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How the Eye Works

Vision is an intricate sense that involves constant interaction between the various structures of the eye and the brain in order to process everything surrounding a person.

The Human Eye


According to Everyday Health, “the human eyeball is capable of producing three-dimensional images in color. It is self-focusing and can switch from making out the tiniest of fine print to observing a faraway mountain peak in less than a second. IThe eyeball is made of water, jelly and protein.”

Below is an illustration of the eyeball:

eyeball

Source:  American Foundation for the Blind, Senior Site.

The National Eye Institute defined the following structures of the eye:

  • Cornea is the clear outer part of the eye's focusing system located at the front of the eye.
  • Fovea is the center of the macula; gives the sharpest vision.
  • Iris is the colored part of the eye that regulates the amount of light entering the eye.
  • Lens is a clear part of the eye behind the iris that helps to focus light or an image on the retina.
  • Macula is the small sensitive area of the retina that gives central vision. It is located in the center of the retina and contains the fovea.
  • Optic Nerve is a bundle of more than one million nerve fibers that carries visual messages from the retina to the brain.
  • Pupil is the opening at the center of the iris. The iris adjusts the size of the pupil and controls the amount of light that can enter the eye.
  • Retina is the light-sensitive tissue lining at the back of the eye. The retina converts light into electrical impulses that are sent to the brain through the optic nerve.
  • Vitreous Gel is a clear gel that fills the inside of the eye.

Forming an Image


The individual structures of the eye can be compared to the various parts of the camera, where each structure functions to ensure clear vision.

The Pasadena Eye Associates discussed the process of forming an image: “Think of the eye as a camera with the cornea behaving much like a lens cover. As the eye's main focusing element, the cornea takes widely diverging rays of light and bends them through the pupil – the dark, round opening in the center of the colored iris. The iris and pupil act like the aperture of a camera. Next in line is the lens, which acts like the lens in a camera, helping to focus light to the back of the eye. The back of the eye is lined with a layer called the retina, which acts much like the film of the camera. The retina is a membrane containing photoreceptor nerve cells that lines the inside back wall of the eye. The photoreceptor nerve cells of the retina change the light rays into electrical impulses and send them through the optic nerve to the brain where an image is perceived. The center of the retina is the macula, which is responsible for sharp vision and reading vision. The peripheral retina is responsible for the peripheral vision. Just as when using a camera, if the ‘film’ is bad in the eye (i.e. the retina), no matter how good the rest of the eye is, you will not get a good picture.”

Sources:

www.everydayhealth.com/vision-center/the-healthy-eye/how-the-eye-works.aspx

www.nei.nih.gov/health/eyediagram/index.asp