Cranial Nerve Examination
There are 12 pairs of nerves that come from the brain, one for each side of the brain. One or more of the nerves can be affected depending on what is the cause. Common conditions include space occupying lesions (tumours or aneurysm), myasthenia gravis and multiple sclerosis, although there are many more.
For a detailed list visit this site.
The cranial nerve examination involves a number of steps as you are testing all 12 of the nerves in one station. Be certain to know which nerve is being tested next and what tests you must perform for each specific nerve.
This guide will take you through each nerve systematically, but personal techniques may be adopted for this station so that it flows best for you. It can seem like a daunting station as there are many steps to it but hopefully this guide will help.
The following equipment is required for a cranial nerve examination:
- Item with distinct odour (e.g. orange/lemon peel, coffee, vinegar, etc)
- Cotton ball
- Pen torch
- Tuning fork
- Neurological reflex hammer
- Snellen charts
- Ishihara plates
Wash your hands, introduce yourself to the patient and clarify their identity. Explain the procedure and obtain consent.
The Olfactory nerve (CN I) is simply tested by offering something familiar for the patient to smell and identify, for example orange/lemon peel, coffee, or vinegar.
The Optic nerve (CN II) is tested in five ways:
The acuity is easily tested with Snellen charts. If the patient normally wears glasses or contact lenses, then this test should be assessed both with and without their vision aids.
Colour vision is tested using Ishihara plates which identify patients who are colour blind.
Visual fields are tested by asking the patient to look directly at you whilst you wiggle 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 patients nose to block any light from entering the eye which is 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.
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?
The Trigeminal nerve (CN V) is involved in sensory supply to the face and motor supply to the muscles of mastication. There are 3 sensory branches of the trigeminal nerve: ophthalmic, maxillary and mandibular.
Initially test the sensory branches by lightly touching the face with a piece of cotton wool followed by a blunt pin in three places on each side of the face:
- 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. Do this by lightly touching the cornea with the cotton wool. This should cause the patient to shut their eyelids.
Ask the patient to then 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.
As previously mentioned the Abducent nerve (CN VI) is tested in the same manner as the oculomotor and trochlear nerves, again in eye movements.
The Facial nerve (CN VII) supplies motor branches to the muscles of facial expression.
This nerve is therefore 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 reveal their teeth.
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.
To carry out 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.
To carry out the 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.
Asking the patient to speak gives a good indication to the efficacy of the muscles. The uvula should be observed before and during the patient saying “aah”. Check that it lies centrally and does not deviate on movement.
Thank your patient and wash your hands. Report any findings to your examiner.