1. Cranial nerve examination involves a number of steps as you are testing all 12 of the nerves in one station. You should therefore be certain that you know which nerve you are testing next and what tests you must perform for that nerve. You may develop your own technique for this station so that it flows best for you, however, this guide will take you through each nerve systematically.
2. The Olfactory nerve (CN I) is simply tested by offering something familiar for the patient to smell and identify – for example coffee or vinegar.
3. The Optic nerve (CN II) is tested in five ways:
Colour vision is tested using Ishara plates, these identify patients who are colour blind.
Visual fields are tested by asking the patient to look directly at you and wiggling one of your fingers in each of the four quadrants. Ask the patient to identify which finger is moving. Visual inattention can be tested by moving both fingers at the same time and checking the patient identifies this.
Visual reflexes comprise direct and concentric reflexes. Place one hand vertically along the nose to block any light from entering the eye not being tested. Shine a pen torch into one eye and check that the pupils on both sides constrict. This should be tested on both sides.
Finally fundoscopy should be performed on both eyes.
4. The Oculomotor nerve (CN III) is involved in movements of the eye. Asking the patient to keep their head perfectly still directly in front of you, you should draw two large joining H’s in front of them using your finger and ask them to follow your finger with their eyes. It is important the patient does not move their head. Always ask if the patient experiences any double vision and if so when is it worse.
5. The Trochlear nerve (CN IV) is tested along with the oculomotor nerve as it is also involved in eye movements.
6. The Trigeminal nerve (CN V) is involved in sensory supply to the face and motor supply to the muscles of mastication. Initially test the sensory branches by lightly touching the face with a piece of cotton wool and then with a blunt pin in three places on each side – around the jawline, on the cheek and on the forehead. The corneal reflex should also be examined as the sensory supply to the cornea is from this nerve. This is done by lightly touching the cornea with the cotton wool. This should cause the patient to shut their eyelids.
For the motor supply, ask the patient to clench their teeth together, observing and feeling the bulk of the masseter and temporalis muscles. Then ask them to open their mouth against resistance. Finally perform the jaw jerk on the patient by placing your left index finger on their chin and striking it with a tendon hammer. This should cause slight protrusion of the jaw.
7. The Abducent nerve (CN VI) is tested in the same manner as the oculmotor nerve, again in eye movements.
8. The Facial nerve (CN VII) supplies motor branches to the muscles of facial expression. Therefore, this nerve is tested by asking the patient to crease up their forehead (raise their eyebrows), close their eyes and keep them closed against resistance, puff out their cheeks and show you their teeth.
9. The Vestibulocochlear nerve (CN VIII) provides innervation to the hearing apparatus of the ear and can be used to differentiate conductive and sensori-neural hearing loss using the Rinne and Weber tests. For the Rinne test, place a sounding tuning fork on the patient’s mastoid process and then next to their ear and ask which is louder, a normal patient will find the second position louder. For Weber’s test, place the tuning fork base down in the centre of the patient’s forehead and ask if it is louder in either ear. Normally it should be heard equally in both ears.
10. The Glossopharyngeal nerve (CN IX) provides sensory supply to the palate. It can be tested with the gag reflex or by touching the arches of the pharynx.
11. The Vagus nerve (CN X) provides motor supply to the pharynx. Asking the patient to speak gives a good indication to the efficacy of the muscles. You should also observe the uvula before and during the patient saying ‘aah’. Check that it lies centrally and does not deviate on movement.
12. The Accessory nerve (CN XI) gives motor supply to the sternocleidomastoid and trapezius muscles. To test it, ask the patient to shrug their shoulders and turn their head against resistance.
13. The Hypoglossal nerve (CN XII) provides motor supply to the muscles of the tongue. Observe the tongue for any signs of wasting or fasciculations. Then ask the patient to stick their tongue out. If the tongue deviates to either side, it suggests a weakening of the muscles on that side.