Date of Award


Degree Type


Degree Name

Master of Science in Vision Science

Committee Chair

Robert L. Yolton


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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