Vertical fixation disparity curve and the effects of vergence training in a normal young adult population

Background: The vertical forced vergence fixation disparity (VFD) curve rep resents the amount of vertical fixation disparity, the steady-state vertica l bifixation error of the eyes, at various levels of vertical vergence dema nd, The main aim of the present study was to examine the effects of vertica l vergence training on the slope of the VFD curve in a normal, young adult population. Methods: Forty-five subjects with normal vision and binocular f unction underwent vertical vergence training for 1 week, The training was d one using a vertical prism bar, and the vertical fixation disparity was mea sured using the Disparometer. Results: The mean slope of the VFD curve in a normal, young adult population was 1.103 min arc/Delta. The slope of the V FD curve decreased significantly after the training and remained flattened for at least 3 months, There was no evidence to support the idea that the d ecrease in the VFD slope was related to the increase of vertical fusional a mplitude. Conclusions: Vertical prism bar training provided a long-term eff ect, both increasing the vertical fusional amplitude and flattening the slo pe of the VFD curve. The decrease in the slope of the VFD curve was thought to be independent of the increase of vertical fusional amplitude. (Optom V is Sci 2000;77:663-669).