Tuning Fork Tests
What are they?
1. These are a bedside assessment of hearing
2. They differentiate conductive (middle or outer ear) deafness from sensorineural
(inner ear or cochlear nerve) deafness
3. They don’t accurately assess hearing thresholds
4. They have inherent errors
When to do them
Following history and otoscopy
When an audiogram is not easily available e.g. in general practice or immediately postoperatively
To confirm that the audiogram is correct
Strike the fork correctly to get a loud ring. The lateral condyle of the femur is good or you can use the olecranon. Do not use a table, chair or your shoe!
Use a heavy fork at 512Hz
For bone conduction press against the patient firmly. This requires counter pressure. For air conduction place the fork 2.5 cm from the EAM (tines parallel with canal). Explain what you want them to do.
Routes of sound into the cochlea
AC - Air conduction: via canal, eardrum and ossicles (the amplifiers)
BC - Bone conduction: direct vibration of the inner ear fluids (misses the amplifiers)
Two common tuning fork tests
There are two common tuning fork tests: Weber and Rinne.
Weber’s test is normally heard in the midline. If it is heard on either side instead this implies a deafness of some type in one ear more than in the other.
Rinne’s test normally shows air conduction to be greater than bone conduction because air conduction goes through the middle ear amplifier. If bone conduction is better than air conduction there is a conductive hearing loss present.
This is a test of symmetry. Press firmly in midline of the forehead.
Ask patient where they hear it loudest: left, right or centre
Patient hears it laterally when asymmetry of hearing exists
Weber towards the deaf ear – conductive loss
Weber away from the deaf ear – sensorineural loss
The line drawings represent a patient who says that they have deafness in the left ear.
Patients only identify the correct ear 75% of the time, and its not so good if there is deafness on both sides.
This test compares the sound of a tuning fork when placed beside the ear and when pressed behind the ear. In the first situation sound is travelling through the air and the ear amplifiers.
In the second it is passing directly to the cochlea without going through the amplifiers. The test should be explained to the patient first.
Ask the patient which is louder. Is it the sound heard behind the ear or the other sound? The patient should hear the air conduction sound louder because of the amplifier.
We abbreviate the results when we write them down so the results are either shown as:
AC>BC if air conduction was heard better than bone. This is also called Rinne +
BC>AC if bone conduction was heard better than air. This is also called Rinne –
AC=BC if the two were the same
The test is done by putting a ringing, 512Hz, heavy based tuning fork 2.5 cm from the patient’s external ear canal with the tines parallel to the ear canal and then moving the fork behind the ear and pressing against the skull.
You may, if you prefer, place the fork behind the ear first and bring it quickly to the side of the ear second.
The patient tells you which is louder.
In conductive hearing loss bone conduction will be louder than air conduction - the fork will sound louder when it is pressed against the skull than it will beside the ear.
BC>AC or Rinne's Negative
In sensory hearing loss the fork will sound louder beside the ear than it does behind the ear.
AC>BC or Rinne's Positive
N.B. A positive Rinne's is a normal Rinne's
Weber tests symmetry. If it lateralizes, one of the ears has greater deafness than the other.
Rinne tests whether an ear has conductive or sensory deafness.
Weber to right
Rinne -ve right or BC>AC
Rinne +ve left or AC>BC
Weber lateralizes to the right. This means that there is either a conductive deafness in the right ear or a sensory deafness in the left ear.
Rinne shows us that there is a conductive loss in the right ear because it is negative on that side.
Right conductive loss e.g. cholesteatoma, perforation, glue ear
Weber to right
Rinne +ve right or AC>BC
Rinne +ve left or AC>BC
Weber lateralizes to the right which means that there is either a conductive loss on the right or a sensory loss on the left.
Rinnes are both normal. In other words, the middle ear amplifier is working normally on both sides. The patient therefore has a left sensory deafness.
Left sensory deafness e.g. acoustic neuroma, labyrinthitis, head trauma
Why not test yourself in the quiz section on Tuning forks.