Vision how do we see

The retina forms the circular shape at the back of the eye surrounded by a layer called the choroid and then another layer called the sclera. Within the retina is the macula the size of a pinpoint, vitreous body and blood vessels. The optic nerve protrudes from the back of the eyeball and consist of blood vessels. When the light enters the eye, it is focused to a pinpoint on the macula, a small area in the centre of the retina at the back of the eye.

The macula is responsible for central detailed vision, allowing you to see fine detail and colour, read and recognise faces. When light stimulates the nerve cells in the retina, messages are sent along the optic nerve to the brain.

This kind of illusion is actually a great way to explain your very complex sense of vision. And I do mean complex. Nearly 70 per cent of all the sensory receptors in your whole body are in the eyes. Not only that, but in order for you to see, perceive, and recognise something—whether it's a flag or a handsome guy in glasses and a sport coat sitting behind a desk—nearly half of your entire cerebral cortex has to get involved.

Vision is considered the dominant sense of humans, and while we can get along without it, and it can be tricked, what you are about to learn is not an illusion.

When we talked about your sense of hearing, we began with the mechanics of sound. So before we get to how your eyeballs work, it makes sense to talk about what they're actually seeing—light bouncing off of stuff. Light is electromagnetic radiation travelling in waves. Remember how the pitch and loudness of a sound is determined by the frequency and amplitude of its wave? Well it's kind of similar with light, except that the frequency of a light wave determines its hue, while the amplitude relates to its brightness.

We register short waves at high frequencies as bluish colours, while long, low frequencies look reddish to us. Meanwhile, that red might appear dull and muted if the wave is moving at a lower amplitude, but super bright if the wave has greater amplitude and thus higher intensity.

But the visible light we're able to see is only a tiny chunk of the full electromagnetic spectrum, which ranges from short gamma and X rays all the way to long radio waves. Just as the ear's mechanoreceptors or the tongue's chemoreceptors convert sounds and chemicals into action potentials, so too do your eyes' photoreceptors convert light energy into nerve impulses that the brain can understand.

Some of the first things you'll notice around your average pair of eyes are all the outer accessories, like the eyebrows that help keep the sweat away if you forgot your headband at raquetball, and the super-sensitive eyelashes that trigger reflexive blinking, like if you're on a sandy beach in a wind storm.

These features, along with the eyelids and tear-producing lacrimal apparatus are there to help protect your fragile eyeballs. The eyeball itself is irregularly spherical, with an adult diameter of about 2. It's essentially hollow, full of fluids that help to keep its shape, and you can really only see about the anterior sixth of the whole ball. The rest of it is tucked into a pocket of protective fat, tethered down by six straplike extrinsic eye muscles, and jammed into the bony orbit of your skull.

While all this gear generally does a fantastic job of keeping your eyeballs inside of your head, which is good, on very rare occasions, perhaps after head trauma, or even a really intense sneeze, those suckers can pop right out—a condition called globe luxation, which you really do not want to Google. I'll just sit here while you Google it. Now, you don't need to pop out an eyeball in order to learn how it's structured.

I'll save you the trouble and tell you that its wall is made up of three distinct layers—the fibrous, vascular, and inner layers. As the two optic nerves enter the brain, they cross over, coming together at a point known as the optic chiasm. Here, signals from the left side of both eyes are diverted to the left side of the brain, and vice versa, allowing the images from both eyes to be combined and compared.

The signals enter the brain via the thalamus, which separates the incoming information into two parts, one containing colour and detail, and the other movement and contrast. The messages then move to the back of the brain, and into the visual cortex. The cortex is laid out so that it mirrors the back of the retina, allowing a detailed image to be reconstructed. Open your eyes, and you are met with an array of different colours, but amazingly you can only detect three different wavelengths of light, corresponding to green, blue, and red.

Combining these three signals in the brain creates millions of different shades. Each eye has between 6 and 7 million cone cells, containing one of three colour-sensitive proteins known as opsins. When photons of light hit the opsins, they change shape, triggering a cascade that produces electrical signals, which in turn transmit the messages to the brain. Well over half of our cone cells respond to red light, around a third to green light, and just two per cent to blue light, giving us vision focused around the yellow-green region of the spectrum.

The vast majority of the cone cells in the human eye are located in the centre of the retina, on a spot known as the fovea, measuring just fractions of a millimetre across.

The optic nerve will send this information to your brain. It is responsible for decoding the electrical information coming from the retina. The vision center interprets the electric form of the image, allowing you to form a visual map. As you can SEE , vision is a complex process. The brain has to do a lot of work to make a picture. But what happens if what you see is blurry?

Maybe you or someone you know may need to wear glasses or contacts in order to see clearly. You may even know someone who is blind and cannot see at all.

How do you think they see the world? Page Baluch, Ashleigh Gonzales. How Do We See?. Do insects see the same thing you do? Visit insect vision to learn more. Human Eye Worksheet. Putting the Touch into Biology. By volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteers page to get the process started.

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