Which nerve may be injured if a person looking inward towards their nose is unable to look down?

Trochlear (iv)- to understand this question, you need to understand how to evaluate the muscles of the eye. since the actions of the extraocular muscles are complex, it is necessary to turn the eye to a position where a single action of each muscle predominates. to isolate the superior and inferior recti, the patient needs to turn the eye outward by approximately 25 degrees. this places the superior rectus in position to raise the eye and the inferior rectus in position to lower the eye. turning the eye inward approximately 50 degrees places the inferior oblique in position to raise the eye and the superior oblique in position to lower the eye. the medial and lateral recti are the easy muscles - they may be checked while the eye is staring straight ahead since they have simple planar actions so, this patient is looking inward, which means that the obliques are being tested. the patient cant look downward, which shows that the superior oblique is not functional. this is the only muscle innervated by the trochlear nerve (cn iv). abducens (cn vi) innervates the lateral rectus muscle, which is tested by asking the patient to move the eye outward. the inferior division of the oculomotor nerve innervates inferior rectus, inferior oblique, and medial rectus. the superior branch of the oculomotor nerve innervates levator palpebrae superioris and superior rectus muscles. finally, the optic nerve (cn ii) provides the special sense of vision, and it is not tested in the eye-movement tests. are you getting the idea that you really need to know about testing the eye muscles? take the time and really understand this concept-youll be glad that you did!