Impaired hearing and deafness

What are impaired hearing and deafness?

The WHO definition of hearing impairment is a hearing loss of more than 25 dB in the best ear. The international consensus is that the average loss should be calculated for the frequencies 1, 2 and 4 kHz.

The categories for levels of hearing impairment are:

The International Classification of Diseases (ICD) classifies hearing disorders by cause. This classification makes a distinction between, among others:

1. Conductive hearing loss: the sound is not conducted properly through the ear canal and/or the middle ear
2. Sensorineural hearing loss: the problem in this case is located in the inner ear (the cochlea).

A conductive hearing loss means that sound cannot reach the inner ear properly, for example due to earwax build-up or an infection in the ear. Hearing losses of this kind may also be caused by problems with the eardrum or the ossicles (the small bones in the inner ear).

Sensorineural hearing loss is usually associated with a condition in the inner ear such as hair cells that fail to function properly. There may also be a problem with the auditory nerve or with the transfer of signals from the hair cells to the auditory nerve.

What are the complaints associated with impaired hearing and deafness?

• Mild: hearing loss noted by the person in question in a noisy setting;
• Moderate: hearing loss that is also a problem for the person concerned in a quiet setting;
• Severe: hearing loss that can only be partially compensated with a hearing aid;
• Very severe/deafness: a hearing loss that is so severe that, even with amplification, the person in question cannot communicate using sound. Additional information is required to communicate such as visual information in the form of visual expressions, lipreading, gestures and body language or tactile information (touch).

Due to the different functions involved with hearing and the associated organs, impaired hearing can have a range of consequences. Somebody with a hearing impairment can face limitations in five different areas: detecting sounds, recognising and discriminating between sounds, understanding speech in a quiet setting, understanding speech in noisy settings and locating sounds.

In addition, many people with hearing impairments are hypersensitive to day-to-day sounds (hyperacusis) such as people's voices or the noise of cups and dishes with cutlery. Finally, tinnitus (ringing in the ears) and problems with balance are common complaints in people with impaired hearing.

Problems with hearing in early childhood can interfere with the development of speech and language with, as additional consequences, the limited or delayed development of knowledge, problems in socio-emotional development and limited participation in society. ²⁰¹

Numerous studies have demonstrated the link between hearing impairment and loneliness, depression and a reduced social network. ²⁰²

People with intellectual disabilities sometimes find it impossible to communicate these symptoms. The people around them may then notice only a change in behaviour.

How common are impaired hearing and deafness in the general population?

Impaired hearing is a common condition in the general population. A survey conducted in 2010 found that almost 2 million people in the Netherlands had hearing problems. The one-year prevalence of hearing impairment in general practice is approximately 4% (for all age groups combined) and it increases significantly with age. In the age group of 65 to 74 years, one-year prevalence was found to be 11.2%, rising to 24.5% in people aged 75 and older. Hearing impairment is more common in men than in women and the course is also more progressive in men. ⁵¹¹

Deafness alone is estimated to occur in 0.07% (7 per 10,000) of the population. ²⁰¹

The estimated rate in US literature is between 0.05% and 0.1%. ²⁰⁴

How common are impaired hearing and deafness in people with intellectual disabilities?

A major Dutch epidemiological study of 1598 adults with intellectual disabilities found hearing impairment in 30%. ²⁰³ In almost half of the cases, the persons themselves and/or their carers were unaware at the beginning of the study that they had any hearing impairment. Hearing impairment was more common in people with Down syndrome (57%) than in people without (24%). People with Down syndrome developed an age-related hearing impairment ten years earlier than people in the general population. The prevalence of hearing impairments hardly increases at all with the severity of intellectual disability. In people with intellectual disabilities, the ratio of mild hearing impairment to severe impairment is 1:1.
An Australian questionnaire survey of 2540 people with intellectual disabilities (in which questionnaires were answered by carers and parents) found that 24% of the study sample had a history of hearing problems. ²⁰⁵

No reliable figures have been found about deafness alone in people with intellectual disabilities.
It is reasonable to expect that deafness (like hearing impairment) may be more prevalent than in the general population owing to the combination of deafness and intellectual disabilities in certain syndromes and perinatal infections.