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Receptors of the Back of the Eye: Retina, Rods, Cones & Fovea

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  1. 0:52 Retina
  2. 1:49 Rods
  3. 3:18 Cones and Fovea
  4. 3:46 Metaphors to Help You Remember
  5. 4:42 Lesson Summary
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Taught by

Artem Cheprasov

Artem is a doctor of veterinary medicine and has taught science and medicine at the college level.

Find out how we see the world in color, what rods and cones are, and how camera film fits into all of this. In addition, you'll find out what the retina is and what gives you the ability to see at night.

Seeing the World in Color

Some people say they see the world through rose-colored glasses. Others, especially when having a sad day, seem to think they see everything in black and white. Regardless of whether their worldview is full of color or not, everyone who can see with their eyes relies on a very important structure in the back of their eye in order to allow them to differentiate all the colors you can possibly think of.

What's even more critical is what is located within this structure. Let's find out what all of these parts of your eyes are and how they help you see images and their colors.

The Retina

The lens focuses light and burns an image on the retina
Image Burned on Retina

As light enters the eye, it goes through the cornea, then through the pupil, and finally through the lens. During this entry, it is refracted, or bent, and then focused by the lens. Once this occurs, an image of what you see in front of you is 'burned,' so to speak, on the retina. The retina is a thin layer of specialized cells located at the back of your eye that help to transmit information provided by light to our brain.

In a way, our retina is like the negative film used in some cameras. Once our eye, or the camera, uses the lens to focus in on an object, it imprints an image on the film, or retina, which can later be developed into a recognizable picture of our world; in our case, all thanks to a machine called our brain.

Rods

In order to recognize what we see in front of us, our retina has several different layers. One of the most important layers is made up of highly-specialized neurons, called photoreceptors, that convert information provided by light into electrical signals that are conducted to our brain. These photoreceptors are called the rods and cones.

Rods are called rods because under the microscope, they are shaped like, of all things, a rod. Finally, those pesky scientists named a structure for what it actually looks like as opposed to someone's unpronounceable last name!

Image of a rod found in the back of the eye
Rods Eye

These rods are located mainly near the periphery, or towards the side of your retina. This is why they are more involved in peripheral vision. This is the vision that helps you see what someone is doing on either side of you without you having to turn your eyes or head in their direction. Peripheral vision helps you see things like a sneaky person trying to take your picture without your consent. In addition, rods are the photoreceptors that give you the ability to see in the dark.

To sum this all up one more time, rods are photoreceptors located near the edges of the retina that are responsible for peripheral and night vision.

The Cones and Fovea

Conversely, cones are photoreceptors that are centered in and around a depression near the center of your retina called the fovea, or more technically referred to as the fovea centralis. Again, cones are photoreceptors located near the center of your retina that are responsible for your ability to see during the day, in color, and in detail.

Metaphors to Help You Remember

Cones are located around the center of the retina
Cones Eye

We can use a couple of metaphors to help us remember which photoreceptors do what.

Cones are like a good painter. They must be masters of watercolors, pay attention to detail, and do their best work in natural daylight, as they can truly see the colors and details of their painting much better that way. Therefore, cones are responsible for color vision and detailed vision, and they work best during the day.

Rods, however, are like a vampire I once met named Rod. He comes out only at night and likes to catch people by surprise, when they're not looking directly at him. Hence, rods are responsible for night vision and peripheral vision, which consists of the images not directly in front of your eyes.

Lesson Summary

Let's hope that Rod never catches you by surprise tonight! Perhaps you can turn on some lights in your room as you fall asleep in order to activate your cones, which are photoreceptors located near the center of your retina that are responsible for your ability to see during the day, in color, and in detail. Most of these cones are centered near or in a depression near the center of your retina called the fovea.

In addition, by turning on the light, you should also be able to scare Rod, our vampire, away, as rods are photoreceptors located near the edges of the retina that are responsible for peripheral and night vision. Rod doesn't like bright lights very much, so he won't bother you with a light on.

In addition, don't forget that the rods and cones are only one part of the retina, which is a thin layer of specialized cells located at the back of your eye that help to transmit information provided by light to our brain.

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