PURPOSE:To improve visual sensation (astigmatism and distortion of image) in the long-distance and short-distance part areas of a progressive multifocal lens, and to reduce the thickness and weight. CONSTITUTION:The difference between curvature rhot along a main meridian curve and curvature rhos perpendicular to the curve is not zero on the main meridian curve in a long-distance or short-distance area. With regard to an astigmatism distribution and two-directional refracting power on the main meridian curve, the astigmatism is less and a bright area is wider than before in the long-distance part area, specially, near the main meridian curve; and the width of the bright area is wider even in the short-distance part area. When factors of the astigmatism of the lens are considered as an aspherical surface factor and a base curve factor due to a base curve, the aspherical surface factor is based upon the difference in the curvature of the curved surface in a convex-side refracting surface and zero in case of a sphere. The aspherical surface factor is represented by the difference in curvature between a maximum and a minimum at each point in the curved surface.
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