Interpreting Audiograms
What is an audiogram?
In this video from hearing aid manufacturer ReSound, we’ll take a closer look at the components that make up an audiogram.
Interpreting Audiograms: A Comprehensive Guide
Audiograms are an essential tool for mapping an individual's hearing capabilities. But how exactly do you understand what these graphs are telling you? In this comprehensive guide, we'll delve deep into how to interpret an audiogram, providing you with the knowledge and understanding necessary to make sense of this critical audiology tool.
What is an Audiogram
An audiogram is a visual representation of a person's hearing ability. It is essentially a graph that illustrates the results of a hearing screening. But why is this important? Understanding an audiogram is key to identifying how much a person's hearing deviates from the norm and, if there is a hearing loss, pinpoints where the problem might be in the hearing pathway.
Blank Audiogram
Blank Audiogram with no thresholds marked
Understanding Frequency and Sound Level
Frequency Measurement
The horizontal axis of the audiogram measures the frequency or pitch of sound in Hertz (Hz), ranging from 125Hz to 8,000Hz. This measurement is crucial because the higher the value, the higher the pitch of the sound. For instance, a frequency of 250 Hz corresponds to the middle C on the piano, while a high-pitched telephone ring is approximately 3,000Hz.
It's important to note that the human ear can typically hear frequencies as low as 20Hz and as high as 20,000Hz. However, the range of 250Hz to 8,000Hz is most commonly tested as most speech sounds fall within this frequency range.
Sound Level Measurement
The vertical axis of the audiogram measures the loudness or level of sounds in decibels (dB). Zero decibels (0dB) does not signify 'no sound' – it merely represents an extremely soft sound. A conversational voice level is around 65dB, and 120dB is very loud – about as loud as a jet taking off when standing 100 yards away.
Reading an Audiogram
The audiogram essentially shows how loud a sound must be for the person to hear it at a particular frequency. Air conduction thresholds for the right ear (the softest sounds the right ear can hear at each frequency) are marked as an 'O' and the left as an 'X' on the audiogram. Bone conduction thresholds are marked on the audiogram as (better ear), [(right ear), or] (left ear).
Recognizing Patterns in Audiograms
In certain cases, a person might not hear high-pitched sounds as well as low-pitched ones. This pattern is evident on the audiogram by observing the sloping line on the graph: as the frequency increases, the required sound level also increases before the person can hear it.
Understanding Audiometry Results
Pure tone audiometry results are categorized into three main terms:
Audiogram Classifications:
- Type of loss (sensorineural, conductive, mixed)
- Degree of loss (mild, moderate, severe, profound)
- Symmetry (similarity between the right and left hearing)
Types of Hearing Loss
Sensorineural Hearing Loss
If the hearing thresholds obtained by bone conduction are the same as the air thresholds, it indicates no blockage in the outer or middle ear. The hearing loss is caused by a loss of sensitivity in the cochlea or hearing nerve, leading to sensorineural hearing loss. Causes can include exposure to excessive noise or the aging process. Medical treatment for sensorineural hearing losses is rare, making the impairment permanent.
Sensorineural Hearing Loss
Audiogram depicting a sensorineural hearing loss
Conductive Hearing Loss
In cases where bone conduction hearing thresholds are normal, but there is a loss of hearing for air conduction sounds, it is referred to as a conductive hearing loss. This signifies that the cochlea is normal, but there's some blockage of sound in the middle or outer ears. Middle ear infections can often cause conductive hearing loss, which can often be corrected by medical or surgical treatment.
Conductive Hearing Loss
Audiogram depicting a conductive hearing loss
Mixed Hearing Loss
A person can have both sensorineural and conductive hearing loss – for example, if a person has a noise-caused impairment and a perforated eardrum. This is known as a mixed hearing loss.
Mixed Hearing Loss
Audiogram depicting a mixed hearing loss
Degrees of Hearing Loss
The degree of hearing loss essentially describes the degree of impact on a person's everyday life. Here's a brief breakdown:
Audiogram Classifications:
- Mild (20 – 40 dB): Soft sounds may be difficult to distinguish.
- Moderate (40 – 60 dB): Conversational speech is hard to hear, especially with background noise.
- Severe (60 – 80 dB): It is challenging to hear speech unless it’s loud.
- Profound (81 dB and above): Almost all sounds are inaudible. Most people with profound hearing loss benefit from a hearing aid, and a cochlear implant may assist these patients.
Mild Hearing Loss
Audiogram depicting a mild hearing loss
Moderate Hearing Loss
Audiogram depicting a moderate hearing loss
Severe Hearing Loss
Audiogram depicting a severe hearing loss
Profound Hearing Loss
Audiogram depicting a profound hearing loss
Hearing is described as normal if the hearing thresholds fall between 0 and 20dB.
Normal Hearing
Audiogram depicting normal hearing thresholds