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“This patient has complained of double vision. Please examine their eyes.”
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- Neurological 0%
This patient has a IVth cranial nerve palsy.
The superior oblique of the eye derives its innervation from the fourth cranial nerve, also known as the trochlear nerve. The functions of the superior oblique muscles are depression, intorsion and abduction of the eyeball. Hence, a patient with fourth nerve palsy will, predominantly, complain of vertical diplopia –usually worse on downward gaze –or torsional or oblique diplopia.
Another important characteristic of the fourth nerve cranial palsy is the development of head tilt. This is usually to reduce the diplopia through picture alignment. The tilt is commonly seen opposite to the lesion. A paradoxical head tilt, is seen in a minority of patients who tilt their heads ipsilateral to the diseased eye, results in a wider separation of the images and, subsequently, disregarding one of the formed images.
The ocular exam will usually not be helpful in localization of the problem. Investigations like Maddox rod test, also known as the cover uncover test and the Parks-Bielschowsky 3-step test are usually employed to correctly localize the problem.
The 3-step test, best in determining vertical strabismus, includes the following steps:
• Determining the side of hypertropia in the primary gaze.
• Subsequently concluding whether the hypertropia is worse on left or right gaze.
• Finally, determining the head tilt that exhibits greater hypertropia.
The Maddox rod test is helpful in measuring excyclotorsion.
Fourth nerve palsy can be congenital or acquired. Congenital type may arise due to developmental issues in the nucleus or the mal-development of the nerve or muscle and even the tendon. Paediatric patients may present with facial asymmetry and torticollis.
The acquired cases are most often idiopathic but can arise most commonly in the setting of a head trauma. Systemic diseases like thyroid dysfunction and multiple sclerosis can also result in palsy as can tumours and vascular malformations compressing the nerve.
Nuclear lesions of the trochlear nerve cause contralateral superior oblique palsy. This should be considered if there is a contralateral Horner’s syndrome or same side relative afferent pupillary defect.
Additionally, compression or ischaemic at the site of the midbrain can cause bilateral trochlear nerve palsies.
Surgical intervention is usually indicated for long standing cases. Botulinum toxin, a neurotoxic protein which blocks neurotransmitter release in the muscles, is used, however its use is greatly discouraged. Surgeries may be used to weaken the antagonist muscles, to lessen the exertion and correct the strabismus.
In mild cases, prisms can be used, when there is no torsional component.
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Question 1 of 4
1. Question1 point(s)Category: Neurological
What is the diagnosis?CorrectIncorrect
Question 2 of 4
2. Question1 point(s)Category: Neurological
What muscle does the IVth cranial nerve innervate?
Question 3 of 4
3. Question1 point(s)Category: Neurological
Which movements of the eye does the superior oblique muscle elicit? Tick all that apply.CorrectIncorrect
Question 4 of 4
4. Question1 point(s)Category: Neurological
Name the IVth cranial nerve.