APPENDIX C: HEARING AID FITTING PROCESS

SCREENING 86 involves identifying early signs of whether a person has hearing loss. In adults, it is usually through self-screening, as many are able to identify if there are suffering from hearing loss. This, however, is not always the case as a stigma associated with hearing loss prevents many people from acknowledging that they have hearing loss. For children under the age of five, there are objective tests such as:

• Otoacoustic Emissions measures the sounds given off in the inner ear when responding to external sound waves (or emissions). The device consists of a small probe that creates sound waves in the patient's ear to measure if hair cells in the inner ear respond to the sound by vibrating. If there is no blockage in the middle or outer ear, then the cochlea (inner ear) may not be functioning properly. If the patient does not respond positively to the otoacoustic emissions test, then they are referred for Auditory Brainstem Respons.
• Auditory Brainstem Response involves the use of non-invasive electrodes that are placed on the patient's head to test whether the brain pathways are working in response to the sounds heard via earphones.

DIAGNOSIS for hearing loss can be complicated as there can be multiple causes for hearing loss. Therefore, diagnosis requires multiple steps to identify the appropriate treatment for the person with hearing loss:

• Otoscopy: a special torch with a lens is used to examine the ear to see whether there are any infections, lacerations, or foreign objects.87
• Tympanometry measures the air pressure in the middle-ear to identify whether the sound is travelling properly through it. While Tympanometry is not always conducted, it should be considered an important step in the diagnostic process to document or rule out the presence of fluid in the middle ear, a middle ear infection, or perforations in the middle ear that could lead to hearing loss but require medical/surgical attention rather than hearing aids.88 89
• Pure tone audiometry (also known as air conduction audiometry) yields an audiogram by testing the person's ability to hear tones of different pitches in each ear. A series of tones are played at varying frequencies and volumes, and the person indicates they have heard the tone by raising a hand or pressing a button.
• Bone conduction audiometry is an advanced step to further diagnose where the hearing loss has occurred. It uses a bone oscillator, placed behind the ears, that transmits sounds through bone vibration to the cochlea or inner ear, bypassing the middle and outer ear.90 This test is helpful in determining if the hearing difficulty is due to a problem in the middle or outer ear. This test is not conducted regularly and only used in non-standard cases where diagnosis after pure-tone audiometry is not confirmed.

FITTING OF HEARING AIDS is the next step in the process. Based on the hearing loss severity, lifestyle and configuration, the audiologist prescribes a hearing aid that would best aid the person to hear well. There are three primary steps in fitting a hearing aid:

• Creation of earmoulds is often the most time-consuming step in the fitting process. In most places, earmoulds impressions are sent to a distant lab where a trained earmould technician develops it and in such instances, it can take up to a week for the user to be fitted with a hearing aid. Alternatively, there are novel fitting methods that have allowed earmoulds to be developed on the spot within 2 hours. Earmoulds are highly recommended in children, but in non-complex, adult cases, users can opt to use eardomes that are readily available.
• Fitting of hearing aids typically requires the use of P.C.-based software, but there are digital hearing aids that have screws (or trimmers) to fit them as well. Most companies have their own proprietary fitting software, but there is an open-source fitting software called NOAH90 also available that can be used for most hearing aids available in the market.
• Real Ear Measurements are an optional step that is often undertaken to measure the sound pressure level in the hearing aid user's ear while the hearing aid is being worn. It measures how the volume and frequency response of the hearing aid affects the ear to identify the best hearing aid settings for the user. This step is not that common. For example, only 30% of audiologists in the U.S. routinely perform this test.91

AURAL REHABILITATION AND AFTERCARE are critical for sustainable and effective rehabilitation of hearing loss via hearing aids:

• Aural/Audiologic Rehabilitation. The fitting of hearing aids is just one aspect of aural rehabilitation. Users should be counselled, trained and instructed on how to use, adjust and manage their hearing aid as well as on visual cues, conversational strategies, and environmental training. Counselling supports the acceptance of hearing loss, reduces product abandonment and improves satisfaction with hearing aids with an overall goal to reduce the negative effects of hearing loss on function, participation and quality of life. Rehabilitation plans should be developed in close partnership with the user and caregiver, if applicable.

  • In children, habilitative or rehabilitative services may vary based on current age, age of onset of the hearing loss, age at diagnosis, severity and type of the hearing loss and the age at which hearing aids were introduced. Habilitation and rehabilitation services for children may involve training in auditory perception, using visual cues, improving speech and developing language as well as care-giver training and counselling.
  • Aural rehabilitation plans may also be influenced by the communication mode the individual is using, which may include auditory-oral, sign language, total communication, cued speech, among others.
  • Aural rehabilitation may also include peer support groups with other individuals with hearing loss to build confidence, skill sets and social support.
• Availability of batteries. Hearing aids need to be used continuously and daily and therefore, they consume a lot of batteries. Batteries usually last between 3-20 days and therefore, it is vital that the user has ample stock or easy access to batteries.
• Replacing earmoulds. Earmoulds need to be regularly replaced as they are susceptible to wear and tear. In adults, earmoulds need to be replaced every 2-3 years92. Because children and infants will outgrow their earmoulds quickly, they need to be replaced even faster. In older children, earmoulds need to be replaced every 6-12 months whereas they need to be replaced every 3-6 months for infants and younger children.
• Readjustment and refitting. Hearing loss is not a static condition and the user's hearing loss can change over time. Further, the user's comfort with the initial amplification can change over time. Thus, there need to be adequate follow-up services to allow users to get their hearing aid re-adjusted and re-fitted.
• Hearing Aid Replacement. Hearing aids usually need to be replaced every 3-5 years.