Question

Mr. Johnson, much to his parents’ dismay, has decided to quit college and to become a
professional skateboarder. In order to bring attention to himself, Mr. Johnson decided to film
himself performing a trick and then to submit it to a cable channel program featuring various
‘daredevils’. Mr. Johnson planned to ride a stair railing at the local strip mall. Unfortunately the
trick failed and Mr. Johnson suffered fractures in his frontal bone as well as several facial bones
making up the orbit of his left eye. After trauma care and a bone reconstruction, Mr. Johnson exhibited external strabismus (eye rotates laterally), he could not focus on objects with his left
eye and his left pupil did not respond to changes in light intensity. A study of the activity of the
extrinsic muscles of his left eye found only the superior oblique and the lateral rectus muscles
were still functional. Further investigation found that the left superior orbital fissure was
compressing one of the cranial nerve associated with the eye.

Answer the following questions:

1. What is the Cranial Nerve Damaged?

2. Function of This Nerve

3. How does the cranial nerves damage relate to the patients symptoms?

Answer 1

Case history,

Mr. Johnson has suffered fracture is his frontal bone as well as facial bones making up the orbit of his left eye. After reconstruction his eye has rotated laterally and he is unable to focus on objects through his left eyes as well as his left eye is not responding to changes in light intensity.

1. The above clinical history indicates that the left oculomotor nerve which is the 3rd cranial nerve has been damaged.

Oculomotor nerve emerges from the midbrain and enters the orbit via the superior orbital fissure. Since the facial bones making up the orbit are damaged, the oculomotor nerve passing through the superior orbital fissure must have been damaged which lead to the above mentioned symptoms.

2. Oculomotor nerve supplies most of the extrinsic muscles of the eyes and controls the eye movements. Eyes muscles innervated by oculomotor nerve are sphincter pupillae, ciliaris muscle, levator palpebrae superiors, superior rectus, inferior rectus, medial rectus, inferior oblique.

Note: superior oblique is supplied by trochlear nerve ( 4th cranial nerve )

Lateral rectus is supplied by abducent nerve ( 6th cranial nerve ).

Thus oculomotor nerve controls most of the movements of the eyeball. It also controls the opening of eyelids through levator palpebrae superioris and constriction of pupils through sphincter pupillae. Accomodation reflex of the eye is also controlled by oculomotor nerve as it supplies ciliaris muscle which changes the shape of the eye lens.

3. As the patient was unable to focus on objects through his left eye which means his accomodation reflex is impaired indicating the damage to the ciliaris muscle supplied by oculomotor nerve.

Also, the patient's left eyeeye is not responding to changes in the light intensity which indicates that his pupillary light reflex is impaired due to the damage of the sphincter pupillae muscle supplied by oculomotor nerve. All these impairments indicates that the oculomotor nerve was damaged due to injury sustained in the facial bones making up the orbit through which oculomotor nerve traverses.