State one function each of iris, pupil, and cornea

Iris: It regulates the amount of light entering the eye by dilating the pupil in light of low intensity and contracting the pupil in high intensity light. Pupil: This is portion of the eye which allows the light to enter the eye.
Cornea: It is a transparent spherical membrane covering the bulge in front of the eyeball. Light enters the eye through cornea where it is refracted the most.