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# Introduction
Deafness is a partial or total inability to hear. WHO defines deafness as hearing threshold of 20dB or better in both ears.

# Classification
 may be classified according to WHO into 5 subtypes/groups:
- Mild- Hearing losses between 26 and 40 dB
- Moderate- Hearing losses between 41 and 55 dB
- Moderately severe- Hearing losses between  56 and 70 dB
- Severe - Hearing losses between 71 and 90 dB
- Profound - Hearing losses greater than 91 dB

# Pathophysiology
In general, sound waves reaching outer ear are conducted down the ear canal to vibrate eardrum, which in turn, transmitted to inner ear via 3 tiny bones. The fluid in the inner ear moves the hair cells which generate impulses that is conducted to brain via cochlear nerve. Any alteration or obstruction in these pathways can lead to hearing loss.
Often, hearing loss is caused by long-term exposure to loud noises, that damage the hair cells.

# Causes
Common causes of hearing loss include: Based on location
- External Ear
Congenital atresia of external auditory meatus (EAC)
Infection- Otitis externa
Trauma
Tumour
Benign Polyp
Cerumen
- Congenital atresia of external auditory meatus (EAC)
- Infection- Otitis externa
- Trauma
- Tumour
- Benign Polyp
- Cerumen
- Middle Ear
Atresia or malformation of ossicular chain
Eustachian tube dysfunction
Infection- Otitis media
Cholesteatoma
Otosclerosis
Jugulotympanic paragangliomas (glomus tumors)
Middle ear barotrauma-sudden, large change in ambient pressure, often during diving or flying
- Atresia or malformation of ossicular chain
- Eustachian tube dysfunction
- Infection- Otitis media
- Cholesteatoma
- Otosclerosis
- Jugulotympanic paragangliomas (glomus tumors)
- Middle ear barotrauma-sudden, large change in ambient pressure, often during diving or flying
- Inner Ear
Congenital malformation of cochlea
Presbycusis- old age related hearing loss
Infection- Viral cochleitis
Meniere disease
Noise exposure
Inner ear barotrauma
Ototoxic drugs
Systemic diseases- diabetic vasculopathy can cause cochlear ischemia
Tumors- acoustic neuroma
- Congenital malformation of cochlea
- Presbycusis- old age related hearing loss
- Infection- Viral cochleitis
- Meniere disease
- Noise exposure
- Inner ear barotrauma
- Ototoxic drugs
- Systemic diseases- diabetic vasculopathy can cause cochlear ischemia
- Tumors- acoustic neuroma

# Differential Diagnosis

# Epidemiology and Demographics
The incidence of hearing loss increases with age. 
In the Beaver Dam cohort in the United States, the prevalence of hearing loss, defined by audiometry:
3 percent ages 21 to 34
6 percent ages 35 to 44
11 percent ages 44 to 54
25 percent ages 55 to 64
43 percent ages 65 to 84
World Health Organization estimates that hearing loss affects 538 million people worldwide.

# Risk Factors
The most potent risk factor in the development of hearing loss is aging. Other risk factors include hereditary causes, occupational noises such as noises from factories, recreational noises such loud noises from firearm or jet engine, ototoxic drugs and illness such as meningitis or diabetes. Some other risk factors for hearing loss could be due to  head trauma and viral infections.

# Natural History, Complications and Prognosis

# Diagnosis
The diagnosis of hearing loss is based on the inability to hear sound( louder than 20dB) based on audiometer test.

# Treatment
Patients with infective aetiology for hearing loss are treated with Antibiotics and analgesics, whereas patients with non-infective/ structural causes are managed with hearing aids and cochlear implants .