What is the tough white covering of the eyeball commonly referred to?

The tough white covering of the eyeball is known as the sclera. This dense connective tissue forms the outer protective layer of the eye and maintains its shape. The sclera is essential for providing structural support and protection for the internal components of the eye, such as the retina and the vitreous body. It also serves as an attachment point for the eye muscles, which help in the movement of the eye.

The other options refer to different parts of the eye: the iris is the colored part that controls the size of the pupil and thus regulates the amount of light entering the eye; the cornea is the clear, dome-shaped surface that covers the front of the eye and is responsible for most of the eye's focusing power; and the choroid is a layer of blood vessels and connective tissue located between the sclera and the retina that supplies nutrients to the eye and absorbs excess light. Understanding these distinctions helps clarify the role of each part within the anatomy of the eye.