Eye | |||
The Eye develops as an extension of the brain, to which it is connected by the optic nerve. The eyeball has three layers: an outer, fibrous layer called the sclera; a coloured middle layer, the choroid, (which at the front becomes the iris, that gives the colour to our eyes), and an inner layer, the retina, which is made up of nerve cells which respond to light. There are two types of cells - rods (about 125 million) which respond to dim light, and cones (about 6 million) which respond to colour, either red, blue or green. | |||
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