Phoria adaptation (PA) helps maintain the vergence posture during near work. Vergence facility (VFAC) and vergence ranges (VRAN) are said to assess different aspects of the vergence eye movement system. The purpose of this experiment was to measure vergence adaptation following VFAC and VRAN testing to more fully understand the role of PA in vergence testing.
30 subjects participated in two testing sessions. In each, the modified Thorington card was used to measure the phoria before and after testing: VRAN and VFAC.
PA occurred with VRAN and VFAC testing. The results from VRAN and VFAC do not correlate. The effect of PA on test results was different. For VRAN, those who passed had significantly more PA than those who did not. This was not true for VFAC testing. These results again suggest that VRAN (slow fusional vergence) and VFAC (fast fusional vergence) assess different aspects of the fusional vergence system