An Overview on the Use of a Low Magnification Telescope in Low Vision

Résumé

A Galilean telescope in its simplest form is a two element system consisting of a positive lens as an objective and a nega­tive lens as an eyepiece. The system is restricted to lower magnifications and smaller fields of view in comparison with a Keplerian telescope. The image through the system, however, is always erect permitting its use for distance viewing for partially sighted patients. Other optical factors besides magnifica­tion and field of view that need to be con­sidered include exit pupil size, focus adjustability, vertex distance, and image quality in terms of color and brightness. Such non optical factors as weight, port­ability, ease of use, appearance and cost are also influencing variables'. In this overview on the clinical use of low power telescopes in the examination room, only a few properties will be exa­mined. The use of a low power full-field telescope in subjective and objective refractions will be discussed. Magnifica­tion through a telescope will also be elaborated upon.