There are two types of hearing loss: conductive and sensorineural. When a condition of the outer or middle ear prevents sound from being transmitted to the inner ear, conductive hearing loss occurs. Sensorineural hearing loss involves a problem with the sensory transducer cells in the cochlea. It can also occur as a result of a problem in the neural pathway to the brain. Air and bone conduction audiometry is required in order to properly identify conductive and sensorineural hearing loss.
Air conduction audiometers transmit sound vibrations to the eardrum for the purpose of identifying obstruction or hearing loss in the outer, middle and inner ear. This type of audiometry effectively measures hearing ability and hearing thresholds. Everyday natural sound waves are carried through the ear. Air conduction audiometry similarly sends sound waves at varying decibel levels congruent to normal hearing in order to identify a hearing threshold. Pure Tone audiometers rely on air conduction as an effective way to screen for hearing loss. In an audiogram air conduction thresholds are marked with an O for the right side and an X for the left side. Occupational health, school, pediatrics and general practice are a few professionals that typically utilize air conduction audiometry alone for screening purposes.
In the case of Bone Conduction audiometry, the audiometer sends sound vibrations through a bone oscillator directly to the inner ear and to the cochlea. Bone conduction thresholds are typically marked with an < sign for the right ear and a > sign for the left. Bone conduction audiometry is used for diagnostic purposes and is instrumental in identifying sensorineural hearing loss. Proper differentiation between conductive and sensorineural hearing loss is to compare hearing threshold levels from both air conduction and bone conduction audiograms. Audiologist, ENTs and other hearing specialists rely on air and bone conduction testing to effectively diagnose hearing conditions.