Direct surfacing optimized lens blank
A semi-finished ophthalmic lens for formation of a plurality of different finished ophthalmic lenses requiring reduced amounts of lens material to be removed for formation of the finished ophthalmic lenses and reduced rates of departure of a surfacing tool and methods of making the same. Lens material is reduced by providing first and second surfaces that have different optical powers, the second optical surface having a second curve that approximates second optical surfaces of a plurality of finished ophthalmic lenses at coordinates at which lenses of the plurality of finished ophthalmic lenses have maximum thicknesses.
1. A semi-finished ophthalmic lens comprising:
a front optical surface having a molded first free form curve;
a back optical surface having a second curve, said second curve being selected based on a plurality of possible finished lens prescriptions for said semi-finished ophthalmic lens; and
wherein said second curve approximates a maximum distance from said front optical surface to said back optical surface for said plurality of possible finished lens prescriptions.
2. The semi-finished ophthalmic lens of claim 1 further comprising a polycarbonate.
3. The semi-finished ophthalmic lens of claim 1 further comprising a thiourethane.
4. The semi-finished ophthalmic lens of claim 1 wherein the maximum distance is at an edge of the lens to be produced.
5. The semi-finished ophthalmic lens of claim 1 wherein the maximum distance is near a center of the lens to be produced.
6. The semi-finished ophthalmic lens of claim 1 further comprising an edge shape that approximates maximum dimensions of an edge shape of said lens to be produced.
7. A semi-finished ophthalmic lens comprising:
a molded front optical surface having a first free form curve;
a back optical surface having a second curve; and
a molded edge shape that is selected based on a plurality of possible finished lens edge shapes for said semi-finished ophthalmic lens, wherein said molded edge shape approximates said plurality of possible finished lens edge shapes.
8. The semi-finished ophthalmic lens of claim 7 wherein the front optical surface comprises a front surface of the semi-finished ophthalmic lens.
9. The semi-finished ophthalmic lens of claim 7 wherein the edge shape is oblong.
10. The semi-finished ophthalmic lens of claim 7 wherein the edge shape is non-symmetric.
11. The semi-finished ophthalmic lens of claim 7 wherein the second curve is approximately representative of a maximum distance from said front optical surface to said back optical surface for said plurality of possible finished lens prescriptions.
12. A method for forming a semi-finished ophthalmic lens comprising:
providing a mold;
said mold having a first free form surface for forming a front surface of said semi-finished ophthalmic lens;
said mold having a second curved surface for forming a back surface of said semi-finished lens, said second curve being selected based on a plurality of possible finished lens prescriptions for said semi-finished lens;
said second curved surface approximates a maximum distance from said front optical surface to said back optical surface for said plurality of possible finished lens prescriptions;
introducing a fluid bulk lens material into said mold;
solidifying the fluid bulk lens material; and
removing a formed semi-finished ophthalmic lens from said mold.
13. The method of claim 12 wherein said mold defines an edge shape of said semi-finished ophthalmic lens that is representative of an edge shape of a lens to be produced.
14. The method of claim 12 wherein said maximum distance is near a center of the finished lens intended to be produced.
15. The method of claim 12 wherein introducing the fluid bulk lens material comprises introducing a polycarbonate.