Patient has changed from having binocular single vision, seeing one image only, to a sudden onset manifest squint and diplopia (double vision)
The double vision will be horizontal, vertical, or both
Due to new weakness of extra-ocular muscles
Investigations
Cover test
Used to detect a manifest squint (tropia) - squint present when the eyes are open and being used
Horizontal double vision with esotropia/exotropia on cover test suggests LR or MR problem
Vertical double vision with hypertropia/hypotropia on cover test suggests SO, SR, IR, IO problem
Ocular motility
Assessed using a pen torch
If the ocular muscles are normal there should be no visible sclera left in either eye in each position of gaze (visible sclera → weak muscle)
CN III (oculomotor nerve) palsy
CN III supplies all extraocular muscles except superior oblique and lateral rectus
Aetiology
Microvascular
Tumour
Aneurysm
MS
Congenital
Clinical presentation
Results in the unopposed action of both the lateral rectus and superior oblique muscles, which pull the eye inferolaterally
As a result, patients typically present with a ‘down and out’ appearance of the affected eye
Oculomotor nerve palsy can also cause ptosis (due to a lack of innervation to levator palpebrae superioris) as well as mydriasis due to the loss of parasympathetic fibres responsible for innervating to the sphincter pupillae muscle
Painful CN III palsy → aneurysm
CN IV (trochlear nerve) palsy
Only innervates the superior oblique muscle
Aetiology
Congenital decompensated
Microvascular
Tumour
Blunt head trauma can result in bilateral CN IV palsy
Clinical presentation
Typically results in vertical diplopia when looking inferiorly, due to loss of the superior oblique’s action of pulling the eye downwards
Affected eye turned upward in primary position
Patients with CN IV palsies may compensate for diplopia with variable head positioning; chin-down head posture is seen in bilateral CN IV palsy and contralateral head tilt is typically seen in unilateral CN IV palsy (common in children)
CN VI (abducens nerve) palsy
Only innervates the lateral rectus muscle
Aetiology
Microvascular
Raised intracranial pressure
Tumour
Congenital
Clinical presentation
Results in unopposed adduction of the eye (by the medial rectus muscle), resulting in a convergent squint or esotropia (eye turns inwards)
Patients typically present with horizontal diplopia which is worsened when they attempt to look towards the affected side
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