PURPOSE: Law enforcement officers regularly conduct tests of physiological responses to assess impairment in drivers. Previous studies showed that visual field decreases with alcohol intoxication. We assessed visual fields at blood alcohol concentrations (BACs) around the per se limit, 0.08 g% for most states and Canada. We also propose a new test that officers may use in addition, or as an alternative, to other tests.
METHODS: We tested 34 volunteer drinkers at baseline and at three intervals after starting drinking. All testing was done with both eyes open. Peripheral visual field was assessed with an arc perimeter, centered 30 cm from the bridge of the nose. The target was moved in from the periphery until the subject was able to identify it. Modified Confrontation Visual Field (MCVF) was assessed with the evaluator standing 60-80 cm from the subject, presenting 1, 2, or 5 fingers at 45 deg lateral angles with respect to midline. On each of three presentations on each side, the evaluator assessed the presence of head turn, incorrect count, saccade or fixation loss, and body sway. BAC was measured with a calibrated breath analysis instrument at each set of evaluations.
RESULTS: Peripheral visual field, averaged over both eyes, decreased linearly with increasing BAC. On the MCVF test, body sway, fixation loss, and the presence of two or more clues all increased linearly with increasing BAC. The overall accuracy of the MCVF test at the 0.08 g% criterion level is 68.4%.
CONCLUSIONS: We confirm the decrease in peripheral visual field with increasing BAC. We also demonstrate increasing difficulty in performing MCVF with increasing BAC. We believe these results will assist the law enforcement community to remove impaired drivers from the road.
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