Design and Fabrication of the Progressive Addition Lenses

摘要

The use of progressive addition lenses (PALs) for the correction of presbyopia has increased dramatically in recent years. These lenses are now being used as the preferred alternative to bifocal and trifocal lenses in many parts of the world. Progressive addition lenses are a kind of opthalmic lenses with freeform surface. The surface curvature of the Progressive addition lenses varies gradually from a minimum value in the upper area, to a maximum value in the lower area. Thus a PAL has a surface with three zones which have very small astigmatism: far-view zone, near-view zone, and intermediate zone. The far view zone and near view zone have relatively constant powers and connected by the intermediate zone with power varies progressively. The design and fabrication technologies of progressive addition lenses have fast progresses because of the massive development of the optical simulation software, multi-axis ultraprecision machining technologies and CNC machining technologies. The design principles of progressive addition lenses are discussed in a historic review. Several kinds of design methods are illustrated, and their advantages and disadvantages are also represented. In the current study, it is shown that the optical characteristics of the different progressive addition lenses designs are significantly different from one another. The different fabrication technologies of Progressive addition lenses are also discussed in the paper. Plastic injection molding and precision-machine turning are the common fabrication technologies for exterior PALs and Interior PALs respectively.