Certified Paraoptometric (CPO) Practice Exam 2026

The sclera is the correct answer because it is the outermost layer of the eye that provides both shape and structural support to the eyeball. Its rigid, fibrous nature helps maintain the eye's form and protects the internal components from mechanical injury. The sclera also serves as an attachment point for the eye muscles, allowing for movement.

While the lens, cornea, and choroid are all critical to the eye's function and health, they play different roles. The lens focuses light onto the retina and changes shape to aid in accommodation. The cornea helps to refract light entering the eye but is more about focusing vision than maintaining shape. The choroid contains blood vessels that supply nutrients to the eye and helps absorb excess light, but it does not contribute directly to the eye's external shape or structure.