Types of Hearing Loss

What is Hearing Loss ?

Hearing loss is the inability to hear partially or totally in one or both ears. Generally, sound is indicated by 'frequency' and 'intensity'. In 'frequency', our ears can normally hear between 20 to 20,000 Hertz. When hearing threshold or the least hearing ability of a person is over 25 dB (decibel), then it can be termed as hearing loss or impairment. Hearing loss treatment involves diagnosis of the type and degree of hearing loss and based on the type and degree of hearing loss the treatment would be either medical or rehabilitative.

Hearing Loss: Facts & Figures

- Approximately, 33% of the world's population above 65 years are affected by significant hearing loss
- In urban and rural India, the prevalence of hearing problem at 60 years of age are about 62% and 56%, respectively
- In India, Hearing Loss has been identified as the topmost cause of sensory deficit
- Every year 7% children are born with hearing disability

Causes of Hearing Loss

We are regularly exposed to various types of sounds, which are surfacing every now and then. Hearing loss or problem can occur from one or multiple reasons; the most common factors as well as specific causes leading to hearing loss among adults and children are:

In Children:
- Genetic Causes
- Prematurity
- Infections
- Drugs

In Adults:
- Noise Induced
- Ototoxic Drug
- Immune Diseases
- Hereditary
- Physical Trauma
- Presbycusis (ageing)

Types of Hearing Loss

Hearing loss can be categorised based on where or what part of the auditory system is damaged. There are four types of hearing loss: conductive hearing loss, sensorineural hearing loss, mixed hearing loss and central hearing impairment.

1. Conductive Hearing Loss

Conductive hearing loss occurs when sound is not conducted efficiently through the outer and middle ears, including the ear canal, eardrum, and the small bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound level, or the ability to hear soft sounds. This type of hearing loss can often be corrected through medicine or surgery.

Presence of fluid in the ear associated with colds, allergies, ear infections (otitis media); or a poorly functioning Eustachian tube are common causes of conductive hearing loss. Other common causes of this hearing loss include a build-up of wax in the ear canal, perforated eardrum, or damaged or defective ossicles.

2. Sensorineural Hearing Loss

Sensorineural hearing loss is the most common type of hearing loss. More than 90 percent of all hearing aid wearers have sensorineural hearing loss. This can occur in one of two ways. The first is when the delicate hearing cells (hair cells) in the inner ear are damaged, and they become unable to convert sound vibrations into the electrical signals needed by the auditory nerve. Secondly, when nerve pathways in the auditory nerve itself become damaged, preventing the signals from reaching the brain.

Sensorineural hearing loss not only involves a reduction in sound level, or ability to hear soft sounds, but also affects the ability to hear and understand speech clearly.

Although this damage can be caused by exposure to loud noise – through working in a noisy environment for too long – the primary cause of sensorineural hearing loss in adults is ageing. Sensorineural hearing loss is a permanent loss and cannot be corrected medically or surgically.

3. Mixed Hearing Loss

Sometimes a sensorineural hearing loss may occur in combination with a conductive hearing loss. In other words there may be damage in the outer or middle ear and the inner ear or auditory nerve. If this happens, the hearing loss is referred to as a mixed hearing loss.

4. Central Hearing Impairment

Central hearing impairment occurs when auditory centers of the brain are affected by injury, tumor, disease, heredity or unknown causes. Central hearing impairment does not necessarily involve (although it may) hearing loss. Central hearing impairment involves auditory discrimination, sound localisation, auditory pattern recognition, the temporal aspects of sounds, and the ability to deal with degraded and competing acoustic signals.