▁was ▁fla wed , ▁as ▁demonstrated ▁in ▁Tur ski ▁( 2 0 1 6 ). ▁This ▁analysis ▁shows ▁that , ▁for ▁a ▁given ▁fix ation ▁point , ▁one ▁has ▁a ▁slightly ▁different ▁hor opter ▁circle ▁for ▁each ▁different ▁choice ▁of ▁the ▁nod al ▁point ’ s ▁location . ▁Moreover , ▁if ▁one ▁changes ▁the ▁fix ation ▁point ▁along ▁a ▁given ▁Vi eth - M üller ▁circle ▁such ▁that ▁the ▁ver gence ▁value ▁remains ▁constant , ▁one ▁obtain s ▁an ▁infinite ▁family ▁of ▁such ▁hor op ters , ▁to ▁the ▁extent ▁that ▁the ▁nod al ▁point ▁devi ates ▁from ▁the ▁eye ’ s ▁rotation ▁center . ▁These ▁statements ▁follow ▁from ▁the ▁Central ▁Ang le ▁Theorem ▁and ▁the ▁fact ▁that ▁three ▁non - col linear ▁points ▁give ▁a ▁unique ▁circle . ▁It ▁can ▁also ▁be ▁shown ▁that , ▁for ▁fix ations ▁along ▁a ▁given ▁Vi eth - M üller ▁circle , ▁all ▁the ▁corresponding ▁hor opter ▁circles ▁intersect ▁at ▁the ▁point ▁of ▁symmetric ▁convergence . ▁This ▁result ▁implies ▁that ▁each ▁member ▁of ▁the ▁infinite ▁family ▁of ▁hor op ters ▁is ▁also ▁composed ▁of ▁a ▁circle ▁in ▁the ▁fix ation ▁plane ▁and ▁a ▁per pend icular ▁straight ▁line ▁passing ▁through ▁the ▁point ▁of ▁symmetric ▁convergence ▁( located ▁on ▁the ▁circle ) ▁so ▁long ▁as ▁the ▁eyes ▁are ▁in ▁primary ▁or ▁secondary ▁position . ▁ ▁When ▁the ▁eyes ▁are ▁in ▁t ert i ary ▁position ▁away ▁from ▁the ▁two ▁basic ▁hor opter ▁lines , ▁the ▁vertical ▁dispar ities ▁due ▁to ▁the ▁differential ▁magn ification ▁of ▁the ▁distance