Hearing Tests
Screening for adults is usually done at their own request. However, some companies require hearing tests. In addition, OSHA (Occupational Safety and Health Administration) requires employers of high-risk hearing loss companies to develop and maintain a hearing conservation program at no cost to the employee. Furthermore, noise levels are required to be at, or below, 85 decibels (db) over an eight-hour shift.
Such a program would require regular hearing (audiometric) testing, noise monitoring, access to earplugs or earmuffs (hearing protective devices), record keeping, and employee training regarding hearing protection. If regular screening indicates that an employee is losing his/her hearing, the employee must be informed and must wear hearing protectors.
Hearing protectors are also required when work noise levels exceed 90 db, if the levels are averaged over eight hours. In order for the hearing protectors to be effective, they must fit properly and be worn continuously during noise exposure. OSHA also requires that an audiologist or an otolaryngologist or other qualified doctor administer the program.
Levels of Hearing Loss
(db – decibal; HL – hearing loss)
- Slight to minimal (16-25 db HL) – has difficulty hearing faint or distant sounds
- Mild (26-30 db HL) – occasionally misses consonants and has increasing difficulty in understanding with noisy backgrounds and faraway speakers
- Moderate (31-50 db HL) – can understand normal conversation if face to face and vocabulary is controlled
- Moderate to severe (51-70 db HL) – may miss most of what is said in a normal conversation and has difficulty listening in a group setting
- Severe (71-90 db HL) – may not be able to hear speech unless very loud and may need amplification to be able to converse normally
- Profound (91 db HL and above) – may not be able to hear speech at all and usually relies on such visual cues as lip reading or sign language
Hearing Exams
A doctor and an audiologist will complete different portions of the hearing examination in order to assess all aspects. Signs and symptoms are evaluated and any pre-existing medical conditions are checked that may be causing a hearing problem. A few of the audiologic exams include such things as audiometry, speech reception, and word recognition.
Tests, other than those listed below, include an MRI (magnetic resonance imaging), which can reveal the presence of a tumor or acoustic neuroma; a CT (computerized tomography) scan is used to check for a temporal bone fracture or other skull abnormalities; blood tests will check for infections; and cardiovascular tests will check the health of the heart and blood vessels. All of these will rule out obvious physical causes for any loss of hearing.
- Acoustic Reflex Test measures the sound level at which the muscles in the middle ear contract in response to sounds that are too loud. During the test, a series of sounds can be heard at varying levels of intensity. The sound level at which an acoustic reflex contraction occurs, or the absence of any acoustic reflex, can help the examiner evaluate hearing loss and locate problems along the auditory pathway.
- Audiologic Exams focus on hearing function. Specialists, called audiologists, use various tests to determine a person’s hearing status and degree of hearing loss. These tests help distinguish between different types of possible impairment, whether one or both ears are involved, or whether diminished capacity includes one or more frequencies. Repeated testings can determine whether the hearing loss is becomting worse. Audiologic tests are usually conducted using electronic equipment in a room designed to muffle sound so that background noise will not interfere with the test.
- Audiometry is a testing method which measures the ability to hear pure tones, as middle C and higher notes through air and through bone. The tuning fork test is a rudimentary form of this type of test.
- Air Conduction: Pure tone air conduction measures the ability to hear different tones of sound, measured in hertz (Hz) and the ability to hear the loudness or intensity of these tones, measured in decibels (db). Using this method, the audiologist begins by placing a pair of earphones over the ears or small, soft tips attached to earphones into the ear canals. In one ear at a time, certain tones are introduced through the earphones. By varying the frequency and intensity of the tones, the examiner can determine the faintest sounds that can be heard (hearing thresholds). When a sound is heard, the patient alerts the examiner by prearranged signals, usually by raising a hand or pressing a button. Responses are recorded on a graph called an audiogram. (To understand the meaning of an Audiogram, see below.)
- Bone Conduction: To check hearing by way of sounds conducted through the bones of the skull can help isolate problems in the outer and middle ear. To do this, the audiologist places a special vibrating device either behind the ear or on the forehead. Vibrations will travel through the skull, bypassing any blockage that may be present in the outer or middle ear. If test results show that hearing is better when sound is conducted through the skull bone than through the air-filled passageways of the outer ear and middle ear, sound is not getting through these areas properly, thus indicating a conductive hearing loss. If results show that hearing is no better via bone conduction than through air conduction, it is likely to be a sensorineural problem within the inner ear.
- Auditory Brainstem Response Test measures the electrical nerve impulses sent from the inner ear to the brain when sounds are heard. Electrodes are placed in the ear canal or near the ear, as well as on the head. Earphones are used to introduce short clicking sounds to the ear. The electrodes record brain-wave activity on a graph as the auditory nerve receives the sound impulses and transmits them to the brain. Because this test does not require a voluntary response from the patient, it is often used to screen hearing in newborns and infants. It can also be used to assess other problems with the auditory nerve.
- Dix-Hallpike Test is used to determine whether a condition known as benign paroxysmal positional vertigo (BPPV) is present. During the test, the patient sits on an examining table and moves his head to the right or left at an angle of about 45 degrees. The patient will then move quickly from a sitting position to a lying one with his head hanging off the back of the table but still at the same angle. The eyes are to be kept open the whole time so that the audiologist can observe their movement. If BPPV is present, vertigo will be experienced after two to ten seconds. The sensation may last for 30 seconds to a minute. This procedure is then repeated for the other ear. The ear that is toward the ground when vertigo is experienced usually determines which ear is affected. A procedure called canalith repositioning is often successful in treating BPPV.
- Electronystagmography is a battery of tests that evaluates the interaction between the inner ear and the eye muscles (vestibulo-ocular reflex). These tests are considered to be one of the best ways of checking the balance mechanism of the inner ear. For the tests, electrodes connected to a computer may be taped to the face or goggles that have small infrared cameras that constantly track the location of the pupils might be worn. Another part of the ENG test is a caloric test, which involves circulating warm water, cool water, or air through a soft tube placed in the outer ear canal. The audiologist will observe eye movements as the different temperatures stimulate the inner ear.
- Imaging Tests are conducted if a tumor, tissue abnormality, or auditory nerve damage is suspected to be the cause of a hearing loss. In such cases, detailed images of the interior of the head help with the diagnosis. Technology to produce these images includes an MRI (magnetic resonance imaging) and a CT (computerized tomography). MRIs create detailed images of soft tissues using magnetic fields and radio waves. CTs produce cross-sectional images of bone structures by using a computer to aggregate information from a series of x-rays. The images provide a glimpse of what would otherwise be unseen and may be useful in locating congenital abnormalities, trauma-related damage, and some tumors.
- Impedence Test measures the ability of the eardrum to reflect sound waves. Too much or too little pressure on the inner side of the eardrum makes it too stiff to conduct and reflect sounds properly. The tester puts a probe covered with a sound-proof material into the outer ear canal and seals up the entrance of the ear. A transmitter in the probe aims sounds at the eardrum. A receiver in the probe measures the reflections while air pumped through the probe changes the pressure in the canal rapidly from high to low. The test is one more way to determine whether the middle ear space is functioning normally.
- Laboratory Tests include blood tests to confirm or rule out possible infectious or inflammatory diseases that are sometimes associated with hearing loss. Such diseases might include syphilis, Rubella (German measles), cytomegalovirus (a gastrointestinal infection), and any autoimmune disorders. Ruling out these and other diseases is particularly important for pregnant women as they can lead to hearing loss in the developing baby. Blood samples may also look for any DNA abnormalities.
- Otoacoustic Emissions Test measures an interesting phenomenon that occurs in the hair cells of the inner ear, which bend with the movement of fluid in the cochlea. The resulting vibrations of the hair cells produce inaudible sounds (echoes) called otoacoustic emissions, which can be measured by placing a probe equipped with a microphone into the ear canal. This test is useful because people with normal hearing produce otoacoustic emissions, but those with hearing loss caused by damaged hair cells do not. This test is also used to screen hearing in newborns and infants because it does not require a voluntary response.
- Otoscopy involves the examination of the ear canal, eardrum, and middle ear using an instrument called an otoscope, which contains a light and magnifying lens. A specially designed microscope may also be used. Generally, this type of examination is painless and takes only a minute or two. During the examination, any possible wax or fluid buildup, tears or perforations in the eardrum will be assessed. The doctor will also see whether the eardrum is translucent and has its normal pearly gray color. A bulging of the eardrum membrane may indicate a middle ear infection.
- Posturography measures the ability to integrate sensory input from all parts of the balance system, including eyes, musculoskeletal nerves, and the vestibular system. This test helps determine which parts of the system that is relied upon the most and which parts may be giving problems. During the test, the patient is asked to stand on a special platform that is sensitive to changes in weight distribution. This helps to calculate the movement of the person’s center of mass. The patient will be asked to maintain balance during conditions in which one or more of the sensory sources are obstructed or altered. A safety harness is worn to ensure that the patient does not fall during the procedure.
- Rotation Tests can measure the vestibulo-ocular reflex, but they tend to be more sensitive to balance problems that affect both ears. For example, the tests may be used to monitor the sense of balance while taking medications that can cause inner ear problems.
During a rotation test, the audiologist may use electrodes or infrared cameras to monitor eye movements while the body is rotated in different directions. Often, the patient will sit in a computer-controlled chair that moves very slowly in a full circle. At faster speeds, it moves back and forth in a very small arc. The testing room is dark most of the time, but a microphone and headset allows the patient to maintain contact with the audiologist.
Another method is having the patient focus on an object and then voluntarily move his head side to side or up and down for brief periods. In some cases, the audiologist may simply watch the eye movements while he/she moves the patient’s head or slowly spins him/her in a swivel chair. - Speech Reception and Speech Discrimination Tests follow a pure tone test (see Audiometry). Speech reception involves an audiologist speaking or playing a recording of two-syllable words as the patient listens through headphones. Each syllable in a word is pronounced with an equal emphasis. When the patient hears the word, he/she repeats it or points to a picture of it. The sound of the words gradually becomes softer until they are no longer heard. The faintest level of speech that can be understood at least half the time is called the speech reception threshold.
Speech discrimination involves the evaluator adjusting the volume and frequency to test understanding. This is done by various kinds of test stimuli, as nonsense syllable, monosyllabic words, or sentences. If the discrimination is 70%, it means that 30% of the words cannot be understood. The greater the discrimination loss, the more difficulty there is in understanding situations with background noise. - Tuning Fork Test is a preliminary exam. Made of steel, a tuning fork is comprised of two long tines and sounds a single tone when struck against a solid object. To conduct the test, vibrating forks with different pitches are placed near the ear to measure hearing sensitivity to air conduction of the sound wave. The forks may also be placed against the head to measure sensitivity to bone conduction of the sound wave. Reduced hearing by air conduction but normal by bone conduction is typically referred to as conductive hearing loss and means that the sound wave has difficulty passing through the ear canal or the middle ear. Hearing that is reduced by both air conduction and bone conduction is generally said to have sensorineural hearing loss, resulting from damage to the inner ear.
- Tympanometry is a test used to check the function of the eardrum or middle ear. It can help detect such problems as a perforated eardrum, fluid in the middle ear, and reduced air pressure in the middle ear resulting in a retraction of the eardrum. To conduct the test, the examiner places a soft probe into the ear canal. As small, varying amounts of air pressure are directed toward the ear, the device measures the corresponding movement of the eardrum. The results are charted on a graph called a tympanogram. Normal response produces a line rising to a sharp peak in the middle of the graph. But if fluid is in the middle ear, the eardrum does not move easily and the graph’s line does not peak. The graph can also reveal whether the air pressure in the middle ear is less than or greater than atmospheric pressure.
- Word Recognition Test determines how well single-syllable words can be identified. As the audiologist says the words or plays them from a recording at a constant, comfortable volume, the patient will repeat them or point to a picture of them. The score reflects the percentage of words correctly identified. The words may be spoken at certain volume levels to determine how well speech at normal conversational levels is heard. Occasionally, background noise is added to see how distraction might affect the understanding. The word recognition test can be performed with and without a hearing aid, which will indicate whether the device is improving the hearing or not.
Understanding an Audiogram
An audiogram gives a visual picture of the ability to detect tones and is displayed on a grid made up of horizonal and vertical lines.
- The vertical lines of the chart represent a range of pitch or frequencies measured in cycles per second called hertz (Hz). This range moves from a bass or low pitch on the left (125 Hz) to a treble or high pitch on the right (8,000 Hz). The most important pitches for speech are 500-3,000 Hz. Some speech sounds carry very low tones, as the “vvv” in vacuum or the “mmm” in morning. Speech sounds as “fff” in food and “thh” as in thanks have a high pitch.
Some people may have symmetrical hearing loss (about at the same in both ears).
Others may have asymmetrical hearing loss (one ear hears better than the other).
Hearing loss may also vary according to frequency. For example, someone may have normal hearing at low and middle frequencies in both ears but may have moderate to severe loss at high frequencies in the left ear and only mild loss at high frequencies in the right ear.
If all the sounds that make up the human speech at normal conversational level were represented on a graph, the result would be a concave-shaped area just above the middle of the graph. This is called the speech spectrum. Softer, high-pitched sounds as “sss” and “thh” would be higher and toward the right within the spectrum. Louder, low-pitched sounds such as “mmm” or “ahh” would be lower and toward the left. Sounds, such as “eee” fall in between.
If the speech spectrum were to be superimposed over an individual’s audiometric test results, it would be easy to see which portions of conversational speech can and cannot be heard.
Audiogram test results are recorded and explained to the patient. A copy can be given to the patient if requested.
