What anatomical structure helps maintain the shape of the eyeball?

The sclera is the fibrous outer layer of the eyeball, commonly referred to as the "whites of the eyes." It plays a crucial role in maintaining the shape and structural integrity of the eyeball. The sclera is composed of dense connective tissue, which provides strength and protection to the inner structures of the eye. It also serves as an attachment point for the extraocular muscles, allowing for eye movement.

In contrast, while the cornea is integral to the eye's refractive ability and overall vision, it does not provide the same structural support and shape maintenance as the sclera. The iris is responsible for regulating the amount of light that enters the eye by controlling the size of the pupil, but it does not contribute to the shape of the eyeball itself. The pupil is merely an opening in the iris and has no structural components to support or maintain the eye's shape. Hence, the sclera is correctly identified as the anatomical structure that helps maintain the shape of the eyeball.