Clinical evaluation of vertical fixation disparity. Part II. Reliability, stability, and association with refractive status, stereoacuity, and vertical heterophoria.

The use of vertical fixation disparity data in the management of patients with vertical heterophoria will be more appropriate and effective when the clinical characteristics of vertical fixation disparity measurements are better understood. In this study the reliability and stability of the vertical fixation disparity curve and the relation of the vertical fixation disparity data to refractive status, stereoacuity, and vertical heterophoria were investigated. The results indicate that although the shape of the vertical fixation disparity curve is stable and can be statistically represented by a straight line, the slope changes with time, more so over weeks and months than during the day, and has no significant relation with the refractive status, with the level of stereoacuity, or with the presence or absence of vertical heterophoria.