Tympanometry is a test used to evaluate the functionality of the eardrum as well as to screen for the presence of fluid or other abnormalities in the middle ear. The test involves placing a snugly-fitting probe into the ear canal. A device called a tympanometer varies the air pressure inside the middle ear while simultaneously emitting a tone. The tympanometer then records the eardrum's response to the changes in air pressure and the amount of sound the eardrum reflects back.
The results are illustrated on a graph called a tympanogram. The tympanogram is classified as Type A, Type B, Type C, or Type Ac. Type A indicates that the eardrum movement is normal. Type B means that eardrum movement is impaired recommending that fluid is present in the middle ear or that the eardrum is perforated. Type C is usually indicative of a blocked or malfunctioning Eustachian tube but can also indicate that the ear drum is bulging outward or collapsed inward. Type Ac indicates an eardrum that is overly compliant, or floppy. This can be caused by the dislocation of the ossicular chain, the bones of the middle ear more commonly known as the hammer, anvil, and stirrup.
Tympanometry can also detect otosclerosis, a condition where the bones of the middle ear are knit together and immobilized resulting in impaired sound transmission to the inner ear. The muscles of the middle ear can be tested with a tympanometer by performing acoustic reflex measurements. This test measures the response of the ear muscles to intense bursts of sound. The muscles attached to the eardrum will reflexively contract to stretch the eardrum and diminish its movement thus protecting the bones of the middle ear by reducing the volume of the sound that reaches them. Lack of acoustic reflex indicates conductive or sensorineural hearing loss.