C h a p t e r 3 8
Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function
975
The Ear and Disorders
of Auditory Function
The ears are paired organs consisting of an external and
middle ear, which function in capturing, transmitting, and
amplifying sound; and an inner ear, which contains the
receptive organs that are stimulated by sound waves (i.e.,
hearing) or head position and movement (i.e., balance).
Disorders of the External Ear
The external ear is a funnel-shaped structure that
conducts sound waves to the tympanic membrane. It
consists of the auricle, the external acoustic meatus
(ear canal), and the lateral surface of the tympanic
membrane
2,46
(Fig. 38-17). Modified sebaceous glands
in the auditory canal secrete a waxlike substance called
cerumen
or
earwax
that has certain antimicrobial
properties and is thought to serve a protective function.
The tympanic membrane or eardrum is a thin,
transparent membrane, approximately 1 cm in diameter,
which separates the external ear from the middle ear.
It is covered with thin skin externally and the mucous
membrane of the middle ear internally. The tympanic
membrane is attached in a manner that allows it to
vibrate freely when audible sound waves enter the
external auditory canal. Movements of the membrane
are transmitted through the middle ear to the inner ear.
Impacted Cerumen
Although the ear normally is self-cleaning, the cerumen
can accumulate in the narrow ear canal, causing
reversible hearing loss.
47
Impacted cerumen usually
produces no symptoms unless it hardens and touches the
tympanic membrane, or the canal becomes irritated by a
buildup of hardened cerumen, causing pain, itching, and
a sensation of fullness. As the canal becomes completely
occluded, there may be a feeling of fullness, a conductive
hearing loss, and tinnitus (i.e., ringing in the ears).
In most cases, cerumen can be removed by gentle
irrigation using a bulb syringe and warm tap water.
Alternatively, health care professionals may remove
cerumen using an otoscope for guidance along with a wire
loop or plastic cerumen curette. A ceruminolytic agent is
usually reserved for impacted or hardened cerumen that
occurs without ear discharge, pain, rash, or irritation.
Otitis Externa
Otitis externa is an inflammation of the external ear
that can vary in severity from mild dermatitis to severe
cellulitis.
46,48
It can be caused by infectious agents,
irritation (e.g., wearing hearing aids or earphones), or
allergic reactions. Predisposing factors include frequent
exposure to moisture in the ear canal (i.e., swimmer’s
ear), trauma to the canal caused by cleaning or scratching,
and allergies or skin conditions such as psoriasis. It
commonly occurs in the summer and is manifested by
itching, redness, tenderness, and narrowing of the ear
canal because of swelling. Inflammation of the auricle
or ear canal makes movement of the ear painful. There
may be watery or purulent drainage and intermittent
hearing loss.
Treatment usually includes the use of ear drops
containing an appropriate antimicrobial or antifungal
agent in combination with a corticosteroid to reduce
inflammation.
48
Persons with acute otitis externa (AOE)
should preferably abstain from water sports, protect the
Tympanic
membrane
Auricle
Semicircular
canals
Pharynx
Eustachian
tube
Cochlea
Cochlear
portion
Vestibular
portion
Cranial
nerve
VIII
External
acoustic
meatus
Malleus
Incus
Stapes
Middle
ear
Inner
ear
FIGURE 38-17.
External, middle,
and internal subdivisions of the
ear.
