2. MLK 2005-2006How the Eye Works Observations

3. MLK 2005-2006How the Eye Works Parts to the Puzzle –Anatomy the study of the names of the structures in the human body When we learn the names of eye parts we are studying Anatomy. –Physiology the study of the functions of body parts When we learn how the eye parts work we are studying Physiology.

4. MLK 2005-2006How the Eye Works Humans Levels of Organization Highest- Organisms Organs (eye) Tissue (eg. lens, pupil, cornea, etc.) Cellular (eg. Rod and cone cells) Atoms - Lowest

5. MLK 2005-2006How the Eye Works Eye Anatomy

6. MLK 2005-2006How the Eye Works The Eye Diagram

7. MLK 2005-2006How the Eye Works Frontal View of the Eye

8. MLK 2005-2006How the Eye Works Vision Summary Light rays enters through the pupil after crossing through the cornea Light rays cross in the lens Retina receives reversed & upside down image Rods & cones are stimulated Optic nerve carries impulse to the brain

9. MLK 2005-2006How the Eye Works Observation: In your ScienceLog notes, copy and carefully label the transverse waves. In your own words, explain what you think wavelength and frequency mean. You have two minutes (2 minutes) to do this activity. The clock is counting

10. MLK 2005-2006How the Eye Works Electromagnetic Spectrum Long wavelength – Radio waves Visible Light – range of wavelengths that humans can see Short wavelength – Gamma rays Decreasing wavelength Increasing frequency

11. MLK 2005-2006How the Eye Works

12. MLK 2005-2006How the Eye Works Law of Reflection

13. MLK 2005-2006How the Eye Works Prism Refraction

14. MLK 2005-2006How the Eye Works Overview of Image Processing

15. MLK 2005-2006How the Eye Works Images and Light The image projected onto the retina is inverted or upside down. Visual processing in the brain reverses the image The pupils regulate the amount of light entering the eye. In bright light they constrict to 1.5 mm. In the dark they dilate to 8 mm. The increase in the depth of field seen under bright light results from a narrower beam of light focussing on the retina. The diameter of the pupils is controlled by the autonomic nervous system

16. MLK 2005-2006How the Eye Works Fixation Point to Focus Point

17. MLK 2005-2006How the Eye Works Focusing Abilities When an object is distant, the light rays are essentially parallel and brought to a focus on the retina. If the object moves closer, the focal point then moves behind the retina. To bring the image into focus on the retina, the lens refractive power must be increased. This is the process of accommodation.

18. MLK 2005-2006How the Eye Works Optics & the focal point Focal point falls on retina, image in focus Focal point falls on beyond retina, image not in focus Lens accommodates to correct focal point, image becomes in focus

19. MLK 2005-2006How the Eye Works Refraction – How the light is bent Most of us (~70%) have a refractive error in which light rays come to a point focus either behind the retina (hyperopia) or in front of it (myopia). Hyperopia Myopia (farsighted) (nearsighted)

20. MLK 2005-2006How the Eye Works Convex or Concave? Convex Concave

21. MLK 2005-2006How the Eye Works Refractive errors Long- or far-sighted Short- or near-sighted Corrective lenses

22. MLK 2005-2006How the Eye Works Converting Light Stimulus to Electrical Impulse Requires great coordination of parts Also occurs with the other senses: –Ears: sound waves –Taste: chemical stimulus –Touch: mechanical stimulation –Scent: chemical stimulus

23. MLK 2005-2006How the Eye Works Cross-section of the eye Choroid Sclera Eyelid 3 main layers (connective tissue) (vascular) Filled with aqueous humour at an intraocular pressure 15mmHg. Supplies nutrients & secreted from the ciliary body. Drains via mesh at junction of cornea & sclera into venous system via canal of Schlemm.

24. MLK 2005-2006How the Eye Works Retina stimulation The photosensitive cells of the retina contain the rods and cone which convert the light stimulus to electrical stimulus.

25. MLK 2005-2006How the Eye Works Rods and Cones

26. MLK 2005-2006How the Eye Works Colour vision: Rods and Cones Light sensitive visual pigments are bound to the cell membranes of the disk-like photoreceptors found within the rods & cones. Rods have one visual pigment, rhodopsin which has an absorption max of 496nm Cones have one of 3 colour sensitive pigments related to rhodopsin. Cones are responsible for colour vision and a contain pigments that can be excited optimally for a) blue (absorption max 419nm) b) green (absorption max 530nm) c) red (absorption max 560nm) White light is seen when all three types of cone are equally stimulated.

27. MLK 2005-2006How the Eye Works Rods and Cones

28. MLK 2005-2006How the Eye Works Cones Cones allow for sharp color vision in bright light –3 types, each with a different pigment –Cones are most concentrated towards the back of the eye

29. MLK 2005-2006How the Eye Works Rods Rods provide for vision in dim light –Most dense at the on the sides of the retina –Contain the pigment rhodopsin

30. MLK 2005-2006How the Eye Works Neuron – Neervvve Cellllls

31. MLK 2005-2006How the Eye Works Braineacts LGN –a part of the thalamus that relays signals from the eye to the visual cortex. –It also receives signals back from the cortex. Retina LGN Primary Visual Cortex Visual Field Rods & Cones

32. MLK 2005-2006How the Eye Works Optic Nerve

33. MLK 2005-2006How the Eye Works Cortical processing …or how do we fill in the gaps?

34. MLK 2005-2006How the Eye Works RAINBOWS In a rainbow, raindrops in the air act like tiny prisms. Light enters the drop at A, is reflected at the back of the drop at B and leaves the drop at C. In the process the sunlight is broken into a spectrum just like it is in a triangular glass prism. The angle between the ray of sunlight coming in and the ray coming out of the drops is 42 degrees for red and 40 degrees for violet rays. This small difference in angles between the returning rays causes us to see the bow.

35. MLK 2005-2006How the Eye Works Challenge Question Explain why the top of the rainbow appears red, while the bottom appears violet and not other way around?

36. MLK 2005-2006How the Eye Works THANK YOU