening of the glass under exposure to light. U.S. Pat. No. 3,208,860 (Armistead et al.) provides the basic description of this family of glasses.
The patent is drawn generally to silicate-based glasses. The preferred compositions are encompassed within the alkali metal oxide-Al.sub.2 O.sub.3 --B.sub.2 O.sub.3 --SiO.sub.2 system. Thus, the preferred base compositions consist essentially, expressed in weight percent on the oxide basis, of about 4-26% Al.sub.2 O.sub.3, 4-26% B.sub.2 O.sub.3, and 40-76% SiO.sub.2, wherein R.sub.2 O is selected from the group of 2-8% Li.sub.2 O, 4-15% Na.sub.2 O, 6-20% K.sub.2 O, 8-25% Rb.sub.2 O, and 10-30% Cs.sub.2 O, the sum of the base glass ingredients constituting at least 85% of the total composition. The patent further observes the advantage of including small quantities of low temperature reducing agents, such as SnO, FeO, CuO, As.sub.2 O.sub.3, and Sb.sub.2 O.sub.3, to improve the photochromic characteristics of the glass. In order to impart preferred photochromic behavior to the glass, a silver halide is present in the glass.
Subsequent work has resulted in the development of a number of specific families of photochromic glasses exhibiting faster darkening and/or fading response. U.S. Pat. No. 4,190,451 (Hares et al.), for example, provides a description of more recently developed photochromic glasses of this type. The glasses described in that patent consist essentially, in weight percent, of about 0-2.5% Li.sub.2 O, 0-9% Na.sub.2 O, 0-17% K.sub.2 O, 0-6% Cs.sub.2 O, 8-20% Li.sub.2 O+Na.sub.2 O+K.sub.2 O+Cs.sub.2 O, 14-23% B.sub.2 O.sub.3, 5-25% Al.sub.2 O.sub.3, 0-25% P.sub.2 O.sub.5, 20-65% SiO.sub.2, 0.004-0.02% CuO, 0.15-0.3% Ag, 0.1-0.25% Cl, and 0.1-0.2% Br, wherein the molar ratio of alkali metal oxides:B.sub.2 O.sub.3 ranges about 0.55-0.85, and the weight ratio Ag:(Cl+Br) ranges about 0.65-0.95. The glasses may also contain up to about 10% total of optional constituents, expressly referring to 0-6% ZrO.sub.2, 0-3% TiO.sub.2, 0-0.5% PbO, 0-7% BaO, 0-4% CaO, 0-3% MgO, 0-6% Nb.sub.2 O.sub.5, 0-4% La.sub.2 O.sub.3 and 0-2% F. Also, up to 1% total of transition metal oxide colorants and/or up to 5% total of rare earth metal oxide colorants can be included without adversely affecting the photochromic behavior of the glass.
U.S. Pat. No. 4,284,686 (Wedding) explains in some detail that certain diseases of the eye and/or visual deficiencies may be caused by, or may be aggravated by, strong sunlight. The patent notes that radiation at the short end of the visible spectrum, that is, at wavelengths on the order of 400-550 nanometers (nm), seems to create the greatest problems for some patients.
The patent observes that the eye contains two different kinds of photoreceptors, viz., cones and rods. The cones comprise the

REFERENCES:
patent: 4284686 (1981-08-01), Wedding
patent: 4454170 (1984-06-01), Gogpfert et al.
patent: 5381193 (1995-01-01), Wedding

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