Tests for Diagnosing Hearing Loss

Sound has two components:

1. Volume
2. Frequency.

Volume or loudness or amplitude is measured in decibels (dB).

Frequency is measured in Hertz (Hz). Usually, a male’s voice is high in volume and low in frequency, while a female’s voice is high in frequency.

Speech has another characteristic – rhythm, which is not measurable, but clearly noticeable. Hearing tests measure a person’s ability to hear sounds and aids in identifying hearing loss.

Tests for Diagnosing Hearing Loss

A. Tests for children aged 6 months or above:

Outer Ear Tests
These tests give information about at what decibel level and at which frequency the baby is able to hear, and whether there is any problem with the outer ear or the middle ear.

i. Pure Tone Audiometry:
In this test, the baby is made to wear headphones. Sounds with different combinations of volumes and frequencies are then presented, in a soundproof environment, and the baby’s responses are recorded on an audiogram. Visual Reinforcement Audiometry (VRA) or Speech Test and Conditioned Play Audiometry (CPA) are Pure Tone Audiometry tests for children in the age group of 6 months to 5 years. This is done by indulging the child in playful activities and recording the responses of the child to sounds made to them.

ii. Bone Conduction Audiometry:
An oscillator is placed either on the forehead or on the bone behind the ear. The oscillator sends pure tone sounds to cochlea directly (not through outer and inner ear) by vibration of the bone of the skull. Tuning Fork Test is to assess bone conduction and the ability to hear by vibration of bones in the skull. Tuning Fork is a metallic device with two prongs. It produces sound when it vibrates. It is an initial diagnostic tool to decide about further testing for assessment of hearing.

Middle Ear Tests
Impedance audiometry is a method to test the resistance of the middle ear to allow the sound to pass through to the inner ear. It is done placing a probe till the ear canal.
Tympanogram helps in knowing the presence of any fluid or pressure in the middle ear or any hole in the ear drum. Middle Ear Muscle Reflex (MEMR) helps in recording the responses to loud sounds.

Tests for Diagnosing Hearing Loss

B. Tests for children of 6 months and below: Inner Ear Test: Oto Acoustic Emissions (OAE) is an important test conducted on new-born babies to assess hearing. This test is done to assess the functioning of the cochlea and is usually performed while a baby is sleeping. A sensitive probe (microphone) is placed in the inner ear canal and is used to emit low-volume sounds into the ear. The sounds reach cochlea which then responds by producing an emission called otoacoustic emission, also referred to as “echo”. This echo travels back through the middle ear, into the ear canal, and is analyzed by the screening unit. The strength of the echo is recorded to assess the possibility of hearing loss. This is an initial diagnostic tool and is done in association with a brain test called ABR/BERA.

Brain Test:
Auditory Brainstem Response (ABR) or Brain Auditory Evoked Response (BAER) or Brainstem Evoked Response Audiometry (BERA) is the best test to assess hearing loss in babies from birth to 6 months of age. In this test, the baby is first put to sleep. Earphones are put on the baby. Electrodes are placed on forehead and a few other places. Sounds at different volumes and frequencies are played. The auditory nerve from cochlea carries these sound signals to the brain. The computer connected to the electrodes records this in the form of wave (brain waves). Interpretation of the activity of brain waves is done to assess the hearing of the baby.

OAE and BERA are mandatory in the USA, UK and many developed countries and all new-born babies have to undergo these tests (new-born hearing screening) before they leave hospital after birth.
These can be administered to children older than 6 months too.