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How do we hear?
Sound travels in waves. These waves are collected by the outer ear and sent through the external auditory canal (also called the ear canal) to the eardrum.
When sound waves hit the eardrum, the waves create vibrations that cause three ossicles (bones) in the middle ear to move. These bones are called the malleus, the incus, and the stapes (also known as the hammer, anvil, and stirrup).
The smallest bone, the stapes, moves the oval window between the middle and inner ear. When the oval window moves, fluid in the inner ear send vibrations to the cochlea.
Within the inner ear, thousands of tiny hairs move as the fluid inside the cochlea moves. The movement of these hairs sends signals through the auditory nerve to the brain. The hearing center of the brain then translates these movements into sounds that we recognize.
Sensorineural hearing loss
This type of hearing loss occurs when there is a problem in the cochlea (part of the inner ear).
Patients with sensorineural hearing loss can have a varying amount of hearing loss (slight to profound) and may have difficulty hearing and understanding speech clearly.
Sensorineural hearing loss is typically treated with the use of hearing aids or other hearing technologies; it cannot be medically or surgically corrected. While this type of hearing loss is permanent, most children will benefit from hearing aids or other hearing technologies, along with hearing therapy.
Conditions associated with sensorineural hearing loss include:
Mixed hearing loss
This type of hearing loss occurs when a child has both conductive hearing loss and sensorineural hearing loss. People with mixed hearing loss may have damage to the outer ear, the middle ear, the inner ear, and/or the nerve that connects the inner ear and the brain.
Auditory neuropathy (also called auditory neuropathy/auditory dys-synchrony)
This type of hearing loss occurs when sound enters the inner ear normally, but is not sent from the inner ear to the brain correctly. People with auditory neuropathy may have normal hearing or hearing loss, and usually have trouble understanding speech. Auditory neuropathy can affect people of all ages. A very small percentage of people with hearing loss have auditory neuropathy.
All types of hearing loss (conductive, sensorineural, or mixed) can vary from mild (only a little hearing loss) to profound (little or no usable hearing).
Most children have some degree of measurable hearing. Only a very small percentage of children with hearing loss experience complete deafness.
The degree of hearing loss refers to how much hearing loss is present. There are five broad categories used to describe the degree of hearing loss. The numbers listed below represent the lowest frequency (or softest) sounds a person can hear.
People with slight hearing loss (20 – 25 dB) may have trouble hearing faint (quiet) speech. They may also have to listen carefully in important or difficult situations.
For people with mild hearing loss, understanding speech can be difficult. They can usually hear well if they are listening to a single person speak in a quiet situation. However, they have trouble hearing faint or distant speaking. People with mild hearing loss usually can benefit from hearing aids or FM systems.
Listening is a strain for people with moderate hearing loss. While they can understand what a person says if the person is close, it can be difficult for them to hear someone else in a noisy environment. People with moderate hearing loss may miss 50 – 75% of speech in a conversation, and often need to have part of the conversation repeated. People with moderate hearing loss usually can benefit from hearing aids or FM systems.
People with moderate – severe hearing loss can miss up to 100% of speech in a conversation, and need for a conversation to be very loud. Again, people with moderate – severe hearing loss usually can benefit from hearing aids or FM systems.
People with severe hearing loss may hear a loud voice, if the person speaking is one foot (12 inches) away from his/her ear. They may be able to identify noises in their environment (for example, a paper rustling or traffic outside), but often appear to be ignoring conversation from the people around them.
People with profound hearing loss are considered to be deaf. They may detect very loud sounds, and are usually aware of vibrations (movements) around them. People with this degree of hearing loss may rely on vision (sight), rather than hearing, as their main way of communicating with other people. People with profound hearing loss may benefit from treatments or therapies that amplify sound (make sounds louder), but may benefit more from a cochlear implant.
For more information about the treatments and therapies mentioned on this page, please click here.
This describes whether the hearing loss is unilateral (hearing loss in one ear only) or bilateral (hearing loss in both ears).
Children with symmetrical hearing loss have the same degree and configuration of hearing loss in both ears. Children with asymmetrical hearing loss have a different degree and/or configuration of hearing loss in each ear.
Progressive hearing loss is hearing loss that becomes worse over time. Sudden hearing loss is hearing loss that occurs quickly (within less than 90 days, or 3 months) and requires immediate medical attention to identify its cause and treatment.
Fluctuating hearing loss is hearing loss that changes, sometimes getting better and sometimes getting worse. This type of hearing loss is usually associated with conductive hearing loss (caused by an ear infection, for example), but may be present in other conditions. Stable hearing loss is hearing loss that does not change over time.
There are many different causes of hearing loss. Hearing loss in infants and children is most commonly caused by fluid in the middle ear or ear infections. These are usually treatable.
People may have syndromic hearing loss (hearing loss associated with other symptoms or features of a condition) or nonsyndromic hearing loss (usually caused by a change within one of the genes related to hearing).
Hearing loss can also happen due to exposures to certain viruses, diseases, or drugs; long-term exposure to noise; complications related to birth; tumors; or aging.