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Lens Materials & Coatings

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Course Introduction
This Section contains two parts�Lens Materials & Coatings and Multifocal Designs. We will compare the relative merits of three spectacle lens materials: Crown Glass, CR 39 Plastic and Polycarbonate. Tints and coatings will be discussed as they are used for absorbtive, protective, and cosmetic purposes on both glass and plastic lens materials.

In the second part of this session, Multifocal Designs, we will present a survey of the common styles of multifocal lenses currently available. These will include flat top, round, Franklin style, ultex, blended, and progressive lens designs . The relative merits and uses of each will be outlined. In addition, the various trifocal and occupational designs will be presented. We will study the concept of the reading addition, discuss image jump, and present a rationale for the development of improved multifocal designs over the years. The difference between fused and one piece multifocal lens designs will be explained.

Since bi-centric grinding or "slab-off" is generally associated with multifocal lenses a discussion of this subject has been included in this session. It includes step by step instructions for calculating slab-off followed by practice exercises. When we apply that which we have already learned about prism and Prentice's Rule, calculating slab-off becomes a simple and logical next step.

Due to improvements in aphakic contact lenses and in intra-ocular lens implant techniques and materials, post-cataract spectacle lenses are now being prescribed with diminishing frequency.

The two sessions we're about to study should answer many questions you might have had regarding lens materials, coatings and multifocal designs. Each of these items is directly applicable to our daily work as opticians.