degree of cataract. Regular exposure to
ultravioletlight increases the risk. Other
causes include injury to the eye, partic-
ularly if a foreign body enters the lens.
Cataract is common in people who have
diabetes mellitus. Long-term use of cor-
ticosteroid drugs may contribute to
cataract development. Congenitalcatar-
act may be due to an infection of the
mother in early pregnancy, especially
with rubella, to the toxic effects of certain
drugs in pregnancy, or be associated
with Down’s syndromeor galactosaemia.
Onset of symptoms is almost imper-
ceptible, although night driving may be
affected early on. There is slow, progres-
sive loss of visual acuity. The person may
become shortsighted and notice distur-
bances in colour perception. When vision
has become seriously impaired, cataract
surgeryis performed to remove the lens.
cataract surgeryRemoval of the lens
from the eye, performed to restore sight
in people whose vision is impaired by a
cataract. The lens is usually replaced
with a plastic implant during the opera-
tion, although for young people and
those with other eye disorders, a con-
tact or spectacle lens fitted after the
operation may be preferable.
catarrhExcessive secretion of mucus by
the mucous membraneslining the nose
(see rhinitis), sinuses (see sinusitus), or
upper air passages, due to inflammation.
catatoniaA state in which a person be-
comes mute or adopts a bizarre, rigid
pose. It is seen in a rare form of schizo-
phreniaand some types of brain disease.
catharsisA term meaning purification
or cleansing. Catharsis is used to refer
to the process of cleaning out the bowels.
Sigmund Freud used the term in psycho-
analytic theoryto describe the expression
of repressed feelings and memories.
catharticA term that means having the
power to purify or cleanse. A cathartic
drug stimulates movement of the bow-
els (see laxative drugs).
catheterA flexible tube inserted into
the body to drain or introduce fluids or
carry out other functions. Catheters are
commonly used to drain urine from the
bladder (see catheterization, urinary).
Other types are used to investigate the
condition of the heart (see catheterization,
cardiac), to widen obstructed blood ves-
sels, or to control bleeding. (See also
balloon catheter.)
catheterization, cardiacA diagnostic
test in which a fine, sterile catheter is
introduced into the heart via a blood
vessel. It is used to diagnose and assess
the extent of congenital heart disease
(see heart disease, congenital) and coro-
nary artery disease,and to diagnose and
treat some disorders of the heart valves
(see valvuloplasty). During the procedure,
the pressure within the heart’s chambers
can be measured, samples of blood and
tissue can be taken, and a radiopaque
substance can be injected to allow the
heart’s cavities to be X-rayed.
catheterization, urinaryInsertion of
a sterile catheterinto the bladderto
drain urine. The procedure is used when
a person is unable to empty the bladder
normally or is incontinent (see inconti-
nence, urinary). Urinary catheterization
is also used during operations, in blad-
der function tests such as cystometry
andcystourethrography, and to monitor
urine production in the critically ill.
CAT scanningAn abbreviation for com-
puterized axial tomographic scanning,
commonly known as CT scanning.
cat-scratch feverAn uncommon dis-
ease that develops after a scratch or
bite by a cat. Three quarters of cases
occur in children. The fever is due to
infection with a small bacterium called
ROCHALIMAEA HENDELAE. The main symp-
tom, appearing after 3–10 days, is a
swollen lymph node near the bite or
scratch. The node may become painful
and tender, and an infected blister may
develop at the site of the injury. A fever,
rash, and headache may occur. Diagno-
sis is confirmed by biopsy of the
swollen lymph node and a skin test.
Analgesic drugs (painkillers) may be
used to relieve the fever and headache.
cats, diseases from Various parasites
and infectious organisms can spread
from cats to humans. The most serious
disease is rabies. Cat-scratch feveris an
uncommon illness caused by infection
with the bacterium ROCHALIMAEA HENDE-
LAEfollowing a cat scratch or bite. Cats
commonly carry the protozoanTOXOPLAS-
MA GONDII, which causes toxoplasmosis.CATARACT SURGERY CATS, DISEASES FROM
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