Illustration of an eyeball. The Human Eye is roughly spherical in shape. It contains the Retina, a layer of nerve tissue composed of millions of light receptors and structures needed to focus light on to it. The Sclera is the tough outer shell of the eyeball and is made up of dense fibrous tissue. A segment of the sclera, the Cornea, allows light to pass into the eye and aid s in focusing. The eyeball is filled with a transparent jelly-like material, the Vitreous Humour, which maintains its spheroid shape.