intorsion การใช้

• When acting alone, superior oblique causes intorsion, inferior oblique, extorsion.
• When the eye is in the primary position ( looking straight ahead ), contraction of the superior oblique produces depression and intorsion in roughly equal amounts.
• When the eye is " abducted " ( looking away from the nose ), the force of intorsion increases, while the force of depression decreases.
• The great importance of intorsion and extorsion produced by the two oblique muscles can only be understood when it is considered with regards to the other muscle actions present.
• Weakness of intorsion results in "'torsional diplopia, "'in which two different visual fields, tilted with respect to each other, are seen at the same time.
• But because the eyes do face forwards, when acting alone, as well as making the eye look up, superior rectus causes it to rotate slightly about the long axis, so the top of the eye moves medially ( intorsion ).
• The force of the tendon s pull therefore has two components : a forward component that tends to pull the eyeball downward ( depression ), and a medial component that tends to rotate the top of the eyeball toward the nose ( intorsion ).
• In fact, each of the six extraocular muscles exerts rotational forces in " all three planes " ( elevation-depression, adduction-abduction, intorsion-extorsion ) to varying degrees, depending on which way the eye is looking.
• To summarize, the actions of the superior oblique muscle are ( 1 ) " depression " of the eyeball, especially when the eye is adducted; and ( 2 ) " intorsion " of the eyeball, especially when the eye is abducted.
• Hence, when inferior rectus contracts so we look down, superior oblique also contracts to prevent extorsion of the eye, and when superior rectus contracts so we look up, inferior oblique contracts to prevent intorsion, thus the undesired rotatory actions of the inferior and superior recti about the long axis of the eye are cancelled out.
• Allowable movements for the superior oblique are ( 1 ) rotation in a vertical plane  looking down and up ( " depression " and " elevation " of the eyeball ) and ( 2 ) rotation in the plane of the face ( " intorsion " and " extorsion " of the eyeball ).