PHENYTOIN
PHOTOREFRACTIVE KERATECTOMY
severe learning difficulties. All newborn
babies are given the
Guthrie test
for
phenylketonuria. Affected babies show
few signs of abnormality, but, unless
phenylalanine is avoided, they develop
neurological disturbances including
epi-
lepsy.
They may have blonde hair and
blue eyes, and their urine may have a
mousy odour. Many have
eczema.
Phenylalanine is found in most protein-
containing foods and in artificial sweet-
eners.
A specially modified
diet
is
generally recommended throughout life,
(and especially during pregnancy, be-
cause high phenylalanine levels in the
mother can damage the fetus).
phenytoin An
anticonvulsant drug
used
to treat
epilepsy
and
trigeminal neuralgia.
Side effects include nausea, dizziness,
tremor, and overgrown and tender gums.
pheromone A substance with a particu-
lar odour that, when released in minute
quantities by an animal, affects the
behaviour or development of other indi-
viduals of the same species.
phimosis Tightness of the foreskin, pre-
venting it from being drawn back over the
glans
(head) of the penis. In uncircum-
cised babies, some degree of phimosis is
normal, but it usually improves by age 3
or 4. In some boys, the condition persists
and may cause the foreskin to balloon
out on urination. Attempts to retract a
tight foreskin may make the condition
worse. Phimosis may also develop in
adult men, causing painful erection that
may lead to
paraphimosis
. Proper clean-
ing of the glans may not be possible, so
balanitis
may develop. Treatment in both
adults and children is by
circumcision.
phlebitis Inflammation of a vein. A clot
often develops, in which case the condi-
tion is termed
thrombophlebitis
.
phlebography The obtaining of
X-ray
images of veins that have been injected
with a
radiopaque
substance. An alter-
native name is
venography
.
phlebotomy Puncture of a vein to remove
blood (see
venepuncture
; v
enesection
.)
phlegm See
sputum.
phobia A persistent, irrational fear of,
and desire to avoid, a particular object
or situation. Many people have minor
phobias. A phobia is considered a psy-
chiatric disorder when it interferes with
normal social functioning. Simple pho-
bias (specific phobias) are the most
common. These may involve fear of par-
ticular animals or situations, such as
enclosed spaces (
claustrophobia
). Animal
phobias usually start in childhood, but
others develop at any time. Treatment
depends on the severity of the condi-
tion and the wishes of the individual.
Agoraphobia
is a more serious phobia,
often causing severe impairment. The
disorder usually starts in the late teens
or early 20s. Social phobia is fear of being
exposed to scrutiny, such as a fear of
eating or speaking in public. This disor-
der usually begins in late childhood or
early adolescence.
Causes of phobias are unknown. Sim-
ple phobias are thought by some to be
a form of
conditioning
. For example, a
person with a fear of dogs may have
been frightened by a dog in childhood.
Exposure to the feared object or situa-
tion causes intense
anxiety
and, in some
cases, a
panic attack.
Phobias may be
associated with
depression
or
obsessive-
compulsive behaviour
. Treatment may be
with
behaviour therapy
and sometimes
antidepressant drugs
.
phocomelia A limb defect in which the
feet and/or the hands are joined to the
trunk by short stumps. The condition is
extremely rare, but used to occur as a
side effect of women taking the drug
thalidomide
in early pregnancy.
pholcodine A
cough
suppressant.
phosphates Salts that are essential in
the diet. A phosphate compound called
ATP
stores energy in cells.
phosphorus An essential
mineral,
pre-
sent in many foods, including cereals,
dairy products, and meat. In the body,
phosphorus is combined with
calcium
to form the bones and teeth.
photocoagulation Destructive heating
of tissue by intense light focused to a
fine point, as in
laser treatment
.
photophobia An uncomfortable sensi-
tivity or intolerance to light. It occurs
with eye disorders, such as
corneal abra-
sion,
and is a feature of
meningitis.
photorefractive keratectomy A sur-
gical treatment for
astigmatism
,
myopia
,
and
hypermetropia
, in which areas of
the
cornea
are shaved away by
laser
.
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