Spectacle lens, spectacle lens design method, and design apparatus

1. A spectacle lens comprising:

a first region which is located in at least a part of a portion of the lens where an angle of torsion of an eyeball of a wearer ranges from 20 to 60 degrees and in which correcting astigmatism has priority over correcting average power based on a prescribed power; and

a second region which is formed inside the first region and in which correcting the average power has priority over correcting the astigmatism.

2. The spectacle lens according to claim 1 , wherein the first region includes a point where a value of the astigmatism is a local minimum having a negative value and a point where the value of the astigmatism is a local maximum having a positive value.

3. The spectacle lens according to claim 1 , wherein the first region includes a region where a value of meridional dioptric power and a value of sagittal dioptric power change in such a way that the value of the meridional dioptric power and the value of the sagittal dioptric power approach each other, intersect each other, and then approach each other again as the angle of torsion of the eyeball increases.

4. The spectacle lens according to claim 1 , wherein a maximum error of the average power of the lens with respect to the prescribed power in the first region is 30% or smaller.

5. The spectacle lens according to claim 1 , wherein the second region includes a region where a value of meridional dioptric power and a value of sagittal dioptric power change in such a way that the value of the meridional dioptric power and the value of the sagittal dioptric power deviate from each other as the angle of torsion of the eyeball increases.

6. A spectacle lens design method comprising:

providing a first region which is located in at least a part of a portion of the lens where an angle of torsion of an eyeball of a wearer ranges from 20 to 60 degrees and in which correcting astigmatism has priority over correcting average power based on a prescribed power; and

providing a second region which is formed inside the first region and in which correcting the average power has priority over correcting the astigmatism.

7. The spectacle lens design method according to claim 6 , wherein the providing the second region includes setting a smaller design diameter of the second region when the prescribed power is negative and as an absolute value of the prescribed power increases.

8. The spectacle lens design method according to claim 6 , wherein a provision of the second region includes using an elliptical design shape of the second region when prescriptions of the spectacle lens include astigmatism correction of negative dioptric power.

9. A spectacle lens design apparatus comprising:

a unit that acquires eyeglass specifications including a prescribed power;

a first unit that designs a first region which is located in at least a part of a portion of the lens where an angle of torsion of an eyeball of a wearer ranges from 20 to 60 degrees and in which correcting astigmatism has priority over correcting average power based on the prescribed power; and

a second unit that designs a second region which is located inside the first region and in which correcting the average power has priority over correcting the astigmatism.

10. The design apparatus according to claim 9 , wherein the second unit includes a unit that sets a smaller design diameter of the second region when the prescribed power is negative and as an absolute value of the prescribed power increases, and sets a fixed design diameter of the second region irrespective of the prescribed power when the prescribed power is positive.