Saturday, March 3, 2012

Hearing Loss Testing and Diagnosing


Initial General Examination

Although hearing loss is very common among adults, particularly those over age 65, the condition is often under diagnosed in older people. Hearing loss can greatly impact a person's quality of life. Therefore, if hearing loss is suspected, it is important that the advice of a doctor specializing in diseases and conditions of the ear, known as an otologist, otolaryngologist, or ear, nose and throat doctor, is sought in order to make a definite medical diagnosis. The ear specialist also will work in close cooperation with audiologists, specialists in hearing disorders.

But at first, as you experience or suspect hearing, your primary physician will perform an initially examination, as the first line of defense. Your ear may be examined using an instrument called an auriscope, which is sometimes also known as an otoscope. An auriscope is a small hand-held torch with a magnifying glass used to examine the eardrum and the passageway that leads to it from the outer ear.

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An auriscope can be used to look for:
  • Discharge – fluid coming out of the ear.
  • A bulging eardrum – indicating that there is infected fluid in the middle ear.
  • A retracted eardrum – indicating uninfected fluid in the middle ear (glue ear).
  • Perforated eardrum – a hole in the eardrum, with or without signs of infection.
  • Earwax or foreign bodies that might be blocking the ear.

Special Hearing Tests

There are a variety of special tests available to accurately diagnose the type and severity of hearing loss.

These include:

  • Air Conduction, Conventional or Standard Audiometry.
This test is commonly used to measure the hearing of adults and older children. A range of test tones, from low to high frequency (perceived as "pitch"), is transmitted through earphones placed on or in each ear, and patients are asked to indicate with a hand raise, button push or verbal response when you hear each sound. This testing determines the very softest signals you can hear at each of the presented frequencies, and indicates frequency regions in which hearing may be impaired. The louder the sounds must be made to be heard, the greater the degree of hearing loss at that particular frequency or frequencies. The frequencies tested are those important for hearing and understanding speech and other environmental sounds.

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  • Bone Conduction.
If testing reveals a hearing loss, another type of headset, a bone vibrator, is used to determine hearing by bone conduction in order to determine the type of hearing loss. This device sends sounds directly to the inner ear, bypassing the outer and middle ear. If the sounds are heard better by bone conduction, the hearing loss is conductive in nature and is likely located in the outer or middle ear. If the sounds are heard equally well with the earphones and the bone vibrator, the hearing loss is sensorineural in nature. A combination of conductive and sensorineural hearing loss also may be present; this is called a mixed hearing loss.

  • Word Recognition.
In addition to tests with tones, word recognition testing is usually performed to evaluate the ability to discriminate differences between the speech sounds of various words, and how clearly the words are heard. During this test, you will be asked to listen to and repeat words. A test called the spondee threshold test determines the level at which you can repeat at least half of a list of familiar two-syllable words (spondees).

  • Whispered Speech Test.

In a whispered speech test, the health professional will ask you to cover the opening of one ear with your finger. The health professional will stand 1 ft (0.3 m) to 2 ft (0.6 m) behind you and whisper a series of words. You will repeat the words that you hear. If you cannot hear the words at a soft whisper, the health professional will keep saying the words more loudly until you can hear them. Each ear is tested separately.

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  • Acoustic Immittance.
These tests are used to assess the status of the middle ear and related structures. A type of acoustic immittance test called, tympanometry, measures the movement of the eardrum to see if it moves normally when pressure changes are applied. Restricted eardrum movement could indicate a problem with the eardrum or middle ear structures. Acoustic reflex testing, a method of determining how the middle ear reacts to loud sounds also might be tested.

  • Otoacoustic Emissions (OAEs).
OAEs are used to assess the function of the cochlea. OAEs are typically present when hearing is normal or near normal, and are typically absent when there is a problem in the cochlea. This test cannot distinguish between conductive and sensorineural hearing loss.

  • Auditory Brainstem Response (ABR).
ABR is a procedure used to measure hearing sensitivity and determine if the neural pathways within the brainstem are transmitting sound properly. This test is used to rule out auditory-neurological problems. Brainwave activity in the auditory centers of the brain is recorded in response to a series of clicks or tones presented to each ear. During this procedure, electrodes are placed on the head to detect the electrical response of the brains to sounds presented while you rest or sleep. The electrodes do not cause pain or discomfort. This test is also called brain stem auditory evoked response (BAER) testing or auditory brain stem evoked potential (ABEP) testing.

  • Vestibular Evoked Myogenic Potential Testing.
This test is used to test one of the balance organs of the inner ear for patients with unexplained dizziness/vertigo or certain types of hearing loss. It requires the patient to turn and hold their head in fixed positions while tones are played through earphones.

Hearing Test Results

Your hearing is considered normal if the following conditions are satisfied:
  • You are able to hear whispered speech accurately.
  • You can hear tones at equal loudness in both ears.
  • You are able to repeat 90% to 95% of the words in a word recognition test.
  • The microphone detects emissions from the inner ear in otoacoustic emissions (OAE) testing.
  • The values recorded on the graph for auditory brain stem response (ABR) testing show that the nerves in the brain responsible for hearing are working normally.

Your hearing is abnormal if:
  • You are not able to hear the whispers during a whispered speech test, or you are able to hear with one ear but not with the other.
  • You hear the tone more loudly in one ear than in the other.
  • You can only hear certain sounds at high decibel levels.
  • You can hear sounds but you cannot understand words.
  • No emissions are detected from the inner ear in otoacoustic emissions (OAE) testing.
  • The values recorded on the graph for auditory brain stem response (ABR) testing show that nerves in the brain responsible for hearing are not functioning normally.

Sound is described in terms of frequency and intensity. Your hearing threshold is how loud the sound of a certain frequency must be for you to hear it.
  • Frequency, or pitch (whether a sound is low or high), is measured in vibrations per second, or hertz (Hz). The human ear can normally hear frequencies from a very low rumble of 16 Hz to a high-pitched whine of 20,000 Hz. The frequencies of normal conversations in a quiet place are 500 Hz to 2,000 Hz.
  • Intensity, or loudness, is measured in decibels (dB). The normal range (threshold or lower limit) of hearing is 0 dB to 25 dB. Normal results show that you hear within these ranges in both ears.

Levels of Hearing Impairment

The hearing threshold in decibels (dB) serves as the official determinant for the level of the hearing impairment.
  • Normal hearing – 0 – 25 dB.
  • Mild decline (Difficulty with faint or distant speech) – 26-40 dB.
  • Moderate decline (Difficulty with conversational speech) – 41-55 dB.
  • Moderate to severe decline (Speech must be loud; difficulty with group conversation) – 56-70 dB.
  • Severe decline (Difficulty with loud speech; understands only shouted or amplified speech) – 71-90 dB.
  • Profound decline (May not understand amplified speech) – 91+ dB.

Factors to Affects the Test

There are several factors which might affect the test results and show the unexpected state of hearing. Note these factors and do your best to avoid their influence (as possible) before you make the test appointment:
  • Being unable to cooperate, follow directions, and understand speech well enough to respond during most tests. It may be difficult to conduct hearing tests on young children or on people who have physical or mental disabilities.
  • Difficulty speaking or understanding the language of the tester.
  • A recent cold or ear infection.
  • Being around loud noises within 16 hours before the test.

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