Examine this patient's eyes.



· Diplopia in all directions except on lateral gaze to the side of the third nerve lesion (because the lateral rectus muscle supplied

by the sixth cranial nerve is intact).

· Painful onset (berry aneurysm or aneurysmal dilatation of the intracavernous part of the carotid artery causing third nerve


· Headaches (migraine, cranial arteritis).

· Obtain history of diabetes or hypertension.


· Unilateral ptosis (from paralysis of the levator palpebrae superioris).

· Dilated pupil reacting slowly or incompletely to light (paralysis of the constrictor of the pupil).

· Paralysis of accommodation (from involvement of ciliary muscle).

· Squint and diplopia resulting from weakness of muscles supplied by the third cranial nerve (superior, inferior, medial recti and

interior oblique). The eye will be in the position of abduction, i.e. down and out (if the fourth and sixth nerves are intact).

· Diplopia may not be obvious until the affected eyelid is elevated manually.

Proceed as follows:

· Exclude associated fourth cranial nerve lesion (supplies the superior oblique) by tilting the head of the patient to the same side

- the affected eye will intort if the fourth cranial nerve is intact. Remember, superior oblique intorts the eye (SIN); inferior oblique

externally rotates the eye.

· Tell the examiner that you would like to check: -The urine for sugar (diabetes mellitus). -The blood pressure (hypertension).

Note, Vascular lesions (such as those associated with diabetes and arteritis) which infarct the third nerve [nay produce a complete

oculomotor palsy with pupillary sparing. The pupillomotor fibres are around the periphery of the third nerve. Compression of the

mass or aneurysm often involves the pupil.


This patient has a R/L third nerve palsy (lesion) due to diabetes mellitus (aetiology).


What are the common causes of a third nerve palsy?

· Hypertension and diabetes are the most common causes of pupil-sparing third nerve palsy. (Note. The presence of pain is not

a good discriminating feature between diabetes and aneurysm, as pain is present in both.) Diabetic third nerve palsy usually

recovers within 3 months.

· Multiple sclerosis.

· Aneurysms of posterior communicating artery (painful ophthalmoplegia).

· Trauma.

· Tumours, collagen, vascular disorder, syphilis.

· Ophthalmoplegic migraine.

· Encephalitis.

· Parasellar neoplasms.

· Meningioma at the wing of sphenoid.

· Basal meningitis.

· Carcinoma at the base of the skull.

How would you investigate such a patient?

· Test blood pressure and urine for sugar.

· ESR to exclude temporal arteritis (in the elderly).

· Edrophonium test to exclude myasthenia if the pupil is not involved.

· Thyroid function tests and orbital ultrasonography to exclude thyroid disease.

· CT scan of the head.

· Arteriography, especially when the pupil is involved and there is severe pain.


When would you suspect a lesion of the third nerve nucleus?

In the following instances:

· Unilateral third nerve palsy with contralateral superior rectus palsy and bilateral partial ptosis.

· Bilateral third nerve palsy (with or without internal ophthalmoplegia associated with spared levator function).

What do you know about the muscles of extraocular movement?

Each eye is moved by three pairs of muscles, and the precise action of these muscles depends on the position of the eye; the

actions are as follows:

· Medial and lateral recti (first pair of muscles): adduct and abduct the eye respectively.

· Superior and inferior recti: elevate and depress the abducted eye.

· Superior and inferior obliques: depress and elevate the adducted eye.

Note. Superior and inferior recti act in the abducted position (mnemonic RAB).

Do you know of any eponymous syndromes in which the third cranial nerve is involved?

· Weber's syndrome: ipsilateral third nerve palsy with contralateral hemiplegia. The lesion is in the midbrain.

· Benedikt's syndrome: ipsilateral third nerve palsy with contralateral involuntary movements such as tremor, chorea and

athetosis. It is due to a lesion of the red nucleus in the midbrain.

· Claude's syndrome: ipsilateral oculomotor paresis with contralateral ataxia and tremor. It is due to a lesion of the third nerve

and red nucleus.

· Nothnagel's syndrome: unilateral oculomotor paralysis combined with ipsilateral cerebellar ataxia.

M. Benedikt (1835-1920), an Austrian physician, described this syndrome in 1889. Sir H.D. Weber (1823-1918) qualified in Bonn and

worked at Guy's Hospital, London. Henri Claude (1869-1945), a French psychiatrist.

Carl Wilhelm Nothnagel (1841-1905), an Austrian physician.