Optical design considerations for contact lens bifocals.

Primary concerns for designing conventional bifocal contact lens optics involve placement of sufficient representation of distance and near optical powers before the pupil and minimizing the presence of secondary images. Geometrical models and lens measurements are used to establish guidelines for predicting bifocal contact lens performance. Proportional optical zone representation, image jump, and power distribution are presented for the most commonly employed bifocal zone configurations. Adequate zone representation and effective lens power are shown to be quite sensitive to variation in pupil size and position. Strategies for optimizing lens performance in view of these effects are discussed.