Type, Degree, and Configuration of Hearing Loss|
Approximately 28 million Americans have a hearing impairment. Hearing loss is one of the most prevalent chronic health conditions in the United States, affecting people of all ages, in all segments of the population, and across all socioeconomic levels. Hearing loss affects approximately 17 in 1,000 children under age 18. Incidence increases with age: approximately 314 in 1,000 people over age 65 have hearing loss. Hearing loss can be hereditary, or it can result from disease, trauma, or long-term exposure to damaging noise or medications. Hearing loss can vary from a mild but important loss of sensitivity, to a total loss of hearing.
Types of Hearing Loss
When describing hearing loss we generally look at three attributes: type
of hearing loss, degree of hearing loss, and the configuration
of the hearing loss.
Hearing loss can be categorized by where or what part of the auditory system
is damaged. There are three basic types of hearing loss:
conductive hearing loss, sensorineural
hearing loss and mixed hearing loss.
Conductive Hearing Loss
Conductive hearing loss occurs when sound is not conducted efficiently
through the outer ear canal to the eardrum
and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss
usually involves a reduction in sound level, or the ability to hear faint
sounds. This type of hearing loss can often be medically or surgically
Examples of conditions that may cause a conductive hearing loss include:
- Conditions associated with middle ear pathology such as fluid in the middle
ear from colds, allergies (serous otitis media), poor eustachian tube function,
ear infection (otitis media), perforated eardrum, benign tumors
- Impacted earwax (cerumen)
- Infection in the ear canal (external otitis)
- Presence of a foreign body
- Absence or malformation of the outer ear, ear canal, or middle ear
Sensorineural Hearing Loss
Sensorineural hearing loss occurs when there is damage to the inner ear
(cochlea) or to the nerve pathways from the inner ear (retrocochlear) to the
brain. Sensorineural hearing loss cannot be medically or surgically corrected.
It is a permanent loss.
Sensorineural hearing loss not only involves a reduction in sound level, or
ability to hear faint sounds, but also affects speech understanding, or ability
to hear clearly.
Sensorineural hearing loss can be caused by diseases, birth injury, drugs
that are toxic to the auditory system, and genetic syndromes. Sensorineural
hearing loss may also occur as a result of noise exposure, viruses, head trauma,
aging, and tumors.
Mixed Hearing Loss
Sometimes a conductive hearing loss occurs in combination with a
sensorineural hearing loss. In other words, there may be damage in the outer or
middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs,
the hearing loss is referred to as a mixed hearing loss.
Degree of Hearing Loss
Degree of hearing loss refers to the severity of the loss. There are five
broad categories that are typically used. The numbers are representative of the
patient's thresholds, or the softest intensity that sound is perceived:
Normal range or no impairment = 0 dB to 20 dB
Mild loss = 20 dB to 40 dB
Moderate loss = 40 dB to 60 dB
Severe loss = 60 dB to 80 dB
Profound loss = 80 dB or more
Configuration of Hearing Loss
The configuration or shape of the hearing loss refers to the extent of
hearing loss at each frequency and the overall picture of hearing that is
created. For example, a hearing loss that only affects the high frequencies
would be described as a high-frequency loss. Its configuration would show good
hearing in the low frequencies and poor hearing in the high frequencies. On the
other hand, if only the low frequencies are affected, the configuration would
show poorer hearing for low tones and better hearing for high tones. Some
hearing loss configurations are flat, indicating the same amount of hearing loss
for low and high tones.
Other descriptors associated with hearing loss are:
- Bilateral versus unilateral. Bilateral hearing loss means
both ears are affected. Unilateral hearing loss means only one ear is affected.
- Symmetrical versus asymmetrical. Symmetrical hearing loss
means that the degree and configuration of hearing loss are the same in each
ear. An asymmetrical hearing loss is one in which the degree and/or
configuration of the loss is different for each ear.
- Progressive versus sudden hearing loss. Progressive hearing
loss is a hearing loss that becomes increasingly worse over time. A sudden
hearing loss is one that has an acute or rapid onset and therefore occurs
quickly, requiring immediate medical attention to determine its cause and
- Fluctuating versus stable hearing loss. Some hearing losses
change -- sometimes getting better, sometimes getting worse. Fluctuating hearing
loss is typically a symptom of conductive hearing loss caused by ear infection
and middle ear fluid, but also presents in other conditions such as Meniere's
Causes of hearing loss
There are many possible causes of hearing loss. These can be divided into two
basic types, called conductive and sensorineural hearing loss.
Conductive hearing loss is caused by anything that interferes with the
transmission of sound from the outer to the inner ear. Possible causes include:
- middle ear infections (otitis media)
- collection of fluid in the middle ear ("glue ear" in children)
- blockage of the outer ear (by wax)
- damage to the eardrum by infection or an injury
- otosclerosis, a condition in which the ossicles of the middle ear become
immobile because of growth of the surrounding bone
- rarely, rheumatoid arthritis affects the joints between the ossicles.
Sensorineural hearing loss is due to damage to the pathway for sound
impulses from the hair cells of the inner ear to the auditory nerve and the
brain. Possible causes include:
- age-related hearing loss - the decline in hearing that many people
experience as they get older
- acoustic trauma (injury caused by loud noise) to the hair cells
- viral infections of the inner ear (may be caused by viruses such as mumps
- Ménière's disease (abnormal pressure in the inner ear)
- certain drugs, such as aspirin, quinine and some antibiotics, which can
affect the hair cells
- acoustic neuroma, a benign (non-cancerous) tumour affecting the auditory
- viral infections of the auditory nerve (such as mumps and rubella)
- infections or inflammation of the brain or brain covering - eg meningitis
- multiple sclerosis
- a brain tumour
- a stroke
Diagnosing hearing loss
In adults, hearing loss may be very gradual, as in age-related hearing loss,
or it can be very sudden, as in some viral infections of the inner ear. If you,
your friends or your family think that your hearing is deteriorating, you should
see your GP.
A person who experiences hearing loss can have a range of tests, usually at
an audiology clinic of the local hospital or health centre. A number of
different professionals may be involved in testing and treatment of hearing
- an ear, nose and throat (ENT) specialist, also called an otolaryngologist
- audiological physician (doctor specialising in hearing problems)
- audiologist (a specialist in the testing of hearing and fitting of hearing
When examining a person with hearing loss, a doctor will want to know how the
hearing loss has developed and what sort of problems it causes.
He or she will also perform a physical examination. Tuning forks and a
special electronic device with headphones (an audiometer) are used to test the
degree of hearing loss.
An audiometer produces sounds of different volumes and pitch (frequencies).
During testing, you are asked to indicate, usually by pushing a button, when you
hear a sound in the headphones. The level at which a person cannot hear a sound
of a certain frequency, is known as their threshold.
Hearing loss is measured in decibels hearing level (dBHL). A person who can
hear sounds across a range of frequencies at 0 to 20 dB is considered to have
normal hearing. The thresholds for the different types of hearing loss are as
Profoundly deaf people, who cannot hear sounds quieter than 95 dB, usually
communicate using sign language and lip reading.
If a sensorineural cause is suspected a number of tests can be performed to
pinpoint where the problem lies. One test is based on otoacoustic emissions.
This measures the responses the cochlea makes to sounds produced by a probe
placed in the outer ear. Another test looks at the auditory brainstem responses,
which measure the activity of the cochlea, auditory nerve and brain when a sound
is heard. None of these hearing tests is uncomfortable.
If the cause of the hearing loss seems to be due to a brain abnormality, a
magnetic resonance imaging (MRI) scan of the head may be recommended.
Treating hearing loss
The treatment of hearing loss depends on the cause. A bacterial infection of
the middle ear can be treated with antibiotics; blockages of the outer and
middle ears can be cleared; damaged eardrums can be repaired surgically; and
ossicles affected by otosclerosis can be replaced with artificial bones. Some
causes of sensorineural hearing loss can also be improved. For example, an
acoustic neuroma can be removed surgically.
If there is no cure for the hearing loss (as with age-related hearing loss),
a hearing aid for one or both ears usually helps most people, whether the
hearing loss is the result of conductive or sensorineural problems. Many
different types of hearing aids are available.