What main role does the cornea serve?

The cornea serves a crucial role in the eye as it protects the lens and iris, which are essential for vision. The cornea is the transparent, dome-shaped surface that covers the front of the eye, and it plays a significant part in light refraction, helping to focus light as it enters the eye. By acting as a barrier, the cornea defends against foreign particles and harmful microorganisms, thereby maintaining the integrity of the internal structures such as the lens and iris that are vital for clear vision.

Unlike the other options, the cornea does not support eyelid movement, contain tear ducts, or line the outer surface of the eye; instead, it is the tissue that directly interfaces with external elements and contributes significantly to the optical properties of the eye. Its role in protecting the more delicate internal components of the eye is fundamental to sustaining overall eye health and function.