Fig 6. Versions. Horizontal versions (dextroversion and levoversion) are produced by contractions of yoked medial rectus (MR) and lateral rectus (LR) muscles. Vertical versions result from combined contractions. Combined contractions of the superior rectus (SR) and inferior oblique (I0) muscles cause supraversion, and combined contractions of the inferior rectus (IR) and superior oblique (SO) muscles cause infraversion. Torsional versions are produced by combined contractions of intortors of one eye (SO and SR) and extortors of the other (IO and IR); dextrocyloversion results from right eye extortors and left eye intortors contracting, and le-vocycloversion results from right eye intortors and left eye extortors contracting.