INTRODUCTION
The number of cases of hearing impairment or deafness is on the increase, over a hundred patients gather weekly at the ENT department of Federal Government and Teaching Hospitals weekly from where they are referred to specialist centers; It is estimated that about 7million Nigerians including children, adults and older people are affected by this health condition.
Hearing is critical to speech and language development, communication speech and learning. It can be devastating on a child’s development especially when it occurs early in life; this chronic illness causes delay in the development of receptive and expressive communication, lead to learning defect and consequently, poor academic performance. The child is often isolated due to poor communication; this often leads to poor self esteem anger and resentment.
Some of the causes of hearing defect include illnesses and trauma such as accidents and fights.
Noise pollution is another leading cause of this problem, apart from the high pitched music that are played in public places such as occasions, market places, churches, bars and night clubs, it is common to see young people wearing ear piece enjoying music from phone, computer or portable music devices, it is worth knowing that over use of ear piece can lead to deafness. Noises from industrial equipments and generator sets are also implicated.
Total or partial hearing loss is also common among deep-sea divers; this is usually referred to as barotraumas or DECOMPRSSION SICKNESS (DCS), this damage could be unilateral (one ear) or bilateral (both ears)
Other causes of hearing loss may include the presence of wax, infection or fluid in the ears and side effects of drugs SEE MORE
What is Hearing Assessment
Hearing assessment is the determination of a patient’s hearing level.
Before hearing evaluation is done, it is important to first of all obtain the patient’s medical history not only concerning the ears but also concerning any other health condition that might have played a role in the hearing impairment. It is also important to examine the ears for the presence of wax, as this can also impair the hearing. The ear drum should be examined to see if it has suffered any damage that may have stopped the transmission of sound to the cochlea.
Hearing loss is not limited to one ear but can occur on both ears and is referred to as bilateral, although the damage can be of various degree in both ears,
The most commonly used hearing assessment is the determination of sound required to be audible (audibility), and this differs from one person to another over a range of about 5decibel from day to day and from person to another.
The level of audibility also fines it application in the monitoring of noise.
TYPES OF HEARING LOSS
The ear is divided into three parts: the external ear, the middle ear, and the inner ear. Each part performs an important function in the process of hearing. Sound waves pass through the canal of the external ear and vibrate in the ear drum which separates the external ear from the middle ear. The three small bones in the middle ear (hammer or milieus, anvil or incus, and stirrup or stapes) act as a transmitters that transmit energy of the sound vibrations to the fluids of the inner ear.
Vibrations in this fluid stimulate the delicate nerve fiber which then carries the sound impulses to the brain where they are interpreted as understandable sound. Each part performs an important function in the process of hearing.
The external ear and the middle ear conduct sound: the inner ear receives it. If there is some difficulty in the external or middle ear, a conductive hearing loss occurs. If the trouble lies in the inner ear, a sensorineural (SNHL) or nerve hearing loss is the result. When there is some difficulty in both the middle and inner ear, a combination of conductive and sensorineural impairment exists.
Conductive Hearing Losses
Any disease affecting the ear canal (external ear), ear drum, middle ear space or the three small ear bones (ear ossicles) may cause a conductive hearing loss by interfering with the transmission of sound to the inner ear. Such a conductive hearing impairment may be due to a perforation (hole) in the ear drum, partial destruction or fixation of one or all of the three little ear bones, or scar tissue around the ear bones or in the ear drum. Other causes of conductive hearing losses include wax in the ear canal, middle ear fluid or infection or any other process that would prevent sound from reaching the inner ear.
Sensorineural Hearing Loss (inner ear hearing loss)
Sensorineural hearing loss is an inner ear hearing loss. This occurs in the cochlea or auditory nerve (eight cranial nerve), the brainstem, or the auditory cortex. The auditory cortex is the region of the brain in which sound is heard. For most cases of sensorineural hearing loss, including sudden SNHL, it is felt that the abnormality is within the cochlea itself.
Signs of Hearing Loss
- Playing loud music
- Using very high volume when listening to news
- Inability to hear sounds like knock on the door,
- Inability to hear in group conversation,
- People complain that you yell when speaking to them
- Inability to hear without looking at the speaker or being close enough to the speaker
- Ringing, buzzing and pains in the ears
- Asking people repeat conversations
- You hear but don’t understand all the words in a conversation
- People accuse you of not responding when they call your name or speak to you.
- Telephone conversation become difficult
TYPES OF AUDIOMETRY
- Subjective
Pure tone audiometry
Speech audiometry
Bekesy
- Objective
Acoustic impedance audiometry or tympanometry
Evoked response audiometry
Process of Hearing Assessment
This is a test that is done using either a manual or automatic audiometer, regardless of the type of device use, the test procedures remain the same.
Usually, the patient is made to remove everything that can interfere with the test result for example, earrings, spectacle and even hearing aids. The ear canal is then examined for any build up of wax or obstruction.
Then, the patient is given instructions on how to respond during the test, for example, the patient is told to show whether he or she can hear a certain sound by putting up a finger or the hand.
Head phones are then fitted tightly around the ears to prevent interference from external sounds; the test is done from one ear to the other and not both ears at the same time and it is best done in a sound proof chamber.
Then during the text, the sound level is usually varied from high to low or low to high sound intensity.
The first threshold test is then done to determine the lowest audible level in which each ear is subjected to sound at a mild pitch or frequency of (1000HZ) KHZ at varying level of loudness and at fixed decibel range, from low to high and then from high to low, the procedure is repeated severally and an average is taken as the test result.
Decibel is the intensity of sound; it is the 1/10th, of a bell on the logarithmic intensity scale.
The threshold can fluctuate due to slight change in the procedure adopted in setting up the test for example, variation of the position of the ear phone on the ears.
The test is done on both ears through a range of usually, 0, 5, 1, 2,3,4,6 and 8 KHz , and the hearing level recorded for each via a range of sound exposure, and from these an average result is determined.
ERROR AND ACCURACY
At the end of the test, a second threshold check should be carried out to see that there was no error, Threshold check should agree with a minimum of 10db and if it does not, a retest should be done.
Four main factors affects the accuracy of eudiometry, they are
Hearing effects: The ear on which the test was first performed, gives poor result, while the second ear is usually better because the patient has become more proficient in detecting t he sound.
Background noise: Audiometric test should be done in sound proof chambers to prevent external sounds from interfering or influencing the test result.
Head phone fit: Some changes in the threshold frequency measurement have been attributed to the difference in d location of the headphone which in turn affects the threshold.
Audiometric testing is subjective and therefore depends on the cooperation of the subject; this is another limitation of this procedure.
Therefore, if the subject is unwilling to cooperate with the test, then a result that cannot be represented will be obtained.
