The Structure & Function of the Eye

How you Detect Light

• Visible light is the part of the electromagnetic spectrum that can be detected by your eyes.

• The process by which your eye gathers light to form the images you see involves several steps.

Step #1

• Light is refracted as it passes through the cornea.

• Cornea = a transparent membrane that protects the eye.

Light passing through the cornea

Step #2

• Light then passes through the pupil.

• Pupil = the opening to the inside of the eye.

Light through pupil

Step #3

• The size of the pupil is controlled by the iris.

• Iris = the colored part of the eye.

• In low light the pupil is large.

• In bright light the pupil is small.

iris

Step #4• The lens of the eye is convex and refracts light

to focus a real image on the back of the eye.• Muscles around the lens change the thickness

of the lens so that objects at different distances can be seen in focus.

Light rays refracted by cornea & lens

lens

Step #5

• The back surface of the eye is called the retina.

• The light forming the real image is detected by receptors in the retina called rods and cones.

retina

Step #6

• Nerves attached to the rods and cones carry information to the brain about the light that strikes the retina.

Nerves sending info to brain

Color blindness test

• This is a test plate in which everyone should see a "12".

Color blindness test

• This plate is designed to separate the type of color defectives and the level to which they are observed. Most will see the number "26" clearly while some will only see a "2" or a "6" or no numerals at all.

Color blindness test

• Can you trace a line from one "X" to the other? Someone with normal color vision will trace a orange/brown purple line and those with a slight deficiency will follow a different path.