Double Vision Flashcards
What happens in 6th nerve palsy?
Patient cannot abduct eye on affected side due to palsy of 6th CN (abducens) which innervates the lateral rectus muscle.
What are the causes of 6th nerve palsy?
- Poor blood supply (microvascular palsy e.g. cavernous sinus thrombosis): HTN, DM, hypercholesterolaemia, smoking
- Direct pressure on 6th nerve can cause damage: tumours, middle ear infections, swelling of neighbouring blood vessels/area
- Raised ICP is very important (affects 6th nerve more than others due to sharp turn before cavernous sinus) - check for papilloedema, common in young people
- Head injuries
- Papilloedema, abx use, weight gain»_space; can lead to idiopathic intracranial HTN (common in obese, young women), can cause bilateral palsy
What are the features of 6th nerve palsy?
- Sudden onset of horizontal double vision - worse when patient looks to affected side
- Limited outward movement of affected eye - patients often compensate by turning head to affected side
- Convergent squint (eyes point in different directions) that is large when patient tries to look at an object in the distance
What are the investigations for 6th nerve palsy?
- Seen by orthoptist (specialist in eye movements) + ophthalmologist
- Examination to test squint + range of movement
- Blood tests and MRI - to investigate cause of palsy (suspecting raised ICP)
When would 6th nerve palsy require further investigation?
- If restriction worsened
- If they had other CN palsies
- If they had bilateral swollen optic nerve heads (papilloedema) - raised ICP, need urgent neuroimaging to rule out compressive lesions
- If they were 35 yrs old or younger, young patients are less likely to have atherosclerotic risk factors so need investigated further.
What is the treatment for 6th nerve palsy?
- Observation: most microvascular palsies will resolve within 3-6 months (as nerve regrows). Spontaneous recovery is less likely if lateral rectus palsy is due to head injury/tumour (nerves may not be able to regrow around obstruction).
- Prisms: can get temporary plastic prisms fitted to patient’s glasses - reduces/completely corrects squint and double vision.
- Botox: if prisms can’t correct squint, botox can be injected into medial rectus muscle to reduce size of squint. Also prevents medial rectus from contracting and shortening which can cause reduced outwards movement of eye, even if lateral rectus starts working normally again.
What is the affect of a 3rd nerve palsy?
- Partial ptosis
- Depressed and divergent (down and out) eye
- Sometimes dilated pupil in affected eye (EMERGENCY, needs neuroimaging immediately)
- Struggles to look up and in
What are the causes of a 3rd nerve palsy?
- Vascular (DM, HTN)
- Tumour
- Hernia (often trans-tentorial hernia)
- Aneurysm (berry aneurysms are common near the posterior communicating artery and CN3 is close to this artery)
Why do aneurysms affect the pupil in 3rd nerve palsy?
Superficial parasympathetics run on the outside of CN3 so if there is compression e.g. aneurysm, will cause pupil involvement. DM and HTN usually affects inside the nerve so spares the pupil.
What does CN3 innervate?
Most of the ophthalmic extra-ocular muscles: superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae superioris.
What is 4th nerve palsy?
- Superior oblique gets paralysed, get nasal upshoot, on exam eye moves up and in
- Causes are congenital, trauma, vasculopathic, tumour
- In congenital causes, they develop stronger muscle to compensate, might only see in a head tilt
What is the summary of the nerve palsies?
- 3rd nerve: down + out, ptosis (think aneurysm)
- 4th nerve: nasal upshoot (think congenital/trauma)
- 6th nerve: crossed eye, double vision (think raised ICP)
- All 3 can be caused by vascular and tumours
- Anybody with eye problems and >65 need to rule out temporal arteritis (scalp tenderness, jaw claudication, general malaise)
What happens to the orbit during trauma?
The inferior orbital floor (blow out fracture) is weaker. so tends to give way first in trauma due to raised ICP from within the orbit. Orbital fat and muscle can get trapped within the fracture. When the patient looks up or down, they will experience diplopia.
Infra-orbital paraesthesia - V2 division of trigeminal nerve may be affected so sensation is lost below the orbit.
What is the immediate management for trauma to the orbit?
- Advise patient not to blow their nose as the communication with the sinuses may mean bacteria enter the orbit causing an orbital infection
- Prescribe broad spectrum antibiotics
- Arrange urgent maxillofacial surgery
What are the investigations for Myasthenia Gravis?
- Acetylcholine receptor antibodies (1st line)
- If ACh receptor antibodies negative, do neurophysiology with repetitive stimulation +/- single fibre studies
- If these tests confirm MG, then do CT thorax (check for thymoma)
- CT/MRI brain - can do to ensure symptoms are not brain issue
- Edrophonium test: rarely done due to risk of bradycardia and breathing difficulties, inject edrophonium chloride, if muscle strength suddenly improves, diagnosis of MG likely
