A 1-Diopter Vertical Prism Induces a Decrease of Head Rotation: A Pilot Investigation

Abstract

Clinical studies in non-specific chronic arthralgia and back pain seem to indicate an association between vertical heterophoria (VH - latent vertical retinal misalignment) and asymmetrical head rotation. Such clinical observations suggest a link between VH and head rotation, but this was never tested. The purpose of this study was to simulate a VH in healthy subjects and examine its influence on the amplitude of active head rotation during 3D motion capture in upright stance. Subjects were asked to rotate their head three times from the straight ahead position and then to the right, back to straight ahead, to the left, and back to the straight ahead again. Three randomized conditions were run: normal viewing, with a 1-diopter prism base down on the dominant eye, or the non-dominant eye. The most important finding is that the experimental VH whichever the eye with the prism induces a significant decrease in the mean angle of head rotation compared to the normal viewing condition. This decrease was significant for rotation to the left. We suggest that the prism-induced VH modifies the reference posture and thereby affects head rotation; further studies are needed to confirm this effect and to extend to other types of dynamic activities.

Keywords: head rotation; heterophoria; motor control; neck; prism; spine; three-dimensional kinematics; upright stance.

Figure 1

Codamotion markers: three placed on the head on a head band – one in the middle of the forehead and two each side of the head above the ears; three placed at the shoulder girdle – one on the spinous process of the first thoracic vertebra and two on the left and right acromions.

Figure 2

Box and whisker plot for open eyes condition (in degrees). (A) Classification of the rotation according to the eye dominancy. (B) Classification of the rotation according to the position of the prism (left or right eye). Asterisk indicates significant difference (p < 0.05).