1. Learning Objectives
Can you label a diagram of the eye and explain the function of each part?
How does the eye focus on near and distant objects, and respond to changes in light intensity?
Petr Novák, Wikipedia

2. Watch the video clip

3. Complete these activities to learn more about your eyes
Iris reflex
Look in a mirror at the size of your pupils.
Get a friend to shine a torch in your eyes and see how the pupil changes.
Print this slide and look at the picture of the hat with your right eye while covering your left eye.
Move the image closer to your face until the rabbit disappears.
Find your blind spot
Find your dominant eye
Hold a pencil vertically at arms length.
Focus on an object in the distance in line with the pencil.
Close your left eye. If the pencil jumps to the side then your left eye is dominant. If not try the same with the right.

4. Structure of the eye Retina Suspensory Ligament Sclera Ciliary Muscle
Vitreous Humour
Pupil
Fovea
Cornea
Optic Nerve
Aqueous Humour
Iris
Blind Spot
Choroid

5. Functions of each part of the eye
Structure
Function
Cornea
It refracts the light and protects the eye.
Iris
Controls how much light enters the pupil.
Lens
Focuses light onto the retina.
Optic Nerve
The bundle of sensory neurones that carry the impulses to the brain.
Retina
Layer of tissue at the back of the eye that contains photoreceptor cells called rods and cones.
Fovea
Area of the retina with highest concentration of cone cells that provides sharp vision.
Aqueous Humour
Maintains the pressure in the eye and nourishes the cornea.
Vitreous Humour
Maintains the shape of the eye and attaches to the retina.
Ciliary muscles
Help change the shape of the lens in accommodation.
Sclera
Tough outer layer that extraocular muscles can attach to.
Pupil
Hole in the center of the eye that lets light in.

6. Rods and cones
Rod cells work well in dim light but can only see black and white.
The cones only work in bright light.
There are three types of cone cells, red, green and blue.

7. How do you see?
The image is refracted, first by the cornea and then by the lens.

8. How do you see?
The image is refracted, first by the cornea and then by the lens.

9. The Iris The iris can change the size of the pupil.
This means it controls the amount of light entering the eye.
It does this using circular and radial muscles.
Pupil
Iris

10. The Iris The iris can change the size of the pupil.
This means it controls the amount of light entering the eye.
It does this using circular and radial muscles.
Bright Light
Circular muscles contract.
Radial muscles relax.
Pupils constrict.
Dim Light
Circular muscles relax.
Radial muscles contract.
Pupils dilate.
Pupil
Iris

11. How do your eyes focus?
Humans can focus on near or distant objects, but not both at the same time. The lens has to change shape.
This is called accommodation.
This is controlled by the ciliary muscles and the suspensory ligaments.

12. Focusing on a distant object. Focusing on a close object.
Accommodation
Focusing on a distant object.
Ciliary muscles relax.
Suspensory ligaments tighten.
Lens is pulled thin.
Focusing on a close object.
Ciliary muscles contract.
Suspensory ligaments slacken.
Lens becomes fatter.

13. Problems with vision
Red-green colour blindness is an inherited condition. They do not have certain specialised cells in the retina.
Click here to take the Ishihara colour blind test.
People with long sight cannot see close things clearly.
People with short sight cannot see things in the distance.