RETRACTOR
REVERSE TRANSCRIPTASE INHIBITORS
R
in turn. The effect of different lenses on
the beam of light determines whether
glasses are needed for various refractive
errors, such as
fyspermetropia, myopia,
or
astigmatism.
Retinoscopy is particu-
larly useful for assessing babies or
young children.
retractor A surgical instrument used to
hold an incision open or to hold back
surrounding tissue.
retrobulbar neuritis A form of
op-tic
neuritis
in which the
optic nerve
be-
comes inflamed behind the eyeball.
retrograde Moving backwards or in an
opposite direction to normal. For exam-
ple, in retrograde ejaculation, semen is
forced into the bladder rather than out
through the tip of the penis (see
ejacu-
lation, disorders of).
retrolental
fibroplasia Also
called
retinopathy
of
prematurity
, a condition
that mainly affects the eyes of prema-
ture infants. The usual cause is high
concentrations of
oxygen
being given as
part of the treatment for
respiratory dis-
tress.
Excess oxygen causes the tissues
at the margin of the
retina
to shut down
their blood vessels. When oxygen con-
centrations return to normal, the affected
tissues may send strands of new vessels
and fibrous scar tissue into the
vitreous
humour
. This may interfere with vision
and cause
retinal detachment
.
Laser
treatment
may be used.
retroperitoneal
fibrosis
Inflam-
mation and scarring
of tissues at the
back of the abdom-
inal
cavity.
The
fibrosis often blocks
the
ureters,
pre-
venting urine flow
from the kidneys.
In
severe
cases,
this results in
kid-
ney failure.
Most
cases occur in mid-
dle-aged men and
are
of
unknown
cause,
but
long-
term treatment with
the
drug
methy-
sergide
can cause
the condition,
retrosternal pain
Pain in the central
region of the chest, behind the sternum.
Causes include irritation of the
oesoph-
agus, angina pectoris,
or
myocardial
infarction.
(See also
chest pain.)
retrovirus
A type of virus whose genetic
material is
RNA
rather than
DNA
and
that uses an enzyme called reverse tran-
scriptase to produce DNA from the RNA
template. The DNAcan then be incor-
porated into its host cells. A notable
example of a retrovirus is
HIV
(human
immunodeficiency virus).
Rett's
syndrome A
brain
disorder,
thought to be a
genetic disorder
, that
only affects girls. Symptoms usually
occur when the child is 12-18 months
old. Acquired skills, such as walking and
communication skills, disappear and the
girl becomes progressively handicapped,
perhaps with signs of
autism.
There are
repetitive writhing movements of the
hands and limbs, and inappropriate out-
bursts of crying or laughter. There is no
cure for Rett's syndrome and sufferers
need constant care and attention. Par-
ents of an affected child should receive
genetic counselling
.
reverse transcriptase inhibitors A
class of drugs used in the treatment of
diseases, including
HIV
infection, that
are caused by retroviruses. The drugs
affect the ability of the virus to reproduce
by blocking reverse transcriptase, a key
490
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