Effect of head and eye positions on fixation disparities, phorias, and ductions at near.

This study evaluated the effects of head and gaze position on near fixation disparity, phoria, and duction findings. A population of 104 non-complaining subjects divided by age into 3 groups participated in the study. The primary head and gaze position along with two others approximating the positions used for reading by nonbifocal and bifocal wearers were used. A statistically significant effect was found for the phoria data from the young group, but the magnitude was clinically insignificant. Changes in head and/or gaze positions did not significantly affect fixation disparities or duction recovery ranges. Phorias and fixation disparities showed statistically significant increases in exo deviation with increasing age regardless of head and/or gaze position. Nine of 23 presbyopic subjects gave erratic findings during fixation disparity testing and this casts doubt upon the clinical usefulness of this procedure with presbyopes.