About Hearing Loss
Types of Hearing Loss
The degree of hearing loss a person has is measured by testing the sensitivity to a sampling of the frequencies that occur in and make up all the sounds of human speech. Hearing loss may be described as being mild, moderate, moderately-severe, severe or even profound depending on the level of intensity necessary for the person to hear the frequencies tested throughout the speech listening range.
The level of the softest sound a person is able to hear at any particular speech frequency would be described as the threshold for hearing at that frequency. This threshold level of sound is expressed in decibels (dB). The softer sounds such as 0 dB are softer than a whisper and with 120 dB as loud as a jet engine .Normal hearing thresholds for adults are considered to be 0 to 20 dB. If a person can hear all the sounds on the hearing test at between 0 and 20 decibels of intensity hearing is considered to be within normal hearing limits.
Conductive Hearing Loss
Conductive hearing loss occurs when there is difficulty with sound getting to the inner ear. The problem may lie with the outer (pinna and ear canal) or middle ear (eardrum and ossicles) whose job it is to amplify external sounds going into the inner ear.
Some causes of conductive hearing loss can include outer or middle ear infections, complete earwax blockage, deterioration of the middle ear bones (ossicles), fixation of the ossicles (otosclerosis), a hole in the tympanic membrane, or absence of the outer ear or middle ear structures.
Conductive hearing losses may be temporary or permanent, depending on the source of the problem. Medical management can correct some cases of conductive hearing loss, while 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, these individuals can hear well again.
Sensorineural Hearing Loss
Sensorineural (sen-sory-nuhral) hearing loss occurs when there is a problem with the sensory receptors of the hearing system, specifically in the cochlea of the inner ear. The majority of sensorineural hearing loss occurs as a result of an abnormality or damage to the hair cells in the cochlea. This abnormality prevents sound from being transmitted to the brain normally, resulting in a hearing loss.
The hair cells may have been abnormal since birth (congenital), damaged as a result of genetics, infection, drugs, trauma or over-exposure to noise (late-onset or acquired), or damaged as a result of the aging process, a kind of hearing loss known as presbycusis (pres-be-cue-sis).
Sensorineural hearing losses are generally permanent and may stay stable or worsen over time. Routine hearing tests are needed to monitor the level of hearing loss. Amplification, including hearing aids or cochlear implants in the most severe cases, is a common treatment recommendation.
Individuals with sensorineural hearing loss may report muffled speech, ringing in the ears (tinnitus), difficulty hearing in background noise or that others do not speak clearly.
Mixed Hearing Loss
Mixed hearing loss occurs when a person has an existing sensorineural hearing loss in combination with a conductive hearing loss. It is, very literally, a mix of sensorineural and conductive hearing losses. This means there is a problem in the inner ear as well as in the outer or middle ear. The conductive hearing loss may be temporary or permanent, depending on the source of the problem.
Mixed hearing loss can sometimes be treated with medical management, and hearing aids are a common treatment recommendation.
Neural Hearing Loss
Neural hearing loss occurs when the auditory nerve that carries impulses from the cochlea to the brain is missing or abnormal. It is difficult to determine the exact location of neural hearing loss. Some causes of neural hearing loss include genetics, acoustic tumors, in-utero exposure to certain infections, severe jaundice in infancy and low birth weight associated with premature birth.
Amplification may be recommended in some cases of neural hearing loss depending on the severity of the damage to the hearing nerve.
Individuals with neural hearing loss often have difficulty understanding speech, even when it is loud enough, as well as in background noise.