The right answer is B. convergence - retinal disparity.
* Movement of both eyes towards the nose. Convergence is a reflex associated with the mechanism of accommodation: a sort of auto-focus that allows you to see clearly in close-up vision, to read, write, observe ... Indeed, the observation distance being close to the face, the gaze axes are oriented nasally.
A convergence deficit, or "lack of convergence", is often the cause of accommodative asthenopia.
In optics, it is said of luminous rays which go towards the same point.
* The retinal disparity corresponds to the interocular difference of the angular differences between the two retinal images of the same point and the center of the corresponding foveas where the point of fixation is projected.
