Cranial Nerve Exam Walkthrough (Basics)

Cranial Nerve Tests
I – OLFACTORY = SMELL
II – OPTIC = Visual acuity=light & accommodation. Fundoscopy. Visual Fields.
III – OCCULOMOTOR – Eye Movements
IV – TROCHLEAR – Eye Movements                  
V – TRIGEMINAL – Facial Sensation, Jaw Jerk, Corneal Reflex
VI – ABDUCENT – Eye Movements
VII – FACIAL – Muscles of facial expression.
VIII – VESTIBULOCOCHLEAR (AUDITORY) – Hearing and Balance
IX – GLOSSOPHARYNGEAL – Palatal Movements - Gag
X – VAGUS – Palatal Movements - Gag             
XI – ACCESSORY (SPINAL ACCESSORY) –Sternomastoid- flexion and rotation of the head.
XII – HYPOGLOSSAL – Tongue (wasting, fasiculations)

The Examinations
 
CN I
“Can You Smell....?” Freshly cut grass, coffee - noticed any problems recently?

CN II
Visual acuity – SNELLEN CHART, 6m away from patient. The pinhole test helps distinguish refractive errors from other causes of visual loss. In refractive visual disturbances, eg: myopia, vision is improved when peering through a small hole. In non-refractive disorders, improvement does not occur.
 
Visual fields Sit opposite your partner, each cover up the opposite eye (one left, one right), put your finger at the periphery of your vision equidistant between you in the centre of each quadrant and move it in until your partner can see it. Repeat for each quadrant.
 
Fundoscopy Get the room as dark as possible, put the ophthalmoscope into your eye socket and hold it firm against the bone. Make sure the light is shining away from you! Look round the room through the ophthalmoscope – if you can’t do this you won’t be able to see anything in the patient. Instruct your partner to look at a distant object. Direct the light into one eye and check for the red reflex – the same as you see with flash photography. Then come close to your partner, looking at the same eye (eg: right to right). Find an artery and follow it to the disc.

CN III, IV AND VI
Eye movements Hold your partner’s chin so there is no temptation to move the head. Hold a finger in front and ask him/her to follow it with their eyes. Move to each side and then up and down. At each position (of six) ask ‘do you see one or two?’. Check for nystagmus at the same time.

Pupil reactions Shine a light in each eye, directed from the side so that the subject does not look directly at the light (why?). Check the reaction in each eye. This is one of three instances in cranial nerve examination where a unilateral sensory stimulus produces a bilateral motor output. Ask the subject to look at a distant object and then at one close to. Watch the pupil reaction. Sorting out which nerve and which muscle is involved can be complex. However, CN lll palsies cause the eye to be turned outwards and downwards (down and out) due to unopposed action of the lV and Vl nerves. There may also be ptosis and a dilated pupil (why?). CN VI palsies cause failure of lateral gaze and isolated CN lV palsies are too rare to worry about at this stage.
 
CN V – masseter, temporalis, medial + lateral pterygoid.
Opthalmic, Mandibular and Maxillary Divisions.
Ask the subject to open the mouth against resistance and then to clench the teeth while you feel over the masseters and temporalis; test each of the sensory divisions for pain and sensation, as you did for skin sensation elsewhere; touch the cornea with a wisp of cotton wool and note the bilateral blink (the second example of a bilateral motor response to a unilateral sensory stimulus). This is unpleasant so don’t try it too often.
 
CN VII
Ask the subject to frown (raise eyebrows!), screw up the eyes, blow out the cheeks, smile or whistle. The last usually produces a smile if not a whistle. Avoid the common ‘show me your teeth’ – they may get taken out!
 
CN VIII
Occlude one ear and whisper into the other a question, such as ‘where do you live?’ The Rinne and the Weber test may seem complex for this stage but they give a clear insight into hearing mechanisms. Strike the tuning fork (517Hz) and hold it in front of the ear and then place the base of the fork on the mastoid. The first should be louder. With the fork in position now simulate conductive deafness by occluding that ear. What does the subject report? Strike the fork and place the base on the forehead. The vibrations should be appreciated equally in both ears. Now occlude one ear. What does the subject report? If you can work out the reasons for these responses you understand much of the physiology of hearing.
 
CN IX AND X
These are usually considered together and, considering the fundamental importance of X in the body, testing is limited. Ask the subject to open the mouth and touch one side of the tonsillar bed with a throat swab. The soft palate should rise up with the uvula in the middle (gag reflex). This is the third example of a bilateral sensory response. The test is uncomfortable and a compromise is to ask the subject to say ‘aah’ which tests the motor component only.
 
CN XI
Ask the subject to lift the shoulders against resistance and then to press each cheek into your hand in turn.


CN XII
Ask the subject to protrude the tongue.