OPTOMETRY
ORAL SURGERY
accompanied by pain on moving the
eyes. Vision usually improves within 6
weeks, but some optic nerve fibres will
be damaged. Recurrent attacks usually
lead to permanent loss of visual acuity.
Most cases are thought to be due to
demyelination of the optic nerve fibres in
multiple sclerosis.
The condition may also
result from inflammation or infection of
tissues around the optic nerve. C
ortico-
steroid drugs
may help to restore vision,
but seem to have little effect on long-
term outcome. (See also
optic atrophy
.)
optometry
The practice of assessing
vision
to establish whether glasses or
contact lenses are needed to correct a
visual defect, as carried out by an
optometrist. Disorders of the eye may
require treatment by an ophthalmolo-
gist. (See
also ophthalmology; optician.)
oral
Concerning the
mouth.
oral contraceptives
A group of oral
drug preparations containing one or
more synthetic female
sex hormones
,
taken by women in a monthly cycle to
prevent pregnancy. “The pill” commonly
refers to the combined or the phased pill,
which both contain an
oestrogen drug
and a
progestogen drug
, and the mini-
pill, which contains only a progestogen.
Oestrogen pills include
ethinylestradiol
;
progestogens include levonorgestrel and
norethisterone
. When used correctly, the
number of pregnancies among women
using oral contraceptives for one year is
less than 1
per cent. Actual failure rates
may be 4 times higher, particularly for
the minipill, which has to be taken at
precisely the same time each day.
Combined and phased pills increase
oestrogen and progesterone levels. This
interferes with the production of two
hormones,
luteinizing hormone
(LH)
and
follicle-stimulating hormone
(FSH),
which in turn prevents ovulation. The
minipill works mainly by making the
mucus lining of the
cervix
too thick to
be penetrated by
sperm.
Oestrogen-containing pills offer protec-
tion against uterine and ovarian cancer,
ovarian cysts
,
endometriosis
, and iron-
deficiency
anaemia.
They also tend to
make menstrual periods regular, lighter,
and relatively pain-free. Possible side
effects include nausea, weight gain,
depression, swollen breasts, reduced sex
drive, increased appetite, leg and abdom-
inal cramps, headaches, and dizziness.
More seriously, there is a risk of
throm-
bosis
causing a
stroke
or a
pulmonary
embolism
.
These pills may also aggravate
heart disease or cause
hypertension
,
gallstones
,
jaundice
, and, very rarely, liver
cancer. All oral contraceptives can cause
bleeding between periods, especially
the minipill. Other possible adverse
effects of the minipill include irregular
periods,
ectopic pregnancy
, and ovarian
cysts. There may be a slightly increased
long-term
risk of breast cancer for
women taking the combined pill.
Oestrogen-based pills should generally
be avoided in women with hypertension,
hyperlipidaemia
,
liver disease
,
migraine
,
otosclerosis
, or who are at increased risk
of a thrombosis. They are not usually pre-
scribed to a woman with a personal or
family history of heart or circulatory dis-
orders, or who suffers from unexplained
vaginal bleeding. The minipill or a low-
oestrogen pill may be used by women
who should avoid oestrogens. Combined
or phased pills may interfere with milk
production and should not be taken
during breast-feeding. Certain drugs
may impair the effectiveness of oral
contraceptives. (See also
contraception.
)
oral
hygiene
Measures to keep the
mouth and teeth clean and reduce the
risk of tooth decay (see
caries, dental
),
gingivitis
and other gum disorders, and
halitosis
. Oral hygiene includes regular,
thorough
toothbrushing
and flossing (see
floss, dental)
to remove
plaque
.
Disclosing
agents
help to reveal build-up of plaque.
Dentures are brushed on all surfaces and
soaked in cleansing solution.
Professional treatment to remove
cal-
culus
and stubborn plaque by scaling
and polishing is usually carried out by a
dentist or dental hygienist during a rou-
tine check-up. In
periodontal disease
,
treatment may be needed more often.
oral rehydration therapy
See
rehy-
dration therapy
.
oral surgery
The branch of surgery
that treats deformity, injury, or disease
of the teeth, jaws, and other parts of the
mouth. Procedures include the extrac-
tion of impacted wisdom teeth (see
O
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