The outer layer

Sclera

The sclera, also called the white of the eye due to its opaque nature, is the tough, fibrous outer layer of the eyeball. It acts as a protective coat, resisting forces which try to alter the eyes natural shape.

It provides an area for connection of the six extraoculuar muscles which help hold the eye in place and also aid in its movements.

In children, the sclera is relatively translucent and so appears bluish in nature due to the underlying tissue. However, it aquires a yellow hue in the aging process.                       

Cornea

The cornea is the domed-shaped structure located at the front of the eye, covering both the iris and the anterior chamber.

It is transparent in nature, therefore allowing light to pass through and into the eye.

The cornea has the abililty to refract light and together with the lens, accounts for two thirds of the eyes optical power. Unlike the lens however, it cannot adjust it's focus.

Cornea diagram courtesy of Wikimedia Commons. This image is in the public domain and thus free of any copy right restrictions.