I
DEAFNESS
day surgery
Surgical treatment carried out in a hos-
pital or clinic without an overnight
stay. The proportion of all operations
performed on a day-surgery basis has
risen substantially in recent years. M od-
ern anaesthetics and surgical techniques,
in particular
minimally invasive surgery
,
allow a swifter recovery than in the
past, so that patients can often return
home w ithin a few hours of surgery.
DDAVP
A brand name for
desmopressin
,
w hich
is a synthetic form of
ADH
(antidiuret-
ic horm one).
DDT
The abbreviation for
the
insecticide
dichlorodiphenyltrichloroethane. DDT
was once widely used in the fight
against diseases transmitted by insects,
particularly in hot climates. However,
some insects have developed resistance
to the toxic effects of DDT, and this
resistance can be passed on to their off-
spring. (See also
pesticides
. )
deafness
Complete or partial loss of hearing in
one or both ears. There are two types
of deafness: conductive deafness, w hich
is
caused
by
faulty
propagation
of
sound from the outer to the inner ear;
and sensorineural deafness, in w hich
there is a failure in the transmission of
sounds to the brain.
CAUSES
The most common cause of conductive
deafness in adults is
earwax
.
Otosclerosis
,
a condition in w hich the stapes (a small
bone in the middle ear) loses its normal
mobility, is a less common cause. In
children, conductive deafness is usually
due to
otitis media
(middle-ear infection)
or
glue ear
(accumulation of sticky fluid
in the middle ear). In rare cases, deaf-
ness results from a ruptured eardrum
(see
eardrum, perforated
) .
Sensorineural deafness may be pres-
ent from birth. This type of deafness
may result from a
birth injury
or damage
resulting from maternal infection with
rubella
in early pregnancy. Damage to the
inner ear may also occur soon after birth
as the result of severe neonatal
jaundice
.
In later life, sensorineural deafness
can be due to damage to the cochlea
and/or labyrinth of the inner ear. It
may result from prolonged exposure to
loud noise, or be caused by
Meniere’s
disease
,
certain drugs, or some viral
infections. The cochlea and labyrinth
also degenerate naturally w ith old age,
resulting in
presbyacusis
.
Sensorineural
deafness due to damage to the acoustic
nerve may be the result of an
acoustic
neuroma
(a noncancerous tumour that
develops on the nerve).
SYMPTOMS AND SIGNS
A baby w ho is congenitally deaf fails to
respond to sounds, and, although cry-
ing is often normal, he or she does not
babble or make the usual baby noises
that lead to speech. In an adult w ho has
started to become deaf, sounds heard
are not only quieter than before, but
may be distorted and less clear.
Deafness may be accompanied by
tin-
nitus
(noises in the ear)
and
vertigo
(dizziness and loss of balance). Some-
times deafness can lead to confusion
and sometimes to
depression.
DIAGNOSIS
Examination of the ear with an
otoscope
(a
viewing instrument with a light attached)
can show if the outer-ear canal is blocked
by wax, or if the eardrum is inflamed, per-
forated, or has fluid behind it.
After a physical examination,
hearing
tests
may be performed; these tests can
determine whether deafness is con-
ductive or sensorineural.
TREATMENT
The treatment depends on the exact
cause
of the
deafness.
Removal
of
excess
earwax
remedies
conductive
deafness in many cases. Otosclerosis
is generally treated by an operation
known as
stapedectomy
,
in w hich the
stapes is replaced with an artificial sub-
stitute. Glue ear may also be treated by
surgery (see
myringotomy
)
and by the
insertion of a
grommet
(a small tube
that allows fluid to drain away from
the middle ear).
Many children who are born deaf
can learn to communicate effectively,
often by using sign language.
Cochlear
implants
(electrodes implanted in the
inner ear that can receive sound sig-
nals) may help profoundly deaf adults
and children, but they are not suitable
for everyone. People w ho have sensori-
neural deafness usually need
hearing-
aids
to increase the volume of sound
reaching the inner ear.
Lip-reading
is
invaluable for people w ho have diffi-
culty hearing, whatever the type and
severity of their deafness. Other aids,
such as an amplifier for the earpiece of
a telephone, are available to help deaf
people perform
everyday tasks.
(See
also
ear
;
hearing
. )
DEAFNESS
M e n i e r e ’s d i s e a s e
v
D ru g
A c o u s t ic
t o x ic it y
n e u r o m a
O c c u p a t io n a l
d e a f n e s s
Some possible causes of deafness
The part ofthe ear affected in each case is shown. Some of
the problems (e.g. earwax, which affects the outer ear, and
glue ear, which affects the middle ear) cause conductive
deafness; others (e.g. drug toxicity and Meniere’s disease,
which affect the inner ear) cause sensorineural deafness.
D
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