Upper CNs Flashcards
What part of the skull does CN 1 (olfactory nerve) go through to finally land in the roof of the nasal cavity?
CN 1 stems from the left & right olfactory bulbs, exits the skull through the cribriform plate & terminates in the roof of the nasal cavity.
What neurological signs might you observe on general observation of the eyes?
- Ptosis (droopy eye)
- Proptosis (eye more “popped out”)
- Pupils unequal size/shape
- Deviation of eye position (convergent or divergent)
- Rash eg herpes zoster, haemangioma in CN 5 distribution =
Sturge-Weber syndrome
What does a visual acuity (VA) of 6/12 mean?
The patient’s best VA is only at the line marked ‘12’ (which could be read by a person with VA = 6/6 but at 12m away)
What visual field defect would occur with a lesion at the Optic chiasm? Right Optic tract?
A lesion at the optic chasm causes a bitemporal hemianopia
A lesion at the optic tract causes a contralateral (Left) homonymous hemianopia
What neurological clinical signs might you observe on the optic disc?
Blurring of the margins of the optic disc = papilloedema = possible raised intracranial pressure (ICP)
* Pallor of the optic disc = possible optic atrophy
What are you trying to assess with the ‘cover test’?
The cover test will detect an underlying strabismus, or ocular deviation, that may not be obvious to direct observation. If there is
strabismus, the affected eye will correct (move back to the central neutral position) when the other eye is covered.
What are three facts about the false image of diplopia?
The false image is usually (i) paler, (ii) less distinct and (iii) always more peripheral then the true image
What are three clinical signs of a lateral rectus (CN 6) palsy?
CN 6 palsy causes (i) failure of lateral movement of the affected eye, (ii) convergent strabismus and (iii) diplopia
What is the definition of nystagmus?
Nystagmus is an involuntary movement of the eyes with a slow drift in one direction and a fast movement back to the original position.
The direction of nystagmus is defined as the fast movement (correcting) although it is the slow drift that is abnormal.
What is myasthenia gravis?
Myasthenia gravis is a disorder of neuromuscular transmission, resulting from binding of autoantibodies to components of the
neuromuscular junction, most commonly the acetylcholine receptor. This leads to muscular weakness with easy ‘fatiguability’, which is
worse on exercise and improves with rest.
What are some causes of unequal pupil size?
- Physiological in 20% of people (<1mm difference)
- Horner’s syndrome (ptosis, miosis, anhydrosis)
- CN 3 palsy (ptosis, eye ‘down and out’, dilated pupil unreactive to direct light and accommodation)
- Other: Uveitis, stroke, subarachnoid haemorrhage, acute angle-closure glaucoma
What does a consensual light reflex mean?
Normally the pupil into which the light is shone constricts briskly – this the direct response
Simultaneously, the other pupil constricts in the same way – this is the consensual response
What would you observe when a RAPD is present?
When the light is shone from the normal eye to the abnormal one, the pupil dilates. This occurs because a lower light stimulus is
registered in the abnormal eye (reduced afferent impulse), causing markedly less reflex pupillary constriction in the abnormal eye;
relaxation after the consensual response dominates
What do the pupils do when testing accommodation?
The accommodation response causes both pupils to constrict as the focus goes from distance to near
