How Is Light Received by the Eye?

The eye is an organ of sight composed of several parts, according to MedicineNet.com, including the cornea, iris, pupil, lens, and retinal cell layers. Other parts are the vitreous gel, fovea, macula, sclera, and optic nerve.

The eye has specialized cells, known as rods and cones, that detect the intensity and color of light photons, says NASA's Imagine the Universe. Rods and cones convert the light photons that enter the eye into nerve signals that register in the brain and result in sight.

The Outer Layer

• The outer layer of the eye, says Library Thinkquest, is made of up the sclera, the white of the eye, and the cornea, a transparent layer that covers the iris and pupil. The cornea is covered with a tear film that keeps the eye moist, according to Macular Degeneration Support. The aqueous chamber sits behind the cornea and is filled with a clear fluid that maintains the pressure of the eye.

  The pupil is where light first enters the eye.

The Middle Layer

• The middle layer if the eye wall, the choroid, consists of blood vessels which transfer nutrients and regulate temperature, says Library Thinkquest. The choroid encircles the iris, which determines eye color, and contracts and expands according to the amount of light available. The pupil, the opening in the center of the iris, also narrows or widens to let in less or more light.

  The lens, a transparent dual-convex body, sits behind the iris. It changes shapes as the eye focuses on images that are near or far, and focuses light onto the retina.

The Inner Layer

• The inner layer is made up of retinal cell layers, says Macular Degeneration Support, including the optic fiber layer and the ganglion cell layer. These layers make up the retina, the membrane at the back of the eye which receives images via light from the lens and transforms them into nerve impulses, which get sent to the brain.

Rods and Cones

• The retina contains millions of cells called rods and cones. Rods are photoreceptor cells located mostly on the side of the retina, and are responsible for peripheral and dim light vision. Cones are located more in the center of the retina and are responsible for central, bright light, fine detail, and color vision.

  A eye contains about one million rods, and seven million cones.

Optic Nerve

• Once the rods and cones of the retina convert light and colors into nerve impulses, these impulses leave the eye at the optik disk and enter the optic nerve. At this point where the optic nerve connects with the retina, there are no rods and cones. This part of the retina is often called the blind spot because it cannot detect light or darkness. Finally, from the optic nerve, the nerve impulses are transmitted into the brain.