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 non-bifocal 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 cast doubt upon the clinical usefulness of this procedure with presbyopes.
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