Progressive-power multifocal lens

A progressive-power multifocal lens whose far-vision portion dioptric power is minus, which comprises, along a principal meridian curve which divides the refracting surface of the lens into a nasal-side portion and a temporal-side portion;

• a far-vision correction portion which deals with a long distance;
• a near-vision correction portion which deals with a short distance;
• and
• a progressive-power portion which connects the refracting power continuously between the far-vision correction portion and the near-vision correction portion at the surfaces of the both portions;
• wherein;
• where a base curve is represented by BC;
• a mean surface refracting power at an arbitrary point on the progressive-power multifocal surface, located at a distance of x (mm) from a far-vision portion eyepoint in the horizontal direction in wear of spectacles and located at a distance of y (mm) from the far-vision portion eyepoint in the vertical direction in wear of spectacles, by P (x,y) (diopter);
• and a mean surface additional refracting power obtained by subtracting the base curve BC from the mean surface refracting power, by ΔP(x,y){=P(x,y)−BC} (diopter);
• the lens fulfills the condition of
• ΔP(x,y)>0 (1)
• in a region which satisfies 15≦(x2+y2)½≦20 in the far-vision correction portion.