How Rods and Cones Allow us to See

Like a camera, the eye transmits light from the world around us into an image that we can perceive. Although it is small, the eye is a complex organ. All structures within the eye must function properly to capture light, focus it, and process messages back to the brain to create a visual image.

How Our Eyes Work

To process vision, the light reflected from an object in our field of view is gathered by the cornea. The cornea then refracts the light rays through the pupil (the center of the iris where light enters the eye). The iris then passes the image onto the crystalline lens. The lens in the eye focuses the light rays, projecting them to a point at the back of the eye called the retina, where the image appears upside down. The retina contains a thin layer of color-sensitive cells called rods and cones that perceive and decode color. These are critical to how our eyes work. The retina then passes visual signals to the brain via the optic nerve. The brain receives the information from both eyes and aggregate the images to process a complete picture.

Impaired vision occurs when a breakdown occurs at any point in this process. From the muscles that control the eyes, to the parts within the eye, to the pathway to the brain, vision impairments result from technical problems during the transitional phases. Other times, the eyes might work perfectly but there is a problem with how the brain interprets the signals it receives.

Rods and Cones: Color Vision and Concept

These crucial parts of our eye are known as photoreceptors. They are specialized cells that are located on the retina, in the back of your eye which processes images. Their roles are very specific: to receive and process signals of light and color, which gives us our vision. Because we rely primarily on vision over other senses, these components are very important to us. The effect of malfunctioning or deficient photoreceptors can be serious.

The retina of the eye has two types of light-sensitive cells called rods and cones, both found in layer at the back of your eye which processes images. Cones are cone shaped structures and are required for bright light (day light) vision. Rods are rod like structures located through the retina except for the fovea, and are required for dim light (twilight/night) vision. Both these visual components contain light sensitive pigments.

The most basic and crucial function of photoreceptors is to perceive light, which is the function of rods. Rods are located throughout the retina except for the very center or fovea. They are specialized to pick up light signals to determine light and shadow. On average, there are 120 million rods in the human eye, which are more than a thousand times as sensitive as individual cones. Rods pick up signals from all directions, improving our peripheral vision, motion sensing and depth perception. However, rods do not perceive color: they are only responsible for light and dark.

Color perception is the role of cones. There are 6 million to 7 million cones in the average human retina. They are mostly concentrated in the center of the retina, around the fovea. There are three types of cone cells and each type has a different sensitivity to light wavelengths. One perceives red (about 64 percent), another perceives green (32 percent) and the third perceives blue light (2 percent). Light enters your eye and stimulates the cone cells when you look at an object. Your brain interprets the signals from the cone cells to help you determine the color of the object. The red, green and blue cones work together to create the color spectrum. For example, when the red and blue cones are simulated in a certain way, you will see purple.

People with normal color vision have all three types of cone cells working correctly. On the other hand, color blindness occurs when one or more of the cone types are faulty. For example, if the green cone is faulty you won’t be able to see colors containing blue clearly. Our vision is a delicate system of intricate processes that gift us with the miracle of sight every day. It is important o fully understand how our eyes work in order to properly appreciate what we are able to see every day.

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