The human person has five biological special senses – hearing, taste, sight, smell, and touch. These senses are perceived by the ear, tongue, eye, nose, and skin respectively. An impairment in the working of any of the above will result in a significant drop in the quality of daily life.
Hearing loss (deafness) is the complete or partial (in which case, hearing impairment is the most appropriate term to employ) inability to hear or appreciate the sound. It accounts for a significant cause of morbidity and mortality, especially in low resource geographies where availability and cost of hearing aids is a luxury most cannot afford.
Normally, human beings can appreciate sound frequencies ranging from 20Hz to 20KHz. Any defects resulting in a diminished perception of this range of frequency will result in hearing loss.
According to the National Institute on Deafness and Other Communication Disorders, disabling hearing loss affects about 2% of adults aged between 45 to 54, 8.5% of adults aged 55 to 64, and nearly 25% of those aged 65 to 74%
Degrees of Hearing Loss
Depending on the severity, hearing impairment can be:
Mild: Individuals with mild hearing loss can hear sounds of frequencies between 25 decibels and 29 decibels. When these individuals find themselves in a noisy environment, they find it difficult to hear spoken words.
Moderate: Individuals with moderate hearing loss can appreciate sound intensities between 40 to 69 decibels. They usually require hearing aids to engage in meaningful and coherent communication.
Severe: Persons in this category can only appreciate very high sound intensities (above 70 to 89 decibels). For these individuals, using a hearing aid does not completely eliminate the difficulties in sound perception, hence the need to incorporate other means of language comprehension like sign-language and lip-reading.
Profound: This is the most severe form of hearing loss. Sound intensities below 90 decibels cannot be heard, some are even incapable of sound appreciation, irrespective of sound intensity. They depend on sign language, lip-reading, or the use of pen and paper.
Types of Hearing Loss
There are several types of hearing loss or deafness. This is classified based on the nature/pathophysiology of the underlying cause and whether it is one-sided or not.
Based on the Nature or Pathophysiology of Hearing Loss
Conductive hearing loss: In this form of deafness, there is defective conduction of sound from the outer ear to the inner ear–from where impulses are transmitted to the brain for interpretation. Several factors account for this type of hearing, including a perforated eardrum, defective or malformed eardrum, excessive buildup of earwax, glue ear, ear infections, the fusion of ear bones, etc.
Sensorineural Hearing Loss: This type of hearing loss is due to damage to the inner ear, the sound conversion organ – cochlea, auditory nerve, or the brain. The most common cause of this form of deafness is the damage to the cochlea hair cells, which is responsible for converting sound waves into nerve impulses. Senile hearing loss arises because of the deterioration in the function of these hair cells as one age. Also, a common cause of loss of hair cell function is chronic exposure to loud sounds.
Mixed Hearing Loss: As the name implies, this type arises from both conductive and sensorineural causes. An infection resulting in the fusion of ear ossicles (bones) and concurrent damage to the cochlea and auditory nerve results in a mixed type of hearing loss.
Based on the Side Affected
Unilateral Hearing Loss: This is when only one ear is affected. Persons with this type of hearing loss find it difficult to hear sounds that are coming from the affected side. Also, localization of the source of sound is often a herculean task, especially in the presence of a lot of background noise.
Bilateral Hearing Loss: Hearing from both ears is impaired and, if severe, it will result in dependence on alternate means of communication, like lip-reading and sign language.
Hearing loss can also be classified as being congenital or acquired. Congenital hearing loss is evident following weeks or months of birth when the newborn does not respond to sound as seen in the pediatric startle response. Acquired deafness occurs postnatally and can be due to trauma, infection, or adverse reaction to drugs.
Causes of Hearing Loss
The following have a causal relationship to deafness
- Congenital syphilis
- Lyme disease
- Streptomycin in the management of tuberculosis
- Quinine-based medications
- Non-steroidal anti-inflammatory drugs
Other causes include:
- Diabetic neuropathy
- Secondhand smoking
- Head trauma
- Heredity as seen in Alport’s syndrome
Health Risks Associated with Hearing Loss
With the obvious benefits of sound perception, the diminution or loss in this sense is associated with various risks. These include but are not limited to:
- COGNITIVE IMPAIRMENT AND DEMENTIA: According to a British study, an untreated hearing is top on the list of modifiable risk factors of dementia – a progressive decline in cognitive function. Several theories have been put up to explain the relationship between hearing loss and declining brain function. Particularly interesting is the theory of disuse neuro-atrophy. This theory proposes that decreased sensory input to the brain causes brain atrophy, which ultimately results in dementia.
- SOCIAL ISOLATION AND DEPRESSIVE MOOD DISORDERS: This stems from the impedance to effective communication imposed by hearing loss. These individuals gradually pull away from social encounters, becoming more and more introverted until stress overruns them and they fall neck-deep into depression. It is a vicious cycle – their physical health deteriorates as they isolate themselves and they become more isolated as their health deteriorates.
- FALLS: It is not yet clear how hearing loss results in falls, but a study of 2,000 people found that those with severe and profound hearing loss recorded a higher number of falls.
- DIABETES AND HEART DISEASE: The vasculopathy associated with diabetes might affect blood flow to the Cochlea, leading to hearing loss. Hence, hearing loss can be an important indicator of diabetic risk. Diabetes is linked to heart diseases, but it is still unclear how hearing loss has a causal relationship with heart diseases.
- INCREASED INCIDENCE OF ROAD TRAFFIC ACCIDENTS: This is quite understandable as hearing is an effective alarm system to impending danger. Individuals with severe hearing loss are at an increased risk of road traffic accidents as they are unable to be alarmed by horning by speeding vehicles.
- SPEECH DIFFICULTY: This is particularly evident in pre-lingual deafness – deafness that occurs before the onset of speech in children. Language learning requires both an input, hearing, and an output mechanism. The defect in either will impede the learning process. Thus, a child cannot vocalize a sound he/she is unable to perceive. This speech difficulty can affect the child’s social interaction and overall mental state.
Symptoms of Hearing Loss
- Difficulty understanding words, especially under background noise
- Gradual need to increase the volume of the television or other electronic before sound can be appreciated
- Muffling of speech
- Difficulty hearing consonants of the alphabet
- Frequently straining your ear or asking people to speak loudly and slowly
- Increasing social withdrawal.
Diagnoses of Hearing Loss and Treatment
It is important to note that when any of the above is noticed, it is time to schedule a visit with an audiologist – a doctor that deals with the problems of the ear and hearing. The doctor will ask you several questions and perform a hearing test. Following a diagnosis, the doctor may recommend a hearing aid.
If you are not sure whether you have any form of hearing impairment, many online websites provide fast and easy hearing tests. You can take a hearing test online by visiting www.mdhearingaid.com
Prevention is advocated to be better than seeking a cure. Here are some preventive measures against hearing loss:
- Avoid recreational or occupational risks like those that expose you to loud noise.
- Protect your ears by using earplugs or glycerin-filled earmuffs.
- Have your ears tested regularly if you are constantly exposed to loud noises. This will aid in early diagnosis and treatment.
- Avoid harmful practices like the insertion of sharp or rough tools into the ear.
Hearing impairment is a significant health burden that causes disability and a reduction in the quality of life. Regular hearing tests, avoidance of predisposing factors, and early diagnosis can result in better outcomes in individuals.