Quality of glass and polycarbonate bifocal dress lenses

A survey of the quality of bifocal glass and polycarbonate dress lenses was conducted to determine how well these lenses conform to the ANSI (American National Standards Institute) Z80.1 standard and to identify processing operations that need improvement. Eight different prescriptions were filled with polycarbonate and glass dress lenses by different laboratories. Conformance to the ANSI Z80.1 standard was determined for seven characteristics of individual lenses and one characteristic (vertical prism imbalance) of the pairs of lenses in prescriptions. The results show that 78% of the glass lenses and 43% of the polycarbonate lenses conformed to ANSI Z80.1 for the seven characteristics of individual lenses. For pairs of lenses, 88% of the glass pairs and 71% of the polycarbonate pairs have acceptable vertical prism imbalance. Glass lenses that did not conform failed for a variety of reasons, none of which dominated. Incorrect add power and excessive prism were the major causes of polycarbonate lenses not conforming.