The Eye

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Parts of the Eye

Main parts of the eye

CONJUCTIVA - lubricates and protects the surface of the eye

CORNEA - refracts (bends) light into the eye. It is transparent and has no blood vessels to supply it with oxygen so the oxygen has to diffuse in from the outer surface

IRIS - controls the diameter of the eye and therefore how much light enters it

LENS - focuses the light onto the RETINA. The retina is light-sensitive and is covered in light receptors called rods and cones.

RODS work best in dim light but cannot detect colour. CONES work best in bright light and can detect colour. Most of the cones are found near the FOVEA.

OPTIC NERVE - sends electrical impulses from the receptors to the brain

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Diagram of the Eye

(http://www.passmyexams.co.uk/GCSE/physics/images/eye_xsection_01.jpg)

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Bright and Dim Light

BRIGHT LIGHT                                                      DIM LIGHT

Circular muscles contract                                     Circular muscles relax

Radial muscles relax                                               Radial muscles contract

The pupils get smaller in size                                  The pupils get larger in size

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Near and Distant Objects

DISTANT OBJECTS                                             NEAR OBJECTS

The ciliary muscles relax                                    The ciliary muscles tighten

The suspensory ligaments tighten                      The suspensory ligaments slacken

The lens becomes thin (less curved)                     The lens becomes thicker (more curved)

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Long-sighted and Short-sighted

LONG-SIGHTED

Unable to focus on near objects

The cornea or lens don't bend the light enough

OR the eyeball is too short

The image is brought into focus behind the retina

SHORT-SIGHTED

Unable to focus on distant objects

The cornea or lens bend the light too much

OR the eyeball is too long

The image is brought into focus in front of the retina

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