content. Disposable soft lenses are for
single use only; extended-wear lenses
are worn for up to a month.
Other types of contact lenses include
rigid scleral lenses, w hich cover the
whole of the front of the eye and are
used to disguise disfigurement; bifocal
contact lenses; and toric contact lenses,
w hich have an uneven surface curva-
ture and can correct
Hard plastic lenses may cause abrasion
of the cornea if w orn for too long. Soft
lens wearers sometimes develop sensi-
tivity of the eyes and lids. Any type of
contact lens may cause redness of the
eye. The most serious complication of
using lenses is infection, w hich can
occasionally cause permanent damage
to the cornea and affect vision; meticu-
lous hygiene lowers the risk.
A service provided by clinics treating
sexually transmitted infections
in w hich
all contacts of a person diagnosed as
having a sexually transmitted infection
are traced and then encouraged to be
examined and treated. Contact tracing
is also used in cases of other infections,
A term used to describe a disease that
can be transferred from person to per-
contagious diseases, such as the com-
mon cold or chickenpox, are
The term “ contagious” does not apply
to the many
typhoid, syphilis, or AIDS, w hich are
spread by other means.
continuous positive airway
A method of
in w hich the air
pressure inside a patient’s airways is
kept above atmospheric pressure.
continuous positive pressure
A rarely used method of
w hich positive pressure is applied to
the airways to produce each inhalation.
The control of fertility to prevent
Contraception can be achieved
by a variety of methods. Some forms
CARE AND INSERTION OF CONTACT LENSES
The care of hard contact lenses may
require the use of several chemical
solutions. A cleaning solution is used
to remove deposits of mucus and
protein from the lenses. A wetting
solution is used before inserting a lens
in the eye. A further solution may also
be used for storage; if used, a storage
solution must be washed off before a
contact lens is inserted.
Soft contact lenses absorb any
chemicals with which they come into
contact, so the solutions used must be
weaker. Disinfection with a chemical or
heating system is needed to prevent
contamination and eye infection. Two
or three solutions may be necessary,
but intermittent cleaning with a third
system, such as an enzyme tablet or an
oxidizing agent, may also be required.
Before touching lenses, wash your
hands thoroughly under running water
and take care to rinse off all traces of
soap. Remove the lens from its container;
for a hard lens, you may prefer to do this
with a rubber sucker. Rinse the lens
thoroughly in the wetting solution.
Do not use tapwater.
Place the contact lens on the tip ofyour
index finger. If it is a soft lens, make sure
that it has not turned inside out. If it has, you
will see an out-turned rim.
Keep both eyes open. Hold the upper lid of
one eye open, and look straight ahead or at
the lens as you bring it up to your eye.
Place the contact lens on your eye, over the iris
and pupil. Look downwards and then release
the lid. If necessary, the lens may be centred by
gently massaging the eyelid. The photograph on
the right shows a hard lens correctly positioned.