How we see
The images we see are made up of light reflected from the objects we look at. This light enters the eye through the cornea. Because this part of the eye is curved, it bends the light, creating an upside-down image on the retina (this is eventually put the right way up by the brain).
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| Focusing on a nearby object | Focusing on a distant object |
What happens when light reaches the retina?
The retina is a complex part of the eye responsible for receiving the object the person is looking at. It has 10 layers and the 2nd layer is the light sensitive layer (photoreceptor layer) which is packed with photosensitive cells called rods and cones. These allow us to see images in colour and detail, and to see at night.
Cones are the cells responsible for daylight vision (photopic vision). There are three kinds - each responding to a different wavelength of light: red, green and blue. The cones allow us to see in colour and detail.
Rods are responsible for night vision (Scotopic vision). They are sensitive to light but not to colour. In darkness, the cones do not function at all.
Sending the image to the brain
Once the image is clearly focused on the sensitive part of the retina, energy in the light that makes up that image creates an electrical signal. Nerve impulses can then carry information about that image to the brain through the optic nerve. The part of the brain responsible for processing visual image is the occipital lobe (area 17-19 are the visual areas)/
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