An Audiogram is used to verify the type and severity of a hearing loss and provides information to determine the most appropriate course of action.
Fig 1: A hearing test is used to measure the softest sounds that a person can hear at different frequency levels and is plotted on an Audiogram where the resulting graph is laid out similar to a piano keyboard with low to high frequencies on the horizontal ‘X’ axis going from left (low) to right (high) and Volume on the vertical ‘Y’ axis starting very quietly at the top becoming louder nearer the bottom.
Fig 2: The first part of a hearing evaluation is called an Air Conduction test where typically, a pure tone stimulus is presented to one ear at a time either via headphones or insert tips over a range of frequencies and decibel (dB) levels and the patient responds each time a signal is heard. The corresponding results are plotted on the audiogram with a Red ‘O’ representing the Right ear and a Blue ‘X' denoting the Left ear.
Fig 3: Following the Air Conduction, a Bone Conduction test is carried out using an oscillator to present the stimulus to the Mastoid bone (the bony protrusion behind the ear), these results are graphed with either a triangle in Red for the right and/or a Blue for the left or a right facing Bracket '[' and a left facing Bracket ‘]’ for the Left depending on the type of test being conducted.
The Normal hearing range is generally considered to be from 0-20dB, a Mild Loss would fall into the 20-40dB range, a Moderate Loss is between 40-70dB, a Severe Loss 70-95dB and Profound 95dB and lower.
In the example above Fig 3, the graph is showing a Mild to Severe Bilateral (both ears) High Frequency Sensorineural Hearing Loss in both ears. The Sensorineural description is given because the Bone Conduction readings are similar to the Air Conduction results. If there was a significant gap between the Air and Bone readings the loss would be described as Conductive and can be indicative of an outer or middle ear disorder. A Sensorineural loss refers to a problem associated with the Inner ear and generally indicates Nerve damage to the Inner ear hair cells.
Our About Hearing section has a couple of short videos graphically demonstrating how the hearing process works and what happens with a Sensorineural loss.