Fig 7. Vergences. Horizontal vergences are produced by simultaneous contractions of the medial rectus (MR) muscles of each eye (convergence) or the lateral rectus (LR) muscles of each eye (divergence). The vertical vergences are caused by combined superior rectus (SR ) and inferior oblique (IO) muscle contractions in one eye and inferior rectus (IR) and superior oblique (SO) muscle contractions in the other; the right eye elevators and the left eye depressors simultaneously contract to produce positive vertical vergence, and the right eye depressors and the left eye elevators simultaneously contract to produce negative vertical vergence. The torsional vergences result from simultaneous combined contractions of either the two intortors (SO and SR) of both eyes, producing incyclovergence, or the two extortors (IO and IR) of both eyes, producing excyclovergence.