MRI may be helpful in the diagnosis, in one study volumes of medial rectus, lateral rectus, and inferior rectus muscles in CPEO were not smaller than normal ( in contrast to the profound atrophy typical of neurogenic paralysis ).
12.
Failure of CN III will result in loss of function of the following muscles : medial rectus, superior rectus, inferior rectus, and inferior oblique as well as muscles that are responsible for opening the eyelid : levator palpebrae superioris muscle and the superior tarsal muscle ( Muller s muscle ).
13.
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.
