The eyeball is surrounded by a thick wall, which is tough and composed of three layers. The wall protects the eyeball from pressure. Inside the eyeball is a substance known as vitreous, which is a thick, jelly-like material that maintains the shape and pressure of the eyeball. It makes up roughly 80% of the eyeball.
The outer layer of the wall of the eye is composed of the sclera and cornea. The sclera covers the white of the eye, which is roughly 5/6 of the eye surface. The cornea covers 1/6 of the eye and is on top of the colored part of the eye. The sclera and cornea feel like soft leather to the touch, and are relatively dehydrated. They serve to protect the inner parts of the eye from the environment. The cornea also does most of the focusing of the light that comes into the eye.