Patent ID: 6334681
Filing Date: 2002-01-01
Classification: G02C

Abstract:
An optical lens element including a front and back surface, at least one surface being continuous, and forming a prescription (Rx) zone and optionally a peripheral temporal zone;a front surface exhibiting a change of base curve across the field of vision of the wearer, the base curves being smoothly blended to avoid a prismatic jump in the Rx zone; at least one of the front and back surfaces bearing a surface correction to at least partially adjust for optical errors, wherein each surface corresponds to the formula Z&af;(x,y)=1/2&it;â€ƒ&it;A2-(1/2&it;A2-Z&af;(x))2-y2where&it;â€ƒ&it;Z&af;(x)=&Sum;n&it;Bn&it;xnwherein Ox is the horizontal direction, Oy is the vertical direction and Oz is the optical axis; the coefficient A2 has a constant value specifying a constant vertical curvature, while the coefficients Bn take different values in different ranges of positive and negative values of x; and base curves are smoothly blended in the horizontal direction according to the formula Z&af;(x)=â€ƒ&it;B0â€²+&Sum;n-14&it;B2&it;nâ€²&it;x2&it;n;â€ƒ&it;x&leq;x0=â€ƒ&it;&Sum;n&it;Bn&it;xn;â€ƒ&it;x0<x&leq;x0â€²=â€ƒ&it;&Sum;n-14&it;B2&it;nâ€³&it;x2&it;n;â€ƒ&it;x>x0â€²wherein x0 and x0â€² are located within or near the edges of the prescription zone, and the coefficients Bn, Bâ€²n and Bâ€³n take different values for the defined ranges of positive and negative values of x.