Toronto Notes

The auditory nerves subserves both hearing and vestibular function.

Examination Technique:

1. Hearing:

• mask the opposite ear and whisper numbers. The patient should not be able to read your lips. Ask the patient to repeat the numbers. If they cannot do so, increase the volume of your voice and repeat as needed. Note any asymmetry.
• compare air versus bone conduction using the Rinne test. Apply the vibrating fork against the mastoid process. Utilize the 512 Hertz tuning fork. Ask the patient when they can no longer hear it, then place it in front of the ear.
• test for lateralization using the Weber test. Apply the vibrating tuning fork to the center of the forehead and ask the patient where they hear it.

2. Vestibular Function:

• the vestibular component of the auditory nerve is tested by observing for nystagmus when extraocular movements are assessed.

Normal Response:

• Rinne – air conduction (perceiving the sound of the tuning fork in front of the ear) is greater than bone conduction (with the tuning fork held against the mastoid process).
• Weber – normally, patients will either hear it equally from both ears or respond that they are not sure.

Abnormal Response:

• Rinne: in conductive hearing loss, bone conduction is greater than air conduction. In sensorineural deafness, air conduction is greater than bone conduction.
• the Weber is abnormal if the patient clearly lateralizes it to one ear. With a conductive hearing loss, the patient lateralizes the sound to the affected ear. With sensorineural deafness the sound is best heard by the non-involved ear.

Examination Technique:

• explain to the patient that you will be touching them with a sharp object. Reassure them that it is disposable and has not been used on anyone else.
• for pain, use either a pin or the sharp end of a broken tongue depressor.
• use a cold tuning fork to assess temperature. If necessary, the tuning fork can be cooled by running it under cold water.
• ask the patient to report whether they feel sharp or dull or cold.
• ask the patient if the two sides feel the same.

The motor component of the trigeminal nerve (V3) supplies the muscles of mastication. The largest of these include the temporalis and masseter muscles.

Examination Technique:

• palpate the temporalis and masseter muscles on either side when the patient clenches their teeth.
• ask the patient to open their mouth and repeat this against resistance. Observe for any deviation of the jaw to one side.
• with their mouth open, ask the patient to protrude their jaw to either side against resistance.
• the jaw-jerk reflex is elicited by the examiner placing their index finger over the middle of the patient’s chin with the mouth slightly open and the jaw relaxed. The index finger is then tapped with a reflex hammer, delivering a downward stroke. The afferent impulse for this reflex is the sensory portion of the trigeminal nerve. The efferent limb is through the motor (V3) branch of the trigeminal nerve.

Normal Response:

• the jaw should not deviate to either side.
• the jaw-jerk is usually absent or weakly present.

Abnormal Response:

• the jaw deviates towards the side of weakness.
• the jaw-jerk is exaggerated and pathologically brisk with lesions affecting the pyramidal pathways above the 5th nerve motor nucleus, especially if the lesions are bilateral.

The 5th cranial nerve, trigeminal, consists of three sensory (V1, V2 and V3) and a motor component, V3.

Sensation is tested to light touch with a cotton wisp, temperature with a cold tuning fork and pain with a disposable pin. If the patient complains of sensory symptoms, it is advisable to perform side to side comparisons moving from the impaired side to the normal side.

Examination Technique:

touch a cotton wisp to the forehead, cheek and chin (avoid the angle of the jaw which is innervated by upper cervical roots)

The corneal reflex allows an objective assessment of facial sensation. The afferent limb is V1 of the trigeminal nerve, the efferent limb is the facial or 7th cranial nerve.

Examination Technique:

• explain to the patient what you will be doing.
• avoid a visual threat response by asking the patient to look up and to the opposite side.
• stimulate the cornea since the scleral conjunctiva is less sensitive.
• touch the cornea lightly with a wisp of cotton, observe the direct (same) eye and consensual (opposite eye) blink in response to corneal stimulation.
• repeat on the opposite side.

A. Peripheral visual field
(a) wiggling fingers
(b) counting fingers
(c) white pin

B. Central visual field
(a) red pin

Examination Technique:

• visual fields are assessed by confrontation , i.e. the examiner compares the patient’s visual field to their own and assumes that theirs is normal.
• first test each eye separately.
• test both eyes together with wiggling fingers.
• the examiner places himself approximately 1 meter away from the patient and advises the patient to look directly at the examiner’s eye for monocular testing or nose for binocular testing. The test object (either a wiggling finger, one or two fingers, or a white pin head) is presented equidistant from the patient’s and examiner’s eye and the patient is asked either to state the number of fingers or say “yes” when they first see a moving target.
• for central vision (the 20 degrees on either side of the vertical meridian) a red pin is used. The patient is instructed to state when they see the pin as red. A red pin is also used to map the blind spot. Vision in the center of the visual field is more detailed than in the peripheral areas. This is because of both the structure of the retina and the connections of its neurons. Light rays from the center of the visual field are focused on the macula in the center of the retina. In the macula, the proportion of cones to rods is high. Cones are important for color vision.

Normal Response:
the normal peripheral monocular visual field extends approximately 90 degrees temporally, 60 degrees nasally, 60 degrees superiorly and 75 degrees inferiorly. It is divided into nasal and temporal halves and superior and inferior altitudinal halves. The normal central visual field extends approximately 30 degrees on all sides of central fixation. The blind spot is located 15 degrees temporal to fixation just below the horizontal meridian. It corresponds to the optic disc.