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Multifocal Designs
Reading Addition






A bifocal lens may be thought of as two lenses combined into one, a larger one sometimes referred to as the carrier lens and a smaller one commonly known as the segment. The power of the bifocal segment is always plus and is known as the reading addition. (Bifocals are used for the correction of presbyopia and are needed to replace plus power which has been lost to the crystalline lens.) To determine the total power through the reading segment, algebraically add the power of the spherical component of the carrier lens to the power of the reading addition. The cylinder and axis remain unchanged.


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