What is Hearing loss (Hypoacusis)?

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Hearing loss or hypoacusis is defined as a functional deficit that arises when a person loses some degree of their auditory capacity. It could occur unilaterally, when it only affects one ear, or bilaterally, when it affects both ears.

Types of Hearing Loss

Hearing loss is classified according to the degree of loss (quantitative classification), the location of the damage causing the deficit (topographic classification) and the age at onset of the loss (chronological classification).

  • Quantitative classification. Considering the repercussions of the impairment and the level of hearing loss, it can be classed as:
    • Mild. Hearing threshold below 30 dB
    • Moderate. Hearing threshold between 30–50 dB
    • Severe. Hearing threshold between 50–80 dB
    • Profound. Hearing threshold between 80–95 dB
    • Cophosis or anacusis (total loss). Hearing threshold above 95 dB

*Note: The threshold at different frequencies must be considered before allocating a patient to a quantitative classification, as they may suffer a different degree of loss in each frequency range.

  • Topographic classification. Depending on the location of the lesion causing the problem, hearing loss can be classified as:
    • Conductive hearing loss. This is related to a problem with the mechanical portion of the ear (the outer and middle ear), in other words, because of damage to structures that conduct sound waves.
    • Sensorineural or perceptive hearing loss. When the damage is in the inner ear, that is, a lesion affecting the organ of Corti (the cochlea), the acoustic pathways or the auditory cerebral cortex.
    • Mixed hearing loss. This is the case of hearing loss caused by different, coexisting lesions that simultaneously affect several or all auditory structures. It can be defined as a combination of conductive and sensorineural hearing loss.
  • Chronological classification. This classification is based on the age of onset:
    • Genetic or hereditary. Transmitted through a defective gene. These cases can be early-onset hearing loss if they are present from birth or late-onset when the impairment develops throughout the patient’s lifetime.
    • Acquired. Induced by unforeseen pathogenic causes. These cases can be prenatal, due to a pathogenic agent that affects the mother during the embryonic stage, perinatal, which is when damage occurs during childbirth, or postnatal, when the structures get damaged at some point during the patient’s lifetime.
    • With respect to language acquisition. There are two types: prelingual deafness, which corresponds to hearing loss before the development of spoken language; and postlingual deafness, in the case of hearing loss that arises after language has been developed.

The WHO affirms that 900 million people will have hearing loss in 2050.

How many people are affected by Hearing loss?

Estimations suggest 360 million people worldwide live with a level of hearing loss that results in impairment (moderate hearing loss), wherein 91% of cases are adults and 56% are men. This corresponds to 5.3% of the world’s population. However, it is estimated that up to 15% of the global adult population has at least some degree of hearing loss. This percentage is much higher amongst people aged over 65, where as many as a third of the population has hearing loss. This figure is particularly interesting when we consider that, globally, the number of people aged 65 or over will grow between 18% and 50% between 2010 and 2020.

To date, the only reference concerning the demographics of hearing loss in Spain stems from a survey by the National Institute of Statistics (INE Survey, 2000), which cited a figure of around 1 million people with impaired hearing.

Substantiated information by:

Ignacio Berdejo Gago
Miguel Caballero Borrego

Published: 18 May 2018
Updated: 18 May 2018

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