1. 12.3 Lens Technologies and the Human Eye

2. Learning Goals
Learn how the human eye works and the common problems with our eyes
Learn about various lens technologies

3. Video:
The Human Eye

4. The Human Eye

5. The Human Eye
Lens: ability to refract light and allow the eye to focus
Ciliary Muscle: changes the shape of the lens
Iris: coloured part of the eye made of muscle fibres that contract and expand to open and close the pupil.
Pupil: the part of the eye that light passes through
Optical Nerve: connects the eye to the brain

6. The Human Eye
The cornea tissue that forms a transparent, curved structure in the front of the eye; refracts light before it enters the eye
The retina a layer of rod and cone cells that respond to light and initiate nerve impulses
Rod cells are very sensitive to light but cannot distinguish between colours
Cone cells detect colours

7. Colour Blindness
There are three types of cone cells: blue, green, and red.
The exact physical causes of colour blindness are still being researched but it is believed that colour blindness is usually caused by faulty cones but sometimes by a fault in the pathway from the cone to the brain.

8. Recall from your study of lenses that when an object is moved, the image also moves. In the eye, however, the distance between the retina and the lens is always the same. So how do we still see clear images at different distances?

9. The Human Eye

10. Video:
Vision Problems

11. 4 Common Vision Problems:
Myopia
Hyperopia
Presbyopia
Astigmatism

12. Myopia Near sightedness Inability to focus on distant objects
Due to an elongated eyeball
Image forms in front of retina
Corrected with glasses or contact lenses with diverging lenses

13. Hyperopia Far sightedness Inability to focus on nearby objects
Due to short eyeball
Image does not form in front of retina, rays meet after
Corrected with glasses or contacts with converging lenses

14. Video:
Myopia and Hyperopia

15. Presbyopia Lenses become stiff
Ciliary muscles cannot make lenses change shape
Cannot focus on nearby objects
Corrected with glasses (bifocals if they are also near sighted)

16. Astigmatism Blurred/distorted vision
Due to incorrectly, oval shaped cornea

17. Video: Laser Eye Surgery

18. Homework
Read 12.3
Chapter 12 Review Questions:
pg 518 # 8,10,12,13,18