Norms for hand-held rotary prism vergences.

Norms of clinically useful techniques provide a means to measure and compare patient performance against a large clinical population of asymptomatic subjects. This study establishes mean values for vergence ranges (break and recovery) at 6 m and 40 cm using hand-held rotary prisms. Secondary effects of eye preference (dominance), order of prism presentation, and differences of results between clinicians were evaluated and found to have no statistical significance. This is another example of the trend to establish normal values for functions routinely measured in the optometric examination. Values are now available for the most commonly used vergence testing methods: the binocular rotary prism in the phoropter, the prism bar, and the handheld rotary prism. Testing can now be accomplished with or without a phoropter and comparisons can be made to normal values.