In the case of the Hoyalux iD Integrated Double Surface progressive design5 shown in figure 7(b), the full reading addition is obtained by incorporating the vertical component of the addition on the convex surface and the horizontal component on the concave surface. It can be seen in figure 7(b) that the convex surface increases in power from +5.00 D to +7.00 D along the vertical meridian, but there is no change in power between distance and near along the horizontal meridians in the intermediate and near zones, which remains +5.00 D. Since the back surface is also -5.00 D along the vertical and horizontal meridians in the distance zone, this area of the lens has zero power.
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