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The eyes are the sense organs of sight, they are spherical organs housed in deep depression of the skull called orbits and are attaches to the wall of the orbit by six muscles which can also move the eye ball.

Light from an external objects enter the eye, The eye curved surface of the cornea, the lens and the humour reflect the light and focus it so that ‘point’ of light from the object produce point of light in the retina. The image thrown in the retina is real upside-down and smaller than the object.

The light sensitive cell are stimulated by the light falling on them and impulses are fired off in the nerve fibres, these impulse pass along the optic nerves to the brain where as a result, an impression is formed of the nature, size, colour and distance of the object. The invasion of the image on the retina is corrected in the optical center of the brain to form the impression of an upright object.

The occuracy if the impression that the brain gains of the image depends on his numerous and how closely packed are the light receiving cell of the retina, since each one can only record the presence or absence of a point of light and in the cones, its colour. If there were only ten cells the images of a house falling on five of them would record and impression of its size, the fact that it was differently coloured at the top and bottom and vague representation of its shape.

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