The macula is the central part of the human retina. It has the highest density of photoreceptors and gives the highest definition vision. It is comprised of three types of cone photoreceptors and a single type of rod photoreceptor. Away from the macula the number of rod photoreceptors increases and the number of cone photoreceptors decreases. The cone photoreceptors provide colour vision in the daytime whilst the rods provide the night vision. The optic nerve transmits the signal from the retina to the brain for visual processing. The iris is the coloured part of the eye and is comprised of two muscles which control the size of the pupil. The pupil controls the passage of light through to the retina.

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