The ear is comprised of three parts: the outer ear, the middle ear, and the inner ear. Each part of the ear has a different function. The primary function of the outer is to carry sounds to the middle ear. Sound becomes amplified in the middle ear before traveling to the inner ear. The inner ear converts the sound into nerve impulses, which are transmitted to the brain so that you may perceive the sound. Hearing loss occurs when there is loss of sound sensitivity produced by an abnormality anywhere in the auditory system.
Types of Hearing Loss:
Conductive Hearing Loss
A conductive hearing loss occurs when sounds cannot efficiently travel from the outer ear to the tympanic membrane (ear drum) and through the ossicles (the tiny bones in the middle ear). Conductive hearing loss involves a reduction in sound level, and the ability to hear very soft sounds. This type of hearing loss is usually medically or surgically corrected.
Some examples of conditions that can cause a conductive hearing loss are:
- Any middle ear pathology such as fluid in the middle ear from colds, allergies (serous otitis media), Eustachian tube dysfunctions, ear infection (otitis media), perforated eardrum and benign tumors.
- Impacted earwax in the ear canal
- Infections in the ear canal (external otitis)
- Presence of any foreign body
- Any absence or malformation of the outer ear, the ear canal or the middle ear
Sensorineural Hearing Loss
Sensorineural hearing loss occurs when there is any damage to the inner ear, the cochlea, or to the nerve pathways from the inner ear (retrocochlear) to the brain. Unfortunately, sensory/neural hearing loss cannot be surgically or medically corrected. It is a permanent hearing loss. A sensory/ neural loss affects the ability to hear soft sounds and it also affects speech understanding, how clear a person hears and understands speech and environmental sounds. A sensory/neural hearing loss may be caused by several factors such as: diseases, birth injury, ototoxic drugs, and genetic syndromes. A sensory/neural hearing loss may also be the result of noise exposure, viruses, head trauma, aging (presbycusis) and tumors.
Mixed Hearing Loss
When a hearing loss results from both a conductive loss and a sensory/neural loss the term mixed hearing loss is used. This usually indicates damage to the outer ear/middle ear and the cochlea(inner ear) or auditory nerve.
Degree of Hearing Loss
Degree of hearing loss refers to the severity (or how bad) of the hearing loss. Degree usually falls within five major categories.
|Degree of Loss|
|Normal hearing or no hearing loss||0 dB to 20dB|
|Mild hearing loss||21 dB to 40 dB|
|Moderate hearing loss||41 dB to 60 dB|
|Severe loss||61dB to 90dB|
|Profound hearing loss||91dB and above|
Configuration of Hearing Losses
The configuration of a hearing loss looks at the shape of the hearing loss as it relates to each frequencies and the overall picture of hearing that is created on the audiogram. A hearing loss that affects the higher frequencies typically is referred to as a high frequency hearing loss. A high frequency configuration would show good hearing in the low to mid frequencies and poor hearing in the high frequencies. The opposite will be true for a low frequency hearing loss, where the individual would have better hearing in the higher frequencies and poor hearing in the lower frequencies.
Some hearing loss configurations can be flat, indicating that the same amount of hearing loss occurs across all the frequencies on the audiogram.
Other descriptors associated with hearing loss are:
- Bilateral versus unilateral. Bilateral hearing loss means both ears are affected. Unilateral hearing loss means only one ear is affected.
- Symmetrical versus asymmetrical. Symmetrical hearing loss means that the degree and configuration of hearing loss are the same in each ear. An asymmetrical hearing loss is one in which the degree and/or configuration of the loss is different for each ear.
- Progressive versus sudden hearing loss. Progressive hearing loss is a hearing loss that becomes increasingly worse over time. A sudden hearing loss is one that has an acute or rapid onset and therefore occurs quickly, requiring immediate medical attention to determine its cause and treatment.
- Fluctuating versus stable hearing loss. Some hearing losses change — sometimes getting better, sometimes getting worse. Fluctuating hearing loss is typically a symptom of conductive hearing loss caused by ear infection and middle ear fluid, but also presents in other conditions such as Meniere’s disease.