- How We Hear
- Hearing Loss
- Hearing Test
- Sudden Hearing Loss
How We Hear
(Click on the image for a larger view of the ear)
The ear is divided into three parts:
- Outer ear - the visible outer portion of the ear, plus the ear canal.
- Middle ear - the eardrum and three small bones (malleus, incus, and stapes ("stay-peas")
- Inner ear - the fluid-filled, snail-shaped cochlea ("coke-lee-a") which contains thousands of tiny hair cells. The cochlea is attached to the hearing (auditory) nerve.
When we hear, sound is first collected by the outer ear and sent down the ear canal to the eardrum (1). The sound vibrates the eardrum, which then vibrates the bones of the middle ear (2-4). Motion of these bones results in movement of the fluid contained in the snail-shaped cochlea (5). As the fluid begins to move, the tiny hair cells lining the cochlea move back and forth to generate an electrical current (6). This electrical current stimulates the hearing nerve, which carries the signal to the brain and is interpreted as sound.
The following diagram illustrates some common sounds and their hearing level:
In general, three types of hearing impairment exist: conductive, sensorineural ("nerve"), or mixed hearing impairment (which is a combination of both a conductive and sensorineural hearing loss).
Conductive Hearing Loss
This type of loss is due to an outer ear or a middle ear problem. Some of the causes of conductive hearing loss include: ear wax, a hole or perforation of the eardrum, fluid behind the ear drum, a middle ear cyst (cholesteatoma), and otosclerosis.
Sensorineural or "nerve" hearing loss
This type of loss is due to an inner ear or hearing nerve problem. Sensorineural or "nerve" hearing loss is most commonly treated with a hearing aid.
In persons who are severely or profoundly hearing impaired in both ears, a cochlear implant is a possible treatment option. A cochlear implant is an electronic device surgically implanted into the inner ear. It bypasses damaged parts of the inner ear and electronically stimulates the hearing nerve.
For persons with deafness in one ear (single-sided deafness), a bone-anchored hearing device or Baha (a semi-implantable hearing device) is a treatment option.
Mixed hearing loss
This type of hearing loss is a combination of a conductive and a sensorineural hearing loss. Treatment depends of the severity of the conductive and sensorineural portions of the hearing loss.
5-Minute Hearing Evaluation
1. Do you have trouble following conversations when two or more people are talking at once?
2. Do people complain that you turn the volume on the TV up too high?
3. Do you have to strain to understand conversation?
4. Do you have trouble hearing in a noisy background?
5. Do you find yourself asking people to "say again"?
6. Do people seem to mumble (not speak clearly)?
7. Do you misunderstand what others are saying and respond inappropriately?
8. Do you have trouble understanding women and/or children?
9. Do people get annoyed because you misunderstand what they say?
If you answered "yes" to three or more of these questions, you may want to see one of the physicians of the Ear Institute of Chicago for a hearing evaluation.
Sudden Hearing Loss
Sudden hearing loss is a hearing loss that occurs within minutes or may develop rapidly over the course of 3 days or less. Sudden hearing loss may be divided into two different types:
Sudden conductive or
Sudden sensorineural (nerve deafness) loss (for more information regarding the difference between conductive and sensorineural hearing loss please click on the hearing loss tab above).
A sudden loss of hearing should be evaluated as soon as possible to determine the cause of the hearing loss. A sudden conductive hearing loss is often easily correctable. However, a sudden sensorineural hearing loss is a medical emergency and must be treated as soon as possible to try to increase the chance of hearing improvement.
Sudden Conductive Hearing Loss
Some common causes of sudden conductive hearing loss include (with their associated treatment in parenthesis):
ear wax impaction (removal in the physician's office)
acute outer or middle ear infection (antibiotic drops and/or antibiotic pills)
trauma to the ear canal (possible surgery)
trauma to the ear drum or middle ear bones (surgery/hearing aid).
Sudden Sensorineural Hearing Loss
As mentioned previously, sudden sensorineural hearing loss is considered a medical emergency. There is a much higher chance of hearing improvement in sudden sensorineural hearing loss if treatment is started within 7-10 days of onset of the hearing loss.
Sudden sensorineural hearing loss may vary from a mild to a profound hearing impairment. Sudden sensorineural hearing loss is most commonly defined as a loss of at least 30 dB in three consecutive frequencies, with the hearing loss developing over 3 days or less. The disorder has an estimated incidence of 5 - 20 cases per 100,000 population.
The following is a list of the most common causes of sudden sensorineural hearing loss (with the order of frequency in parenthesis):
There are various proposed theories as to the cause of sudden hearing loss.
The most common theories of the cause of sudden sensorineural hearing loss include viral infection (causing swelling in the inner ear), vascular occlusion (blockage of blood flow to the inner ear), and intralabyrinthine membrane breaks (a break of the delicate membranes in the inner ear). The majority of evidence points to some type of swelling (also known as inflammation) in the inner ear as the most common cause of sudden sensorineural hearing loss. The swelling is believed to be due to a virus.
A herpes type virus is believed to be the most common cause of sudden sensorineural hearing loss. The herpes virus lays dormant in our bodies and reactivates for an unknown reason.
Because the majority of sudden sensorineural hearing loss is believed to be of viral origin, oral steroids have been used to treat the condition.
Most of the treatments studied in randomized controlled trials can be divided into three different categories: 1) corticosteroid treatment; 2) specific antiviral therapy; and 3) specific treatment of vascular insufficiency. The justification for steroid treatment is based upon a presumed inflammatory process within the inner ear. Such inflammation might arise from a viral infection, an autoimmune mechanism, or even as a sequel of autolytic changes surrounding an area of ischemia or infarction. In other words, steroid therapy is non-specific and may be beneficial in cases of differing causes.