In adults of employable age, the impact of hearing loss on potential employment, quality of life and general function is much higher than has been commonly realised, and is equivalent to the disability burden of many health conditions recognised as national health priorities.5 For example, in terms of disability burden, mild hearing loss is comparable with mild asthma; moderate hearing loss is comparable with severe pain related to degenerative spinal disease (such as a slipped disc); and severe hearing loss is comparable with pneumonia or severe diabetes associated with visual failure.
Hearing loss and cognitive decline
Recognition of the association between hearing loss and cognitive decline is increasing. A longitudinal study of hearing changes and cognition over decades in the same population indicates a very strong correlation and a possible causative association.6,7 Hearing loss may place an additional load on the mental resources of a vulnerable brain such that the person with hearing loss has to work harder to decode and process sounds. This additional load may mean that there are reduced resources for memory and other cognitive functions, leading to brain changes presenting as dementia. Up to 9% of the global burden of dementia is linked to hearing changes of varying degree (https://www.thelancet.com/infographics/dementia2017).6 Whether the treatment of hearing loss will halt the progression of, or perhaps reverse, dementia is still being investigated.
How a cochlear implant works
A cochlear implant is an electronic prosthesis that works by bypassing the residual damaged hearing elements within the organ of Corti and directly stimulating the intact nerve endings in the auditory nerve. The device has two components:
- a fully implanted intracochlear electrode attached to a receiver stimulator package, which is inserted during cochlear implant surgery (Figure 5)
- an external speech processor unit that sits behind the ear and looks like a sophisticated hearing aid (Figure 6).
Both components are required for the cochlear implant system to function properly. The microphone within the speech processor unit captures speech and environmental sounds (Figure 6). The sounds are then processed within the electronic package to a series of electrical pulses and transmitted wirelessly to the internal receiver–stimulator unit. The internal unit then further processes the signals and sends them down the multiple channels of the intra-cochlear electrode array (Figure 5), which in turn stimulates the intact auditory nerve endings. These intact auditory nerves carry electrical signals through the higher pathways and eventually the auditory cortex where they are perceived as speech and sound sensations.