Which is not a part of the first tunic of the eye?

The first tunic of the eye, also known as the fibrous tunic, consists of structures that provide support and shape to the eye. This tunic is primarily made up of the sclera and the cornea. The cornea is the transparent front part of the eye that allows light to enter, while the sclera is the white, protective outer layer that maintains the eye's shape.

Additionally, the limbus, which is the border area between the cornea and the sclera, is considered part of this first tunic as it plays a role in the eye's structural integrity.

The iris, however, is not included in the first tunic. Instead, it is part of the middle tunic, also known as the uvea, which includes the iris, ciliary body, and choroid. The primary function of the iris is to control the amount of light that enters the eye by adjusting the size of the pupil, which is not a function related to the protective and structural roles of the first tunic. Therefore, identifying the iris as not being part of the first tunic highlights its distinct anatomical and functional separation from the fibrous layer of the eye.