Types of Hearing Loss, their Causes and their ManagementMost people would be surprised to learn just how many people worldwide are affected by hearing loss to the point where its effects are disabling. In a recent survey conducted by the World Health Organisation, the number was found to be 360 million, or a little over 5% of the world’s population, of which around 32 million were children. About a third of the adults affected were aged 65 or over, and this group was found to be most prevalent in Sub-Saharan Africa, South Asia and Asia Pacific. Perhaps the most disturbing of the WHO findings, however, was that almost two thirds of disabling auditory impairment among children could be attributed to causes that were considered to be preventable.
The accepted standard for a person with normal audition is the ability to detect sounds of 25 decibels or greater with each ear, although many people are able to detect sounds of far lower volume. In a subject where this figure is determined to be above the accepted normal threshold, he or she is considered to be experiencing some degree of hearing loss. It is customary to categorise the severity of impairment as mild, moderate, severe or profound. Most of those in whom the impairment is mild to severe will generally be able to communicate through speech with the help of a suitable amplification aid, whilst a small proportion of these may only benefit from a cochlear implant. For those who are regarded as profoundly deaf, sign language continues to remain their sole means of communication.
What then are the causes of diminished audition? They fall into two categories – congenital and acquired. In the former category, genetic factors, both hereditary and non-hereditary, can be responsible, as can complications of pregnancy and childbirth. These include maternal infections, such as syphilis and rubella, and the use of certain drugs, such as anti-malarial products or diuretics during pregnancy. Complications of birth, including prolonged anoxia and neonatal jaundice, are also known causes of congenital hearing loss.
Among the factors responsible for acquired impairment are chronic ear infections, and infectious diseases, of which mumps, measles and meningitis are most commonly implicated. Head injuries, the use of common medications, including aspirin, ibuprofen and certain antibiotics, and exposure to various ototoxic chemicals, such as lead and toluene, are all known to be among the causes of deafness in a small proportion of subjects. However, by far the most common cause in both children and adults, worldwide, is prolonged and repeated exposure to excessive levels of noise, and none of us are immune to its potentially damaging effects. Now recognised globally as the leading form of work-related illness, and costing industries hundreds of millions in compensation claims each year, despite this, NIHL or noise induced hearing loss is preventable. All that is required are some well-fitting ear plugs.
While tightening legislation is helping to reduce the incidence of NIHL in the workplace, prevalence among the general public is growing, especially in teenagers and even pre-teens. Night club music and even that delivered by earphones from a portable music player can reach levels of 100dB or more, while repeated studies have shown that just 2 hours of exposure to a volume of 90dB is sufficient to cause permanent damage. More significant, however, is that this damage is cumulative and is compounded by further exposures, whether in a club, at work or on the street.
The onset of auditory impairment is gradual, and those affected are often the last to become aware of it. The signs, however, are evident enough, and include a frequent need to ask others to repeat themselves, and complaints by others about the high volume at which your radio or TV’s sound is set. Often, these signs are accompanied by a ringing in the ears. Together, these symptoms indicate that it is time for action, and the first step should be to consult an audiologist. At Ear Institute clinics, no referral is needed* and, following a physical examination of the ears, an audiogram is performed to determine the frequencies affected and the extent of the impairment.
Further tests differentiate between conductive and sensorineural hearing loss and, together with the audiogram, will determine the most suitable means with which to manage the condition, which in most cases, will be a hearing aid, adjusted to amplify sound at the frequencies affected. In addition, Ear Institute clinics offer cochlear implants for those with severe conductive or sensory impairment, and who are thus unable to benefit from conventional aids.
*Not all medical aids are equal; terms, conditions and exclusions may vary.