EALES’ DISEASE
E
Eales’ disease
A rare condition seen mainly in young
men that is characterized by inflamma-
tion of the retinal veins and recurrent
vitreous haemorrhage (leakage of blood
into the
vitreous humour
,
the gel-like
substance that fills the rear chamber of
the
eye
) .
The presence of blood in the
vitreous hum our may affect vision and
lead to headaches. If vision is impaired,
laser treatment
may be performed to pre-
vent further haemorrhage.
ear
The organ of hearing and balance. The
ear consists of three parts: the outer ear,
the middle ear, and the inner ear. The
outer and middle ear are concerned
mainly with the collection and trans-
mission
of sound. The inner ear is
responsible for analysing sound waves;
it
also
contains
the
mechanism
by
w hich the body keeps its balance.
OUTER EAR
The outer ear comprises the pinna (the
visible part of the ear), w hich is com-
posed of folds of skin and
cartilage
,
and
the ear canal, w hich is approximately
2.5
cm long in adults.
The outer part of the ear canal is
composed of cartilage and produces
ear-
wax
,
w hich
traps
dust
and
foreign
bodies. The canal is closed at its inner
end by the eardrum, a thin, fibrous, cir-
cular membrane that is covered with a
layer of skin. The eardrum vibrates in
response to the changes in air pressure
that constitute sound.
MIDDLE EAR
The middle ear is a small cavity between
the eardrum and the inner ear that con-
ducts sound to the inner ear by means
of three tiny, linked, movable bones
known as
ossicles
.
The first bone, the
malleus, is joined to the inner surface of
the eardrum. The second, the incus, has
one broad joint with the malleus (which
lies almost parallel to it) and a delicate
joint to the third bone, the stapes. The
base of the stapes fills the oval window
leading to the inner ear.
The middle ear is cut off from the out-
side by the eardrum. However, it is not
completely airtight; a ventilation pas-
sage, called the
eustachian tube
, runs
forwards and downwards into the back
of the nose. The eustachian tube is
normally kept closed, but it opens by
muscular contraction when an individ-
ual yawns or swallows.
The middle ear acts as a transformer,
passing the vibrations of sound from
the air outside (which is a thin medium)
to the fluid within the inner ear (which
is a thicker medium).
INNER EAR
The inner ear is an intricate series of
structures contained deep within the
bones of the skull. It consists of a maze
of winding passages, collectively known
as the labyrinth. The front part, called
the cochlea, is a tube that resembles a
snail’s shell, containing nerve fibres that
detect different sound frequencies. (For
more information about how this sys-
tem works, see
hearing
. )
The rear part of the inner ear con-
tains three semicircular canals and is
concerned with balance. The semicircu-
lar canals are connected to a cavity
called the vestibule and contain hair
cells bathed in fluid. Some of these cells
are sensitive to gravity and acceleration;
others respond to the positions and
movement of the head. Information
from the inner ear is conducted to the
brain via the
vestibulocochlear nerve
.
(See
also
disorders of the ear
box.)
earache
Pain in the
ear
,
w hich may originate in
the ear itself or may result from a disor-
der in one of the structures situated
ANATOMY OF THE EAR
The outer ear comprises the pinna and ear canal; the middle ear - the eardrum,
malleus, incus, stapes, and eustachian tube; and the inner ear - the vestibule,
semicircular canals, and cochlea. Sensory impulses from the inner ear pass to the
brain via the vestibulocochlear nerve.
V e s t ib u l e
E a r d r u m
C o c h l e a
E u s t a c h i a n t u b e
252
previous page 251 BMA A Z Family Medical Encyclopedia   2004 read online next page 253 BMA A Z Family Medical Encyclopedia   2004 read online Home Toggle text on/off