Hearing loss, or deafness, is the partial or total loss in one or both ears of the ability to transform sound vibrations into the electrical energy understood by the brain. Despite the ear’s delicate nature, it is remarkably resilient. Still factors such as aging, illness and injury can impair your ability to hear properly.
More than 28 million Americans have a hearing loss. And roughly 50 percent of American seniors have a hearing loss by age 65. Unfortunately, many patients avoid confronting the problem, and there is usually a delay of 5-7 years between a loss of hearing and a professional diagnosis. Given the ever-improving technology in amplification, this represents a great deal of lost time with poor hearing.
In hearing, sound is gathered by the outer ear, amplified by the eardrum and three tiny bones in the middle ear and transduced into an electrical nerve signal by the inner ear. This signal is sent via the hearing nerve to the brain. When the impulse reaches the auditory cortex of the brain, we experience the sensation of hearing.
Injury or disease at any point in the anatomy results in hearing loss. Thus, there are four basic types of hearing loss:
Conductive Hearing Loss
Conductive hearing loss (CHL) refers to a mechanical failure to move sound vibration from the outside world through the outer and middle ear to the inner ear. The simplest example is the plugging of your ear canal. Wax impaction in the ear canal and fluid build-up in the middle ear are perhaps the most common examples of dampening the transmission of sound through the ear. Otosclerosis is a less common, often inherited disease resulting in conductive loss.
CHL affects the lower frequencies and makes it especially difficult to hear vowel sounds. Since vowels contain the "power of speech" the person perceives speech and other sounds as being much "quieter" than normal. If the sound is loud enough, a person with a CHL can hear and understand clearly. Conductive hearing losses can often be treated.
Sensorineural Hearing Loss
Sensorineural hearing loss (SNHL) is the most common type of hearing loss and is caused by damage to the inner ear and/or the auditory nerve. Noise exposure, diseases, certain medications and aging can destroy parts of the inner ear and cause permanent hearing loss. Once damaged, the inner ear cannot be repaired. A "cochlear implant" is available for some who have a profound hearing loss and do not gain benefit from conventional hearing aids. Sometimes, SNHL is accompanied by intolerance to loud sounds.
In contrast to conductive hearing losses, SNHL hearing loss usually affects high frequencies the most, which impairs a person’s ability to perceive consonant sounds.
Mixed Hearing Loss
A mixed hearing loss occurs when you have both CHL and SNHL. For example, if a child who has permanent SNHL gets a middle ear infection, he or she will experience both a conductive and a sensorineural hearing loss.
Retro-Cochlear Hearing Loss
Retro-cochlear hearing loss is caused by problems of the hearing nerve or the part of the brain that receives signals from the hearing nerve. With retro-cochlear hearing loss, you may have poorer ability to recognize speech than might be suspected based on your ability to hear pure tones. An acoustic tumor may be involved and may lie on the auditory nerve, brainstem or in the brain.
The diagnosis of a hearing loss is made by taking a careful history, performing an accurate exam, and thoughtfully utilizing diagnostic testing, including audiometry (a hearing test), computed tomography (CT) and magnetic resonance imaging (MRI). At MOSA, we have on-site audiologist who is dedicated to aiding in the diagnosis and treatment of hearing loss, including fitting and dispensing hearing aids.