Hearing loss may be partial or complete (deafness). Conditions affecting the outer ear and middle ear may affect the conduction of sound and is therefore known as conductive hearing loss. Another type of impairment is sensorineural hearing loss, which affects the conversion of mechanical sounds waves into electrical impulses which is then transmitted to the brain. This occurs in the inner ear.
In people of all ages, noise-induced hearing loss and earwax are the main causes of hearing loss, which is usually partial. In the elderly, age results in degenerative changes that may lead to hearing loss which is known as presbycusis (or presbyacusis).
Causes of Hearing Loss
The causes of hearing loss can be divided according to the affected component of auditory perception. As mentioned above, it may be either conductive or sensorineural. If both are involved, then it is referred to as mixed hearing loss.
Conductive Hearing Loss
- Wax buildup is the most common cause. Constant interference may cause impacted wax that forms a plug in the ear canal.
- Foreign bodies in the ear is more commonly seen in children and may cause sudden, unilateral hearing loss. Swelling of the ear canal firmly grasps the foreign body thereby making it difficult to remove and further occluding the canal.
- Trauma to the ear drum (perforation) and sometimes extending to the ossicles may arise from injuries like an ear slap or sharp objects inserted down the ear canal, or changes in pressure (barotrauma) due to diving or flying.
- Otitis externa and otitis media may result in partial, usually temporary, impairment of the sense of hearing. Most cases are acute. Otitis externa affects the ear canal and may be due to constant irritation with water, dust, dirt and foreign objects, followed by an infection. Otitis media is a middle ear infection resulting in an fluid accumulation (effusion) within the middle ear cavity.
- Fluid accumulation in the middle ear (effusion) is a feature of otitis media, especially chronic cases. These chronic infections can severely impair hearing – either resulting in loss of hearing or muffled sounds. Chronic untreated infections can result in damage to the eardrum and ossicles. A blocked eustachian tube is usually present.
- Blocked eustachian tube is often a result of an upper respiratory tract infection or middle ear infection. Mucus in the tube or swelling of the walls causes an occlusion. This allows for fluid accumulation in the middle ear or affects the equilibrium of air pressure on either side of the eardrum.
- Other less common causes include :
- Otosclerosis
- Tumors in the middle ear
Sensorineural Hearing Loss
- Noise-induced hearing loss (acoustic trauma) is a result of loud noises. This may be linked to prolonged exposure to moderate or loud noises within the work environment and is referred to as occupation-induced hearing loss. Both high volume and prolonged exposure to sound may result in acoustic trauma. Sudden, short bursts of sound higher than 120 dB (decibels) or prolonged exposure to sounds higher than 85dB may result in noise-induced hearing loss.
- Trauma including injury during childbirth, especially to the temporal bone of the skull.
- Prenatal infections like German measles (rubella) or herpes is known to cause hearing loss. This may remain unnoticed until after 3 to 6 months of age.
- Infections such as measles, meningitis, mumps and scarlet fever.
- Presbycusis (age-related hearing loss)
- Genetic disorders
- Other less common causes include :
- Acoustic neuroma
- Ménière’s disease
- Unknown causes (idiopathic)
