Name the essential parts of the human eye.

(N/A) The essential parts of the human eye are as follows:
$(i)$ Cornea: The transparent outer layer that protects the eye and helps focus light.
$(ii)$ Iris: The colored part of the eye that controls the size of the pupil.
$(iii)$ Pupil: The opening in the center of the iris that allows light to enter the eye.
$(iv)$ Eye lens: $A$ transparent,biconvex structure that focuses light onto the retina.
$(v)$ Ciliary muscles: Muscles that change the shape of the lens to adjust focus.
$(vi)$ Retina: The light-sensitive layer at the back of the eye where images are formed.