Parameters of contact lens-spectacle telescopic systems and considerations in prescribing.

Contact lens-spectacle telescopic systems provide an alternative to conventional spectacle-mounted telescopes. There is a need to describe the parameters of such systems, the interrelations between them, and the use of such relations in selecting values for prescribing. Graphical representation of ocular (contact) lens power, objective (spectacle) lens power, separation (vertex distance), and magnification are presented. Skillful prescribing involves selection of the best set of parameters to achieve the desired visual goal in spite of the practical limitations imposed by facial features, lens availability, and appearance. Additional factors (not graphically represented) are induced vergence amplification, altered depth perception, and apparent motion, all unique to telescopic systems. One patient is described and selection of appropriate parameters is discussed. General application of the selection process is described.