Which part of the eye acts to protect and support its structure?

The sclera is the part of the eye that provides protection and structural support. It is the white, outer layer of the eyeball, composed of dense connective tissue. Its primary role is to maintain the shape of the eye and protect the inner components from injury. In addition to providing a protective barrier, the sclera serves as an attachment point for the eye muscles that control eye movements, aiding in vision stability.

The iris, while important for regulating the amount of light entering the eye, does not primarily function to support or protect the eye's structure. The pupil is simply the opening in the iris that allows light to enter; it doesn’t have a structural or protective role. The ciliary body is responsible for producing aqueous humor and altering the shape of the lens for focusing but does not provide the outer protection that the sclera does.