THEaudiometry is an exam which consists in evaluating thehearing, thanks to instruments producing sounds or words that the patient must listen to, detect and sometimes repeat.

There are two types of audiometry:

• Tonal audiometry, which assesses the threshold of sound perception.
• Speech audiometry, which helps determine language comprehension and the ability to discriminate between phonemes.

These two examinations are perfectly complementary.

Audiometry is recommended:

• to screen and assess severity of hearing loss (in children and adults), especially in people exposed to loud noises or who have received certain treatments
• to differentiate the conductive hearing loss (related to damage to the outer ear, such as a cerumen plug or a problem with the eardrum, or the middle ear, such as otitis or injury to the ossicles) sensorineural hearing loss (due to inner ear dysfunction, such as damage to sensory cells or the auditory nerve).

Tonal audiometry is performed in a soundproof booth. The principle is to broadcast pure tones of varying intensity and frequency (from 125 to 8000 Hertz). The patient must press a button as soon as he hears the slightest sound, no matter how small.

Since sound reaches the inner ear through the air (via the eardrum and ossicles) and through the bone, tone audiometry will test both:

• using headphones for air conduction
• by applying a vibration directly to the cranial box using vibrators placed behind the ear for the bone conduction

The results are entered on a curve where the frequencies are on the abscissa and the perceived intensities are on the ordinate.

Speech audiometry complements tonal audiometry. It is also carried out in a soundproof cabin. Via headphones or a loudspeaker, the patient is offered lists of 10 words (one or two syllables) at different intensities, in order to assess his understanding. The patient must repeat them.

The percentage of correctly perceived words makes it possible to establish a curve.

The test makes it possible to describe:

• le intelligibility threshold : intensity from which 50% of the words are understood
• le maximum intelligibility : maximum percentage of words understood
• le percentage of discrimination : percentage of words understood at an intensity of 35 decibels higher than that of intelligibility

Note that these two examinations are subjective, they require the active participation of the patient and cannot be performed in very young children.

The results obtained are entered on a curve called an audiogram.

On a tonal audiogram, the curve reveals the patient’s hearing level compared to so-called normal reference values.

Depending on the results, the doctor will be able to diagnose the type of deafness the patient has:

• conductive hearing loss, if the bone curve is better than the air curve
• sensorineural hearing loss, if the bone and air curves are identical
• or mixed deafness (when it is both at the same time)

He can also determine the level of deafness:

• slight if the loss is between 20 and 40 decibels
• moderate if the loss is between 40 and 70 decibels
• severe if the loss is between 70 and 90 decibels
• deep if the loss is greater than 90 decibels
• or total if no hearing is measurable

On a speech audiogram, a normal curve has an italic S shape. Note that normality corresponds to a score of 100% at an intensity level below 20 decibels.

Depending on the results, the doctor can assess the social consequences of deafness. On a hearing-impaired subject, he will be able to appreciate the usefulness of a hearing aid and direct him towards adequate care.