The first step in an audiologic assessment is a preliminary examination in which the audiologist examines the structures of the outer and middle ears with an otoscope. This examination, called an OTOSCOPY, helps detect structural anomalies as well as mechanical impediments to sound conduction (such as compacted CERUMEN in the auditory canal or an infected or damaged TYMPANIC MEMBRANE). The preliminary examination also includes a health history in which the audiologist asks questions about any existing hearing loss, risk factors for hearing loss (including noise exposure), medications, and illnesses such as MEASLES and RUBELLA (German measles).
An audiologist conducts the procedures of audiometry, a battery of tests that measure the ability to discern sounds at different frequencies (pitch) and intensities (volume). During the audiometric examination the person sits in a soundproof booth and the audiologist sits in a control booth. Common audiometric procedures include
- Pure-tone audiometry, which measures the range of sound a person can hear. For this procedure, the audiologist produces tones at certain frequencies and intensities, and the person indicates whether he or she hears them. The audiologist tests each EAR separately.
- Conditioned-play audiometry and visual-reinforcement audiometry, which adapt conventional audiometry to children. These methods use games and visual rewards to elicit responses to the tones.
- Speech audiometry, which determines the lowest sound frequency and intensity at which a person can hear and repeat two-syllable spoken words (speech-reception threshold), and how well the person can hear and repeat single syllable words spoken at a consistent intensity (word recognition).
- Pure-tone BONE-conduction audiometry, which delivers tones through a vibrating device placed against the bone near the ear. This bypasses the outer and middle ear when there are conductive obstructions present (such as OTITIS media or compacted cerumen in the auditory canal).
The audiologist reports results in decibel (dB) of threshold (sound intensity) for 500 Hertz (Hz), 1,000 Hz, and 2,000 Hz, the frequencies of everyday speech and activities. An audiogram summarizes and presents this information for each ear in a graphic presentation. Any identified hearing loss may require additional tests.
Other Hearing Tests
Sometimes health-care providers need further information to identify the nature and cause of hearing loss, particularly in infants and young children. Other tests for refined assessment include
- auditory evoked potentials, in which electrodes attached to the head measure NERVE transmissions in response to sound
- auditory brainstem response, an auditory evoked potential that specifically measures the response of the eighth cranial nerve (vestibulocochlear or auditory nerve)
- otoacoustic emissions, which measure the response of the cochlea to sound stimulation
- acoustic immittance measures, which assess the function of the middle ear:
† tympanometry, to assess eardrum function
† acoustic reflex, to determine whether the ear responds to loud sounds
† static acoustic impedance, to measure volume of air within the ear canal
- balance assessment to determine vestibular function/dysfunction
Audiologic assessment helps determine the appropriate therapeutic course for hearing loss. Doctors often can correct conductive hearing loss through medical or surgical interventions. Sensorineural hearing loss requires hearing aids or other solutions (such as a COCHLEAR IMPLANT) to improve hearing ability. Mild hearing loss (26 to 30 dB) is the point at which a person is likely to benefit from a HEARING AID. At the level of severe hearing loss (71 to 90 dB), a person is unable to understand speech without a hearing aid. Because hearing is essential for development of language and communication skills, it is especially important to provide immediate intervention for hearing loss in children.