Weber and Rinne Tests
Weber test
A vibrating 512 Hz tuning fork is placed centrally on the forehead and the patient is asked where they can hear the sound:
- A normal result is that it is heard equally as loudly on both sides
- Conductive hearing loss – louder on the side of the abnormal ear
- Sensorineural hearing loss – quieter on the side of the abnormal ear
Rinne test
A vibrating 512 Hz tuning fork is placed on the mastoid process and the patient is asked if they can hear the sound. While still vibrating, the tuning fork is placed in front of the ear canal:
Normal result: air conduction is louder than bone conduction (Rinne positive)
Abnormal result: bone conduction is louder than air conduction (Rinne negative)
Interpretation
- Normal result:
- Rinne result: air conduction is louder than bone conduction bilaterally
- Weber result: sound heard equally as loud on both sides
- Conductive hearing loss:
- Rinne result: bone conduction is louder than air conduction in the affected ear and air conduction is louder than bone conduction in the unaffected ear
- Weber result: louder on the side of the affected ear
- Sensorineural hearing loss:
- Rinne result: air conduction is louder than bone conduction bilaterally
- Weber result: louder on the side of the unaffected ear
Audiometry
Overview
Pure tone audiometry involves listening to different frequencies of sounds at different volumes and pressing a button when the sound is heard. It is used to assess the degree of hearing loss.
They produce audiograms which are graphs that show the results of audiometry. In general:
- Anything >20 dB is normal
- In conductive hearing loss, bone conduction is higher than air conduction
- In sensorineural hearing loss, bone air and bone conduction are lower than the 20 dB line
- In mixed hearing loss, bone and air conduction are below the 20 dB line, but air conduction is lower than bone
Hearing Tests in Infants and Children
Visual reinforcement audiometry
Visual reinforcement audiometry (VRA) is generally done in children aged 6 months to 2.5 years old. Sounds are played and when the child turns to the sound they are rewarded with a flashing toy or moving image. Once the child associates the sound and visual reward, the volume and pitch of the sound are varied to test the child’s hearing.
Play audiometry
Play audiometry is performed in children aged 1.5 to 5 years old. During the test, sounds are played and the child is asked to perform a simple task when they hear the sound. Usually, this involves putting a ball in a bucket. The volume and pitch of the sound are changed to test the child’s hearing.
Bone conduction test
In addition to the above tests, a small vibrating device is placed behind the ear. This device passes sound directly to the inner ear through the bones in the head and can identify which part of the ear is not functioning properly.
Tympanometry
Overview
Tympanometry is not a test of hearing but measures the compliance (flexibility) of the tympanic membrane. A soft rubber tube is placed at the entrance of the ear and air is blown into the ear. Some of the sound is reflected which is detected and plotted on a chart known as a tympanogram.
Caloric Reflex Test
Overview
The caloric reflex test tests the vestibulo-ocular reflex (VOR). This is the reflex that keeps our gaze focused on an object when we turn our heads. If you turn your head to the right while reading this text, your eyes move to the left so that you can keep reading this text clearly. Turning your head to one side increases the activity of the ipsilateral semicircular canal.
Method
Cold or warm water is placed into the external auditory canal:
Cold water causes the eyes to turn to the ipsilateral ear and causes horizontal nystagmus to the contralateral ear
Warm water causes the eyes to turn to the contralateral ear and causes horizontal nystagmus to the ipsilateral ear.
- Warm water increases the temperature of the fluid in the horizontal canal, causing it to expand in volume and rise, mimicking a turn of the head to the ipsilateral side
An absence of reactive eye movements suggests impaired vestibular function (specifically the horizontal semicircular canal) on the side being stimulated.
- Cold water decreases the temperature of the fluid in the horizontal canal, causing it to decrease in volume and fall, mimicking a turn of the head to the contralateral side
This can be remembered with the COWS mnemonic: Cold water = nystagmus to the Opposite side, Warm water = nystagmus to the Same side.
