What Are the Types of Hearing Loss?
07 December 2020
The human ear is a fascinating and complex piece of engineering. In a normal functioning ear, sound arrives at the outer ear, or pinna, and travels down the ear canal, where it meets the tympanic membrane, also known as the eardrum. The sound waves vibrate the eardrum, which in turn vibrates three tiny bones in the middle ear in a chain reaction.
These three tiny bones, the tiniest in the human body, are called the malleus, incus, and stapes. The vibration of these three bones culminates in a pumping motion that causes movement in the cochlea in the inner ear, a small, snail-shaped organ that is filled with fluid. Hair cells inside the cochlea are stimulated by the movement of the fluid in the cochlea, sending a signal to the auditory nerve, which in turn, carries the signal to the brain, where it is interpreted and recognized as sound. The entire process takes a split second to complete.¹
Obviously, in a system this complex, sometimes things can go wrong. There are three types of hearing loss, conductive, sensorineural, and mixed hearing loss (a combination of conductive and sensorineural). A comprehensive audiological evaluation is necessary to identify which type and severity of hearing loss an individual has, as well as treatment steps.
Conductive hearing loss
Conductive hearing loss occurs when there is a disturbance to one or more of the structures in the outer or middle ear. Causes of conductive hearing loss can include fluid in the middle ear space from congestion due to allergies or colds, perforations (holes) in the eardrum, benign tumors, impacted cerumen (earwax), presence of a foreign body in the ear canal, infection in the outer ear canal (often called Swimmer’s Ear), poor Eustachian tube function, or absence or malformation of the outer ear, ear canal, or middle ear.
Another common cause is otosclerosis, or a stiffening of the chain of bones in the middle ear. Conductive hearing loss results in a reduction of the intensity of the sound that reaches the inner ear, but where the inner ear itself is intact. This means that an individual with conductive hearing loss would usually find that as long as a sound is loud enough, they are able to hear it clearly and without distortion. The cause of conductive hearing loss can be often identified and treated medically or surgically, and partial or total improvement to the hearing loss is often possible.²
Sensorineural hearing loss
Sensorineural hearing loss occurs when there has been damage or dysfunction of the inner ear, or the auditory nerve. The most common form of sensorineural hearing loss is age-related hearing loss, also known as presbycusis. Other common causes of sensorineural hearing loss can include noise trauma, genetic hearing loss, medications that are toxic to hearing, head trauma, malformation of the inner ear, illnesses and/or high fever, and even tumors on the auditory nerve. This type of hearing loss can be sudden or gradual. Sensorineural hearing loss includes a reduction in the loudness of the sound like conductive hearing loss, but unlike those with conductive hearing loss, a reduction in speech understanding ability is often present. It is usually irreversible and permanent.
Mixed hearing loss
Mixed hearing loss is a combination of both conductive and sensorineural hearing losses, and is often reflective of two or more different conditions affecting the ear in both the inner ear, and the outer or middle ear. It may require a combination of treatments.³