Cranial Nerve Examination

Cranial Nerve ExaminationCreated OnJune 1, 2020Last Updated OnJune 1, 2020byadmin You are here: Main Clinical Examination Cranial Nerve Examination < All Topics Table of Contents Cranial Nerves: 12 pairs Origin: Cerebrum Olfactory (I) Optic (II) Midbrain Trochlear (IV) Midbrain-pontine junction Oculomotor (III) Pons Trigeminal (V) Ponto-medullary Junction Abducens (VI) Facial (VII) Vestibulocochlear (VIII) Medulla Glossopharyngeal (IX) Vagus (X) Accessory XI) Hypoglossal (XII) Modalities: Sensory (afferent) Modalities: General somatic sensory (GSS) – Sensation from skin. General visceral sensory (GVS) – Sensation from viscera. Special somatic sensory (SSS) – Senses derived from ectoderm (sight, sound, balance). Special visceral sensory (SVS) – Senses derived from endoderm (taste, smell). Motor (efferent) Modalities: General somatic motor (GSM) – Skeletal muscles. General visceral motor (GVM) – Smooth muscles of gut and autonomic motor. Special visceral motor (SVM) – Muscles derived from pharyngeal arches. Equipment required: Pen torch Snellen chart Ishihara plates Ophthalmoscope Cotton wool Neuro-tip Tuning fork (512hz) Glass of water Coffee bean or lemon slice Introduction: Wash hands before examination Introduce yourself Confirm patient details – name/DOB Explain the examination and gain consent Position patient on a chair at eye level – approximately one arm’s length away Ask if the patient currently has any pain. Cranial nerve I (olfactory nerve):   Exit: cribriform plate Modalities: SVS   Function: smell Have patient to close his/her eyes Occlude one nostril and test the other nostril using nonirritating substances (such as vanilla, lemon, cloves, coffee). Bring the substance near to the patent nostril and ask patient to smell. He/she should identify the smell rather than just report that it can be smelt. Compare 2 sides. Abnormal findings: Hyposmia/Anosmia (Reduced/Loss of sense of smell) Obstruction – Nasal polyps, enlarged turbinates, rhinitis, nasal septum deviation Head trauma causing damage to olfactory filaments – Anterior cranial fossa fracture Intracranial Lesions – Abscess, Tumour Degenerative disorder – Parkinson’s disease, Alzheimer’s disease, Lewy Body dementia Genetic – Kallmann’s syndrome Parosmia (Distorted odor perception) Head trauma – Skull fracture Infection – Recovery state of post-influenza anosmia, Sinusitis Adverse effect of drugs – Streptomycin, Thyrothiricin Cranial nerve II (ophthalmic nerve):   Exit: optic canal   Modalities: SSS   Function: vision Assess the visual acuity Ensure good lighting, ask patient to put on their reading glasses if they use them. Use a Snellen chart with a distance of 6 meters from the patient. Or hold a handheld Snellen chart at a comfortable reading distance (Arm length). Cover one eye with a card and have the patient to read from top down until he can no longer identify the letters. Repeat for the other eye. For each eye, record the smallest line patient could read. Normal vision is 6/6. Causes of Decreased visual acuity Papillitis Retrobulbar neuritis Refractive errors Myopia Presbyopia Astigmatism Primary ocular disorders Iridocyclitis Corneal opacities Cataracts Vitreous opacities Retinal detachment Glaucoma. If the patient is unable to read at 6 metres: Move closer to 3m If still unable – move closer to 1m If still unable – assess the ability to count fingers If still unable – assess the ability to detect moving hand If still unable- assess the light perception **Repeat visual acuity using a pinhole if the patient does not achieve at least 6/9. Assess the visual field Sit directly in front of patient about 1 meter away and have the patient to keep looking at your eyes. Hold your hands out midway between you and the patient to the full extend that you can barely see them out of the corner of your eye. Wiggle a fingertip and ask the patient to point to it as soon as he sees it moves. Do this at 10, 8, 2 and 4 o’clock. If abnormally is found, test all 4 quadrants of each eye individually. *Causes of visual field loss has been discussed under Visual Disturbance – Common neurological symptoms. Fundoscopic examination Perform fundoscopy in a dim room. Have patient to focus on distant wall. Hold the ophthalmoscope in your right hand and use your right eye to examine patient’s right eye. Place your free hand on the patient’s forehead, catch the upper eyelid and gently retract it against the orbital rim. This prevents the upper eyelid from obscuring your view. From a distance about 10cm bring the red reflex into focus. *An absence of red reflex indicates cataract or retinoblastoma. Slowly come close to the patient’s head so that you are touching the hand you are resting on the patient’s forehead. Bring the optic disc into view. Note the disc colour, presence of venous pulsations, papilledema or haemorrhages. Follow the blood vessels as they extend from the optic disc in 4 directions: Superotemporally, inferotemporally, superonasally and inferonasally. Ask the patient to look directly at the light to locate the center of macula. Ask patient to keep their eye still while you look around the macula. Findings for papilledema Loss of venous pulsations Swelling of optic nerve head, so loss of disc margin Disc hyperemia Flame shaped haemorrhages Assess the pupillary function (CN II and CN III) Light reflex: Afferent pathway: Optic nerve, chiasma, optic tract (CN II) Centre: Pretectal nucleus in the midbrain Efferent pathway: Edinger-westphal nucleus, Oculomotor nerve, ciliary ganglion and short ciliary nerve (CN III) Effector muscle: Sphincter pupillae Steps: Assess the pupils’ shape and symmetry. Dim room lights as necessary. Ask the patient to look into distance to avoid effect of accommodation. Shine a bright light (yellow light) obliquely into each pupil. Look for both direct and consensual constriction. Record pupil size in mm and any asymmetrical or irregularity To assess the afferent pathway (swinging light test): Swing a bright light from one eye to the other The eye with optic nerve lesion will show a positive consensual light reflex but will not show a positive direct light reflex. Affected pupil starts to dilate when direct light is thrown into that eye (Marcus Gunn’s Pupil). Assess the color vision Use Ishihara chart to assess red-green vision. Cranial nerve III (oculomotor nerve), IV (trochlear), VI (abducens):   Exit: superior orbital fissure Modalities: CN III – GSM & GVM CN IV – GSM CN VI – GSM   Function: CN III -movement of eyeball, pupillary contraction and accommodation CN IV – supplies the superior oblique muscle CN VI – supplies the lateral rectus muscle Visual inspection Sit facing the patient about 1 metre away. Inspect for head turns or tilts in the direction of underacting muscles. Look for any ptosis. Ptosis may be congenital or acquired, unilateral or bilateral. Unilateral Ptosis Bilateral Ptosis Third nerve lesion: Compression of third nerve by the uncus of temporal lobe during cerebral herniation Compression of third nerve by aneurysm of posterior communicating artery, posterior cerebral artery, or internal carotid artery Cavernous sinus thrombosis (usually the fourth and sixth cranial nerves are also involved) Third nerve palsy can occur without involving the pupillary fibres in the following conditions: Diabetes mellitus Hypertension Atherosclerosis Collagen vascular disease. Lesion of cervical sympathetic pathway (Horner’s syndrome) Trauma Lesions of the upper eyelid. Myopathies Myasthenia gravis Bilateral Horner’s syndrome Bilateral ptosis occurs when there is a lesion of the third nerve nucleus, supplying the levator palpabrae superioris in the midbrain Snake bite Botulism. Hold pen torch and ask patient to look at the light. Look at the position of the light reflection on the cornea. Does the reflection of light hit the same location in each eye? 2. Assess the eye movement Stand/sit directly in front the patient 3-6 feet away Ask patient to follow your finger without moving their head. And ask them to notify you if they have diplopia. Move your finger to one side, then up and down then to the other side and repeat (six cardinal direction), forming a letter H in the air. Observe for nystagmus for each eye...

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