Hearing loss is best described by varying degrees, not percentages. Hearing loss may be "mild", "moderate", "moderately-severe", "severe" or "profound" and may vary across pitches.
The degree of loss is determined by a simple hearing test where the individual is presented with a variety of tones at different pitches and amount of volume. The volume or intensity of sounds that one hears is measured in decibels (dB). The softest whisper is 0 dB while a jet engine is as loud as 125 dB. The softest sounds one can hear are called thresholds. Normal hearing thresholds for adults range form 0 to 25dB.
What Is Hearing Loss?
Most permanent hearing loss is due to damage to hair cells in the cochlea located in the inner ear. Picture someone playing a piano with an entire section of keys not working because the strings inside the piano are missing. They are playing a song you should know but you don't recognize it because large segments of the music are missing. Well, that is how your brain is trying to hear if you are missing parts of the speech frequencies. Instead of damaged piano strings, large segments of hair cells are damaged. Just like the music, words can become unintelligible.
What Causes Hearing Loss?
The causes of hearing loss are many and the impact of each on hearing is varied. Sometimes the cause is readily apparent, such as a wax build-up in the external ear canal or an ear infection. At other times, the cause of the hearing loss is physiological or mechanical in nature.
Types of Hearing Loss
There are many kinds of hearing loss. Each one has its own unique causes and consequences.
Conductive Hearing Loss:
This type of hearing loss occurs when there is a problem with the way sound is conducted, or transmitted, to the inner ear where the cochlea is located. The problem may lie in the outer ear (pinna, auditory canal, or ear drum) or the middle ear (the ossicles or Eustachian tubes). The inner ear remains unaffected by this type of hearing loss.
Some causes of conductive hearing loss include outer or middle ear infections, complete blockage of the auditory canal by earwax buildup or introduction of a foreign object, a ruptured ear drum, deterioration or arthritic buildup of the ossicles, blockage of the Eustachian tubes, or absence of the outer or middle ear structures.
Conductive hearing losses may be temporary or permanent, depending on the source of the problem. Medical management in the form of antibiotics can be used in some cases to treat infections, and there are many excellent ear wash products that can effectively remove earwax buildup. Also, surgical procedures can be used to replace damaged or malfunctioning ossicles in severe cases. Finally, amplification may be a recommended treatment option in more long-standing or permanent cases.
Individuals with conductive hearing loss may report that sounds are muffled or quiet. Generally, when sounds are made louder, hearing improves in such individuals.
Sensorineural Hearing Loss:
This type of hearing loss occurs when there is damage to or an abnormality in the sensory hair cell receptors in the hearing system, specifically in the cochlea of the inner ear. Such abnormalities prevent sounds from being transmitted to the brain in a normal fashion, resulting in hearing loss.
The hair cells may have been abnormal from birth or damaged as a result of infection, drugs, trauma, or over-exposure to extremely loud sounds. People working in and around loud machinery are particularly susceptible to this type of hearing loss. It is also becoming more common in younger people who attend loud concerts or listen to music using headphones with the sound set too high. The condition can also be a result of the aging process, a kind of hearing loss known as presbycusis (pres-be-cue-sis).
Individuals with sensorineuronal hearing loss may report muffled speech, ringing in the ears (tinnitus), difficulty hearing when there is loud background noise, or complaints that other people do not speak clearly.
Hearing aids are generally recommended as a treatment option in such cases.
Mixed hearing Loss:
As its name implies, this condition occurs when a person has a sensorineural hearing loss in combination with a conductive hearing loss. This means there is a problem in the inner ear as well as in the outer or middle ear.
Mixed hearing loss is often treated with a combination of medical management and the fitting of proper hearing aids.
Neuronal Hearing Loss:
Neuronal hearing loss occurs when the auditory nerve that carries electrical impulses from the cochlea to the brain is missing, damaged, or abnormal. It is difficult to determine the exact location of neuronal hearing loss. Some causes of neuronal hearing loss include genetics, acoustic tumors, in-utero exposure to certain infections, severe jaundice in infancy, and low birth weight associated with premature birth.
Individuals with this type of hearing loss often have difficulty understanding speech, even when it is loud enough, as well as difficulties with background noise.
Amplification in the form of proper hearing aids may be recommended in some cases depending on the severity of damage to the auditory nerve.
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