Common multifocal lens styles. (A, B) Executive bifocal and trifocal. (C, D) Round-top bifocal and trifocal. (E, F) Flat-top ("D" segment) bifocal and trifocal. (G) Invisible, or blended, bifocal. (H) Progressive addition multifocal lens.(1) Distance correction. (2) Corridor of increasing plus power. (3) Maximum plus power of near segment. (4) Zone of significant distortion.