Comparative study involving bitoric effect of hard resin lenses mounted in optyl frames, zylonite frames, and metal frames.

It has been noted clinically that hard resin lenses mounted in rimmed frames exhibited bitoricity. The manufacturers of optyl plastic frames claim that the molecular structure of optyl eliminates the bitoric effect. This study involves "clocking" hard resin lenses mounted in frames fashioned of optyl, zylonite plastic, and metal mountings to test this hypothesis. The results are important because of the increasing use of optical CR 39 plastic in the fabrication of eyewear.