Progressive multifocal ophthalmic lens
AssigneeKabushiki Kaisha Suwa Seikosha
InventorsToshihide Shinohara, Sakiho Okazaki
Life of this patent
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Abstract
Progressive multifocal ophthalmic lenses are provided having a far vision viewing zone, a near vision viewing zone and an intermediate vision viewing zone therebetween. A principal meridian curve extends vertically through the far, intermediate and near vision viewing zones. The surface power along the principal meridian curve in the intermediate vision viewing zone varies progressively. The sizes of the zones and configuration of the zones are set by predetermined conditions and equations. The construction provides improved lenses for use in activities such as sports, driving, shopping and the like.
Claims12
A progressive multifocal ophthalmic lens comprising first and second refractive surfaces facing each other, said first refractive surface having upper and lower portions and including a far vision viewing zone in said upper portion for viewing mainly distant objects, a near vision viewing zone in said lower portion for viewing mainly nearby objects, and an intermediate vision viewing zone for viewing mainly intermediate objects between said far and near vision viewing zones, said intermediate vision viewing zone having an intermediate vision viewing zone central portion and said near vision viewing zone having a near vision viewing zone central portion, said first refractive surface having a principal meridian curve extending vertically in the general center of said far, intermediate and near vision viewing zones, the surface power along said principal meridian curve in said intermediate vision viewing zone progressively increasing from a far vision viewing zone reference focal power (D1 diopter) to a near vision viewing zone reference focal power (D2 diopter), and an additional power Ad [Ad=D2-D1] of said first refractive surface being about 1.5 diopter or more, said intermediate vision viewing zone central portion and said near vision viewing zone central portion extending on opposite sides of said principal meridian curve,
- the principal curvatures at each arbitrary point on said first refractive surface being C1 and C2, each point on said first refractive surface in said intermediate vision viewing zone central portion satisfying the condition:
- .vertline.C1-C2 .vertline..ltoreq.1/(N-1) (m.sup.-1),
- wherein m.sup.-1 =1/meters, and each point on said first refractive surface in said near vision viewing zone central portion satisfying the conditions:
- ##EQU3## where N is the refractive index of the lens material, the minimum width of said intermediate vision viewing zone central portion and the maximum width of said near vision viewing zone central portion being S(mm) and W(mm), respectively,
- said minimum width S and said maximum width W satisfying the conditions:
- W.ltoreq.30/A (mm)
- W.ltoreq.1.5.times.S (mm),
- where A is the value of the additional power Ad expressed in units of diopter,
- and the gradient of the variation of the surface power at each arbitrary point along said principal meridian curve is G(diopter/mm),
- every point along said principal meridian curve in said intermediate vision viewing zone satisfying the condition:
- G.ltoreq.Ad/18 (diopter/mm),
- where Ad is the additional power in units of diopter.
Dependencies are inferred from the claim text.