Progressive multi-focal ophthalmic lens

• US 4,950,057 A
• Filed: 12/20/1989
• Issued: 08/21/1990
• Est. Priority Date: 11/30/1987
• Status: Expired due to Term

• Current Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Original Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Inventors: Shirayanagi, Moriyasu
• Primary Examiner(s): Sugarman, Scott J.
• Application Number:
  US07/456,209
• Time in Patent Office: 244 Days
• Field of Search: 351/168-172, 350/452, 350/432-435
• US Class Current: 351/169
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power
• CPC Class Codes: G02C 2202/20 Diffractive and Fresnel lenses or lens portions
• CPC Class Codes: G02C 7/061 Spectacle lenses with progressively varying focal power

Abstract

A progressive multi-focal ophthalmic lens having a front refracting surface and a rear refracting surface one of which is a progressive surface whose refractive power changes continuously with the other being a non-progressive surface. The progressive surface is formed as a Fresnel lens surface composed of microscopic steps so that the macroscopic shape of the progressive surface generally conforms to that of the non-progressive surface.

Claims

1. In a progressive multi-focal ophthalmic lens having a front refracting surface and a rear refracting surface one of which is a progressive surface whose refractive power changes continuously with the other being a non-progressive surface, the improvement wherein said progressive surface is formed as a Fresnel lens surface composed of microscopic steps so that the macroscopic shape of said progressive surface generally conforms to that of said non-progressive surface.

2. A progressive multi-focal ophthalmic lens according to claim 1 wherein said front refracting surface is progressive and said rear refracting surface is non-progressive.

3. A progressive multi-focal ophthalmic lens according to claim 1 wherein said front refracting surface is non-progressive and said rear refracting surface is progressive.

4. A progressive multi-focal ophthalmic lens according to claim 1 wherein said Fresnel lens surface has a macroscopic shape expressed by:

##EQU12## assuming an orthogonal coordinate system, with the central axis of the lens as the x-axis, and the y- and z-axes being perpendicular to the x-axis and crossing each other at right angles in a plane tangent to said Fresnel lens surface, where Fm is a Fresnel coefficient, and X₀ is expressed by;

##EQU13## where An is an asphericity coefficient.

5. A progressive multi-focal ophthalmic lens according to claim 4 wherein X₁ is approximately equal to:

##EQU14## where R₁ is the radius of curvature of the Fresnel lens surface, and the non-progressive surface has an x-coordinate expressed by;

##EQU15## where Tc is the thickness of the lens at its center.

6. A progressive multi-focal ophthalmic lens according to claim 5 wherein Lm=0.

7. A progressive multi-focal ophthalmic lens according to claim 4 whose refractive power is expressed by a spherical power S of +3.00 D and an addition power Add of 2.75 D and wherein X₁ is approximately equal to:

##EQU16## where R₁ is the radius of curvature of the Fresnel lens surface, and the non-progressive surface has an x-coordinate expressed by;

##EQU17## where Tc is the thickness of the lens at its center.