HUMAN EYE

A human eye is roughly 2.3 cm in diameter and is almost a spherical ball filled with fluid (Vitreous Humour)
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It consists of the following parts:
Sclera: It is the outer covering, a protective tough white layer called the sclera (white part of the eye).
Cornea: The front transparent part of the sclera is called the cornea. Light enters the eye through the cornea.
Iris: A dark muscular tissue and ring-like structure behind the cornea is known as the iris. The colour of the iris actually indicates the colour of the eye. The iris also helps regulate or adjust exposure by adjusting the iris.
Pupil: A small opening in the iris is known as a pupil. Its size is controlled with the help of iris. It controls the amount of light that enters the eye.
Lens: Behind the pupil, there is a transparent structure called a lens. By the action of ciliary muscles, it changes its shape to focus light on the retina. It becomes thinner to focus on distant objects and becomes thicker to focus on the nearby objects.
Retina: It is a light-sensitive layer that consists of numerous nerve cells. It converts images formed by the lens into electrical impulses. These electrical impulses are then transmitted to the brain through optic nerves.
Optic nerves: Optic nerves are of two types. These include cones and rods.
Cones: Cones are the nerve cells that are more sensitive to bright light. They help in detailed central and colour vision.
Rods: Rods are the optic nerve cells that are more sensitive to dim lights. They help in peripheral vision.