CATATONIA
emotion, particularly laughter, it occurs
almost exclusively in sufferers of sleep
disorders such as
narcolepsy
.
cataract
Loss of transparency of the
lens
of the
eye, as a result of changes in its protein
fibres. At an advanced stage, the front
part
of the
lens
becomes
densely
opaque, but the cataract never causes
total blindness. A densely opalescent
lens w ill still transmit light, but the
clarity and detail of the image w ill be
lost. Cataract usually occurs in both
eyes, but in most cases one eye is more
seriously affected than the other.
CAUSES
Almost everyone
over
65
has some
degree of cataract; the condition might
be considered part of the normal aging
process. Regular exposure to
ultraviolet
light
increases the risk.
Other causes of cataract include an
injury to the eye, particularly if a for-
eign body enters the lens. Cataract is
also common in people with
diabetes
mellitus
and may develop at an earlier
age if blood sugar levels are not well
controlled. Long-term use of
cortico-
steroid drugs
may contribute to cataract.
Congenital
cataract may be due to an
infection of the mother in early preg-
nancy, especially with
rubella
(German
measles), or to the toxic effects of cer-
tain drugs in pregnancy. It may also be
associated w ith
Down’s syndrome
or the
rare genetic disorder
galactosaemia
.
SYMPTOMS
Cataract is entirely painless and causes
only visual symptoms. The onset of
symptoms
is
almost
imperceptible,
although night driving may be affected
in the early stages. There is slow, pro-
gressive loss of visual acuity (increasing
blurring of vision). The person may
become shortsighted and notice distur-
bances in colour perception.
TREATMENT
W hen vision has become significantly
impaired,
cataract surgery
is performed
to remove the lens and replace it with
an implant. Provided the eye is other-
wise healthy, cataract surgery generally
gives excellent results.
cataract surgery
Removal of the
lens
from the eye. Catar-
act surgery is done to restore sight in
people whose vision is impaired by a
cataract
.
The lens is usually replaced
with a plastic implant during the oper-
ation. Alternatively, for young people
and those with other eye disorders, a
contact lens or spectacle lens fitted after
the operation may be preferable.
catarrh
Oversecretion of mucus by inflamed
mucous membranes
(see
rhinitis
), sinuses
(see
sinusitus
) or air passages.
catatonia
A state in w hich a person becomes
mute or adopts a bizarre, rigid pose.
The eyes usually remain open and the
person may seem awake, but they make
no voluntary movements. The state is
seen in a rare form of
schizophrenia
and
some types of brain disease.
PROCEDURE FOR CATARACT SURGERY
In a normal, healthy lens there is no
interference with the passage of light
rays. Even when peripheral opacities
develop, vision is not limited until the
central zone is affected. Dense nuclear
Dense nuclear cataract
Normal lens
------> -
---
>
-----
>■
----->
----->
Peripheral cataract
-------
y
------
>
------- >
-------- >
--------
y
opacities, however, such as that shown
on the right, cause deteriorating vision.
The affected lens cannot be restored
to its former transparency, hence the
need for surgical replacement.
Appearance of cataract
In preparation for surgery, measurements are
taken of the cornea and the eye’s length to
calculate the power of the lens implant that will
be needed to restore vision fully. The operation
may be performed using general or local
anaesthesia; there is no pain in either case.
Instruments of remarkable delicacy and
precision are used for the procedure, usually
with the help of microscope magnification.
I
An ultrasound probe is
inserted into the lens
capsule through a small
incision in the cornea. The
incision is made using a
diamond tipped instrument.
2
The ultrasound probe
softens the lens by
emitting sound waves. Itthen
sucks out the softened lens
tissue. Only the front part of
the lens capsule is removed.
3
An artificial lens is placed
inside the lens capsule.
The incision in the cornea is
left to heal naturally, or it may
be closed with a few surgical
stitches.
C
149
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