How Hearing Works
The ear sensory organs consist of the auditory system, which is responsible for the detection of sound, and the vestibular system that help to maintain body balance.
The ear can be further divided into three parts: the outer ear, the middle ear and the inner ear. Any damage along the hearing pathway in all three parts can cause hearing loss and are classified into conductive, sensorineural or mixed hearing loss.
Types of Hearing Loss
Conductive Hearing Loss
Conductive hearing loss is the result of abnormality to the outer or middle ear, which blocks the normal transmission of sound to the inner ear.
Common causes includes:
- Impacted earwax
- Middle ear infection
- Perforated eardrum
- Otosclerosis
Conductive hearing loss can usually be treated medically or surgically. For patients who are not suited for such treatments, hearing aids or advanced middle ear implantable devices can be used to improve hearing ability.
Sensorineural Hearing Loss
Sensorineural hearing loss is the most common form of hearing impairment. Such loss tends to be permanent and occurs as a result of damage to the sensory parts of the inner ear and/or the neural system, while the mechanisms of the outer and middle ear remain intact.
Common causes include:
- Presbyacusis (age-induced)
- Noise induced
- Ototoxic medication
- Viral or bacterial infection
Hearing aids or advanced implantable devices can be used to improve the hearing ability for this group of patients.
Mixed Hearing Loss
Mixed hearing loss is hearing loss caused by a combination of both conductive and sensorineural elements (i.e. the outer and/or the middle ear, as well as the inner ear). For this group of patients, hearing aids and advanced implantable devices can be used to improve the hearing ability.
Understanding Hearing Test Results
The audiogram is a graphical display of the hearing test results, with the graph indicating the softest sounds the patient can hear at various frequencies.
Note: Don’t worry if you do not fully understand the information written on this page. Our audiologists will take the time to explain your personal hearing test results to you in simple, understandable terms.
The audiogram is normalised to normal hearing level with the normal hearing limit between 0 to 25 dB HL. In addition, symbols ‘X’ and ‘O’ are often used to indicate the hearing thresholds for left and right ears respectively.
The severity of the hearing impairment is classified as follows:
0 to 25 dB HL Normal
No significant hearing difficulty.
25 to 40 dB HL Mild
Difficulty with soft speech but manages well with most situations.
40 to 55 dB HL Moderate
Difficulty understanding speech, especially in noisy situations. TV and radio volume often have to be adjusted louder.
55 dB HL to 70 dB HL Moderate to Severe
Clarity of speech is significantly affected. Speech needs to be louder and individual may have difficulty with group conversations and noisy situations.
70 dB HL to 90 dB HL Severe
Normal conversational speech is inaudible. Speech understanding is poor even with increased volume.
above 90 dB HL Profound
Speech intelligibility is poor even with hearing aid amplification. Cochlear implants would be a better alternative.
With the speech letters super-imposed onto the audiogram (example as shown above), you can have a better understanding of the impact of various degrees of hearing impairment on an individual’s hearing ability.