Specific oculomotor deficit after acute methadone. I. Saccadic eye movements.
Changes in saccadic eye movements before and after up to 10 mg oral methadone were measured electrooculographically in nontolerant nondependent humans. Undershoot of initial saccades increased with increasing size of horizontal target displacement (to 36 degrees) from a central viewing position. Dosage as low as 5 mg caused significant increase in saccade undershoot especially to target displacements greater than 10-15 degrees. Latency from target displacement to onset of initial saccade also increased after methadone. These results, in combination with the lack of significant drug effect on latency between initial saccade and corrective saccade, and on initial saccade duration, maximum velocity, and time to maximum velocity indicate methadone action on specific sensory, rather than motor, components of saccadic response. The similarity of alteration of saccadic response after methadone and after lesion of the upper layers of the superior colliculus in primates, as reported in the literature, suggests that opiate binding sites in the upper layers of the superior colliculus may be physiologically active.