Bma Illustrated Medical Dictionary

and also occurs in some Mediterranean
countries. In addition, there are several
types of cutaneousleishmaniasis, 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.
lensThe internal optical component of
the eyeresponsible for focusing; also
called the crystalline lens. It is situated
behind the irisand 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

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 dislocationDisplacement of the
crystalline lensfrom 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-
iarybody. 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 glaucomaif

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 implantA plastic prosthesisused

to replace the removed opaque lensin

cataract surgery.

lentigoA 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).

leprosySee Hansen’s disease.

leptinA proteinthat has a role in the

regulation of fat storage by the body.

leptospirosisA rare disease caused by

a type of spirochaetebacterium 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. Antibioticdrugsare effec-

tive treatment but kidney and liver

function may recover only slowly. The

nervous system may also be affected,

often producing signs of meningitis.

lesionAn 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.

lethargyA feeling of tiredness, drowsi-

ness, or lack of energy.

leukaemiaAny 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 chronictypes (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

lymphocytesor lymphoblasts (precursors

of lymphocytes), the leukaemia is called

LENS LEUKAEMIA

L

Iris

Retina

Cornea

Lens

LENS

Ciliary body