1. 2 Mechanisms that take place in the eye 1) Pupil reflex (controls the amount of light that enters the eyes) 2) Accommodation (focusing)

2. 1) Pupil reflex - controls the amount of light that enters the eyes

3. Image formation in eye

4. Controlling light entry into eye Pupil enlarges when? Pupil dims when?

6. How pupil reflex works… High Low Becomes smaller Becomes bigger Contracts Relaxes Relaxes Contracts Radial muscle Circular muscle Pupil Light intensity

7. Action of the iris

8. 2) Accommodation (focusing)

10. Normal vision occurs when light is focused directly on the retina rather than in front or behind it

13. Near object Distant object Suspensory ligaments

14. Focusing for far vision (>7m) - parallel rays - circular muscle relaxes - flatter; less convex

15. Focusing for near vision - circular muscle contracts - more convex - diverging rays

16. How accommodation works… Distant Parallel Thinner; less convex Taut Relax Diverging Near Thicker; more convex Slacken Contract Ciliary Muscles Suspensory ligaments Lens Light rays Object

21. Is seeing believing?

22. Stare at the pattern for 30 seconds or longer. Than immediately look at a blank sheet of white paper. Optical illusion1

25. Optical illusion2 Is it really a square?

27. Optical illusion3 Are the centre circles equal sizes?

29. Optical illusion4 Are the red lines of different lengths?