Assistive Technology: Hearing Products
Original Editors - Lucinda hampton
Top Contributors - Lucinda hampton, Naomi O'Reilly, Kim Jackson and Angeliki Chorti
Introduction[edit | edit source]
Over 5% of the world’s population (430 million people) require rehabilitation to address their ‘disabling’ hearing loss (432 million adults and 34 million children). It is estimated that by 2050 over 700 million people (one in every ten people) will have disabling hearing loss.
- ‘Disabling’ hearing loss refers to hearing loss greater than 35 decibels (dB) in the better hearing ear.
- Nearly 80% of people with disabling hearing loss live in low- and middle-income countries.
- The prevalence of hearing loss increases with age, among those older than 60 years, over 25% are affected by disabling hearing loss.[1]
- Only a fifth of people who would benefit from a hearing aid actually use one. Hearing loss is associated with social isolation and depression, which is suggested to be twice as prevalent in hearing loss. It has also been identified as an independent risk factor for cognitive decline and AD.[2]
Definition[edit | edit source]
Hearing aids, by definition, are sound-amplifying devices that increase the user's ability to detect noise. The components of a non-invasive hearing aid vary widely but broadly consist of a microphone, amplifier, receiver, and battery. The microphone converts external acoustic energy into electrical energy, which is amplified by the amplifier. The receiver detects this and converts it back into acoustic energy, projecting sound into the ear canal. The amplification is driven by the battery, which can be made from zinc-air batteries, mercury, alkaline or rechargeable batteries. A non-invasive hearing aid aims to increase the sound levels delivered to and hence detected by the hair cells in the cochlea.
Function[edit | edit source]
Hearing aids may be indicated in various pathologies that cause sensorineural hearing loss, conductive hearing loss, or single-sided hearing loss.
Selection[edit | edit source]
There are various hearing aids, and their selection is not a ‘one-size fits all’ approach. Selection is influenced by factors that include audiometric deficit (laterality, frequency, and degree of loss), cosmesis, and the patient’s needs, lifestyle, and priorities.
Types [edit | edit source]
Behind the ear (BTE) hearing aids sit behind the pinna. A plastic tube connects the hearing aid to an earmold or ‘open’ silicone ear tip according to the patient's needs. They are commonly used because they are capable of various levels of amplification, and their power and performance can be modified relatively easily.[4] They are robust, cheap, and easier to manipulate for patients with reduced dexterity. Patients who require amplification for moderate to profound hearing losses will require an earmould, which may be less cosmetically appealing than the open fitting option.
The receiver in the canal (RIC) hearing aids are similar to the BTE, except the receiver is located at an ‘open’ silicone earpiece that sits in the canal, rather than inside the hearing aid casing near the microphone and amplifier. This set up allows higher amplification levels without the risk of acoustic feedback (sound escaping the canal and circling back through the hearing aid again), thus more suited to patients with high frequency ski-slope’ hearing losses and those who prioritize cosmetics of the device.
In the ear (ITE), in the canal (ITC), and completely in the canal (CIC), hearing aids are broadly grouped as custom-shape hearing aids. These are the most discrete hearing aids and, therefore, advantageous in a patient population that prefers an improved aesthetic. They can be used in a range of hearing losses, and because the receiver is closer to the eardrum, there is better amplification of high frequencies, important for speech discrimination.[4] This is useful in environments that have a high level of background noise and in patients with presbycusis. However, like RIC and open canal hearing aids, custom-made hearing aids may not be suitable if large amounts of amplification are needed, as they use smaller batteries.
Finally, contralateral routing of signals (CROS) and bilateral contralateral routing of signals (BiCROS) are used for unilateral hearing loss and asymmetrical hearing loss, respectively, in cases where a conventional hearing aid provides little benefit. Here, a microphone is placed on the side of worse hearing, and the signal is transmitted to the better hearing ear, where this signal is amplified.[2]
References [edit | edit source]
see adding references tutorial.
- ↑ WHO Hearing Loss Available:https://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss ( accessed 3.7.2021)
- ↑ 2.0 2.1 Schuster-Bruce J, Gosnell E. Conventional Hearing Aid Indications And Selection. [Updated 2020 Dec 24]. Available: https://www.ncbi.nlm.nih.gov/books/NBK567712/ ( accessed 3.7.2021)
