COCHLEAR IMPLANT
tion
between
the
groin
and
wrist
pulses, and blood pressure that is high-
er in the arms than in the legs.
DIAGNOSIS AND TREATMENT
X-rays confirm the diagnosis. Surgery to
correct the defect is usually performed
before four years of age.
Coat’s disease
A disease that causes a progressive dete-
rioration
in vision.
It is
congenital
(present at birth) but usually begins in
childhood, and affects boys more than
girls. The cause is unknown.
In Coat’s disease, the capillaries (tiny
blood
vessels)
supplying
the
retina
become
damaged and leak fluid
(a
process called exudation). As a result,
the retina does not function properly.
Usually, only one eye is affected. Vision
may be impaired in the centre of the
visual field or around the edges. In
some cases, a squint develops. There is
also a risk of retinal detachment.
Diagnosis involves viewing the retina
through an ophthalmoscope, and by
imaging the blood vessels using
fluores-
cein
dye. Treatment may involve sealing
the capillaries by phototherapy (treat-
ment with light rays) or cryotherapy
(treatment with cold). If given early
enough, it may stabilize the disease and
may
even improve vision.
In some
cases, the disease stabilizes by itself.
cobalamin
A complex molecule that contains
co-
balt
and is part of
vitamin B
12
.
cobalt
A metallic element. Cobalt is found in
foods as a constituent of
vitamin B
12
.
A
radioactive form is used in
radiotherapy
.
Cobb syndrome
A very rare disorder in w hich spinal
cord
angiomas
(noncancerous tumours
of the blood or lymph vessels) occur
together w ith arteriovenous malforma-
tions (abnormal connections between
arteries and veins)
in the
overlying
skin.
It
is
congenital
(present
from
birth) but is almost never inherited.
The
symptoms
usually
appear
in
childhood or adolescence; they include
weakness, paralysis, loss of sensation,
and loss of bowel and bladder control.
Treatment includes surgery to block the
blood flow to the abnormal vessels (see
embolization
)
and to relieve pressure on
the
spinal
cord
(see
decompression,
spinal canal
).
co-beneldopa
A preparation
containing
the
drugs
benserazide
and
levodopa
;
co-benel-
dopa
is
used
in
the
treatment
of
Parkinson’s disease
.
cocaine
A drug obtained from the leaves of the
coca plant E
rtthroxtion
coca
. In the
past, cocaine was used as a local anaes-
thetic (see
anaesthesia, local
) for m inor
surgical procedures, but it has largely
been replaced by other anaesthetics due
to its potential for abuse.
Cocaine affects the brain, producing
euphoria and increased energy. These
effects have led to its illicit use (see
drug abuse
) .
Regular inhalation of the
drug can damage the lining of the nose
and may eventually cause perforation of
the septum (the tissue separating the
two sides of the nose). Continued use
of the drug can cause dependence (see
drug dependence
), and, if high doses
are
taken,
may
result
in
psychosis
,
w hich can cause users to become vio-
lent. Overdose of cocaine can cause
seizures and
cardiac arrest
.
Crack, w hich is a purified form of
cocaine, produces a more rapid and
intense reaction; and deaths have occur-
red as a result of the drug’s adverse
effects on the heart.
cocci
Spherical
bacteria,
some of w hich cause
infections in humans (see
staphylococcal
infections; streptococcal infections
) .
coccus
The singular of
cocci
.
coccydynia
A pain in the region of the
coccyx
.
Coc-
cydynia may result from a blow to the
base of the spine in a fall, prolonged
pressure due to poor posture when
sitting, or the use of the lithotomy pos-
ition
(lying on the back with hips
and knees bent) during childbirth. The
pain usually eases in time. Treatment
may include heat, injections of a local
anaesthetic, and
manipulation
.
coccyx
A small, triangular bone, commonly
called the tailbone, made up of four
tiny bones fused together at the base of
the
spine
.
Together w ith a larger bone
called the
sacrum
,
situated just above it,
the coccyx forms the back section of
the
pelvis
. T h e r e
is very little movement
between the coccyx and sacrum, and
later in life the two structures com-
monly become fused together.
cochlea
The spiral-shaped organ situated in the
labyrinth
of the inner ear that enables
hearing
.
A structure known as the
organ
of Corti
,
inside the cochlea, can detect
sound vibrations of different frequen-
cies and converts them into electrical
impulses. These electrical impulses are
then transmitted to the brain via the
vestibulocochlear nerve
.
Sound waves of
different frequencies stimulate different
areas inside the cochlea, enabling us to
hear and differentiate between a wide
variety of sounds.
cochlear implant
A device that is used to treat profoundly
deaf people w ho are not helped by
hearing aids. Unlike a hearing aid,
w hich
amplifies
sounds,
a
cochlear
implant converts sounds into electrical
signals that are relayed to the cochlear
nerve deep in the inner ear (see
coch-
lear implant box
,
overleaf).
The implant consists of tiny elec-
trodes that are surgically implanted in
the
cochlea,
and
a receiver that is
embedded in the skull just behind and
above the ear. A microphone, sound
processor,
and transmitter
are worn
externally. A cochlear implant does not
restore normal hearing, but it enables
patterns of sound to be detected. Com-
bined with lip-reading, it may enable
speech to be understood.
C
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