Limitation of eye movement (CN injury)
| Oculomotor Nerve (CN III) | Trochlear Nerve (CN IV) | Abducens nerve (CN VI) | |
|---|---|---|---|
| Key anatomy | Arises from midbrain → passes through lateral aspect of cavernous sinus, Exits skull through superior orbital fissure | Arises from midbrain and travels through lateral aspect of cavernous sinus, Exits skull through superior orbital fissure | Arises from pons → travels through cavernous sinus, Exits skull through superior orbital fissure |
| Function | Motor: innervates four extraocular muscles, levator palpebrae superioris muscle (elevation of upper eyelid), sphincter pupillae muscle (pupillary constriction), ciliary muscle (accommodation) Reflexes: efferent pathway of pupillary light reflex, efferent pathway of accommodation reflex | Motor: superior oblique muscle of eye (intorsion, depression & abduction of eye) | Motor: lateral rectus muscle of eye (abducts eye) |
| Assessment | Eye movements, Accommodation reflex and Pupillary light response | Eye movements | Eye movements |
| Clinical effects of injury | # Depressed & abducted eye (down & out) # Diplopia, Ptosis # Fixed and dilated pupil with loss of accommodation and abnormal pupillary light reflex | # Weakness of downward gaze (difficulty reading/walking downstairs) # Vertical diplopia # Eye is extorted & may be elevated (patient head tilts to opposite side to compensate) | # Horizontal diplopia # Convergent squint at rest (eye turned inwards) with inability to abduct eye |
| Causes of injury | Aneurysms (carotid or posterior communicating) Tumours / Trauma / Cavernous sinus disease / DM | Cavernous sinus disease Raised intracranial pressure | Cavernous sinus disease Wernicke-Korsakoff syndrome |