lens. It is connected at its outer edge to
the ciliary body and has a central aper-
ture, the pupil, through which light
enters the eye and falls on the retina.
The iris constantly contracts and dilates
to alter the size of the pupil, which con-
trols the amount of light that passes
through the pupil.
iritisAn inflammation of the iris, now
often termed an “anterior uveitis”.
ironA mineral essential for the forma-
tion of certain enzymes, haemoglobin
(the oxygen-carrying pigment in red
blood cells), and myoglobin(the oxy-
gen-carrying pigment in muscle cells). It
is found in foods such as liver, cereals,
fish, green leafy vegetables, nuts, and
beans. During pregnancy, supplements
may be needed. Iron deficiency leading
to anaemia (see anaemia, iron deficiency)
is usually caused by abnormal blood
loss, such as from a peptic ulcer or heavy
periods, but may also be due to diet.
Iron supplements may cause nausea,
abdominal pain, constipation, or diar-
rhoea and may colour the faeces black.
Excessive iron in the tissues is a feature
of haemochromatosis, which results in
organ damage, commonly cirrhosis.
iron-deficiency anaemiaSee anaemia,
iron-deficiency.
iron lungA large machine formerly used
to maintain breathing, especially in
people paralysed by poliomyelitis. The
iron lung has been replaced by more
efficient means of maintaining breath-
ing (see ventilation).
irradiationSee radiation hazards; radio-
therapy.
irradiation of foodThe treatment of
food with ionizing radiationto kill bacte-
ria, moulds, insects, and other parasites.
It improves the keeping qualities of
food and is a means of controlling some
types of food poisoning. It does not
destroy bacterial toxins, however, and
may destroy vitamins. Irradiation does
not render food radioactive.
irrigation, woundCleansing of a deep
wound by repeatedly washing it out with
a medicated solution or sterile saline.
irritable bladderIntermittent, uncon-
trolled contractions of the muscles in the
bladderwall that may cause urge incon-
tinence (see incontinence, urinary). It can
occur temporarily if there is a urinary
tract infection (see cystitis); a catheter
present within the bladder; a bladder
stone (see calculus, urinary tract); or an
obstruction to the outflow of urine by
an enlarged prostate gland. In some
cases, symptoms may be relieved by
antispasmodic drugs; other treatment is
directed at any underlying cause. Blad-
der training may also be used.
irritable bowel syndrome (IBS)A
combination of intermittent abdominal
pain and constipation, diarrhoea, or
bouts of each, that occurs in the absence
of other diagnosed disease.IBS affects
about 10–20 per cent of adults; it is twice
as common in women as in men, usually
beginning in early or middle adulthood.
It is usually recurrent throughout life
but is unlikely to lead to complications.
Symptoms include intermittent cramp-
like pain in the abdomen, abdominal
distension, often on the left side, tran-
sient relief of pain by bowel movement
or passing wind, sense of incomplete
evacuation of the bowels, and excessive
wind. Anxiety and stress tend to exacer-
bate the condition.
If constipation is the main problem, a
high-fibre diet or bulk-forming agents,
such as branor methylcellulose, may be
helpful. Short courses of antidiarrhoeal
drugsmay be given for persistent diar-
rhoea. Antispasmodic drugs may be
prescribed to relieve muscular spasm.
Hypnosis, psychotherapy, and counselling
have proved effective in some cases.
ischaemiaInsufficient blood supply to
a specific organ or tissue. It is usually
caused by disease of the blood vessels,
such as atherosclerosis, but may also
result from injury, constriction of a ves-
sel due to spasm of the muscles in the
vessel wall, or inadequate blood flow
due to inefficient pumping of the heart.
Symptoms depend on the area affected.
Treatment may include vasodilator
drugsto widen the blood vessels or,
in more severe cases, an angioplasty
or bypass operation.
ischiumOne of the bones that form the
lower part of the pelvis.
isolationNursing procedures (also called
barrier nursing) designed to prevent a
patient from infecting others or fromIRITIS ISOLATION
I