Effects of a chiropractic adjustment on changes in pupillary diameter: a model for evaluating somatovisceral response

The relationship between a cervical chiropractic adjustment, in subluxated vs. unsubluxated subjects, and autonomic response monitored as change in pupillary diameter was evaluated in 15 subjects. The results indicate that: a) a successful adjustment elicits either a parasympathetic or sympathetic response; b) the vertebral level at which the adjustment is administered has undetectable specificity for the parasympathetic or sympathetic input to the pupil; c) unsubluxated subjects generally exhibit no change in pupillary diameter following a sham adjustment and d) subluxated subjects exhibit variable preadjustment pupillary diameters, with significant pupillary diameter changes in response to an adjustment. These data suggest that autonomic input to the pupil may be influenced by subluxation, as well as the magnitude and direction of force exerted during the chiropractic adjustment. An anatomical pathway through which the observed responses may occur is proposed.