, ▁movements ▁that ▁bring ▁the ▁top ▁of ▁the ▁eye ▁toward ▁the ▁nose ▁( int ors ion ) ▁or ▁away ▁from ▁the ▁nose ▁( ext ors ion ). ▁Hor izontal ▁movement ▁is ▁controlled ▁entirely ▁by ▁the ▁med ial ▁and ▁later al ▁rect us ▁mus cles ; ▁the ▁med ial ▁rect us ▁mus cle ▁is ▁responsible ▁for ▁ad du ction , ▁the ▁later al ▁rect us ▁mus cle ▁for ▁ab du ction . ▁Vert ical ▁movement ▁requires ▁the ▁coordin ated ▁action ▁of ▁the ▁superior ▁and ▁inferior ▁rect us ▁mus cles , ▁as ▁well ▁as ▁the ▁ob lique ▁mus cles . ▁The ▁relative ▁contribution ▁of ▁the ▁rect us ▁and ▁ob lique ▁groups ▁depends ▁on ▁the ▁horizontal ▁position ▁of ▁the ▁eye . ▁In ▁the ▁primary ▁position ▁( ey es ▁straight ▁ahead ), ▁both ▁of ▁these ▁groups ▁contribute ▁to ▁vertical ▁movement . ▁E lev ation ▁is ▁due ▁to ▁the ▁action ▁of ▁the ▁superior ▁rect us ▁and ▁inferior ▁ob lique ▁mus cles , ▁while ▁de pression ▁is ▁due ▁to ▁the ▁action ▁of ▁the ▁inferior ▁rect us ▁and ▁superior ▁ob lique ▁mus cles . ▁When ▁the ▁eye ▁is ▁ab duct ed , ▁the ▁rect us ▁mus cles ▁are ▁the ▁prime ▁vertical ▁mo vers . ▁E lev ation ▁is ▁due ▁to ▁the ▁action ▁of ▁the ▁superior ▁rect us , ▁and ▁de pression ▁is ▁due ▁to ▁the ▁action ▁of ▁the ▁inferior ▁rect us . ▁When ▁the ▁eye ▁is ▁ad duct ed , ▁the ▁ob lique ▁mus cles ▁are ▁the ▁prime ▁vertical ▁mo vers . ▁E lev ation ▁is ▁due ▁to ▁the ▁action