Fig. 16. Horizontal movements (adduction and abduction) are produced by contractions of medial rectus (MR) and lateral rectus (LR) muscles. The vertical movements and cycloductions result from combined contractions of vertical rectus and oblique muscles. Combined contraction of superior rectus (SR) and inferior oblique (IO) muscles produces supraduction; combined contractions of inferior rectus (IR) and superior oblique (SO) muscles produce infraduction. Incycloduction is caused by combined SO and SR contractions, and excycloduction is caused by combined IO and IR contractions. In abduction, vertical rectus muscles are the prime vertical movers and obliques are the prime torsional movers; in adduction this is reversed. (Parks M: Ocular Motility and Strabismus. Hagerstown, MD: Harper & Row, 1975.)