This part is clear to let light through and is called the cornea. The drawing below shows the inside parts of your eyes. The coloured ring is the iris and the black hole in the middle is the pupil. Light rays get inside your eye through the pupil. Behind the pupil is a lens, a bit like the lens in a camera or slide projector - it is used to focus and helps you to see things clearly.
Special muscles stretch and relax the lens to change focus.
Inside the eye the space is filled with a clear jelly, called the vitreous, to keep the eyeball round. The retina lines the inner two thirds of the eye and catches the light coming through the lens. The light is then converted into electrical signals which travel down the optic nerve.