Fig 1. Ductions. Horizontal ductions (adduction and abduction) are produced by contractions of the medial rectus (MR) and lateral rectus (LR) muscles. Vertical ductions and cycloductions result from combined contractions of the vertical rectus and oblique muscles. Combined contractions of the superior rectus (SR) and inferior oblique (I0) muscles produce supraduction; combined contractions of the inferior rectus (IR) and superior oblique (SO) muscles produce infraduction. Incy-cloduction is caused by combined SO and SR contractions, and excycloduction is caused by combined IO and IR contractions. In abduction the vertical rectus muscles are the prime vertical movers, and the obliques are the prime torsional movers; in adduction this is reversed.