Cranial nerve testing Flashcards
What questions might you ask before testing the olfactory nerve?
“Have you experienced any changes in your sense of smell recently?”
“Have you had a blocked nose recently?”
“Do either of your nostrils feel blocked?”
How would you test the olfactory nerve?
Smell test: occlude one nostril, patient tries to identify a smell presented to the other nostril. Change the smells and repeat for other side
If a patient suffers from anosmia following a head injury, where is the likely location of the lesion?
Olfactory cortex, in the inferior temporal lobe
What questions might you ask before testing the optic nerve?
“Have you experienced any changes in your vision lately?” “Any blurriness?” “Any double vision?”
Name some tests that may be performed to assess the optic nerve
Light reflex
Accommodation reflex
Visual fields
Visual acuity
Fundoscopy - using an ophthalmoscope
Ishihara plates
How is the light reflex test performed?
Check patient isnt sensitive to bright light!
Ask them to focus on a distant object (point one out). Shine light into one eye (from the side) and remove the light, while watching the response of one eye. Then shine again and watch the response of the other eye (direct and consensual)
Repeat w other eye
What limb of the light reflex involves the optic nerve? What response is expected to be seen?
Afferent limb
constriction of both pupils
How is the accomodation reflex performed? How does this test optic nerve?
Fix eyes on distant object (POINT ONE OUT!) then ask patient to quickly look at your finger/pen (distance = around 6 inches)
The optic nerve is responsible for the afferent limb, i.e. information from visual fields is sent to oculomotor nuclei and Edwinger-Westphal nucleus to carry out the response
How is the visual field test performed?
Sit around 1m apart (arm width away), remove glasses if possible. Patients look into your eyes and then close one, and you close the opposite.
Bring your wiggling finger from each quadrant into centre slowly, and the patient says when they can see it. Ensure your finger is equidistant. Repeat to other eye
Where would homonymous hemianopia indicate a lesion?
Optic tract
What does a Snellen fraction of 6/60 mean?
The patient can read something at 6m that someone with normal vision can read at 60m
What question might be asked before testing the oculomotor nerve?
“Have you had any pain on eye movement recently?”
What tests can be performed to assess the oculomotor nerve?
H-test
Light reflex
Accommodation reflex
What positions in the H test assess muscles innervated by the oculomotor nerve?
SR: look up and out to test
IR: look down and out to test
MR: look in to test
IO: look up and in to test
What would you expect to find if the patient had third nerve palsy?
Affected eye would be down and out (unopposed action of LR and SO), eyelid may droop, pupil may be dilated
What limb of the light reflex is tested for oculomotor nerve?
Efferent limb - constriction of the pupils is via CN III as it innervates sphincter pupillae
What would you expect to see in the light reflex test if a patient had:
- an afferent defect, or an
- an efferent defect
Afferent= no response (=dilation) in either eye when the light is shone in the affected eye, but both eyes constrict when light is shone into healthy
Efferent= shining light into affected eye would cause the other eye to constrict, and shining light into non-affected would cause that same eye to constrict (affected one wouldnt constrict at all)
What response of the accomodation reflex does CN III control?
Efferent limb: i.e.
Eye convergence, via MR
Pupil constriction
How would you test the trochlear nerve?
First ask if they have had any pain on eye movement recently
Inverted U test - as to assess SO they need to look down and in but doing both at the same time can make them go cross-eyed / dizzy
How would you test the abducens nerve?
First ask if they have had any pain on eye movement recently
H-test: tested when the eyes are abducted (LR)
