Magnification limitations of a contact lens telescope.

A contact lens telescope (CLTS) may have some applications as a low vision aid. In certain circumstances, it offers the possibility of a larger field of view and may simplify the optical alignment difficulties of the user who has a central scotoma. Such devices in the past have usually been limited to magnifications of 2X or less. I examined the magnification potential of these devices by using an unusually high contact lens power and measuring the actual visual acuity improvement (functional magnification) achievable by young, normally sighted subjects. The results show the functional magnification to be significantly reduced compared with the theoretical magnification calculated by the afocal telescope magnification formula. This degradation of functional magnification would be expected to be even greater when used by the visually impaired.