blepharoplastyA cosmetic operation
to remove wrinkled, drooping skin from
the upper and/or lower eyelids.
blepharospasmProlonged, involuntary,
contraction of one of the muscles con-
trolling the eyelids, causing them to
close. It may be due to photophobia,
damage to the cornea, or dystonia, for
which botulinum toxin(a muscle relax-
ant) treatment is highly effective.
blind loop syndromeA condition in
which a redundant area or dead end
(blind loop) in the small intestine
becomes colonized with bacteria. This
results in abnormal faeces and poor
absorption of nutrients. The syndrome
may result from surgery or a stricture
(narrowing) in the intestine due to a
disorder such as Crohn’s disease. It is
characterized by steatorrhoea(pale yel-
low, foul-smelling, fatty, bulky faeces
that are difficult to flush away), tired-
ness, and weight loss. Antibiotic drug
treatment usually cures the condition.
blindnessInability to see. Definitions
of blindness and partial sight vary. In
the UK, blindness is defined as a cor-
rected visual acuityof 3/60 or less in the
better eye, or a visual fieldof no more
than 20 degrees in the better eye. Blind-
ness may result from injury to, or
disease or degeneration of, the eyeball;
the optic nerve or nerve pathways con-
necting the eye to the brain; or the
brain itself. Clouding of the cornea may
result from Sjögren’s syndrome, vitamin
A deficiency, chemical damage, infec-
tions, and injury. Corneal ulcers can
cause blindness due to scarring of the
cornea. Uveitisand cataractsare other
common causes of blindness. Diabetes
mellitus, hypertension, or injury can all
cause bleeding into the cavity of the
eyeball and subsequent loss of vision.
Bleeding into the fluid in front of the
lens (hyphaema) or behind the lens
(vitreous haemorrhage)can also result
in loss of vision. Other conditions that
may cause blindness include glaucoma;
retinal artery occlusionor retinal vein
occlusion; age-related macular degener-
ation; retinopathy; retinal detachment;
tumours such as retinoblastomaand
malignant melanomaof the eye; and
retinal haemorrhage.
Loss of vision may be due to nerve con-
duction problems. These problems may
be the result of pressure caused by a
tumour; reduced blood supply to the
optic nerve; optic neuritis; or toxic or
nutritional deficiencies. Blindness can
result if there is pressure on the visual
cortex from a brain tumouror brain
haemorrhage, or if the blood supply to
the cortex is reduced following a stroke.
Treatment depends on the underlying
cause. If the loss of vision cannot be
corrected, the patient may then be reg-
istered as legally blind or partially
sighted. (See also eye; vision,loss of.)
blind spotThe small, oval-shaped area
on the retina of the eye where the optic
nerve leaves the eyeball. The area is not
sensitive to light because it has no light
receptors (nerve endings responsive to
light). The blind spot can also be used
to describe the part of the visual fieldin
which objects cannot be detected.
blisterA collection of fluid beneath the
outer layer of the skin that forms a
raised area. A blister contains fluid that
has leaked from blood vessels in under-
lying skin layers after minor damage
and protects the damaged tissue. Com-
mon causes are burnsand friction.
Blisters may also occur with pemphigus,
pemphigoid, dermatitis herpetiformis,
some types of porphyria, and some skin
diseases. These include eczema, epider-
molysis bullosa,impetigo, and erythema
multiforme. Small blisters develop in
the viral infections chickenpox, herpes
zoster(shingles), and herpes simplex.
Generally, blisters are best left intact,
but large or unexplained blisters need
medical attention.
bloatingDistension of the abdomen,
commonly due to wind in the stomach
or intestine (see abdominal swelling).
blocked noseSee nasal congestion;
nasal obstruction.
blockingInability to express true feel-
ings or thoughts, usually as a result of
emotional or mental conflict. In Freudi-
an- based psychotherapies, blocking is
regarded as originating from repression
of painful emotions in early life. A very
specific form of thought blocking occurs
in schizophrenia: trains of thought are
persistently interrupted involuntarily toBLEPHAROPLASTY BLOCKING
B