We can think of the eye as a kind of camera

The iris behind the cornea is light- sensitive and corresponds to the aperture of the camera. This can be set near or far, depending on the amount of light falling on it.

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The light rays penetrate the lens of the eye, and fall on the retina. Millions of light- sensitive cells convert the light into signals sent to the brain via the optic nerve.

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These are put together to make images, and are interested by the brain there are two types of cells in the retina:

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The light- sensitive rods that help us see in the dark and the less sensitive cones that help us see colours.