Conductive Hearing Loss
What is conductive hearing loss?
Conductive hearing loss occurs when the outer or middle ear is dysplastic or does not work properly. So, sound waves cannot be efficiently conducted to the inner ear. In case of a temporary dysfunction, it is often possible to correct conductive hearing loss with surgery and/or treatment with medication.
Common causes of conductive hearing loss include:
- Injury of the outer ear
- Blockage of the ear canal due to ear wax (cerumen) or other small objects like food, beads, or insects
- Infections of the outer or middle ear
- Perforation of the eardrum (tympanic membrane)
- Congenital deformities e.g. Down Syndrome, Franceschetti Syndrome, Treacher Collins Syndrome, or Achondroplasia (dwarfism)
The audiogram below demonstrates conductive hearing loss. In this example, the inner ear works properly but something inhibits sound from getting passing through the outer/middle ear to the inner ear.
The hearing loss displayed above ranges from 30–50 dB HL in the right ear and between 35–45 dB in the left ear. This person could only perceive fragments of normal speech, which has a loudness level of about 65 dB. A normal hearing person has a dynamic range of up to 65 dB between listening threshold (at 0 dB) and speech level (at 65 dB). This person only has a dynamic range of about 20 dB. This difference of about 45 dB must be amplified to enable the person to perceive speech and sounds appropriately.
Depending on the diagnosis, amplification is usually provided by:
- Conventional hearing aids (sometimes not possible due to chronic inflammation, effusion, and/or dysplasia of the outer ear/ear canal)
- Bone-conduction hearing instruments: Behind-the-ear shell with a vibrating transducer, placed on the skull using a headband or retainer
- Bone-anchored hearing aid (BAHA): A vibrating hearing solution which is attached to the skull using a screw which is implanted behind the ear
If the inner ear is unimpaired, bone-conduction hearing solutions do not deliver any amplification. Their task is only to make sounds audible by an adequate vibration of the skull, which transfers the sound information directly to the inner ear. Starting from there, the hearing process continues normally.