describe human eye and its working

A human eye is roughly a spherical ball. 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 cornea. Light enters the eye through the cornea.
• Iris: A dark muscular tissue and ring like structure behind the cornea are known as the iris. The color of iris actually indicates the color of the eye. Ex: A person with brown eyes have the brown iris.
•  Pupil: A small opening in the iris is known as a pupil. Its size is controlled by 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 distant objects and becomes thicker to focus 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.

There are two types of optic nerves:

• Cones: Cones are the nerve cells that are more sensitive to bright light. They help in detailed central and color vision.
• Rods: Rods are the optic nerve cells that are more sensitive to dim lights. They help in peripheral vision.

At the junction of optic nerve and retina, there are no sensory nerve cells. So no vision is possible at that point and is known as a blind spot.

This was a brief introduction about the human eye, its parts, and their functions.