Hearing loss, deafness, hard of hearing, hearing impairment (a term considered derogatory by many in the community), is a partial or total inability to hear. In children it may affect the development of language and can cause work related difficulties for adults.
It is caused by many factors, including: genetics, aging, exposure to noise, illness, chemicals and physical trauma. Hearing testing may be used to determine the severity of the hearing loss. While the results are expressed in decibels, hearing loss is usually described as mild, mild-moderate, moderate, moderately severe, severe, or profound. Hearing loss is usually acquired by a person who at some point in life had no hearing impairment.
There are a number of measures that can prevent hearing loss and include avoidance of loud noise, chemical agents, and physical trauma. Testing for poor hearing is recommended for all newborns. But, in some cases such as due to disease, illness, or genetics, it is impossible to reverse or prevent. Hearing aids are partially effective for many.
In our Gambian community, there is quite a number of individuals suffering from deafness. The following are some of the major causes of hearing lost.
Age
There is a progressive loss of ability to hear high frequencies with increasing age known as presbycusis. This begins in early adulthood, but does not usually interfere with ability to understand conversation until much later. Although genetically variable it is a normal concomitant of aging and is distinct from hearing losses caused by noise exposure, toxins or disease agents.
Noise
Noise is the cause of approximately half of all cases of hearing loss, causing some degree of problems in 5% of the population globally.
Many people are unaware of the presence of environmental sound at damaging levels, or of the level at which sound becomes harmful. Common sources of damaging noise levels include car stereos, children’s toys, transportation, crowds, lawn and maintenance equipment, power tools, gun use, and even hair dryers. Noise damage is cumulative; all sources of damage must be considered to assess risk. If one is exposed to loud sound (including music) at high levels or for extended durations, then hearing impairment will occur. Sound levels increase with proximity; as the source is brought closer to the ear, the sound level increases. Mainly, deafness or hard of hearing happens in the older.
Genetic
Hearing loss can be inherited. Around 75-80% of all cases are inherited by recessive genes, 20-25% are inherited by dominant genes, 1-2% are inherited by X-linked patterns, and fewer than 1% are inherited by mitochondrial inheritance.
When looking at the genetics of deafness, there are 2 different forms, syndromic and nonsyndromic. Syndromic deafness occurs when there are other medical problems aside from deafness in an individual. This accounts for around 30% of deaf individuals who are deaf from a genetic standpoint. Nonsyndromic deafness occurs when there are no other problems associated with an individual other than deafness. From a genetic standpoint, this accounts for the other 70% of cases, which attributes to the vast majority of hereditary hearing loss.
Illness
Measles may cause auditory nerve damage.
Meningitis may damage the auditory nerve or the cochlea
Autoimmune disease has only recently been recognized as a potential cause for cochlear damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Wegener’s granulomatosis is one of the autoimmune conditions that may precipitate hearing loss.
Mumps (Epidemic parotitis) may result in profound sensorineural hearing loss, unilateral (one ear) or bilateral (both ears).
Presbycusis is a progressive hearing impairment accompanying age, typically affecting sensitivity to higher frequencies.
Adenoids that do not disappear by adolescence may continue to grow and may obstruct the Eustachian tube, causing conductive hearing impairment and nasal infections that can spread to the middle ear.
People with HIV/AIDS frequently experience auditory system anomalies.
Chlamydia may cause hearing loss in newborns to whom the disease has been passed at birth.
Fetal alcohol syndrome is reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake.
Premature birth causes sensorineural hearing loss approximately 5% of the time.
Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of infected children will eventually become deaf.
Otosclerosis is a hardening of the stapes (or stirrup) in the middle ear and causes conductive hearing loss.
Neurological disorders
Neurological disorders such as multiple sclerosis and strokes can have an effect on hearing as well. Multiple sclerosis, or MS, is an autoimmune disease where the immune system attacks the myelin sheath, a covering that protects the nerves. Once the myelin sheaths are destroyed they cannot be repaired. Without the myelin to protect the nerves, nerves become damaged, creating disorientation for the patient. This is a painful process and may end in the debilitation of the affected person until they are paralyzed and have one or more senses gone.
Chemicals
In addition to medications, hearing loss can also result from specific drugs; metals, such as lead; solvents, such as toluene (found in crude oil, gasoline and automobile exhaust, for example). Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss.
Physical trauma
There can be damage either to the ear itself or to the brain centers that process the aural information conveyed by the ears.
People who sustain head injury are especially vulnerable to hearing loss, either temporary or permanent.
Neurobiological factors
From a neurobiological perspective, there are simply two reasons that could cause a person to be deaf: either there is something wrong with the mechanical portion of the process, meaning the ear, or there is something wrong with the neural portion of the process, meaning the brain.
Diagnosis of Deafness
The severity of a hearing impairment is ranked according to the additional intensity above a nominal threshold that a sound must be before being detected by an individual; it is (measured in decibels of hearing loss, or dB HL). Hearing impairment may be ranked as mild, moderate, moderately severe, severe or profound as defined below:
Mild:
for adults: between 26 and 40 dB HL
for children: between 20 and 40 dB HL
Moderate: between 41 and 54 dB HL
Moderately severe: between 55 and 70 dB HL
Severe: between 71 and 90 dB HL
Profound: 91 dB HL or greater
Totally Deaf: Have no hearing at all.
Classification
Hearing impairments are categorized by their type, their severity, and the age of onset (before or after language is acquired). Furthermore, a hearing impairment may exist in only one ear (unilateral) or in both ears (bilateral). There are three main types of hearing impairments, conductive hearing impairment and sensorineural hearing impairment and a combination of the two called mixed hearing loss.
Conductive hearing loss
A conductive hearing impairment is present when the sound is not reaching the inner ear, the cochlea. This can be due to external ear canal malformation, dysfunction of the eardrum or malfunction of the bones of the middle ear. The ear drum may show defects from small to total resulting in hearing loss of different degree. Scar tissue after ear infections may also make the ear drum dysfunction as well as when it is retracted and adherent to the medial part of the middle ear.
Dysfunction of the three small bones of the middle ear – malleus, incus, and stapes – may cause conductive hearing loss. The mobility of the ossicles may be impaired for different reasons and disruption of the ossicular chain due to trauma, infection or anchylosis may also cause hearing loss.
Sensorineural hearing loss
A sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea, the nerve that transmits the impulses from the cochlea to the hearing centre in the brain or damage in the brain. The most common reason for sensorineural hearing impairment is damage to the hair cells in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing.
Mixed hearing loss
Mixed hearing loss is a combination of the two types discussed above. Chronic ear infection (a fairly common diagnosis) can cause a defective ear drum or middle-ear ossicle damages, or both. Surgery is often attempted but not always successful. On top of the conductive loss, a sensory component is often added. If the ear is dry and not infected, an air conduction aid could be tried; if the ear is draining, a direct bone condition hearing aid is often the best solution. If the conductive part of the hearing loss is more than 30-35 dB, an air conduction device could have problems overcoming this gap. A direct bone conduction aid like the Baha or the Ponto could, in this situation, be a good option.
Some of the methods used in Preventing Deafness
It is estimated that half of cases of hearing loss are preventable. A number of preventative strategies are effective including: immunization against rubella to reduce congenital infections, immunization against H. influenza and S. pneumoniae to reduce cases of otitis media, and avoiding or protecting against excessive noise exposure. Education on the perils of hazardous noise exposure increases the use of hearing the this protectors.
Before I conclude this article, I will like to shed light on few things. Just the beginning of this week, I paid a visit to the school for the Deaf, I was amazed with their mode of communication! Some doctors believe that being deaf makes a person more social but I got to believe this through their interactions in the school environment. Am encouraging parent not to see or treat them different, we are all equals. Being differently able is not a disability…….
