The audiogram is the basic test of hearing. It is performed with the patient in a sound-proof room where he/she will respond to tones of varying intensity and frequency. Air and bone conduction can be tested this way, and the results will produce a graph that plots hearing sensitivity against frequency for each ear. The test also includes speech recognition, which involves presenting single words to the patient at a specific volume level to assess their ability to understand words without the benefit of context (“open-set speech”). These techniques can be used to test hearing in children beginning at approximately three years of age.
The tympanogram is a test in which air pressure is applied to the ear canal via an “insert” (sealed plug with an attached tube) for the purpose of evaluating the compliance of the middle ear system. This test can provide objective information about how well-aerated the middle ear is, which is in turn a reflection of Eustachian tube function. It is helpful in determining whether there is fluid in the middle ear or a perforation (hole) in the eardrum, among other things.
This test measures involuntary reflexes of the stapedius muscle which occur in the middle ear in response to sound. It is performed by presenting a moderately loud sound to the ear and measuring the absence or presence of these reflexes. This test is helpful in the diagnosis of conditions such as otosclerosis and superior canal dehiscence syndrome.
Auditory Brainstem Response (ABR/BAER)
This test measures the function of the nerves which carry signals from the inner ear to the brain. It is performed by introducing sound to the ear and measuring the latency of the signals along several points in the neural pathway between the inner ear and brain. Its primary clinical use is in screening for vestibular schwannoma (acoustic neuroma), a benign tumor arising from the balance nerve. The test has largely been supplanted by MRI scanning of the brain with gadolinium (contrast dye), although it is still used in some situations because of its ability to provide a quick and cost-effective result, although it may miss tumors smaller than 1 centimeter in size. The test can also be used to measure hearing in patients who are comatose, in infants or very young children, and to detect malingering (faking a hearing loss).
Video Nystagmography (VNG)
This is a group of tests which are used to assess function of the vestibular (balance) system by having the patient perform certain tasks or by doing things to them while measuring the response in their eyes, specifically noting the presence of nystagmus (involuntary jerking movements in the eyes caused by stimulation to the vestibular system). During the test, the patient wears a pair of goggles over their eyes which block out incoming light. The goggles contain a small red light which the patient will track with their eyes, and a camera records the movement of the patient’s eyes as well as any nystagmus. The patient will be leaned back on a table and have their head placed into different positions (Dix-Hallpike maneuver) to see whether they become dizzy or have position-induced nystagmus, which is very helpful in the evaluation of benign paroxysmal positional vertigo (BPPV). Additionally, the patient may have warm or cool air or water applied to their ear canal, which normally induces nystagmus, and can alert the physician to the possibility of weakness in the vestibular system.
This test is used to measure pressure inside the inner ear. Its primary purpose is in screening for endolymphatic hydrops (elevated inner ear pressure that is responsible for Meniere’s disease). It is performed by introducing a clicking noise to the ear while electrical signals are measured on the side of the face. The result is a ratio of two measured values and the test has a fairly high margin for error. Nonetheless, it is often useful in the screening and monitoring of Meniere’s disease.
This is a test that is performed to determine whether a patient is a candidate for cochlear implantation. While wearing their hearing aids, the patient repeats a set of words back to the audiologist, either in quiet or with noise introduced to make it more difficult. A score of 40% or less with or without noise is currently considered candidacy for cochlear implantation by Medicare criteria.
Otoacoustic Emissions (OAE)
This is a test for function of the outer hair cells, a group of specialized cells in the cochlea that are essential for hearing function. The test detects the presence of low intensity sounds that are generated by the cochlea that can be measured in the ear by a special microphone. While not a test of hearing per se, the test is useful for hearing screening in infants and children, detecting malingering, and monitoring for ototoxicity (damage to the inner ear from chemicals or medications).
Vestibular Evoked Myogenic Potentials (VEMP)
This is a test that detects a reflex that originates in the inner ear in response to sound, but which is measured over the surface of muscles in the neck or around the eyes. Its primary clinical use is in establishing the diagnosis of semicircular canal dehiscence syndrome, although it may also sometimes be helpful in the evaluation of Meniere’s disease.
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