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Cranial Nerve III, IV and VI |
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| Oculomotor, Trochlear, and Abducens Nerves
Introduction
- These nerves are presented together as they are examined simultaneously during the cranial nerve exam while testing for ocular movements. Movements of the eyes are assessed through the six cardinal points of gaze: pupil size, response to light, saccades, convergence, divergence, and opening of the upper eyelids
Tests to be performed
- Response to light
- Tracking
- Saccades
- Convergence and divergence
Expected findings
- Equal pupil size, equal and consensual response to light and accommodation, symmetric eye movements in all six points of gaze, and normal tone and movement of the upper eyelids
Equipment
- Pen flashlight and two pencils
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Section:
Cranial Nerves III, IV and VI |
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Page 1 of 11 |
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Oculomotor Nerve Anatomy Review
Lower motor neuron axons leave the oculomotor complex and course ventrally in the tegmentum of the midbrain through the red nucleus and through the medial aspect of the cerebral peduncles to emerge in the interpeduncular fossa at the junction of the midbrain and the pons. The somatic motor fibers combine with parasympathetic fibers from the Edinger-Westphal nucleus to form the oculomotor nerve. The nerve pierces and enters the cavernous sinus where it runs along the lateral wall through the superior orbital fissure. The nerve splits into superior and inferior divisions and innervates the levator palpebrae superioris, superior, inferior, and medial rectus and inferior oblique. Parasympathetic fibers leave the nerve to the inferior rectus to synapse at the ciliary ganglion. Postganglionic fibers leave the ciliary ganglion to innervate the constrictor pupillae and the ciliary muscles, controlling the size of the pupil and the diameter of the lens. A lower motor neuron lesion will result in oculomotor ophthalmoplegia i.e., the eye being displaced laterally due to the unopposed action of lateral rectus, drooping of the eyelid, dilated pupil and diplopia may also be present.
