Hearing Loss

Hearing loss, or deafness, is the partial or total inability to hear sound in one or both ears. The human ear is amazing. It is one of the smallest and most complex organs in the body, capable of turning the tiniest disturbances in air molecules into a form the brain can understand - and doing so instantaneously, over an enormous range of pitch and loudness. Considering the ear's delicacy, it is remarkably resilient. Nevertheless, illness or injury can impair our ability to hear properly.

In recent years, substantial advances have made it possible to determine the cause of hearing impairment in nearly all cases, and to treat the hearing loss in many ears.


Degrees of hearing loss

  • Normal hearing (0-25 dB): At this level, hearing is within normal limits.

  • Mild hearing loss (26-40 dB): Mild hearing loss may cause inattention, difficulty suppressing background noise, and increased listening efforts. Patients with this degree of loss may not hear soft speech. Children may be fatigued after listening for long periods.

  • Moderate hearing loss (41-55 dB): Moderate hearing loss may affect language development, syntax and articulation, interaction with peers, and self-esteem. Patients with this degree of loss have trouble hearing some conversational speech.

  • Moderate-severe hearing loss (56-70 dB): Moderate-severe hearing loss may cause difficulty with speech and decreased speech intelligibility. Patients with this degree of loss do not hear most conversational-level speech.

  • Severe hearing loss (71-90 dB): Severe hearing loss may affect voice quality.

  • Profound hearing loss (>90 dB): With profound hearing loss (deafness), speech and language deteriorate.


Types of hearing loss

  • Conductive

  • Conductive hearing loss has normal bone-conduction thresholds, but air-conduction thresholds are poorer than normal by at least 10 dB.

  • Conductive hearing loss is secondary to an outer ear or middle ear abnormality, which can include abnormalities of the tympanic membrane. The abnormality reduces the effective intensity of the air-conducted signal reaching the cochlea, but it does not affect the bone-conducted signal that does not pass through the outer or middle ear.

  • Examples of abnormalities include occlusion of the external auditory canal by cerumen or a mass, middle ear infection and/or fluid, perforation of the tympanic membrane, or ossicular abnormalities. Pure-tone air-conduction thresholds are poorer than bone-conduction thresholds by more than 10 dB (see image).
  • Sensorineural

  • Sensorineural hearing loss has bone- and air-conduction thresholds within 10 dB of each other, and thresholds are higher than 25 dB HL. (See image)

  • Sensorineural hearing loss is secondary to cochlear abnormalities and/or an abnormality of the auditory nerve or central auditory pathways. Because, in this type of hearing loss, the outer ear and middle ear do not reduce the signal intensity of the air-conducted signal, both air- and bone-conducted signals are effective in stimulating the cochlea. Pure-tone air- and bone-conduction thresholds are within 10 dB.

  • Examples included presbycusis, noise-induced hearing loss, Ménière disease, and retrocochlear lesions such as vestibular schwannoma.
  • Mixed

  • Mixed hearing loss has conductive and sensorineural components.

  • This type of hearing loss has sensorineural and conductive components. Pure-tone air-conduction thresholds are poorer than bone-conduction thresholds by more than 10 dB, and bone-conduction thresholds are less than 25 dB (see image).