title: Bifocal contact lenses.
abstract: A brief description of the construction and optical behavior of three general forms of hard contact lens bifocals are described. Each is considered from the standpoint of essential fitting criteria and brief techniques and qualifications affecting potential success are noted. The authors' technique utilized over many years of fitting segmented forms of contact lens bifocals is described in detail. Applications of principles affecting positioning and rotation of such lenses associated with edge design and lid action are noted. A simple clinical technique for determining appropriate segment height and position and viability of segment translation a priori to ordering contact lenses is described. Summarization indicates that common principles apply to all forms varied only by aspects of the individual constructions, and that these principles may also apply to the newly presented soft contact lens versions of bifocals.
mesh_terms: D003261:Contact Lenses / Q000592:standards*; D005143:Eyelids / Q000502:physiology; D006801:Humans; D055095:Optics and Photonics; D011305:Presbyopia / Q000628:therapy*