Information on Hearing Loss - Understanding Hearing Loss: Diagnosis and Evaluation

When a hearing loss is first diagnosed, the test results may seem confusing. Although hearing loss is often described as a percentage, it is too complex to describe with one number. For these reasons we've designed this booklet as a service to our patients, to answer some of the most commonly asked questions about hearing loss and hearing tests.

 

What is An Audiogram And What Does it Tell Me?

Audiologists are professionals who specialize in evaluating hearing loss and conduct hearing tests. The results from the tests are recorded on an audiogram. An audiogram is a graph showing hearing sensitivity.

The degree of hearing loss is determined by measuring hearing threshold, the levels in decibels (dB) at which a signal is just barely heard. The louder sounds must be made to be heard, the greater the degree of hearing loss. Thresholds are measured at several frequencies (pitches) and graphed on the audiogram. The frequencies tested are those important for hearing and understanding speech and other environmental sounds. Frequency is noted in Hertz (Hz).

How Much Hearing Loss Do I Have?

Those with mild hearing loss (26-45 dB) typically hear one-on-one conversation if they can see the speaker's face and are listening at close range. With a mild hearing loss, there may be difficulty hearing and understanding someone who is speaking from a distance or has a soft voice. Understanding conversation in noisy backgrounds also may be difficult. For young children who are learning speech and language, even a mild hearing loss can have serious effects on speech and language development.

With moderate hearing loss (45-65 dB) conversational levels of speech are difficult to hear and understand, even in quiet backgrounds. Listening in noise is extremely difficult.

With severe hearing loss (66-85 dB) hearing is difficult in all situations. Speech may only be heard if a speaker is talking loudly or at close range. Those with profound hearing loss may not hear even loud speech or environmental sounds and may not use hearing as a primary method of communicating.

How Does Hearing Loss Affect Listening To Speech?

Another important term is the configuration of hearing loss. This refers to the pattern or shape of the hearing loss on the audiogram. Both the degree and the configuration of hearing loss will affect the ability to detect certain speech sounds. More hearing loss in one frequency region than another will affect the ability to hear sounds which have most of their energy in that region.

This graph shows the frequency and intensity where sounds of speech occur in average conversation. For example, an "s" sound has energy between 4000 and 8000 hertz (Hz) at an intensity of approximately 35 dB hearing level (HL). A person with hearing thresholds greater than 35 dB HL in that region may not hear the "s" sound.

Hearing test results for an individual with normal low frequency hearing, sloping to severe hearing loss, also are shown on the graph. For this hearing loss, speech sounds with energy form 250 to 1000 Hz will be heard, but speech sounds with energy at frequencies above 1000 Hz will not be heard. This loss of some speech components but not others can cause speech to sound muffled or distorted.

What Type of Hearing Loss Do I Have?

The ear has three major parts: the outer, middle and inner ear. The types of hearing loss depends on what part of the ear is affected.

The outer ear is the part that can be seen and includes the ear canal. The middle ear includes the ear drum, three middle ear bones (ossicles) and the eustachian tube. Hair cells are in the inner ear, or cochlea. Nerve fibers attached to the hair cells communicate with the brain.

A hearing problem located in the outer or middle ear is called a conductive hearing loss. This type of hearing loss is more likely to respond to medical or surgical treatment.

A hearing problem in the inner ear is called a sensorineural hearing loss. This kind of hearing loss is usually permanent.

A problem involving the outer or middle ear and inner ear is called a mixed hearing loss.

A physician who specializes in treatment of ear and hearing problems (otolaryngologist or otologist) can determine whether the hearing loss could be improved with medical or surgical treatment. A consultation is important to determine if treatment would be beneficial or if additional tests are necessary. It is also important to determine whether other health problems are related to the hearing loss.

How is Hearing Tested?

Hearing is tested using earphones or loudspeakers which send sounds to the ear canal and through the middle ear to reach the inner ear. There can be hearing loss in one or both ears. It is neccesary to obtain results with earphones to have information about each ear. If testing reveals a hearing loss, another device, a bone vibrator, is used to determine the type of hearing loss. It sends sound to the inner ear, bypassing the ear canal and middle ear.

With conductive hearing loss, sounds can be heard at softer levels when listening through the bone vibrator than through the earphone. With sensorineural hearing loss, sounds will be heard at similar levels through both devices.

Word recognition testing shows how clearly words are heard when they are presented at different listening levels. In this test, the patient listens to and repeats words. The more words that are repeated correctly, the better the word recognition ability.

Often a test called a tympanogram is performed to see if there is any evidence of middle ear problems which can contribute to hearing loss.

How is Hearing Tested in Young Children?

Special test methods are used with infants, toddlers and young children.

For very young infants the auditory brainstem response test (ABR) may be used. Electrodes are placed on the child's scalp using an adhesive. Then as the child sleeps, sounds are played through earphones. Responses to the sounds are used to determine the degree of hearing loss.

Another method which is currently under development is called otoacoustic emissions, or OAEs. For this test, a tiny microphone is placed in the ear canal, and responses are analyzed to determine hearing capacity.

After six months of age, infants, toddlers and older children may be tested with gamelike activities such as Visual Reinforcement Audiometry (VRA) or Conditioned Play Audiometry (CPA). For these, a child's responses to sounds are observed by audiologists. An older child may press a button or raise a hand in response to sounds.

Is it Necessary To Repeat Hearing Tests?

For conductive hearing loss, hearing should be retested after medical or surgical treatment.

For sensorineural hearing loss, the audiologist or physician will recommend when repeat testing should be done. Since hearing may change or fluctuate, it is important to detect this as early as possible to prevent further loss and to obtain medical treatment if needed. Also, changes in hearing may require changes in hearing aids or hearing aid settings.

For More Information

Hearing loss can affect communication. Understanding hearing loss and hearing test results are helpful in making informed decisions. If you have any further questions about hearing loss or would like more information, please call (402) 498-6520 or write to:

Audiology Department
Boys Town National Research Hospital
555 North 30th Street
Omaha, NE 68131