Types of Hearing Loss
Hearing loss/impairment is a silent and exhausting condition which affects over 278 million people all over the world. Hearing loss varies from mild to total hearing loss. Many people in the world live with the hearing loss either without knowing that they have it, or by accepting it and do not seek any treatment. Hearing losses can be defined under following three categories:
Conductive Hearing losses
Conductive hearing loss happens when there is difficulty passing sound waves through outer ear, eardrums (tympanic membrane) or Middle ear (Ossicles).
This is usually caused due to blockage (excess ear wax build-up/deposits or any residual fluid due to ear infection) in the outer or middle ear. Ear infection fluid is more prevalent in children. Conductive hearing loss can also happen due to some irregularity in the structure of the ear (outer ear, middle ear or ear canal). A perforated eardrum can also cause conductive hearing loss.
Otosclerosis (which causes irregular growth of bone in the middle ear) can also cause serious conductive hearing loss. The excessive bone in the middle ear prevents the ossicles from moving freely.
Conductive hearing loss results in making the sounds quieter (usually the sound is not distorted in conductive hearing loss). A conductive hearing loss can either be temporary or permanent depending on its cause.
Most of the time, conductive hearing loss can often be treated with medical care, or a minor surgery. Some possible causes of conductive hearing loss are:
- Residual fluid due to influenza/cold
- Residual fluid due to infection
- Poor function of auditory tube
- Ruptured eardrum
- Extra earwax
- External object in ear
- Irregular structure of the ear
Sensorineural Hearing losses (SSHL)
SNHL occurs due to problems in the inner ear, vestibulocochlear nerve (8th cranial nerve) or in the brain. SNHL hearing loss can range from mild to total deafness.
SNHL is also referred to as sensory, cochlear, neural or inner ear hearing loss/impairment.
A permanent SNHL is caused by damage of the hair cells inside the cochlea or the hearing nerve. Damage to the cochlea is age related and is happens naturally at old age (hearing loss due to old age is also called presbycusis). In addition to old age, SSHL can also be caused due to other factors, such as:
- Exposure to loud sounds
- Ototoxic drugs
- Certain diseases like Rubella
- Complications at the time of birth
- Head injury
- Benign tumours on the vestibulocochlear nerve
- Genetic – some people are more likely to have hearing loss.
Unlike conductive hearing loss which only make sounds quieter and not distorted, SNHL also reduces the quality of the sound that is heard (in addition to making it quieter). People with SNHL often struggle to understand speech. There is no cure for the damage of hair cells in cochlea, this makes SNHL irreversible and it cannot be treated at present times.
Mixed Hearing losses
A mixed hearing loss occurs when there are simultaneous problems in the outer/middle ear (conductive pathway) and in the inner ear (nerve pathway). In other words, there is problem with both sensorineural hearing loss and conductive hearing loss, which are defined above.
An example of a mixed hearing loss is sensorineural hearing loss caused by loud noise exposure and conductive loss caused by a ruptured eardrum. As explained in the sections above, conductive hearing loss may be treated, but sensorineural hearing loss is most likely to be permanent.
Hearing aids can be used for mixed hearing loss, but it should be checked if there is an active underlying cause (ear infection, influenza etc.) for the hearing loss. The cause of mixed hearing loss/impairment are same as those of sensorineural hearing loss and conductive hearing loss as described above.