What is the sclera primarily known for?

The sclera is primarily known for being the outer coat of the eye, which serves several important functions. As the tough, white outer layer of the eyeball, the sclera not only provides structural support and shape to the eye but also protects the inner components from injury and infection. Its durability allows it to withstand various mechanical stresses, maintaining the integrity of the eye.

In contrast, while transparency is a characteristic of certain parts of the eye, such as the cornea, it does not apply to the sclera, which is opaque. The sclera does not control the entry of light; instead, that function is primarily performed by the cornea and the iris. Measuring visual acuity is carried out through specific tests and is not a direct function of any eye structure, including the sclera itself. Thus, focusing on its role as the outer protective layer underscores the sclera's significance in maintaining eye health and function.