Hearing loss is described by type and degree of loss. The type of hearing loss is determined by the location of the dysfunction. The degree of loss is determined by how much power is needed to hear sound. The ear is divided into the outer ear, middle ear and inner ear. In this article, I will discuss at the outer and middle sections of the ear as well as any hearing loss that may originate in these areas.
Outer Ear Anatomy and Function
The outer ear extends from the pinna (the area your glasses sit on) through the entire ear canal. The shape and structure of the pinna and the ear canal assist in increasing particular pitches or frequencies that you hear. These frequencies are increased by 10-12 dB because of the design of the pinna. The shape of the pinna helps to localize sound and determine the elevation or height of a sound. In addition, the outer ear helps to distinguish sounds that come from in front of you verses those that come from behind you. The canal protects the middle ear and houses glands that secrete an oily substance that helps keep the canal healthy (and that insects find noxious!).
Hearing Loss of the Outer Ear
If the pinna is absent, you can still hear as long as the canal is completely formed. However, if the canal is absent or only partially open, a hearing loss will be evident. A hearing loss occurs when the sound is unable to reach the middle ear. This impairment creates a conductive hearing loss. A conductive hearing loss can be caused by anything obstructing the ear canal. Examples of possible obstructions are: excessive wax, a foreign object, collapsed canal or external otitis, which is excessive inflammation of the canal wall and is very painful!
Middle Ear Anatomy and Function
The middle ear is a small air filled cavity that is lined with mucous membrane. Inside this cavity are the smallest bones in the body called the ossicular chain. These tiny bones are connected together by ligaments and two tiny muscles. The middle ear bones’ primary function is to increase the level of sound into the inner ear by 25-30 dB. This is due to the lever mechanism of the ossicular chain and the size difference between the eardrum and the connection to the inner ear. Air is introduced into the middle ear via a tube called the eustachian tube. This tube extends from the middle ear to the upper part of the throat. This tube is designed to remain closed and will open to equalize pressure when a person yawns or swallows. The air in this cavity allows the eardrum to vibrate and in turn send sound vibration into the inner ear.
Hearing Loss of the Middle Ear
If there is a hole in the eardrum, absent eardrum or a significantly scarred eardrum, a conductive hearing loss may occur. If the bones of the ossicular chain become soft, spongy or the attachments between the bones become stiff and inflexible, a conductive loss occurs. Abnormal eustachian tube function will result in abnormal positive or negative pressure in the middle ear. Prolonged negative pressure creates a buildup of fluid in the middle ear cavity, causing a conductive hearing loss. Abnormal middle ear pressure may cause your own voice to sound louder than normal to you when you speak. This may be extremely distracting if it occurs for a long period of time.
Treatment for Conductive Hearing Loss
Surgical treatment and hearing aid treatment for conductive hearing loss has vastly improved in the last 15 years. Conductive hearing loss may be a medically manageable condition; an ear infection may require treatment; an eardrum may be repaired or replaced and if the ossicular chain is not functioning normally or is missing, a surgeon can replace it with a titanium device. For some people with conductive hearing loss, medical treatment completely resolves the problem; however, if the middle ear damage or abnormality is extensive, the surgery may not return the hearing to normal. In this case, it is best to supplement medical management with hearing aids. Traditional hearing aids provide amazing benefit for conductive hearing loss and will help the individual once again connect with the world around them. The BAHA bone anchored hearing aid is another option if a person is not able to wear a traditional hearing aid. Some individuals with chronic drainage or with a canal that is not open are great candidates for the BAHA. QCBN
By Karon Lynn, Au.D.
