Aspheric multifocal diffractive ophthalmic lens

1 . A multifocal ophthalmic lens comprising:

a lens element having an anterior surface and a posterior surface;

a refractive zone, or base surface having aspherically produced multifocal powers disposed on one of the anterior and posterior surfaces; and

a near focus diffractive multifocal zone disposed on one of the anterior and posterior surfaces.

2 . The lens according to claim 1 wherein the diffractive multifocal zone is an annulus.

3 . The lens according to claim 1 wherein the diffractive multifocal zone is central zone.

4 . The lens according to claim 1 wherein the refractive zone enhances depth of field around distant vision.

5 . The lens according to claim 1 wherein the refractive zone comprises a distant and intermediate focus refractive multifocal zone.

6 . The lens according to claim 1 wherein the diffractive multifocal zone enhances depth of focus around distant vision.

7 . The lens according to claim 1 wherein said base surface of the diffractive multifocal zone comprises a distant and intermediate focus diffractive multifocal zone.

8 . The lens according to claim 1 wherein the diffractive multifocal zone comprises a plurality of grooves, the grooves being apodized from a height directing light along a diffractive order associated with near focus to a height directing light along a diffractive order associated with distant focus.

9 . The lens according to claim 1 wherein the diffractive multifocal zone is recessed into one of the anterior and posterior surfaces.

10 . The lens according to claim 1 wherein said lens element is an intraocular lens.

11 . The lens according to claim 1 wherein said lens element is a contact lens.

12 . The lens according to claim 1 wherein said lens element is an artificial cornea.

13 . The lens according to claim 1 wherein said lens element is a lamellar implant.

14 . A method of designing an aspheric multifocal diffractive surface comprising

a) selecting a base surface with asphericity providing multifocal powers;

b) calculating diffractive structure phase coefficients that produce near focus for a selected add power to serve as non-zero order diffraction;

c) numerically calculating a 100% efficiency groove shape h(r i ) that produces the defined phase coefficients and groove width defining by the phase function modulo 2πp cycle where p=1,2, . . . ; and

d) modifying a groove shape h(r i ) of the diffractive zone to create a required balance of light between zero-order for distant vision and non-zero diffraction order for near vision for this groove location;

15 . The method of calculating of light balance between distant and near foci of the diffractive groove defined by the formula:

h

′



(

r

i

)

=

S

-

[

T

0



(

r

i

)

-

T

-

1



(

r

i

)

]

2



S

·

h



(

r

i

)

where T 0 (r i )=diffraction efficiency for distant focus, i.e. 0-order diffraction;

T −1 (r i )=diffraction efficiency for near focus, i.e. (−1)-order diffraction;

T 0 (r)+T −1 (r)=S, where S is within 0.81 to 1.0.