Conductive hearing loss:
Humans have and ear drum and tiny bones in the middle ear that conduct sound in a mechanical way. Sometimes, due to a number of reasons (see below for examples) the middle ear cannot conduct or transmit sound to the inner ear (an important part of the auditory system) producing hearing loss. This hearing loss is usually manifested as a reduction in sound level or the ability to hear faint sounds. This type of hearing loss can often be corrected medically or surgically or improved by the use of a hearing aid.
Some possible causes of conductive hearing loss:
- Impacted earwax (cerumen)
- Perforated eardrum
- Fluid in the middle ear from colds
- Ear infection (otitis media)
- Allergies (serous otitis media)
- Benign tumors
- Poor eustachian tube function
- Presence of a foreign body
- Infection in the ear canal (external otitis)
- Surfers ear (exotosis)
- Absence or malformation of the outer ear, ear canal, or middle ear
Sensorineural hearing loss (SNHL)
Humans have an inner ear (cochea) and neural pathways that take the sound from the conduction pathways and transmit to higher levels up the auditory pathyway. Hearing loss occurs when there is damage to the cochlea or to the nerve pathways from the inner ear to the brain. SNHL usually cannot be medically or surgically corrected. This is the most common type of permanent hearing loss and can be successfully treated with hearing aids.
Some possible causes of SNHL:
- Exposure to loud noise or music
- Hereditary congenital (at birth) loss
- Hearing loss that runs in the family (genetic or hereditary)
- Head trauma
- Malformation of the inner ear
- Drugs that are toxic to hearing
- Sudden hearing loss that is unexplained
Noise and hearing loss prevention:
The world is a very noisy place and hearing loss is becoming more prevalent with the noisy world. It is estimated that 31 million people from ages 6 to 69 have noise induced hearing loss and is growing steadily (Niskar et al, 2001; NIDCD, 2008). Your first indication that you may be in an unhealthy environment is if you feel pain at your ears. You may also notice that if someone has suggested hearing protection for your safety you may also be in an unhealthy hearing environment. Noise can be of many forms such as a siren on a fire truck to music. If the noise is played at the right intensity, loud enough or long enough or if an individual is very susceptible to noise it can cause damage to the inner ear (cochlea) or the auditory nerve. Please refer to ASHA for further explanation on noise and hearing loss prevention.
Niskar AS, Kieszak SM, Holmes AE, Esteban E, Rubin C, Brody DJ. Estimated prevalence of noise induced hearing threshold shifts among children 6 to 19 years of age: The third national health and nutritional examination survey. 1988-1994, United States. Pediatrics 2001;108:40–43.
National Institute on Deafness and Other Communication Disorders. Quick Statistics. Bethesda, MD: U.S. Department of Health and Human Services; August 2008.
Mixed hearing loss
Humans may have damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve providing both a conductive and SN Hearing loss. A mixed hearing loss is when both types of losses are present. Sometimes this can be medically treated although because of the permanent nature of the loss hearing aids are often preferred.