Comparison of simultaneously obtained objective and subjective measurements of fixation disparity.

Simultaneous objective (based on binocular eye movement record) and subjective (nonius-line displacement) measurements of horizontal and vertical fixation disparity were carried out in order to evaluate the reliability of the nonius-line method of measuring ocular deviation. Significant differences were found between the subjective and objective measurements. These differences indicate that the nonius-line method is unreliable for the measurement of ocular deviation or fusional status.