What Is the White Outer Covering of the Eye?

Each layer of the eye is important to its function.

The eyes have three functional layers called tunics or coats: the tunica interna or retina, the vascular tunic or choroid, and the fibrous tunic or sclera. Each is very different and each is vital to the overall function of the eyes.

The Whites of Their Eyes

The sclera is the white outer layer of the eye.

The sclera is the white of the eye. It is a tough, fibrous membrane that covers most of the eye. The very small area of the cornea and iris is the only part of the eye not covered by the sclera. The iris and cornea emerge from the sclera giving color to the eyes and where sight begins.

Function

The muscles and ligaments allow for eye movement.

The sclera allows for the gross function of the eyes. The muscles and ligaments that allow movement attach to the sclera. The sclera also gives shape to the eyeball and protection because of the tough, fibrous and elastic makeup of this layer.

Considerations

Squinting begins with the sclera.

Besides the functions already listed, the sclera also aids in the mechanics of sight itself. The flexibility of the sclera allows for the eyeball to take different shapes. When someone squints, muscles and ligaments squeeze and reshape the eyeball in an effort to focus or shield the eyes.

References

• "Principles of Anatomy and Physiology"; Gerard J. Tortora, Nicholas P. Anagnostakos; 1990
• "Human Biology"; Sylvia S. Mader; 2004
• Thinkquest: Anatomy: Internal Structures

Resources

• Bartleby: "Gray's Anatomy": The Tunics of the Eye