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Background: Testing of vergence ranges is a routine clinical procedure providing valuable information about the patient's binocular status. Unfortunately, obtaining this information from non-verbal or very young patients has proven difficult or impossible in many situations, due to lack of subjective response. This study explored a new prism bar technique for obtaining vergence ranges using an objective procedure in a randomized, modified examiner-masked routine that allows for vergence measurement without a verbal response., Methods: In the first of two experiments, subjective and objective vergence ranges at 40 cm were obtained using a nonluminous target (printed picture of dog's head) from 29 adult subjects. The second experiment compared a self-illuminated target (transilluminator) to that of the nonluminous target in subjective and objective vergence range measurements using nine subjects from the first experiment., Results: The results of both of these experiments suggest that, at least in the adult population, the vergence range values obtained objectively compare favorably with those obtained subjectively. However, the transilluminator yielded greater variance for all measures and, for one variable, base-out to break, did yield statistically different results between objective and subjective findings., Conclusions: Objective and subjective vergence range measurements appear to yield consistently comparable results in the adult population. The use of a non-luminous target appears to yield more consistent results, most likely due to the poor accommodative nature of a self-illuminated target (transilluminator).