Basic Functions of the Human Eye

The eyes are the two most complicated and complex organs in the body. The main function of the eyes is to work with the brain to provide vision.

How Do They Do It.?

The eyes are connected to the brain. It is the brain that interprets what we see or perceive. The transfer of light plays an important role in the sense of sight. To see we must have light and our eyes must be connected to the brain.

How It Works.

Light passes through the cornea to the lens.

Together the cornea and the lens focus the rays of light to the retina.

The retina absorbs the light, converts it to electrochemical impulses which are transferred along the optic nerve to the brain.

The whole process of sight works like a camera.

The iris and the pupil control the amount of light to be allowed into the eye.

In darkness the pupils dilate and become large to let more light into the eyes.

In bright light the pupils contract allowing less light into the eyes.

The lens adjust to help to focus on items far away or close up.

The Human Eye Consists of the Following Parts and the Parts Support the Specific Functions Listed.


The cornea is the clear window at the front of the eye which transmits and focuses light into the eye. Some patients have laser surgery to reshape the cornea and changes the focus of the eye which produces better vision.


The pupil is a dark opening in the center of the eye through which light passes.


The retina is a layer of nerves that lines the back of the eye. The retina senses the light, it creates electrical pulses and sends them to the optic nerves which take the visual messages to the brain.


The lens is a transparent biconvex body located immediately behind the iris. It focuses light in to the retina. With aging the lens could get cloudy resulting in cataracts and the need for removal of the lens and replacement with intraocular lens. The lens sometimes deteriorate which brings on the need for reading glasses.

Optic Nerve

The optic nerve connects the retina to the brain. Its like a cable. It is a bundle of nerves with over a million nerve fibers that takes the visual image to the brain. The brain is the interpreter of what we see. Glaucoma is the commonest condition related to the Optic nerve. World-wide, glaucoma is the second leading cause of blindness..


The sclera is commonly called the white of the eye. It surrounds the iris.


The macula contains special light sensitive cells which allow us to see fine details clearly in the center of the visual field. Fovea is the center of the macular which provides the sharpest vision. Age Related Macular Degeneration (ARMD) an age related eye disease can affect the macular.

Vitreous Humor

This is a clear gelatinous substance that fills the central cavity of the eye.


The iris is the colored part of the eye. It gives the eye its color. The eye color varies based on the amount of pigment present, resulting in brown eyes, dark eyes, blue eyes or green eyes. The iris also regulates the amount of light entering the eye.


This is a layer of blood vessels located between the retina and the sclera.

In addition, the lacrimal glands produce tears. Tears clean the cornea. The salty tears has lysozyme which kills bacteria and prevents eye infections. Tears also coats the eyes when you blink. Blinking is a reflex action that protects the eye balls.

The eye brows, eyelids and the eyelashes also cover, protect and keep particles from entering the eye.

The human eye is like a camera. It is the sense of sight. It is the window of the soul.

The main purpose of the eye is for us to see the wonders and the beauty of life, nature and all the gifts of the universe.


The University of Michigan Kellogg Eye Center.

Clear Vision CK