1. Human Vision Outcome C4 – Explain how human vision works

2. The human eye –Sclera – white tissue surrounding our cornea –Iris – the muscle which contracts and dilates our pupil –Pupil – the opening which allows light into our eye

3. The human eye –Cornea – a transparent tissue which covers our pupil and iris. It’s job is to refract light –Retina – Region in the back of our eye where images are formed –Lens – Convex lenses in our eye refract and focus light onto our retina –Optic Nerve – Nerve tissue which sends signals to our brain

4. How the parts of our eye work together –Light enters through our pupil and into our eye. The amount of light that enters our eye is controlled by the Iris –For an image to form correctly, the light is first refracted by our cornea and refracted again by our lens

5. How the parts of our eye work together –Focusing of the image is done by tiny muscles, that can change the shape of our lens

6. How the parts of our eye work together –The refracted light then forms an image on our Retina –Our retina is a light sensitive layer inside our eye –Little cells called Rod cells are sensitive to the level of light (dim or bright) –Little cells called Cone cells are sensitive to colour –The level of light and colour detected by rods and cones are sent as electrical signals down the optic nerve and to our brain –Where the optic nerve is, there is a blind spot

7. The Cornea-Lens-Retina system –This is the system used to describe the formation of images in the human eye –Steps: 1.Light rays coming from its source is primarily focused by the cornea (via refraction) 2.This light continues on through our lens which does the fine focusing (via refraction again) 3.The light rays will then converge on our Retina forming an (inverted) image

8. The Cornea-Lens-Retina system –Fine focusing of images are done by the contracting and relaxing of muscles surrounding our lens. –Distant objects require a “thinner” lens to focus. So muscles surrounding the lens will relax and the lens will flatten out –Close objects require a “thicker” lens to focus. So muscles surrounding the lens will contract and the lens will become thicker

9. Drawing of a thick and thinner lens

10. Common vision problems –Near-sightedness – people can see nearby objects clearly, but not far away objects –Problem : Light rays converge in front of the Retina –Solution: Wearing glasses that have concave lenses will refract the light enough such that the light rays will converge on the retina

11. Common vision problems –Far-sightedness – people can see far away objects clearly, but not nearby objects –Problem: Light rays converge behind the retina –Solution: Wearing glasses that have convex lenses will refract the light such that the light rays will converge on the retina

12. Correcting and extending vision –Modern technology can now use laser surgery to correct vision. It reshapes the cornea –What are some things that can “extend” our vision? 30 SECONDS TO THINK OF AN ANSWER WITH YOUR PARTNER15 SECONDS LEFT TIME IS UP

13. Similarities and differences in eyes and other optical systems

15. Telescopes

17. TURN TO YOUR PARTNER (TTYP) –Question: Using the figure provided to you, answer: –Wavelengths longer than visible light include????? 30 SECONDS TO THINK OF AN ANSWER WITH YOUR PARTNER15 SECONDS LEFT TIME IS UP –Wavelengths shorter than visible light include????? 30 SECONDS TO THINK OF AN ANSWER WITH YOUR PARTNER15 SECONDS LEFT TIME IS UP

18. Electromagnetic radiation –How are these different? –TURN TO YOUR PARTNER AND ANSWER: –What 3 differences do specific electromagnetic radiation have from one another… For example: Contrast UV rays to Radiowaves ONE MINUTE TO THINK OF AN ANSWER WITH YOUR PARTNER 30 SECONDS LEFT TIME IS UP