|
|
Professional Audiology Clinic Ltd. provides various diagnostic tests to determine your hearing levels. Generally there are two categories of hearing loss depending on the area of the ear affected. It is possible to have a combination of the two categories and /or hearing loss in one ear rather than both (binaural).
Sensorineural Hearing Loss
Sensorineural hearing loss describes what happens when the sound pathway that moves sound from the inner organ of hearing (cochlea) along the auditory nerve to the brain is damaged. Damage can be done to hair cells in the cochlea (inner ear organ) from exposure to loud noise and/or the natural aging process. When hair cells are unresponsive, sounds are not properly transmitted to the auditory nerve in the brain. Sensorineural hearing loss accounts for about 90% of all hearing losses.
Conductive Hearing Loss
When the structures of the outer or middle ear fail to conduct sound waves to the inner ear properly, the result is conductive hearing loss. This type of loss may be temporary and may be reversed through surgery or other medical means. Causes include ear infections, injury to the ear, such as a punctured eardrum, or even a build-up of wax in the ear canal. Because children are prone to ear infections, it's important to have their hearing checked frequently and to be aware of the signs of hearing loss.
Central Hearing Loss
Central hearing loss is a rare type of hearing loss that results from damage or impairment to the nerves or nuclei of the central nervous system, either in the pathways to the brain or in the brain itself.
What Causes Hearing Loss?
There several causes of hearing loss, below are a few contributors:
Aging
Hearing loss is a natural consequence of getting older. Our hearing ability worsens from our 30s or 40s and onwards and almost half of people over the age of 50 have difficulties understanding speech in noisy situations. And when we reach our 80s, more than 75% of us suffer from a hearing loss.
Exposure to noise
High levels of noise at work can cause hearing loss. But also loud music can damage one's hearing severely. Music is the main reason that so many young people suffer from diminished hearing.
Other causes
Hearing loss can have other causes than ones mentioned above. Disease, chronic and/or severe infections, drugs, physical damage, hereditary conditions, viral or bacterial infection, certain drugs, acoustic tumors, certain neurological conditions can also play a part.
How the Ear Works
The ear is an amazing and complex organ comprising three parts: the outer ear, the middle ear and the inner ear. From the inner ear the auditory nerve transmits information to the brain for processing. Below are the three main sections:
 |
The outer ear (a)
The outer ear includes the auricle, the auditory canal and the eardrum. It funnels sounds from the surrounding environment into the hearing system. The auricle helps to gather the sound waves, and the auditory canal then directs them to the eardrum.
|
| |
|
 |
The middle ear (b)
The middle ear is an air-filled cavity, which contains the smallest bones in the human body - the malleus, incus and stapes. These are connected to the eardrum on one side, and on the other side to a thin membrane-covered opening on the wall of the inner ear, the Oval Window. The middle ear is also connected to the throat via the Eustachian tube which keeps the air pressure in the middle ear equalized. |
| |
|
 |
The inner ear (c)
In the inner ear the auditory input is processed by the cochlea, while information affecting balance is processed by the semicircular canals. Along the entire length of the fluid filled cochlea there are tiny hair cells. The hair cells are bent when the fluid is displaced by sound waves passed on by the middle ear bones. This triggers a chemical response, which activates the corresponding nerve endings. These then transmit the message to the area of the brain in charge of interpreting auditory input. Just an idea of how complex this organ is there are approximately 40 000 hair cells in a normal cochlea, which is the size of a pea! |
As mentioned, Professional Audiology Clinic Ltd. employs various diagnostic tests, depending on your hearing situation. When hearing thresholds are assessed in the soundbooth, we use an audiogram to record levels of threshold at various frequencies.
Detailed view of ear anatomy 152K
What is an Audiogram?
An audiogram is a graphic representation of our hearing, with decibels on the left side of the chart, with frequency in Hertz on the top part of the chart moving sideways to the right. There is an excellent guide to better understanding audiograms on the American Academy of Audiology website.
Understanding Your Audiogram
by Dr. Allan S. Mehr, FAAA
 |
An audiogram is a picture of your hearing. The results of your hearing test are recorded on an audiogram. The audiogram to the left demonstrates different sounds and where they would be represented on an audiogram. The yellow, banana-shaped figure represents all the sounds that make up the human voice when speaking at normal conversational levels. |
| |
|
 |
The vertical lines on an audiogram represent pitch or frequency. The 125 Hertz (Hz) vertical line on the left side of the audiogram represents a very low pitch sound and each vertical line to the right represents a higher pitch sound. Moving from left to right on the audiogram would be consistent with moving from left to right on a piano keyboard. The most important pitches for speech are 500-3000 Hz. |
| |
|
 |
The horizontal lines represent loudness or intensity. The 0 decibel (dB) line near the top of the audiogram represents an extremely soft sound. Each horizontal line below represents a louder sound. Moving from the top to the bottom would be consistent with hitting the piano key harder or turning up the volume control on your stereo. |
| |
|
 |
Therefore, every point on an audiogram represents a different sound. For example, point A on the audiogram to the left represents a soft low-pitch sound and point B represents a soft high-pitch sound. Point C represents a loud mid-pitch sound. |
| |
|
 |
The softest sound you are able to hear at each pitch is recorded on the audiogram. The softest sound you are able to hear is called your threshold. Thresholds of 0-25 dB are considered normal (for adults). The audiogram to the left demonstrates the different degrees of hearing loss. |
| |
|
 |
The audiogram to the left represents the hearing of an individual with normal hearing in the low frequencies (pitch) sloping to a severe high frequency hearing loss in the left ear and a moderate to severe hearing loss in the right ear. The blue X's indicate the thresholds for the left ear and the red O's indicate the thresholds for the right ear. |
| |
|
 |
If we now superimpose the normal speech area on the audiogram, we can obtain some information regarding this individual's ability to hear speech. The listener is able to hear all the low and mid speech sounds but is not able to hear the high pitch speech sounds (i.e., F, S, TH) in the left ear (blue X's). The listener is not able to hear any of the normal speech sounds in the right ear. This person would rely on the left ear for speech understanding and would probably experience difficulty hearing in noisy environments. |
Degress of hearing loss
|
Decibel Loss |
Hearing Loss
|
16-25 |
Slight: problems if listening conditions or acoustics are poor (i.e. a noisy party, hockey game) |
26-40 |
Mild: difficulty hearing soft or distant speech in church or theatre; may benefit from a hearing aid. |
41-55 |
Moderate: conversation heard from 1-2 metres, but understanding speech in a strain, especially in background noise; hearing aids may be required. |
56-70 |
Moderately severe: conversation must be loud and nearby; hearing aids should be complemented by other devised and speech reading instruction |
71-90 |
Severe: cannot hear loud speech or understand speech on the telephone; besides hearing aids, other technology and speech reading, counseling and speech therapy may be recommended. |
91+ |
Profound: some very loud sounds may be heard or felt through vibration. Speech reading training, speech therapy and counseling may be required to help achieve successful communication strategies. |
Putting decibels into perspective
|
Decibel (SPL)
|
Source (with distance)
|
250 |
Inside of tornado; conventional or nuclear bomb explosion at 5m |
180 |
Rocket engine at 30m; Krakatoa explosion at 160km in air |
150 |
Jet engine at 30m |
140 |
Rifle being fired at 1m |
130 |
Threshold of pain; train horn at 10m |
120 |
Rock concert; jet aircraft taking off at 100m |
110 |
Accelerating motorcycle at 5 m; chainsaw at 1m |
100 |
Jackhammer at 2m |
90 |
Loud factory; heavy truck at 1m |
80 |
Vacuum cleaner at 1m; curb-side of busy street |
70 |
Busy traffic at 5m |
60 |
Office or restaurant inside |
50 |
Quiet restaurant inside |
40 |
Residential area at night |
30 |
Theatre, no talking |
10 |
Human breathing at 3m |
0 |
Threshold of human hearing (with healthy ears) |
|
