Parallel-testing infinity balance. Instrument and technique for the parallel testing of binocular vision.

Routine refraction involves a series of tests during which changes carried out in the latter part of the routine may alter parameters already considered to have been fixed. These earlier parameters, although thought to have been fixed, are therefore not always valid. No binocular testing device is presently available which allows the practitioner to be aware of how the changing of one parameter affects the others. The Parallel-Testing Infinity Balance (PTIB) has been designed to provide that tool. It is an adaptation of the Turville Infinity Balance. It has the potential for binocular balancing, including suppression, astigmatic distortion, image size and shape variation, and vertical and horizontal imbalances. There follows a discussion of its design and use.