Variability of monocular visual acuity during binocular viewing

Two patients observed changes in the visual acuity of one eye when both eyes were viewing simultaneously in certain directions of gaze. While viewing targets presented during the Turville Infinity Balance (TIB) test, the acuity of the affected or amblyopic eye improved when the nonamblyopic eye was covered and binocular vision suspended. The vision of the amblyopic eye was also improved when an appropriate prism was held in front of either eye. The direction of the prism base was based upon the interrelations of horizontal, vertical, and cyclotorsional anisophoria and the amount of prism was the minimum necessary to improve the vision in the amblyopic eye and neutralize vertical fixation disparity. The correlation of variable monocular acuity, stereopsis, and fixation disparity with oculomotor balance is recorded and discussed.