Sensorineural Hearing Loss
What is sensorineural hearing loss?
Sensorineural hearing loss is the most common type of hearing loss. It can originate in the inner ear or along the auditory nerve. It frequently occurs in the inner ear (cochlea) when the hair cells are damaged and can no longer transmit neuro-electrical impulses to the brain. Sensorineural hearing loss can be congenital (present at birth) or acquired later in life.
Possible causes of sensorineural hearing loss include the following:
- Hereditary factors
- Viral infections
- Premature birth
- Birth trauma such as anoxia (oxygen deprivation)
- Reactions to ototoxic (poisonous to the hearing system) drugs
- Head injury
- Noise exposure
- Ear infections
- Other diseases
The following audiogram displays a sloping hearing loss from 20 decibels (dB) hearing level (HL) in the low frequencies up to 75 dB HL in the higher frequencies, and (nearly) equal in both ears. Such a hearing loss can usually be countered effectively by conventional hearing aids.
If sensorineural hearing loss in speech relevant frequencies exceeds values of about 80–90 dB HL, it might become difficult to make speech adequately audible. Even though the person suffers from profound hearing loss, extremely loud sounds are just as uncomfortable they would be to a normal hearing person. The challenge here is to fit the complete speech spectrum into the individual’s residual dynamic hearing range. If this range is reduced to 10–20 dB, conventional hearing aids cannot provide sufficient amplification.
In these cases, a cochlear implant (CI) might be the solution. A cochlear implant processes sounds and transforms them directly into electric impulses. The cochlear implant replaces the functionality of the inner ear. The electric impulses directly stimulate the auditory nerve and the auditory process in the brain is thus triggered. But, for the brain to interpret sounds correctly, patients need to have either adequate former listening experiences or should be treated with a CI within the first four years of life.
Even under ideal conditions, patients provided with a cochlear implant need a lot of auditory training and continuous support. However, there is no guarantee that a CI will work to every patient’s satisfaction.