12.3 Lens Technologies and the Human Eye

Learning Goals• Learn how the human eye works and

the common problems with our eyes

• Learn about various lens technologies

Video:The Human Eye

The Human Eye

The Human EyeLens: 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

The Human EyeThe 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

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.

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?

The Human Eye

Video:Vision Problems

4 Common Vision Problems:

1. Myopia

2. Hyperopia

3. Presbyopia

4. Astigmatism

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

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

Video:Myopia and Hyperopia

• 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)

Presbyopia

• Blurred/distorted vision• Due to incorrectly, oval

shaped cornea

Astigmatism

Video:Laser Eye Surgery

https://www.youtube.com/watch?v=0V4I2xzwGd4

https://www.youtube.com/watch?v=KDgZZhARLsQ

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

Homework