On determining the relationship between blood alcohol concentration and smooth pursuit eye movements.

Residual impairment after alcohol consumption implies that the relationship between blood alcohol concentration (BAC) and deficits in performance of some task is not the same when becoming intoxicated as it is when returning to sobriety. A pilot study was performed to determine the feasibility of and the appropriate methodology for studies on residual impairment of smooth pursuit performance. Four subjects consumed alcohol for 2 h. Measurements of BAC and smooth pursuit eye movements were made every 30 min during drinking and for 4 h after drinking. Pursuits were elicited by having subjects track a sinusoidal target (0.40 Hz and 0.60 Hz) for 10 s. Impairment of smooth pursuit was quantified with frequency analysis scores. Frequency analysis scores declined as BAC increased. As BAC decreased, frequency analysis scores tended to increase toward pre-drink levels. The relationship between BAC and frequency analysis score was not significantly different on the ascending and descending limbs of the blood alcohol curve. However, the idea that residual impairment does not occur could not be conclusively demonstrated for several reasons. First, as BAC returned to pre-drink levels, frequency analysis scores were inconsistent for each subject perhaps because of boredom and fatigue. Second, the relationship between BAC and frequency analysis score varied between subjects. Finally, because the recording periods were short, the effect of alcohol on sustained attention could not be assessed. In this paper, potential artifacts in studies of residual impairment of pursuits are discussed and potential solutions to the methodological problems encountered in the pilot study are provided.

The effect of experience on the detection of small eye movements.

PURPOSE: The purpose of this study was to determine whether experience improves detection of small eye movements similar to those seen in the cover test during ideal conditions. METHODS: Three groups of examiners with varying amounts of experience in eye movement detection tasks were studied. Eight examiners were 1st-year optometry students, six were 4th-year optometry students, and six were practicing optometrists. To determine thresholds for eye movement detection, examiners indicated the horizontal direction in which the eyes of one of the experimenters moved. The direction and extent of each eye movement was randomly selected. The extent of the eye movement was one of eight logarithmic steps from a maximum that was determined through an initial session where the approximate sensitivity of the examiners was found (generally +/- 1.75 prism diopters). RESULTS: Detection thresholds were determined by fitting the data with a cumulative Gaussian function. The mean horizontal eye movement eye movement necessary to obtain 99% correct judgments was 2.65 prism diopters for the 1st-year students, 2.47 prism diopters for the 4th-year students, and 2.40 prism diopters for the practicing optometrists. CONCLUSIONS: The results indicate that during ideal conditions, little or no training is required for efficient detection of small eye movements.