CAUSES FOR HEARING LOSS & DEAFNESS

The Hearing Process can be summarized into a one sentence as; altering an acoustic stimulus that enters and move through our ear canals, into a form of neurological message that the brain can identify, process and comprehend. 

Simply, hearing process can be described by 6 basic steps.

1. Sound transfers into the ear canal and causes the eardrum to move
2. The eardrum will vibrate with vibrates with the different sounds
3. These sound vibrations make their way through the ossicles to the cochlea
4. Sound vibrations make the fluid in the cochlea travel like ocean waves
5. Movement of fluid in turn makes the hair cells. The auditory nerve picks up any neural signals created by the hair cells. Hair cells at one end of the cochlea transfer low pitch sound information and hair cells at the opposite end transfer high pitch sound information.
6. The auditory nerve moves signals to the brain where they are then translated into recognizable and meaningful sounds. It is the brain that “hears”.

Head trauma, neurologic diseases, medical disorders or the process of simply aging, can result in changes in the ability of the brain to process auditory stimuli effectively. This can lead to symptoms that indicate hearing loss; such as poor attention, inappropriate responses, and confusion. 

Hearing loss and deafness can be considered as the most common sensory defect among humans and affecting human population in 10 percent of people aged 65 years or older. 

It is important to identify the different levels of hearing loss or deafness. Hearing loss can be defined as a reduced ability to hear sounds in the same way as other people. Deafness occurs when a person cannot understand speech through hearing, even when sound is amplified. 

There are four levels of deafness or hearing impairment. 

• Mild deafness or mild hearing impairment: The person can only detect sounds between 25 and 29 decibels (dB). They may find it hard to understand the words other people are saying, especially if there is a lot of background noise.
• Moderate deafness or moderate hearing impairment: The person can only detect sounds between 40 and 69 dB. Following a conversation using hearing alone is very difficult without using a hearing aid.
• Severe deafness: The person only hears sounds above 70 to 89 dB. A severely deaf person must either lip-read or use sign language in order to communicate, even if they have a hearing aid.
• Profound deafness: Anybody who cannot hear a sound below 90dB has profound deafness. Some people with profound deafness cannot hear anything at all, at any decibel level. Communication is carried out using sign language, lip-reading, or reading and writing.

Hearing loss is a multi-factorial defect caused by both genetic and environmental factors. 

However, when a hearing loss occurs due to genetic factors, most commonly, mutations in a single gene can lead to hearing loss.  These kind of hearing losses can be inherited from generation to generation through various kinds of genetically transmitting methods including autosomal dominant, autosomal recessive, X-linked or mitochondrial mode. This type of hearing loss can be defined as hereditary hearing loss. Hereditary hearing loss and deafness can be divided into two categories; syndromic or nonsyndromic. Syndromic hearing impairment is associated with malformations of the external ear, with malformations in other organs, or with medical problems involving other organ systems. Nonsyndromic hearing impairment has no associated visible abnormalities of the external ear or any related medical problems; however, it can be associated with abnormalities of the middle ear and/or inner ear.

According to the physiology of hearing, there are three different types of hearing loss:

1. Conductive hearing loss
2. Sensorineural hearing loss 
3. Mixed hearing loss

Conductive hearing loss- This means that the vibrations are not passing through from the outer ear to the inner ear, specifically the cochlea. This type can occur for many reasons, including:

• an excessive build-up of earwax
• glue ear – empty middle part of the ear canal fills up with fluid
• an ear infection with inflammation and fluid buildup- Ear infections can leave scar tissue, which might reduce eardrum function.
• a perforated eardrum
• malfunction of eardrum ossicles (the smallest bones which are in middle ear)- due to infection, trauma, or fusing together in a condition known as ankylosis (a condition of abnormal stiffening and immobility of a joint due to fusion of a bone).
• a defective eardrum

Sensorineural hearing loss –This kind of hearing loss is normally due to damaged hair cells in the cochlea. As humans grow older, hair cells lose some of their function, and hearing deteriorates. Long-term exposure to loud noises, especially high-frequency sounds, is another common reason for hair cell damage. Damaged hair cells cannot be replaced. Sensorineural total deafness may occur as a result of congenital deformities, inner ear infections, or head trauma. And also can occur due to damage to the auditory nerve and brain damage.

Mixed hearing loss– This is a combination of conductive and sensorineural hearing loss. Long-term ear infections can damage both the eardrum and the ossicles. 

Except the previously mentioned conditions in the ear and damaging to the neural pathways which are responsible for hearing process, there are several other diseases that can cause deafness. In these cases hearing loss occurs as a secondary impairment of that particular disease. The diseases including chicken pox, cytomegalovirus, mumps, syphilis and lyme disease are considered as common infectious diseases causing for deafness. Inflammatory conditions like meningitis, arthritis also can be causative diseases for deafness. Few recent studies have shown that people with diabetes are more likely to have some kind of hearing loss. The people with the condition called “sickle cell disease” which occurs due to a mutation in a gene, which leads to the production of an abnormal version of heamoglobin molecule, also tend to experience some extent of hearing loss. As well as patients with cancers and hyperthyroidism, also tend to experience hearing loss.

According to the amount of hearing in relation to starting to speak or understanding speech of a child, hearing loss can be categorized further into two categories. Those categories are pre-lingual deafness and post-lingual deafness.

Pre-lingual deafness-This is an inability to fully or partially hear before learning how to utter or understand speech.

An individual with pre-lingual deafness was born with a congenital deformity or will have lost hearing during infancy. In the majority of cases, people with pre-lingual deafness have hearing parents and siblings. Many are also born into families who did not already know sign language. They consequently also tend to have slow language development. The few who were born into signing families tend not to face delays in language development. If children with pre-lingual deafness are given cochlear implants before the age of 4 years, they can acquire oral language successfully.

Post-lingual deafness- Most people with hearing loss have post-lingual deafness. They acquired spoken language before their hearing was diminished. A medication side effect, trauma, infection, or disease may have caused losing their sense of hearing. In most of people with post-lingual deafness, hearing loss onsets gradually.

However, deafness can occur at birth or become evident later in a person’s life.  Anyone could get hearing loss due to some kind of reason in any time in a lifetime. Consider disability as an identity. Ask how people experiencing deafness identify with their disability. Let’s gather with the deaf community, and let’s see deafness as a diversity in human experience rather than a different ability or a disease that needs to be always cured.

Penned by Piyumi Nadeesha