1. Light and Sight

2. How do we see?

3. Electromagnetic Waves: Seeing Objects and Color
Essential Question: How are wavelengths detected by the human eye?

4. Sight
Visible light is the part of the electromagnetic spectrum that you can see.
Remember………………

5. The Electromagnetic Spectrum
The electromagnetic spectrum is the range of electromagnetic waves extending from radio waves to gamma rays
Increasing frequency
R O Y G B I V

6. White light is made up of all the wavelengths of visible light.
The colors of visible light are created by electromagnetic energy of various wavelengths (frequencies). See below
White light is made up of all the wavelengths of visible light.

7. Electromagnetic Waves: Seeing Color
When white light is refracted, it can be separated into its component colors. As light passes through a prism, refraction causes light to bend and separate into many colors.

9. A rainbow is produced when a raindrop acts like a prism causing white light to refract (bend) and separate into many colors

10. Electromagnetic Waves: Seeing Color
Humans see different wavelengths of light as different colors.
Humans see long wavelengths as red
Humans see short wavelengths as violet
Some colors, like pink and brown, are seen when certain combinations of wavelengths are present.

11. Electromagnetic Waves: Seeing Color
If we see an object because light is reflected off the object by a light source and white light is made up of all the wavelengths of visible light, why do objects have different colors? The color of an object is determined by the wavelengths (color) of light it reflects. So, if an object reflects one wavelength (color), it absorbs all the other wavelengths (colors) of visible light.

12. In this example, the sun is the light source
In this example, the sun is the light source. The sun’s light appears white because it is made up of all the wavelengths of visible light.
However, humans see the apple as red because all of the other wavelengths (or colors) are absorbed by the apple. The wavelength that we see as red is reflected off the apple.

14. Seeing Color An object that reflects all colors makes it look white
An object that reflects none of the light and only absorbs it looks black

15. We only see a very small portion of the sun’s energy.
So, what is the path that this energy travels so that we can see?

16. Visual Pathway

17. BINOCULAR VISION
Humans have binocular vision…vision where both eyes aim at the same visual target, at the same time; both eyes work together -- simultaneously, equally and accurately -- as a coordinated team.

18. Parts of the Eye Pupil Lens Iris Cornea Retina Sclera Conjunctiva
Ciliary body
Vitreous body
Aqueous chamber
Optic nerve
Rods
Cones
Blind spot

20. Sclera and Cornea
The sclera, or white of the eye, forms the outermost layer of the eyeball.
The sclera consists of a firm fibrous membrane that maintains the shape of the eye and gives attachment to the extrinsic muscles of the eye.

21. Anteriorly the sclera continues as a clear transparent epithelial membrane, the cornea.
Light rays pass through the cornea to reach the retina.
The cornea is involved in refracting (bending) light rays to focus them on the retina.

23. Ciliary Body
The ciliary body consists of ciliary muscle (smooth muscle fibers) and secretory epithelial cells.
It gives attachment to the suspensory ligament which, at its other end, is attached to the capsule enclosing the lens.
Contraction and relaxation of the ciliary muscle changes the thickness of the lens, which bends light rays entering the eye to focus them on the retina.

24. Iris
The iris is the visible colored part of the eye and lies behind the cornea and in front of the lens.
It divides the anterior segment of the eye into anterior and posterior chambers which contain the fluids of the eye..
It is a circular body composed of pigment cells and two layers of smooth muscle fibers, one circular and the other radiating.
In the center of the iris is called the pupil.

25. The iris is supplied by nerves.
Stimulation of the nerves can constrict or dilate the pupil .
The color of the iris is genetically determined and depends on the number of pigment cells present.
Albinos have no pigment cells and people with blue eyes have fewer than those with brown eyes.

26. Lens
The lens is a highly elastic circular biconvex body, lying immediately behind the pupil.
It consists of fibers enclosed within a capsule and it is suspended from the ciliary body by the suspensory ligament.
Its thickness is controlled by the ciliary muscle through the suspensory ligament.

28. When the ciliary muscle contracts, it moves forward, releasing its pull on the lens, increasing its thickness.
The nearer is the object being viewed, the thicker the lens becomes to allow focusing.
The lens refracts light rays reflected by objects in front of the eye.

29. Retina The retina is the innermost layer of the wall of the eye.
It is an extremely delicate structure and is well adapted for stimulation by light rays.
It is composed of several layers of nerve cell bodies

30. Near the center of the posterior part is the macula lutea, or yellow spot.
In the centre of the yellow spot is a little depression called the fovea centralis, consisting of only cones. This is where vision is greatest.

34. The light-sensitive layer consists of sensory receptor cells: rods and cones.
The rods and cones contain photosensitive pigments that convert light rays into nerve impulses.
Rods see white and black.
Cones see color. There are 3 colored cones: Red, Blue, and Green.

35. The small area of retina where the optic nerve leaves the eye is the optic disc or blind spot.
It has no light­ sensitive cells

37. Interior of the eye
The space between the cornea and the lens, is incompletely divided into anterior and posterior chambers by the iris.
Both chambers contain a clear aqueous fluid secreted into the posterior chamber by ciliary glands.

38. There is continuous production and drainage but the intraocular pressure remains fairly constant An increase in this pressure causes glaucoma.
Aqueous fluid supplies nutrients and removes wastes from the transparent structures in the front of the eye that have no blood supply, i.e. the cornea, lens and lens capsule.

39. Behind the lens of the eyeball is the vitreous body.
This is a soft, colorless, transparent, jelly-like substance composed of 99% water, some salts and mucoprotein.
The vitreous body maintains intraocular pressure to support the retina and prevent the eyeball from collapsing or changing shape.

40. DIAGRAM OF THE EYE Ciliary Muscle Lens Pupil Vitreous Optic Nerve
Choroid Coat (Choroid Membrane)
Macula
Retina
Yellow Spot (Fovea Centralis)
Scleratic Coat (Sclera)
Iris
Cornea

43. Ciliary Body
Blind spot

46. Lens Introduction
Lenses are very useful.
e.g. in cameras, projectors, telescopes, microscopes and eyes
There are two types of lenses that we will
talk about :
-convex
-concave

47. CONCAVE or NEGATIVE lenses will DIVERGE (spread out) light rays
DRAW IT!

48. Concave lens
The correct name of nearsightedness is myopia. Myopia occurs when the eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. A concave lens is usually used to correct this problem.

49. Near-Sighted (Myopia)

50. Convex lens
The correct name for farsightedness is Hyperopia. The shape of your eye does not bend light correctly, resulting in a blurred image. A convex lens is usually used to correct this problem.

51. Far-Sighted (Hypermetropia)

52. Astigmatism
Cornea is oval shaped instead of spherical. This causes light to focus on two or more spots.

53. Think prefixes! To converge means… A. To come together
B. To spread apart

54. Again, think prefixes… To spread apart would mean to A. converge
B. diverge

55. Convex lenses Convex lens - thicker at the center than at the edge.
Contact lens

56. Convex lenses Converging lens bend the light inwards
You may remember ‘converging’ as ‘concentrating’.

57. Concave lenses
Concave lens - thinner at the center than at the edge.

58. Concave lenses Diverging lens bend the light outwards
You may remember ‘diverging’ as ‘dividing’.

59. Mirrors

60. Spherical mirrors can be convex, like the outside of a spoon.

61. Spherical mirrors can also be concave, like the inside of a spoon.

62. Mini Quiz: Keep your eyes on your own paper!
What is the hole in the eye that light enters?
What is the name of the nerve that takes visual information to the brain?
Draw a concave lens.
What is the blindspot?
Which receptor detects color? Rods or Cones?

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