messageds = new Array() messageds[0] = null; messageds[1] = "Sclera:

a tough outer sheath." messageds[2] = "Ciliary muscles:

change shape of lens when
focusing." messageds[3] = "Aqueous humour:

clear fluid between the lens
and the cornea." messageds[4] = "Conjunctiva:

forms a moist covering over
the cornea." messageds[5] = "Cornea:

a window that partly focuses
light rays." messageds[6] = "Iris:

adjusts the amount of light
that pases through its central
hole, the pupil." messageds[7] = "Lens:

adjusts to focus light rays
from objects at different
distances." messageds[8] = "Blind spot:

has no light-sensitive cells" messageds[9] = "Optic nerve:

carries nerve signals from
the eye to the brain. " messageds[10] = "Yellow spot

highly sensitive
area of the retina" messageds[11] = "Retina:

detects light rays and turns
them into nerve signals." messageds[12] = "Choroid:

provides oxygen and
nourishment for the eye's
outer layers and retina." messageds[13] = "Vitreous humour:

clear jelly that fills the
eyeball." messageds[24] = "The Eye

Your two eyes provide an
incredibly detailed, constantly
updated, three-dimensional,
colour view of the world. Light
rays enter the eye through the
cornea, a domed window at
the front. They are detected by
the retina, a layer of light-
sensitive cells. The retina is
not much larger than a
postage stamp-and even
thinner. From the pattern of
light rays, the eye generates
patterns of nerve signals and
sends them to your brain. The
parts of your brain specialized
for dealing with sight, the
visual centres analyse all the
information coming in from
the eyes. It is your brain that
tells you what kinds of shapes
and forms, shades and
colours, positions and
movements you are looking
at."