Depth Of Vision

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The structure of the human eye The shape of the eye is almost spherical and has a diameter of 2.5 cm. Light enters the cornea and the refraction is 1.37. Between the cornea and the eye lens is the aqueous humour and its refraction is 1.33, the same as the water. The aqueous humour is separated into two parts by the iris which is the coloured part of the eye. The pupil is an aperture which is at the centre of the iris and lets the light enters the eye lens. In order to adjust the intensity of light, the pupil can increase or decrease in diameter. The eye lens is attached to the ciliary muscle by ligaments and controls the curvature of the lens. Light passing through the lens then enters a second chamber called the vitreous humour which is a jelly like substance. The light reaches the back surface of the eye, the retina. The retina is covered with light sensitive cells (rods and cones) that record the arrival of light. Light reaching the rods and cones is converted into tiny electrical signals in nerve fibres attached to these cells and all converge to the optic nerve. The optic nerve transmits the electrical signals to the brain. The fovea is a spot where vision is exceptionally acute and is located on the principal axis of the eye. Depth of vision A set of parallel rays refract and pass through the same point on the principal axis of the lens which is called the focal point of the lens and its distance from the optical centre of the lens is called the focal length. The depth of vision is the range of object distances from the eye within the objects can be seen clearly. It depends on the distance of the object, the further the object is from the eye, the larger is the depth of vision. If the object is close to the eye, the depth of vision is reduced. If brighter light is used, the depth of vision will increase; this is caused because the iris will reduce the

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