What is a primary feature of the sclera?

The primary feature of the sclera is that it acts as a tough protective layer. The sclera is the white outer coating of the eye, made primarily of dense connective tissue. Its durability provides essential protection for the internal structures of the eye, such as the retina, lens, and vitreous body, helping to maintain the eye's shape and integrity. This protective function is crucial in preventing injuries and infections that could threaten vision.

While the other options present characteristics of different components of the eye, they do not accurately describe the sclera. The sclera does not change color with light exposure, as that is more characteristic of the iris. It is not transparent for light entry; the cornea, not the sclera, is responsible for allowing light to enter the eye. Additionally, the sclera does not contain photoreceptors; photoreceptors are found in the retina, where light is converted into neural signals. Thus, the defining feature of the sclera being a tough protective layer is fundamental to understanding its role in ocular anatomy and function.