Cranial nerves examination Flashcards
Testing CN I
Relies on subjective response Can use bottles of odours or ask patient if they have noticed a change in smell. Loss can indicate damage to the cribiform plate or tumours
Testing CN II
Snellen chart: visual acuity Ischihara plates: colour vision Confrontation test: visual fields Pupillary light reflex Accomodation reflex Blink reflex Fundoscopy
Describe the pupillary light reflex
Pupil size is controlled by pupillary light reflexes, which operate over the range of light intensities experienced in moderately bright daylight.
Photosensitive cells detect light which is conveyed to the pretectum of the midbrain via the optic nerve. Neurones fro the pretectum travel to the Edinger-Westphal nuclei which contains parasympathetic neurones that run with left and right oculomotor nerves to the ciliary ganglia. Ciliary nerves leave the ganglion to the pupillary sphincter. Increase in light causes pupil constriction.
Both pupils constrict because there are reciprocal connections between the midbrain and the oculomotor nuclei
Direction of movement of muscles of the eye
Causes of loss of pupillary light reflex
Optic nerve damage - loss of sensory response e.g. left:
Direct reflex is lost. When the left eye is stimulated, neither pupil constricts. Direct reflex in the right eye is intact. When light is shone into the right eye, both pupils constrict because reflex from right optic nerve is intact.
Oculomotor nerve damage - loss of motor control e.g. left
Direct reflex is lost in the left eye. Whe light is shone into the left eye, the right pupil constricts because the left eye can still signal to the brain via the optic nerve, but due to damage the left is unable to constrict. When the right eye is stimulated, only the right pupil constricts.
Nerves controlling movements of the eye
Oculomotor
Trochlear
Abducens
Testing CN V
Sensation of the face - test for cutanous sensation
Test motor supply to muscles of mastication by palpation of masseter and temporalis when teeth are clenched
Corneal reflex
Testing for CN VII
Motor to muscles of facial expression: Ask patient to raise eyebrows, blow out cheeks, smile, purse lips. Look for asymmetry of movement between the two sides.
Parasympathetic to lacrimal gland, sublingual and submandibular glands, glands of the nose. Not tested.
Taste to anterior 2/3 of the tongue. Not tested
Test for CN VIII
Otoscopy: check EAM is clear
Test hearing with whisper at a distance, by the ear, then spoken voice. Use tragal masking to eliminate non-test ear.
Tuning fork tests 512hZ: Weber test - fork at the forehead, Rinne, in front of the ear and bone.
Conductive hearing loss: bone conduction, Weber louder on affected side Sensorineural: No sound heard in Rinne test, sound louder in normal unaffected ear
Test for CN IX
Gag reflex (not normally done)
Test for CN X
Sensory and parasympathetic funcions not testable
Motor fibres to levator palati and muscles of the pharynx and larynx. Observe elevation of the soft palate, character of cough and phonation.
Test for CN XI
Observe elevaton of the shoulders with and without resistance (trapezius)
Observe ability to turn head to each side. (sternocleidomastoid)
Test for CN XII
Muscles of the tongue. Tongue deviates towards affected side in motor loss.
Describe the visual field defects resulting from lesions in these areas
- Right optic nerve: Total loss of vision in the right eye (mononuclear field loss)
- Optic chiasm: Loss of vision in the lateral half of both eyes (bitemporal hemianopia)
- Right optic tract: Loss of vision in the left half of the visual fields in both eyes. (homonymous hemianopia)
- Temporal lesion: Loss of the upper left quarter of both eyes (homonymous quadrantopia)N.B. Parietal lobe lesion causes loss in the lower left quadrant of both eyes.
5&6: Occipital cortex: Homonymous hemianopia with macular sparing.
