Hearing Loss refers to a decrease in a person’s sensitivity to sound.
Where does it occurs?
A hearing loss can occur anywhere in the auditory system.
This common category of hearing loss is a condition of the outer and/or middle ear. It occurs when sounds from the outside world cannot be transmitted normally through the ear canal and/or middle ear to the inner ear.
Causes of conductive hearing loss include excess cerumen (wax), foreign bodies in the ear canal, and malformations and diseases of the outer ear and middle ear structures. The most common cause of conductive hearing loss (primarily in children) is otitis media, a form of ear infection where fluid is secreted into the middle ear, sometimes called glue ear.
Cochlea damage is the most common form of hearing impairment and the type associated with uncomfortable loudness and distortion of sound.
The deterioration in hearing occurs in the inner ear mainly because of damage to the hair cells in the cochlea. Most often the hair cells become unable to respond to the sound and the process of converting sound vibration into electrical signals needed by the hearing nerve is impeded. This has the effect of increasing thresholds and reducing the clarity of sounds.
The extent of damage and the type of hair cells destroyed will determine the degree of hearing loss. As a basic rule, the smaller the number of hair cells damaged the lower the hearing loss.
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Although this type of hearing loss can be caused by a variety of reasons, such as, heredity, disease ( e.g. Menières), infection, acoustic trauma (e.g. noise exposure), ageing (presbyacusis).
There are other less common causes of hearing loss (e.g. neural and central) that will not be discussed here.
Hearing loss may occur in both ears known as bilateral hearing loss or in only one ear referred to as unilateral hearing loss.
Hearing may be similar for both ears referred to as symmetrical or it may differ between the two ears, asymmetrical.
When does it happen? Hearing loss can be either acquired or congenital, pre-lingual or post-lingual.
- Acquired hearing losses occur after birth as a result of disease or trauma and in some cases, ageing.
- When a hearing loss is acquired before the age when children begin to talk, typically 2 ½ years, the loss is classified as pre-lingual.
- Post-lingual hearing losses are acquired after a child has begun to talk, typically after 2 ½ years.
