Eyelids
The
eyelids protect the eyes from the environment, injury and
light. They maintain a smooth corneal surface by spreading
tears evenly over the eye. The lids are composed of an
outer layer of skin, a middle layer made of muscle and tissue
that gives them form, and an inner layer of moist conjunctival
tissue.
Pupil
The
pupil is the black, circular opening in the center of the
iris. It opens and closes in order to regulate the amount
of light entering the eyeball.
Sclera
The
sclera, commonly known as "the white of the eye," is
the tough, opaque tissue that serves as the eye's protective
outer coat.
Iris
The
colored part of the eye is called the iris. It controls
light levels inside the eye similar to the aperture on a
camera. The round opening in the center of the iris is
called the pupil. The iris is embedded with tiny muscles
that dilate (widen) and constrict (narrow) the pupil size.
Cornea
 The
cornea is the transparent, dome-shaped window covering
the front of the eye. It is a powerful refracting surface,
providing 2/3 of the eye's focusing power. Like the crystal on a
watch, it gives us a clear window to look through.
Lens
The
purpose of the lens is to focus light onto the back of the
eye. The nucleus, the innermost part of the lens is
surrounded by softer material called the cortex. The lens
is encased in a capsular-like bag and suspended within the eye
by tiny guy wires called zonules.
Conjunctiva
The
conjunctiva is the thin, transparent tissue that covers the
outer surface of the eye. It begins at the outer edge of
the cornea, covers the visible part of the eye, and lines the
inside of the eyelids. It is nourished by tiny blood
vessels that are nearly invisible to the naked eye.
Vitreous
The
vitreous is a thick, transparent substance that fills the center
of the eye. It is composed mainly of water and comprises about
2/3 of the eye's volume, giving it form and shape.
Choroid
 The
choroid lies between the retina and sclera. It is composed
of layers of blood vessels that nourish the back of the eye.
Optic
Nerve
The
optic nerve transmits electrical impulses from the retina to the
brain. It connects to the back of the eye near the
macula. The visible portion of the optic nerve is
called the optic disc.
The
Macula
 The
macula is located roughly in the center of the retina, temporal
to the optic nerve.
It is a small and highly sensitive part of the retina
responsible for detailed central vision. The fovea is the
very center of the macula.
The macula allows us to appreciate detail and perform
tasks that require central vision such reading.
The
Retina
 The
retina is a very thin layer of tissue that lines the inner part
of the eye.
It is responsible for capturing the light rays that enter
the eye. Much like the film's role in
photography. These light impulses are then sent to
the brain for processing, via the optic nerve.
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