How we hear
The sounds that we hear in the world around us are the result of a complex process events that begins with airborne sound waves entering our outer ear canals. Sound waves occur when the air is mechanically disturbed. Sound is measured by Frequency or pitch. This determines if the sound is a high tone or a low tone. The intensity or loudness of the sound is measured in decibels , dB. These sound waves travelling down the ear canal cause the ear drum or tympanic membrane, to vibrate. These mechanical vibrations are transmitted via the bones in the middle ear cavity to the stapes, through the oval window and in to the cochlea. The cochlea is filled with fluid. The vibrations move the fluid and stimulate thousands of hair cells which line the cochlea. These vibrations are then converted to electrical impulses, sent along the auditory nerve to our brain where we perceive them as sound.
What is hearing loss?
Hearing loss can be present from birth due to genetic or developmental abnormalities, or arise through trauma, disease or loud noise exposure during the lifetime of an individual. The degree of hearing impairment can vary from mild to profound and causes significant social and personal difficulties. It results in communication problems and can lead to depression, confusion and isolation. Recent studies have indicated a connection between untreated hearing loss and dementia.
There are two main types of hearing loss:
Sensorineural Hearing Loss
Sensitive hair cells inside the cochlea, or organ of hearing, are damaged, either naturally through ageing or prolonged noise exposure. Quite often a person suffering with this type of hearing loss will not recognize that they have a problem due to their hearing deteriorating over a very long period of time. Sensorineural hearing loss can also result from ototoxicity. Certain types of medication can have a toxic effect on the cochlea and vestibular system in the inner ear and result in hearing loss.
Common causes include:
- Normal ageing process
- Noise exposure
- Genetic disposition
- Viral infection of the inner ear
- Head injuries
Although a sensorineural hearing loss is irreversible, in the majority of cases the prescription of an appropriate hearing aid can be an important step in helping to establish lost social ties, regaining confidence and regenerating a new lease of life. If you suspect you have a hearing loss, it is important to see a qualified hearing aid audiologist.
Conductive Hearing Loss
When sounds are unable to pass from your outer ear to your inner ear, often as the result of a blockage, such as earwax or a build-up of fluid in the middle ear cavity a hearing loss will result. Head trauma with resulting ossicular chain dislocation, Otosclerosis, or excessive bone growth in the middle can also result in a conductive hearing loss.
Common causes include:
- Earwax build-up
- A common ear infection associated with colds or flu
- A perforation or hole in the eardrum
- Disease of the three middle ear bones
- A birth defect where the ear has not developed properly
- Severe trauma such as a car accident or knock to the head
Once again If you suspect you have a hearing loss, it is important to see a qualified hearing aid audiologist.
Mixed Hearing Loss
Sometimes both types of hearing loss occur at the same time, this is known as a mixed hearing loss. This occurs when someone has a combination of sensorineural and conductive hearing loss. This results in a disruption to the transmission of sound through the outer and middle ear as well as damage to the hair cells in the inner ear.
Common Cause:
- Large Vestibular Aqueduct Syndrome (LVAS) resulting in enlargement of the canal between the inner ear and the cranial cavity.
Hearing loss in adults
Permanent acquired hearing loss of a significant degree affects one in 12 of the adult population in Ireland. In the over 70-age group this rises to some 50%. A quarter of a million adults in Ireland will have a permanent hearing impairment, due mainly to ageing – presbycusis and/or noise exposure – NIHL. This affects their quality of life, communication, social activity and participation to varying degrees.
Hearing loss in children
The total instances at school entry of unilateral (in one ear) and bilateral (in both ears) mild to profound hearing loss is thought to be of the order of 1 to 2 per 1,000; that means between 3,000 to 4,500 preschool and school age children in Ireland will have a permanent hearing impairment, with potential consequences for education, communication, literacy, social and emotional development, and later employability. The Health Service Executive now run the Newborn Hearing Screening Program to identify moderate, severe and profound hearing impairments in newborn babies. Newborns identified with a hearing difficulty have a better chance of developing speech and language skills and of making the most of social and emotional interaction from an early age.
Tinnitus
Tinnitus is the name for the condition whereby people experience or hear sounds which do not have an external origin. The noises may be heard as ringing, buzzing, whistling, roaring, whining, clicking or other variations. One or both ears may be affected.
Tinnitus can result from a number of events and conditions. Exposure to loud noise is a common one; it can also be associated with ageing, head or ear surgery or certain drugs and medication. In some people, tinnitus develops after a cold or flu, an ear infection or a period of severe stress. Temporary tinnitus following a night at a loud party, concert or nightclub is common, but repeated exposure to loud noise and music can result in long-term damage and a resulting hearing difficulty, including permanent tinnitus. In some cases there is no known cause for tinnitus. Tinnitus is not a psychological illness, but it can cause psychological distress and can be debilitating to the suffer in some cases.
A diagnostic hearing test and tinnitus assessment should be the first step in an audiological evaluation of tinnitus, since about 90 percent of tinnitus cases occur with hearing loss. In these cases quite often an appropriate hearing aid prescription, fitting and aural rehabilitation program will help manage the tinnitus. In some cases referral to an Ear Nose and Throat specialists may be recommended for a more in depth investigation into the underlying cause of the tinnitus. Several members of ISHAA specialize in Tinnitus Assessments and they can advise you further. You can search for a hearing aid audiologist near to you in the “ find a hearing aid audiologist” section above.
