Structure and Function of the Eye

Human Eye :

• The human eye is an organ which reacts to light and pressure. As a sense organ, the mammalian eye allows vision. A Normal Eye looks like,

Parts of Human Eye

• The front part of the Eye includes:

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• Iris: the colored part.

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• Cornea: a clear dome over the iris.

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• Pupil: the black circular opening in the iris that lets light in.

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• Sclera: the white of your eye.

Eye Anatomy

Iris

IRIS

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(colored part)

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^•Colored part of eye

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^•Controls light entering

Function:

Controls the amount of light entering the eye

Cornea

CORNEA

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(clear lens in front of eye)

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^•transparent covering of the front of the eye

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^•Allows for the passage of light into the eye and functions as a fixed lens.

Function:

Allows for the passage of light into the eye and it also focuses

the light.

Pupil

PUPIL (black hole)

^•black hole in iris

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^•where light enters

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Function:

Pupil size is controlled by iris muscles

Pupil Expansion

When the eye needs more light to enter (when it is dark), the pupils get larger; allowing more light to enter the eye

Pupil Contraction

When the eye needs less light to enter (when it is very bright), the pupils get smaller; allowing less light to enter the eye.

Sclera

SCLERA – a tough white skin (made of tissue) that covers all of the eyeball except the cornea.

Function: Supports eyeball and provides attachment for muscles

Retina

^•Internal membrane

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^•Contains light-receptive cells (rods and cones)

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^•Converts light to electrical signals

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Function:

Converts light waves to electrical signals

Optic Nerve

OPTIC NERVE

Transmits electrical impulses from retina to the brain

Creates blind spot

Brain takes inverted image and flips it so we can see

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Function:

Transmits electrical signals from retina to the brain

Blind spot

(Optic disk illustration )

Close your right eye and look directly at the number 3. Can you see the yellow spot in your peripheral vision? Now slowly move towards or away from the screen. At some point, the yellow spot will disappear.

Functions Cont.

• The eye has many parts that must work together to produce clear vision:

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• The sclera, or white part of the eye, protects the eyeball.

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• The pupil, or black dot at the center of the eye, is a hole through which light can enter the eye.

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• The iris, or colored part of the eye, surrounds the pupil.

The Refractive Structures

• These structures bend the light so that a clear image is produced.

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• They are:

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• tears

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• cornea

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• lens

Lids and Lashes

• Main function is the protection of the eye.

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• They also help to distribute tears which wash and lubricate the eyes.