C h a p t e r 3 8
Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function
989
The habituation effect is characterized by decreased
sensitivity and duration of symptoms. It may occur in
as little as 2 weeks or take as long as 6 months. Balance
retraining exercises consist of activities directed toward
improving individual components of balance that may
be abnormal. General conditioning exercises, a vital
part of the rehabilitation process, are individualized to
the person’s preferences and lifestyle.
SUMMARY CONCEPTS
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Receptors for the vestibular system that respond
to changes in rotational and linear acceleration of
the head are located in the fluid-filled semicircular
ducts of the inner ear.
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The vestibular system has extensive
interconnections with neural pathways controlling
vision, hearing, balance, and autonomic nervous
system function. Signals from the vestibular
system initiate head and eye movements to
stabilize the visual field and make adjustments in
the posture muscles that maintain balance.
■■
Disorders of vestibular function can result
from repeated stimulation of the vestibular
system such as during car, air, and boat travel
(motion sickness); acute infection of the
vestibular pathways (acute vestibular neuritis);
dislodgement of otoliths that participate in the
receptor function of the vestibular system (benign
paroxysmal positional vertigo); or distention of
the endolymphatic compartment of the inner ear
(Ménière disease).
R E V I EW E X E R C I S E S
1.
The mother of a 3-year-old boy notices that
his left eye is red and watering when she picks
him up from day care. He keeps rubbing his
eye as though it itches. The next morning, she
notices that both eyes are red, swollen, and
watering. Being concerned, she takes him to the
pediatrician in the morning and is told that he
has “conjunctivitis.” She is told that the infection
should go away by itself.
A.
What part of the eye is involved?
B.
What type of conjunctivitis do you think this
child has (bacterial, viral, or allergic)?
C.
Why didn’t the pediatrician order an
antimicrobial drug?
D.
Is the condition contagious? What measures
should she take to prevent its spread?
2.
During a routine eye examination to get new
glasses because she had been having difficulty with
her distant vision, a 75-year-old woman is told that
she is developing cataracts.
A.
What types of visual changes occur as the result
of a cataract?
B.
What can the woman do to prevent the
cataracts from getting worse?
C.
What treatment may she eventually need?
3.
A 50-year-old woman is told by her eye doctor
that her intraocular pressure is slightly elevated
and that although there is no evidence of
damage to her eyes at this time, she is at risk for
developing glaucoma and should have regular eye
examinations.
A.
Describe the physiologic mechanisms involved
in the regulation of intraocular pressure.
B.
Differentiate between open-angle and angle-
closure glaucoma in terms of their pathology,
manifestations, and treatment.
C.
See Figure 38-12 to relate the “optic disk
cupping” that occurs with glaucoma to the
visual field loss that occurs with the disorder.
4.
The parents of a newborn infant have been told
that their son has congenital cataracts and will
require cataract surgery to prevent losing his
sight.
A.
Explain why the infant is at risk for losing his
sight if the cataracts are not removed.
B.
When should this procedure be done to prevent
loss of vision?
5.
A mother notices that her 13-month-old child
is fussy and tugging at his ear and refuses to eat
his breakfast. When she takes his temperature,
it is 100°F. Although the child attends day care,
his mother has kept him home and made an
appointment with the child’s pediatrician. In the
physician’s office, his temperature is 100.2°F, he
is somewhat irritable, and he has a clear nasal
drainage. His left tympanic membrane shows
normal landmarks and motility on pneumatic
otoscopy. His right tympanic membrane is
erythematous and there is decreased motility on
pneumatic otoscopy.
A.
What risk factors are present that predispose
this child to the development of acute otitis
media?
B.
Are his signs and symptoms typical of otitis
media in a child of this age?
C.
What are the most likely pathogens? What
treatment would be indicated?
D.
Later in the week, the mother notices that
the child does not seem to hear as well as he
did before developing the infection. Is this a
common occurrence, and should the mother be
concerned about transient hearing loss in a child
of this age?
