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Maximum base-in (BI) and base-out (BO) fusion vergence ranges were measured in 38 normal subjects using 3 different clinical procedures. These procedures used different instruments, instructions, and vergence stimuli (Risley prisms, vectograms, and video-displayed contour and random dot stereograms) presented at 50.8 cm. Test-retest measures, which were taken on each test for each subject, indicated high positive correlations between test and retest measures for most vergence tests. Paired inter-test correlations among five different tests varied as a function of the pairing as well as type of measure taken (BI, BO, break, recovery). It was concluded that different methods of measuring vergence provide different kinds of information and such tests may not be used interchangeably.
Feldman et al. (Thu,) studied this question.