LENS
LEUKAEMIA
and also occurs in some Mediterranean
countries. In addition, there are several
types of
cutaneous
leishmaniasis, some
of which are prevalent in the Middle
East, North Africa, and in the Mediter-
ranean. Kala-azar causes persistent fever,
enlargement of the
spleen, anaemia,
and, later, darkening of the skin. The ill-
ness may develop any time up to
2
years after infection, and, if untreated,
may be fatal. The cutaneous forms have
the appearance of a persistent ulcer at
the site of the sandfly bite.
All varieties of leishmaniasis can be
treated with drugs, such as sodium sti-
bogluconate, given by intramuscular or
intravenous
injection.
lens
The internal optical component of
the
eye
responsible for focusing; also
called the crystalline lens. It is situated
behind the
iris
and is suspended on
delicate fibres from the
ciliary body
. The
lens is elastic, transparent, and slightly
less convex on the front surface than on
the back. Changing its curvature alters
LENS
the focus so that near or distant objects
can be seen sharply (see
accommoda-
tion
). Opacification of the lens is called
cataract.
(See also
lens dislocation.)
lens dislocation
Displacement of the
crystalline
lens
from its normal position
in the eye. Lens dislocation is almost
always caused by an injury that ruptures
the fibres connecting the lens to the
cil-
iary body.
In
Marfan's syndrome,
these
fibres are particularly weak and lens dis-
location is common.
A dislocated lens may produce severe
visual distortion or double vision, and
sometimes causes a form of
glaucoma
if
drainage of fluid from the front of the
eye is affected. If glaucoma is severe,
the lens may need to be removed. (See
also
aphakia
.)
lens implant
A plastic
prosthesis
used
to replace the removed opaque
lens
in
cataract surgery
.
lentigo
A flat, brown area of skin similar
to a freckle. Lentigines (the plural of
lentigo) are usually harmless and need
no treatment. However, any areas of
raised, darker brown skin within a len-
tigo need investigation, as such areas
could develop into malignant melan-
omas (see
melanoma, malignant
).
leprosy
See
Hansen's disease
.
leptin
A
protein
that has a role in the
regulation of fat storage by the body.
leptospirosis
A rare disease caused by
a type of
spirochaete
bacterium that is
harboured by rodents and excreted in
their urine. It is also known as Weil's
disease. Symptoms include fever, chills,
headache, severe muscle aches, and a
skin rash. Kidney and liver damage are
also common.
Antibiotic drugs
are effec-
tive treatment but kidney and liver
function may recover only slowly. The
nervous system may also be affected,
often producing signs of
meningitis
.
lesion
An all-encompassing term for any
abnormality of structure or function in
any part of the body. The term may refer
to a wound, infection, tumour, abscess,
or chemical abnormality.
lethargy
A feeling of
tiredness
,
drowsi-
ness, or lack of energy.
leukaemia
Any of several types of can-
cer in which there is a disorganized
proliferation of white
blood cells
within
the bone marrow. Organs such as the
liver, spleen, lymph nodes, or brain may
cease to function properly if they be-
come infiltrated by abnormal cells.
Leukaemias are classified into
acute
and
chronic
types (acute types generally
develop faster than chronic leukaemia).
They are also classified according to the
type of white cell that is proliferating
abnormally. If the abnormal cells are
lymphocytes
or lymphoblasts (precursors
of lymphocytes), the leukaemia is called
337
previous page 335 BMA Illustrated Medical Dictionary read online next page 337 BMA Illustrated Medical Dictionary read online Home Toggle text on/off