GLASSES
GLIPIZIDE
G
glasses
Optical devices that use lenses
to correct focusing errors in the eyes to
achieve clear vision. Lenses are made of
glass or plastic, and the shape and
thickness are chosen during a
vision test.
Convex lenses are needed for
hypermet-
ropia
(longsightedness), and concave
lenses for
myopia
(shortsightedness).
Tinted lenses protect the eyes from sun-
light. (See also
bfocal; contact lenses)
glass eye
See
eye, artficial.
glass test
A test for
meningitis
that
involves pressing a clear glass against a
rash. If the rash remains visible, it may
be a form of
purpura
, which sometimes
occurs in meningitis.
GLASS TEST
Rash visible through glass
glaucoma
A condition in which the
pressure of the fluid in the
eye
is abnor-
mally high, causing the compression
and obstruction of the small blood ves-
sels that nourish the
retina
.
This may
result in nerve fibre destruction and
gradual loss of vision.
The most common form of glaucoma
is chronic simple (open-angle) glauco-
ma, which rarely occurs before age 40
and often causes no symptoms until
visual loss is advanced. It is caused by a
gradual blockage of the outflow of
aque-
ous humour
over a period of years,
causing a slow rise in pressure. The
condition tends to run in families.
In acute (closed-angle) glaucoma, there
is a sudden obstruction to the outflow
of aqueous humour from the eye and
the pressure rises suddenly. This causes
a severe, dull pain in and above the eye,
fogginess of vision, and the perception
of haloes around lights at night. Nausea
and vomiting may occur, and the eye
may be red with a dilated pupil.
Congenital glaucoma is due to an ab-
normality in the drainage angles of the
eyes before birth. Glaucoma can also be
caused by eye injury or a serious eye dis-
ease such as
uveitis
or
lens dislocation
.
Applanation
tonometry
is used to check
for glaucoma by measuring the pressure
within the eye. An
ophthalmoscope
may
show depression of the head of the
optic nerve due to the increase in pres-
sure. Visual field testing will be needed
to assess whether vision has already
been damaged, because longstanding
or severe glaucoma can result in loss of
peripheral vision (see
tunnel vision
).
Prompt treatment is essential to pre-
vent permanent loss of vision. Chronic
simple glaucoma can usually be con-
trolled with eye-drops (e.g.
timolol
) or
tablets that reduce pressure in the eye.
Treatment needs to be continued for life.
If drugs are ineffective, surgery may be
needed to unblock the drainage chan-
nel or create an artificial channel. Acute
glaucoma requires emergency drug treat-
ment, often in hospital. Surgery, usually
iridectomy,
may be necessary to prevent
a further attack.
glibenclamide
An oral hypoglycaemic
drug (see
hypoglycaemics, oral)
used to
treat type
2
diabetes mellitus
.
gliclazide
An oral hypoglycaemic drug
(see
hypoglycaemics, oral)
used to treat
type
2
diabetes mellitus
in conjunction
with dieting. Side effects are usually mild.
glioblastoma
multiforme
A
fast-
growing and highly cancerous type of
primary
brain
tumour
.
Glioblastoma
multiforme is a type of
glioma
that often
develops in the
cerebrum
. The cause is
unknown. Treatment may include sur-
gery,
radiotherapy
, and/or
chemotherapy
.
glioma
A type of
brain tumour
arising
from the supporting connective tissue,
(glial cells), in the brain. Types of
glioma include
astrocytoma
,
glioblastoma
multforme
,
ependymoma, medulloblas-
toma
,
and
oligodendroglioma
.
Symptoms,
diagnosis, and treatment are as for
other types of brain tumour.
glipizide
An oral hypoglycaemic drug
(see
hypoglycaemics, oral)
used to treat
type 2
diabetes mellitus
. Side effects are
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