Chapter 1 10 Hearing loss With a prevalence estimate of 1.3 billion adults worldwide, hearing loss is the most common sensory impairment in humans (Ciorba et al., 2012; James et al., 2018). Hearing loss can be related to the anatomy and physiology of the ear, but it can also affect the hearing function, functioning in everyday activities, and participation in life situations (Dillon, 2008). Therefore, hearing can be considered to be a sociocultural phenomenon, rather than an isolated medical problem (Danermark et al., 2013; Granberg et al., 2014). Anatomy and physiology The term hearing loss is used to describe an impairment of one or both ears that results in hearing difficulties. Depending on where the impairment is located, three types of hearing loss can be distinguished: conductive, sensorineural, and mixed hearing loss (Michels et al., 2019). Conductive hearing loss results from a disruption in the ear canal and/or the middle ear, causing sounds to be conducted inefficiently to the inner ear. Possible causes are obstruction of the ear canal – for example by cerumen – or middle ear diseases, such as otitis media. The more common type of hearing loss, sensorineural hearing loss, involves a distorted conversion of sounds in the inner ear and/or the auditory nerve and is most often caused by ageing or by excessive noise exposure (Rabinowitz, 2000). If conductive and sensorineural hearing loss occur in combination it is called mixed hearing loss. Hearing loss can be related to tinnitus or hyperacusis, ear disorders that may share their pathophysiology with that of hearing loss (Nelson & Chen, 2004). One of the possible explanations is that sensorineural hearing loss causes the brain to receive an incongruous neuralmessage. As a reaction, the brainmay ‘turnup the volume’ resulting in either everyday sounds being perceived too loud, even painfully so (hyperacusis) or a persistent perception of a sound that has no external source (tinnitus) (Baguley et al., 2013; Sheldrake et al., 2015). Although most individuals with hyperacusis or tinnitus also suffer from hearing loss, hyperacusis and tinnitus can also occur in isolation. Hearing function For both conductive and sensorineural hearing loss, reduced sensitivity of sounds is the most obvious symptom, requiring soft sounds to be louder to be heard.
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