The eye
The eye is a sense organ that responds to
light.
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Structure
|
Function
|
|
Cornea
|
Refracts light - bends it as it enters the eye
|
|
Iris
|
Controls how much light enters the pupil
|
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Lens
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Focuses light onto the retina
|
|
Retina
|
Contains the light receptors
|
|
Optic nerve
|
Carries impulses between the eye and the brain
|
The retina
Light
passes through the eyeball to the retina.
There
are two main types of light receptors - rods and cones. Rods are more sensitive
to light than cones. There are three different types of cone cells which
produce colour vision.
|
Rods |
Cones
|
|
|
Number in the retina
|
120 million
|
7 million
|
|
Where concentrated
|
Outer edges of the retina
|
The fovea
|
|
Work best in
|
Dim light
|
Bright light
|
The pupil reflex
The amount of light entering the eye is controlled by a reflex action.
The size of the pupil changes in response to bright or
dim light. This is controlled by the muscles of the iris.
1.
How an eye reacts to dim light
1.
How an eye reacts to bright light
Accommodation
The
ability of the lens to change
its shape to focus near and distant
objects is called accommodation.
|
Position of object
|
Ciliary muscles
|
Suspensory ligaments
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Muscle tension on lens
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Lens shape
|
|
Near
|
Contract
|
Slackened
|
Low
|
Fat
|
|
Distant
|
Relax
|
Stretched
|
High
|
Thin
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