Hearing loss occurs when there is a problem with one or more parts of the ear and can affect people of all ages. But to understand the causes of hearing loss, it’s useful to have a basic grasp of normal function. 

In air conduction, sound waves travel through the external ear canal to vibrate the eardrum. The vibration of the eardrum is transmitted to the hearing organ (cochlea) via three small bones (ossicles) in the middle ear. This stimulates the sensory cells in the cochlea, which then sends impulses to the hearing nerve (auditory nerve) and onto the brain. 

Hearing by bone conduction occurs when sound waves cause the bones of the skull to vibrate, which directly stimulate the hearing organ (cochlea), resulting in hearing.

Hearing Loss Causes

There are two types of hearing loss, and they may have different causes. 

Conductive Hearing Loss

Conductive hearing loss occurs when sound waves cannot be transmitted properly from the external environment to the cochlea. The problem could lie in the outer ear canal, eardrum, middle ear bones or middle ear space. Common causes of conductive hearing loss include:

• Obstruction in the external ear canal is caused by wax, foreign body or infection (otitis externa).
• Perforated eardrum — usually a result of trauma or chronic infection.
• Dislocated, damaged, or fixed ossicles (malleus, incus or stapes) — from trauma or chronic diseases that erode the ossicles over time or otosclerosis that cause the ossicles to be fixed.
• Otitis media — a middle ear infection, usually with fluid in the middle ear space.

Sensorineural Hearing Loss

Sensorineural hearing loss occurs when there is damage to the hearing organ (cochlea) or hearing nerve (auditory nerve). Common causes include:

• Ageing (presbycusis)
• Acute and chronic exposure to loud noise can cause damage to the sensory cells in the cochlea
• Infections of the inner ear by viruses and bacteria such as mumps, measles and influenza
• Ménière disease — a disease that causes tinnitus, hearing loss and dizziness
• Acoustic neuroma — a tumour of the vestibular nerve, which lies in close proximity to the auditory nerve and affects its function
• Ototoxic drugs — some drugs can damage the nerves involved in hearing or the sensory cells in the cochlea. Examples include:

1. Antibiotics including aminoglycosides (gentamicin, vancomycin)
2. Diuretics including frusemide
3. Antineoplastics (cancer drugs)

Hearing Loss Symptoms

Hearing loss may be gradual or sudden and can affect one or both ears.

The affected person usually complains of difficulty in holding a normal conversation, especially in a noisy environment. There may be complaints from others around that the person does not respond when called or speaks louder than normal.

There may be associated symptoms like tinnitus (ringing in the ears) or vertigo (spinning sensation).

Pain and discharge from the ear are often associated with ear infections.

Hearing Loss Prevention

Noise-induced hearing loss is usually irreversible and progresses with each exposure. People who work with heavy machinery or in the construction industry should use proper ear protection when working around loud noises, especially when working for prolonged periods. They should also undergo regular hearing tests to ensure that their hearing is not worsening. Youngsters should not use earphones or visit discotheques. 

Hearing Loss Diagnosis and Hearing Tests

A complete history, ENT examination and relevant investigations are necessary for a diagnosis. The ENT physician will perform a thorough head and neck examination, particularly the ear canal and tympanic membrane. An endoscopic examination of the nose and nasopharynx may also be necessary. Occasionally, a neurologic examination will be done.

A hearing test (audiogram) will be performed to confirm the presence and indicate the severity and type of hearing loss. A tympanogram may also be performed to detect problems of the eardrum and middle ear. Radiological imaging studies such as CT scans or MRIs (magnetic resonance imaging) may be ordered to detect an acoustic neuroma.

Hearing Loss Treatment Options

Medical Treatment for Hearing Loss

Medical treatment depends on the underlying problem. Treatment may range from observation and reassurance to medications and a discussion on surgical options. If the cause of hearing loss is due to wax and foreign body in the ear canal, it can be removed under a microscope by the ENT surgeon.

In cases of external ear infections, a topical antibiotic is needed. If there is an eardrum perforation, the underlying infection has to be treated. Surgical repair of the ear perforation may be necessary if the perforation persists for more than three months or there is a problem of recurrent ear infections with ear discharge. If the cause of the hearing loss is due to medication, the medication will be stopped or changed.

For presbycusis (hearing loss due to old age), no treatment is needed though the affected individual will be advised to protect his hearing and evaluated on whether hearing aid help is needed.

Hearing Aids

Conventional hearing aids are amplification devices that detect environmental sounds and present and amplify them into the external ear canal. They are useful for both conductive as well as sensorineural hearing loss. The modern aids vary from very small completely-in-the-canal to the traditional behind-the-ear hearing aids. A trained audiologist will help customise the hearing aid for optimal sound.

The side effects of hearing aids include occlusion effect (sense of blockage of the ear), feedback and a propensity for ear infections.

Hearing Implants

With advances in technology, implants to aid hearing have been developed. Two main types of surgical implants are available. Middle ear implants are used in people who have tried hearing aids but are unable to use them or fail to benefit from them. It can be used for those with sensorineural hearing loss and conductive hearing loss. It comprises of a transducer that is attached to the ossicles or directly to the round window (part of the cochlea). It vibrates the middle ear structures and amplifies the transmission of sound.

Cochlear implants are used in someone with moderate to severe sensorineural hearing loss. The ENT surgeon will insert the electrical electrode of the implant directly into the cochlea and directly stimulate the nerve endings in the cochlea to bypass any problem in the cochlea. Cochlear implants are used in both paediatrics and adults. 

For information about hearing tests, read more here. If you have a question about hearing loss, it may have been answered here.  Read this article to learn what can cause hearing loss in children. 

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