The retina - Light-sensitive layer at the back of the eyeball
onto which incoming light is focused. It contains cells that respond to colours,
different shades of grey, and movement. These cells trigger nerve impulses that
are carried by the optic nerve to the brain, where a visual image is formed.
The cornea - The dome-shaped, transparent layer that forms
the front of the eyeball. It bends light entering the eye into the lens, and
hence helps to focus images onto the retina. It contains no blood vessels and is
extremely sensitive to pain.
The lens - Transparent elastic structure situated behind the
pupil of the eye that focuses incoming light onto the retina. Muscles in the eye
can adjust the shape of the lens and make it more flattened to focus on distant
objects, or make it more rounded to focus on near objects.
The vitreous humour - The transparent jelly-like substance
that fills the eyeball between the lens and the retina.