Which layer is NOT a part of the fibrous tunic?

The iris is not considered a part of the fibrous tunic of the eye; instead, it belongs to the uvea, which is the middle layer of the eye. The fibrous tunic comprises the sclera and the cornea, which provide structure and protection to the eye. The sclera is the white outer layer that maintains the shape of the eyeball, while the cornea is the transparent front part that refracts light entering the eye. The limbus, the border area between the sclera and the cornea, is also part of the fibrous tunic. Understanding these distinctions is crucial for grasping the anatomical structure of the eye and its functions.