12 Cranial Nerves and Assessment

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12 Cranial Nerves and Assessment 1) Nerve: Type: Function: Test:

Olfactory

(I)

Sensory Sense of smell You’ll need three substances with distinctive but familiar odors; for example, coffee, tobacco, and cloves. Ask your patient to close his or her eyes, and occlude her left nostril with her finger. Hold one of these substances under his / her right nostril, and ask her to identify the odor. Follow the same procedure with the other two substances. Then, repeat the entire test on the other nostril.

Normal findings: Patient detects and correctly identifies all three odors. Possible causes of abnormalities: Temporary impairment from common cold; head trauma resulting in Parosmia (perversion of sense of smell); compression of Olfactory bulb by meningiomas or anterior fossa aneurysm; tumor infiltration in frontal lobe; or temporal lobe lesions, resulting in Olfactory hallucinations.

2) Nerve: Type: Function: Test:

Optic

( II )

Sensory Vision Visual acuity Use Snellen chart or an E chart to test your patient’s visual acuity. Normal Findings: Patient’s vision fields should be approximately the same as your own ( provided your own vision is normal ). Test: Internal eye structure Examine your patient’s eyes with an opthalmoscope. Normal Findings: Optic disc appears yellowish-pink and is round or oval, with clearly defined edges. Fundus appears uniformly orange, with optic disc located one side. Blood vessels extend outward from optic disc along borders of the fundus. Possible causes of abnormalities: Optic neuritis, toxic substances ( fro example, alcohol abuse ), head trauma, chronic nephritis, Diabetes mellitus, anemia, nutritional deficiencies, multiple sclerosis, chronic hypertension, intracranial tumors or aneurysms, or increased intracranial pressure.

(2) 3) Nerve/s:

- Oculomotor ( III )

- Trochlear - Abducens

( IV ) ( VI )

Type: Function:

Motor Oculomotor: Innervates extrinsic eyemuscles and ciliary muscle Trochlear : Innervates superior oblique muscle Abducens : Innervates external rectus muscle Important: These three (3) nerves operate as a unit and should be tested and evaluated together. Test: Extrinsic Eye muscles Ask the patient to open his or her eyes. Instruct him or her to focus on a point directly in front of him / her. Observe her ability to focus on one point effectively. Normal Findings: Lower edges of lids meet bottom edges of irises; upper lids cover approximately 2mm of irises. Test:

Direct papillary response Carefully note each pupil’s size. Darken the room, and check your patient’s eyes with a penlight. To do this, shine the light directly into one of your patient’s pupils, as she keeps his / her other eye closed. Note the pupil’s reaction. Then, check the other eye. Normal Findings: Pupils constrict and remain constricted with light; pupils dilate when light is removed. Test:

Consensual papillary responses Darken the room, but make sure your patient keeps both eyes open. Position the penlight directly in front of his / her right eye. Turn the penlight ON, and observe the reaction of his or her left pupil. Then, check the other eye. Normal Findings: Pupils constrict bilaterally and remain constricted with light. Test:

Extraocular eye movement Begin by familiarizing yourself with the six cardinal fields of gaze. As you know each of these fields corresponds to one of your patient’s extraocular muscles. Check the field separately. First, hold a pencil 12” (30 cm.) in front of your patient’s nose. Ask your patient to hold his / her head still and follow the pencil’s movement with his / her eyes. Then, slowly move the pencil to your right side, then to your left, then, when the pencil’s approximately 24 “ ( 60 cm) from your starting point, or your patient’s eye movement stops ( in either or both eyes ), hold the pencil still. Note the position of the iris in relation to each eye’s midline. Repea