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The Human Eye

 

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Vision Defects

Correction of Sight Defects - (wearing of glasses or spectacles)

Eye - structure (for A level Physics)

Eye - photodetector function (for A level)

Depth of field and depth of focus

The eye is essentially a closed sphere into which light passes through a lens and strikes a light sensitive surface. A simplified anatomy of the eye is shown in the diagram below

You are expected to be able to label such a diagram and explain the function of each part of the eye.

You should also know that:

the Retina is the coating of the interior surface at the back of the eye. It consists of an array of light-sensitive receptors called rods and cones which convert the light energy into electrical signals. It plays the role of the film in a camera.

Rods are sensitive to dim light and do not respond to colour. They allow us to see in dim light conditions.

Cones are sensitive to bright light and colour (blue, red and green).

When image is formed on the retina the image is inverted, real, and diminished. The ability of the eye to form an image on the curved surface of the retina is extremely important in human vision.

The blind spot, located where the optic nerve meets the eye, contains no photo-receptors.

The optic nerve transmits impulses to the brain. A crossover takes place. The optic nerve of each eye sends the information to the opposite hemisphere of the brain.

One eye is usually dominant, controlling perspective. The use of two eyes (binocular vision) is necessary to obtain the correct perception of depth.

The brain is capable of making adjustments and corrections, so in spite of the poor optical qualities in the human eye (compared to other types of lenses and optical systems) no optical system yet devised can rival the superb qualities of human vision!!