Which layer of the eyeball is considered the fibrous tunic?

The fibrous tunic of the eyeball consists of two main structures: the cornea and the sclera. The cornea is the transparent front part of the eye that allows light to enter and provides most of the eye's optical power, while the sclera is the tough, protective outer layer that maintains the shape of the eyeball. Together, these components form the fibrous tunic, which provides structural support and protection to the more delicate inner layers of the eye.

The other options involve various components of the eye but do not correctly define the fibrous tunic. The retina is part of the inner neural layer, responsible for converting light into neural signals, while the choroid, iris, and ciliary body are part of the vascular tunic (or uvea).