Cranial nerve examination Flashcards
(38 cards)
Recall 2 causes of pupil asymmetry that you may see on cranial nerve examination
Horner’s: causes small reactive pupil
CN III palsy: causes large pupil
How far away from a Snellen chart should the patient stand for visual acuity testing?
6 metres
In what pathology is RAPD seen?
Optic neuritis (eg MS)
Recall 3 causes of ptosis
CNIII pathology
Horner’s
Myasthaenia gravis
Name the 3 branches of the trigeminal nerve
Ophthalmic
Maxillary
Mandibular
Which branch of the trigeminal nerve has a motor element, and what does it control?
Mandibular
Muscles of mastication
Which cranial nerve forms the afferent and efferent limbs of the corneal reflex?
Afferent = CNV Efferent = CNVII
Which portion of the tongue gets its sensory supply (taste) from the facial nerve?
Anterior two thirds
How can facial nerve palsy affect hearing?
Supplies stapedius muscle. If this is damaged –> hyperacusis
How can the vestibular function of CNVIII be tested?
Turning test - Ask the patient to march on the spot with eyes closed and arms outstretched. If there is a lesion, they will turn towards it.
Recall the direction of deviation of the tongue and the uvula when there is a lesion
Tongue: towards lesion (CNXII)
Uvula: away from lesion (CNX)
How can the olfactory nerve be tested?
Ask them to smell coffee/ nail varnish/ vanilla essence
Must test BOTH nostrils
How can the sensory portion of the optic nerve be tested?
- Assess acuity with Snellen chart (or ask them to read time off clock behind you)
- Assess colour vision using Ishihara plates
- Assess for neglect/ inattention by holding your hands out in periphery of vision and wiggling fields on each side and then both at same time and asking pt which side you are wiggling fingers on
- Assess fields - nb. these are CIRCULAR so you need to start behing the patient and come forwards as well as up and down
How can the motor function of the optic nerve be tested?
Nil
How can the optic nerve reflexes be tested?
- Direct and consensual light reflexes - shine pen torch into eye and assess for constriction of ipsilateral and then contralateral pupil
- Swinging light test (more info on a different card)
- Test accommodation reflex (normal –> BL convergeance and constriction)
How should the swinging light test be performed?
- Ask the patient to look at a far away object to prevent the pupil constricting due to accommodation
- Shine the beam into the first eye for at least 3 seconds, to allow the pupil to stabilise
- Observe the other – eye – does it also constrict?
- Move the beam to the other eye, quickly but not straight across the nose
- Hold for 3 seconds again, note – does the pupil being illuminated stay the same size or get bigger?
- Repeat for the other eye
If a RAPD is present, then when the light is shone into the affected eye the pupils will constrict a little but not fully, due to the afferent defect. When you then shine into the unaffected eye, the pupils will both constrict further.
How can the motor function of the oculomotor nerve be assessed?
Mnemonic: Are Pupils Moving Nice and Smoothly?
- Look for pupil Asymmetry - abnormally large pupil may be due to CN III palsy
- Inspect for Ptosis
- Assess eye Movements (H test)
- Assess for Nystagmus
- Assess for Saccades
How can you assess for nystagmus and saccades?
Get them to follow your finger (smooth pursuit?) until gaze is lateral and then hold to see if there is nystagmus.
To assess for saccades, then get them to look from your hand on one side to your pen on the other very quickly.
How does a trochlear nerve palsy appear?
Vertical diplopia when looking inferiorly due to superior oblique dysfunction
How does an abducens nerve palsy appear?
Due to lateral rectus palsy, there is unopposed adduction which causes a convergent squint
How can eye movements be tested?
Rather than H test, best to check horizontal, then vertical, then down and out eye movements as this isolates the movements controlled by CNIII, IV (down and out) and VI (abduction).
Remember to ask about pain and double-vision – if there is double vision, ask them to cover each eye in turn to see which one produces the more’ real’ image (and therefore which is responsible for creating the ‘false’ 2nd image).
How can the sensory portion of the trigeminal nerve be tested?
Need to test ophthalmic, mandibular and maxillary branches (lateral aspect of forehead, cheek and lower jaw) by lightly touching these areas bilaterally and comparing each side of face.
Nb UMN lesions will be forehead-sparing.
How can the motor function of the trigeminal nerve be assessed?
Palpate the muscles of mastication - temporalis and masseter
How can the trigeminal nerve reflexes be assessed?
Corneal reflex: you need to put the cotton wool over the black bit of the pupil as this is the cornea, not the white bit (sclera) of the eye (CNVII is efferent)
Jaw jerk: put thumb on chin with patient’s mouth open and tap thumb with tendon hammer. Should cause slight closure of the mouth.
