How do we see?

The visual system takes up a very large part of the brain—some say that as much as 30% of prime cortical real estate is specialized for visual processing in humans (Orban et al., 2004). This tells us that vision is important for human survival; language, touch, and audition, for example, get a far smaller slice of the cortical pie. 

So, what happens to all visual information? 

All the different parts of your eyes work together to help you see.

First, light passes through the cornea (the clear front layer of the eye). The cornea is shaped like a dome and bends light to help the eye focus. Some of this light enters the eye through an opening called the pupil (PYOO-pul). The iris (the colored part of the eye) controls how much light the pupil lets in.

Next, light passes through the lens (a clear inner part of the eye). The lens works together with the cornea to focus light correctly on the retina.
When light hits the retina (a light-sensitive layer of tissue at the back of the eye), special cells called photoreceptors turn the light into electrical signals.
These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see.
Your eyes also need tears to work correctly. Tears keep your eyes wet and smooth, and help focus light so you can see clearly. They also protect your eyes from infections and irritating things, like dirt and dust.

Every time you blink, a thin layer of tears called a “tear film” spreads across the surface of your cornea (the clear outer layer of the eye). Tears come from glands above your eyes, then drain into your tear ducts (small holes in the inner corners of your eyes) and down through your nose.

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