There is provided a spectacle lens, which includes a central portion that is located at a middle section of the spectacle lens, average transmission power within the central portion being substantially constant, an upper portion that is located on upper side of the central portion, average transmission power within the upper portion changing continuously from a lower end of the upper portion to a top end of the spectacle lens, and a lower portion that is located on lower side of the central portion, average transmission power within the lower portion changing continuously from a top end of the lower portion to a lower end of the spectacle lens.
1. A spectacle lens, comprising:
a central portion that is located at a middle section of said spectacle lens, average transmission power within said central portion being substantially constant;
a clear vision area whose horizontal size is configured to be the greatest in said central portion;
an upper portion that is located on upper side of said central portion, average transmission power within said upper portion changing continuously from a lower end of said upper portion to a top end of said spectacle lens; and
a lower portion that is located on lower side of said central portion, average transmission power within said lower portion changing continuously from a top end of said lower portion to a lower end of said spectacle lens.
2. The spectacle lens according to claim 1 , wherein the horizontal size of said clear vision area on a point on said lens initially decreases and then increases as the point proceeds downward or upward from said central portion.
3. The spectacle lens according to claim 1 , wherein said central portion is configured to be a middle portion for a middle vision.
4. The spectacle lens according to claim 1 , wherein said spectacle lens satisfies a condition:
6 mm≦W≦15 mm
where W in mm represents a size of said central portion in a vertical direction.
5. The spectacle lens according to claim 4 , wherein said spectacle lens satisfies a condition:
8 mm≦W≦15 mm.
6. The spectacle lens according to claim 1 ,
wherein the average transmission power within said upper portion continuously decreases from the lower end of said upper portion to the top end of said spectacle lens;
wherein the average transmission power within said lower portion continuously increases from the top end of said lower portion to the lower end of said spectacle lens.
7. The spectacle lens according to claim 1 , wherein said spectacle lens is configured such that distribution of aberration is asymmetrical with respect to main meridian.
8. The spectacle lens according to claim 1 ,
wherein said central portion, said upper portion and said lower portion are formed on a surface of said spectacle lens;
wherein said surface is configured to have a non-umbilical region along main meridian.
9. The spectacle lens according to claim 8 ,
wherein a form of said surface within said upper portion and said lower portion is changed according to dioptric power in the vicinity of a center of said spectacle lens so as to provide changes of the average transmission power within said upper portion and said lower portion.
10. The spectacle lens according to claim 8 ,
wherein the dioptric power in the vicinity of a center of said spectacle lens is negative,
wherein at least at a point of interest along the main meridian within the upper portion, surface power in a direction parallel to the main meridian is greater than surface power in a direction perpendicular to the main meridian.
11. The spectacle lens according to claim 10 ,
wherein said spectacle lens satisfies a condition:
P 1(14)> P 2(14)
where P 1 ( 14 ) represents the surface power of the cross section parallel to the main meridian at the point of interest which is shifted upward by 14 mm from a center position of said central portion in vertical direction, and P 2 ( 14 ) represents the surface power of the cross section perpendicular to the main meridian at the point of interest which is shifted upward by 14 mm from the center position of said central portion in vertical direction.
12. The spectacle lens according to claim 8 ,
wherein the dioptric power in the vicinity of a center of said spectacle lens is positive,
wherein at least at a point of interest along the main meridian within said lower portion, surface power in a direction parallel to the main meridian is less than surface power in a direction perpendicular to the main meridian.
13. The spectacle lens according to claim 12 ,
wherein said spectacle lens, satisfies a condition:
P 1(−14)> P 2(−14)
where P 1 (− 14 ) represents the surface power of the cross section parallel to the main meridian at the point of interest which is shifted downward by 14 mm from a center position of said central portion in vertical direction, and P 2 (− 14 ) represents the surface power of the cross section perpendicular to the main meridian at the point of interest which is shifted downward by 14 mm from the center position of said central portion in vertical direction.
14. The spectacle lens according to claim 1 ,
wherein a form of a back surface of said spectacle lens is changed according to a position on the back surface of said spectacle lens so as to provide changes of average transmission power of said spectacle lens.
15. A spectacle lens, comprising:
a central portion that is located at a middle section of said spectacle lens, average transmission power within said central portion being substantially constant;
an upper portion that is located on upper side of said central portion, average transmission power within said upper portion changing continuously from a lower end of said upper portion to a top end of said spectacle lens;
a lower portion that is located on lower side of said central portion, average transmission power within said lower portion changing continuously from a top end of said lower portion to a lower end of said spectacle lens; and
a clear vision area having a horizontal size configured to be the greatest in said central portion, wherein the horizontal size of said clear vision area on a point on said lens initially decreases and then increases as the point proceeds downward or upward from said central portion.
16. A spectacle lens, comprising:
a central portion that is located at a middle section of said spectacle lens, average transmission power within said central portion being substantially constant;
an upper portion that is located on upper side of said central portion, average transmission power within said upper portion changing continuously from a lower end of said upper portion to a top end of said spectacle lens; and
a lower portion that is located on lower side of said central portion, average transmission power within said lower portion changing continuously from a top end of said lower portion to a lower end of said spectacle lens;
wherein the average transmission power within said upper portion continuously decreases from the lower end of said upper portion to the top end of said spectacle lens; and
wherein the average transmission power within said lower portion continuously increases from the top end of said lower portion to the lower end of said spectacle lens.