Types of Hearing loss
Hearing loss is typically described as being conductive, sensorineural, or mixed.
A. Conductive hearing loss refers to an impairment of one’s ability to conduct airborne sound through the middle ear to the inner ear. Scar tissue or otosclerosis, the abnormal growth of bone within the middle ear, can lead to restricted movement of the ossicles. Recently it has been shown that there can also be conductive problems with the basilar membrane of the inner ear that reduce the efficiency of energy transfer to the hair cells.
Some common causes of conductive hearing loss include:
- Blockage in the external canal, e.g. by wax or a foreign body
- Perforation of the tympanic membrane
- Fluid in the middle ear e.g. as a result of infection, or due to blockage of the Eustachian tube (chronic secretory otitis media)
- Damage to the ossicles e.g. due to trauma, otosclerosis
Many of the causes of conductive hearing loss can be corrected by treatment or hearing aids.
B. Sensorineural hearing loss refers to impairment of the sensory unit consisting of the auditory nerve and the hair cells that excite it. Sensorineural hearing loss results from disorders of the cochlea (the cochlea is in the inner ear) or the auditory nerve and its central connections.
Causes of sensorineural hearing loss can be divided into two groups:
i. Congenital deafness
Congenital deafness may present at birth and it is the aim of newborn hearing screening to identify these babies at an early age. Some congenital conditions may not become evident until the child is older.
During the pre and perinatal periods babies are subjected to various factors, which can affect their hearing, for example, infections such as mumps, meningitis, cytomegalovirus and rubella.
ii. Acquired deafness
Similarly in adults other causes include:
- Exposure to sustained or sudden loud noise
- Ménières disease
- Toxic reactions to medication
- Trauma such as a severe head injury
Age related hearing loss (Presbycusis)
It first affects the highest pitches or frequencies. This means that many of the consonants such as the letters “F”, “S” “T” and the sound “SH” are not heard properly. This affects conversation and understanding of what is said on the telephone.
Hearing aids are devices that amplify sounds. They can be used in both conductive and sensorineural hearing loss. Their use usually improves the affected person’s quality of life considerably. However, among people who are profoundly deaf, some may get very limited (or even zero benefit) from hearing aids, but this is not predictable from the audiogram alone. They last 5 years on average.
The hearing aid consists of-:
- A microphone to pick up sound signals
- A battery powered amplifier to amplify sound signals
- A receiver to deliver the amplified sound to the ear canal
Digital aids are programmable to individual hearing requirements. The settings can be controlled to match the hearing loss frequency only, thereby cutting out amplification of background noises. However, the benefit is limited in real life situations. Many digital hearing aids are designed to reduce steady kinds of background noise, such as the rumble of traffic or the whirr of a fan. This can make listening more comfortable, but it does not necessarily enable the user to pick out a single voice from everything else going on, especially when several people are talking at once.
Directional microphone systems amplify sounds that come from the front of the person more than sounds to the side or behind them. This makes it easier for the person to focus on what they want to listen to in a noisy place. The user can switch between directional and all round sound, depending on what they need to hear at the time. Some digital aids will detect where the noise is coming from and automatically adjust to reduce the noise selectively. However, a hearing aid cannot know what the person wants to listen to.
Hearing aids require reasonable care and cleaning and are powered by dry batteries which need replacing from time to time.
Book an appointment with HealthSense Specialist Dr. YT Pang to look at your ENT problems and get cured.