Hearing loss is best described by the degree and type of loss and not by percentages. Hearing loss may be mild, moderate, moderately-severe, severe or profound and may vary across pitches. It is determined by a simple hearing test as the amount of volume loss you experience compared to an accepted standard of normal hearing. The volume, or intensity, of sounds you hear is measured in decibels (dB), 0 dB being the softest whisper and 120 dB being equivalent to a jet engine. The softest sounds one can hear are called thresholds. Normal hearing thresholds for adults are considered to be between 0 to 20 dB.
Conductive Hearing Loss
Conductive hearing loss occurs when there is a problem with the way sound is conducted to the inner ear or cochlea. The problem may lie in the outer ear (pinna or ear canal), eardrum (tympanic membrane), or the middle ear (ossicles and Eustachian tube). The inner ear remains unaffected in this type of hearing loss.
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.
Some causes of conductive hearing loss can include middle ear fluid, 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.
Most conductive hearing losses are temporary, but some can be long lasting or permanent. Medical or surgical treatments can correct some causes of conductive hearing loss, while amplification may be a recommended treatment option in more long-standing or permanent situations.
Sensorineural Hearing Loss
Sensorineural (sen-sory-nuhral) hearing loss occurs when there is a problem with the neurologic transmission of sounds in the hearing system. Most generally this occurs in the cochlea of the inner ear. The majority of sensorineural hearing loss occurs as a result 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 infection, drugs, trauma, or over-exposure to noise. Most commonly, however, the hair cells of the cochlea gradually deteriorate over time as a result of the aging process. This type of loss is known as presbycusis (pres-be-cue-sis).
Sensorineural hearing losses are generally permanent and may generally remain stable or worsen over time. Routine hearing tests are needed to monitor the progression of the hearing loss. Amplification, including hearing aids or other devices, are 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. The most common description of sensorineural hearing loss is that a person can hear that someone is talking, but cannot always understand what they are saying.
Mixed Hearing Loss
Mixed hearing loss occurs when a person has a 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 component may be temporary or permanent, depending on the source of the problem.
Mixed hearing loss can sometimes be treated with medical or surgical 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. 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.
Individuals with neural hearing loss often have difficulty understanding speech, even when it is loud enough, especially in the presence of background noise.
Amplification may be recommended in some cases of neural hearing loss depending on the severity of the damage to the hearing nerve. And, depending on the cause, other treatment options may be beneficial.