EXTROVERT
EYE
extrovert
A person whose interests are
constantly directed outwards, to other
people and the environment. Extroverts
are active, sociable, and have many out-
side interests. (See also
personality.)
exudation
The discharge of fluid from
blood vessels
into surrounding tissue. In
most cases, exudation is due to
inflam-
mation.
Exudate contains
cells
(mainly
white blood cells) and protein.
eye
The organ of sight. The eye consists
of structures that focus an image on to
the
retina
at the back of the eye and
nerve cells that convert this image into
electrical impulses. These impulses are
carried by the
optic nerve
to the visual
cortex (an area at the back of the brain
concerned with
vision
) for interpretation.
The eyes work in conjunction with
each other, under the control of the
brain, aligning themselves on an object
so that a clear image is formed on each
retina. If necessary, the eyes sharpen
images by altering focus in an automat-
ic process called
accommodation
.
The eyeballs lie within the bony
orbits
.
Each eyeball is moved by six delicate
muscles. The eye has a tough outer
coat, the
sclera.
At the front of the scle-
ra, the transparent
cornea
serves as the
main “lens” of the eye and does most of
the focusing. Behind the cornea is a
chamber of watery fluid, at the back of
which is the
iris
with its
pupil
, which
appears black. Tiny muscles alter the
size of the pupil in response to changes
in light intensity to control the amount
of light entering the eye. Immediately
behind the iris is the
lens
, suspended by
fibres from a circular muscle ring called
the
ciliary body
. Contraction of the cil-
iary body changes the shape of the lens,
enabling fine focusing. Behind the lens
is the main cavity of the eye, containing
a clear gel, the vitreous humour. On the
inside of the back of the eye is the reti-
na, a complex structure of nerve tissue.
The retina requires a constant supply of
oxygen and glucose, and a network of
blood vessels, the
choroid
, surrounds it.
The eyeball is sealed off from the out-
side by a flexible membrane called the
conjunctiva
, which is attached to the
skin at the corners of the eye and forms
the inner lining of the lids. The conjunc-
tiva contains tear- and mucus-secreting
glands. They, along with an oily secre-
tion from the meibomian glands in the
lids, provide the tear film that protects
the cornea and conjunctiva. The blink
Choroid
Retina
Sclera
EYE
Bony orbit
Ciliary body
Pupil
Retinal blood
Cavity containing
vessel
, vitreous humour
Optic
Eye muscle
Cornea
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