Hearing Tests for Adults
Voice tests and tuning fork tests are easily carried out in a doctor’s office with little or no equipment.
A good idea of how well a patient hears can be established through simple observation – can he/she hear normal conversational voice or do you have to raise your voice to make yourself clear? If a patient is deaf, you need to know roughly how much and what type (conductive, sensorineural or mixed) of hearing loss he/she has. Simple voice/whisper tests can be conducted for a crude assessment of hearing level.
Tuning fork tests
Tuning fork tests can help with lateralising deafness and with deciding which type of hearing loss is present.
TIPS FOR TUNING FORK TESTS
- Use a 512-KHz fork with a good heavy base.
- If the hearing is equal in both ears, the Weber test will not lateralise to one side (i.e. the patient will hear the sound in the middle).
- If the Weber is to one side, this can indicate that the other side has little or no hearing, or that there is a conductive deafness on the side the patient identifies as better. Try it yourself – put your finger firmly in the external canal of your own ear and place the tuning fork on your head; you should hear it louder on the side you have blocked as you have given yourself a mild conductive hearing loss.
- The Rinne test is negative if the patient hears the sound better by bone conduction. Usually this means there is a conductive loss on that side.
- Be careful interpreting the Rinne test if the patient has profound hearing loss on one side. A Rinne negative may be because he/ she hears sound transmitted across the head from a good ear – false negative Rinne. Masking of the good ear with a noise box helps overcome this problem.
- Tuning fork tests are quick and easy but skilled audiometry is essential to assess and classify deafness.
Pure Tone Audiometry
Voice tests and tuning fork tests are helpful, but fairly crude. Formal testing is required for an accurate assessment of hearing levels. For adults and older children who can co-operate (age 4 years upwards), this is best done by pure tone audiometry (PTA).
Evoked Response Audiometry
PTA needs the patient’s co-operation and is therefore a subjective test. To test the hearing objectively a stimulus is presented to the ear and the resultant changes in electrical activity in the nervous system can be measured. These techniques, evoked or electrical response audiometry (ERA), are widely used in children and in disputed cases in adults.
Electrical signals are generated by the normal inner ear in response to a sound. These are referred to as ‘otoacoustic emissions’ (OAE) and are used as a screening test for hearing in newborn children. OAEs will be absent if the child is deaf.
Hearing tests in children
PTA can be very difficult in young children (under 4 years) or in older children and adults with learning difficulties. A skilled tester can use various behavioural audiometry techniques to obtain an accurate assessment of the child’s hearing.
Tympanometry relies on a device that puffs a small current of air into the ear and measures the degree of ‘distensibility’ of the eardrum and middle ear. A normal trace with a peak suggests that the drum is intact and there is air under normal pressure. A ‘flat’ tympanogram is typical of a middle ear effusion/glue ear.