The Human Eye Chapter 14
Objectives <ul><li>Students should be able to: </li></ul><ul><ul><li>State the relationship between receptors, the central...
Sense organs <ul><li>Sense organs are receptors that receive stimuli from the environment and inform your body of any chan...
14.2  The Human Eye Upper eyelid pupil cornea Lower eyelid iris Conjunctiva (covers sclera) Tear gland eyelashes
<ul><li>Cornea </li></ul><ul><li>Transparent layer continuous with sclera (white portion of the eye) </li></ul><ul><li>Spe...
<ul><li>Iris </li></ul><ul><li>A circular sheet of muscles </li></ul><ul><li>Controls the amount of light entering the eye...
<ul><li>Eyelids </li></ul><ul><li>Protect the cornea from mechanical damage </li></ul><ul><li>Eyelashes </li></ul><ul><li>...
Chapter 14 The Human Eye Structure and Function of the Eye (Concept Map) January 11, 2010
Vertical Section of The Human Eye January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
Vertical Section of The Human Eye Attaches lens  to ciliary body January 11, 2010 Copyright © 2006-2011 Marshall Cavendish...
Vertical Section of The Human Eye Controls amount  of light entering the eye January 11, 2010 Copyright © 2006-2011 Marsha...
Vertical Section of The Human Eye Refracts light rays; keeps eyeball firm January 11, 2010 Copyright © 2006-2011 Marshall ...
Vertical Section of The Human Eye Allows light to  enter the eye January 11, 2010 Copyright © 2006-2011 Marshall Cavendish...
Vertical Section of The Human Eye Refracts light rays  into pupil January 11, 2010 Copyright © 2006-2011 Marshall Cavendis...
Vertical Section of The Human Eye lens Focuses light rays  onto retina January 11, 2010 Copyright © 2006-2011 Marshall Cav...
Vertical Section of The Human Eye ciliary  body Contains ciliary  muscles which  control curvature  or thickness of the  l...
Vertical Section of The Human Eye viterous humour Refracts light rays; keeps eyeball firm January 11, 2010 Copyright © 200...
Vertical Section of The Human Eye Controls movement  of eyeball January 11, 2010 Copyright © 2006-2011 Marshall Cavendish ...
Vertical Section of The Human Eye Protects against  mechanical injury January 11, 2010 Copyright © 2006-2011 Marshall Cave...
Vertical Section of The Human Eye Pigmented black to prevent internal reflection  of light; blood vessels  bring oxygen an...
Vertical Section of The Human Eye Region where images are sharply focused January 11, 2010 Copyright © 2006-2011 Marshall ...
Vertical Section of The Human Eye Transmit nerve impulses from eye to brain optic nerve January 11, 2010 Copyright © 2006-...
Vertical Section of The Human Eye Region over optic nerve; no photoreceptors,  so insensitive to light blind spot January ...
Vertical Section of The Human Eye Light-sensitive layer containing cones responsible for colour  vision in bright light an...
Controlling the entry of light into the eye <ul><li>The pupil of the eye controls the amount of light that enters the eye ...
Chapter 14 The Human Eye Action of Iris in Bright Light January 11, 2010
Action of Iris in Bright Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Lt...
Action of Iris in Bright Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Lt...
Action of Iris in Bright Light Pupil constricts and this reduces the amount of light entering the eye January 11, 2010 Cop...
Chapter 14 The Human Eye Action of Iris in Dim Light January 11, 2010
Action of Iris in Dim Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. ...
Action of Iris in Dim Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. ...
Action of Iris in Dim Light Pupil dilates and this increases the amount of light entering the eye January 11, 2010 Copyrig...
<ul><li>High light intensity, Circular muscles contract, radial muscles relax </li></ul><ul><li>Pupil becomes smaller </li...
What is the pupil reflex? <ul><li>It is a reflex action (recall ‘Nervous System) </li></ul><ul><li>Pupil changes in size a...
<ul><li>Stimulus ( change in light intensity ) </li></ul><ul><li>Receptor ( retina ) </li></ul><ul><li>Sensory neurone in ...
14.3 How do we see? <ul><li>Light falling on object is reflected.  Reflected rays fall on the eye. </li></ul><ul><li>These...
Continue…. <ul><li>The image on the retina stimulates either the rods or the cones depending on the intensity of the light...
Continue…. <ul><li>Impulses produced by light falling on the rods and cones are transmitted via the optic nerve to the rea...
Chapter 14 The Human Eye How Do We See? January 11, 2010
How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  January 11, ...
How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  January 11, ...
How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  January 11, ...
How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  January 11, ...
How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  January 11, ...
Focusing (Accommodation) <ul><li>This is the adjustment of the lens of the eye so that clear images of objects at differen...
Chapter 14 The Human Eye How Eyes Focus on Distant Objects January 11, 2010
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte....
How Eyes Focus on Distant Objects Vertical section of the eye Enlarged portion of eye (front view) January 11, 2010 Copyri...
How Eyes Focus on Distant Objects Vertical section of the eye Enlarged portion of eye (front view) January 11, 2010 Copyri...
How Eyes Focus on Distant Objects Photoreceptors stimulated Transmission of nerves to brain Vertical section of the eye En...
<ul><li>Far object, circular muscles of the ciliary body relax </li></ul><ul><li>Suspensory ligaments are pulled tight, ca...
Chapter 14 The Human Eye How Eyes Focus on Near Objects January 11, 2010
How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Lt...
How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Lt...
How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Lt...
How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Vertical sect...
How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Vertical sect...
How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Lt...
How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Lt...
How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Vertical sect...
How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Vertical sect...
How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Vertical sect...
How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Vertical sect...
<ul><li>Near object, circular muscles of the ciliary body contracts </li></ul><ul><li>Suspensory ligaments releases the pu...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Pupil Refl...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Pupil Refl...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  <ul><li>In...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Pupil Refl...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  <ul><li>In...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Pupil Refl...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Pupil Refl...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Pupil Refl...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  Pupil Refl...
Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.  <ul><li>Di...
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Chapter 14 Animal Receptor Organs

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  • Chapter 14 Animal Receptor Organs

    1. 1. The Human Eye Chapter 14
    2. 2. Objectives <ul><li>Students should be able to: </li></ul><ul><ul><li>State the relationship between receptors, the central nervous system and the effectors </li></ul></ul><ul><ul><li>Describe the gross structure of the eye as seen in front view and in horizontal section </li></ul></ul><ul><ul><li>State the principal functions of component parts of the eye in producing a focussed image of near and distant objects on the retina </li></ul></ul><ul><ul><li>Describe the pupil reflex in response to bright and dim light </li></ul></ul>
    3. 3. Sense organs <ul><li>Sense organs are receptors that receive stimuli from the environment and inform your body of any changes in the environment </li></ul>
    4. 4. 14.2 The Human Eye Upper eyelid pupil cornea Lower eyelid iris Conjunctiva (covers sclera) Tear gland eyelashes
    5. 5. <ul><li>Cornea </li></ul><ul><li>Transparent layer continuous with sclera (white portion of the eye) </li></ul><ul><li>Specialised form of conjunctiva </li></ul><ul><li>Refracts or bend light rays into the eye </li></ul><ul><li>Conjunctiva </li></ul><ul><li>Transparent membrane </li></ul><ul><li>Secretes mucus, thus helping to keep the front of the eyeball moist </li></ul>
    6. 6. <ul><li>Iris </li></ul><ul><li>A circular sheet of muscles </li></ul><ul><li>Controls the amount of light entering the eye </li></ul><ul><li>Pupil </li></ul><ul><li>A hole in the centre of the iris </li></ul><ul><li>Allows light to enter the eye </li></ul>
    7. 7. <ul><li>Eyelids </li></ul><ul><li>Protect the cornea from mechanical damage </li></ul><ul><li>Eyelashes </li></ul><ul><li>Help to shield the eye from dust particles </li></ul><ul><li>Tear gland </li></ul><ul><li>Secretes tears to wash away dust particles </li></ul><ul><li>Secretes tears to keep the cornea moist for atmospheric oxygen to dissolve </li></ul><ul><li>Secretes tears to lubricate conjunctiva, helping to reduce friction when the eyelids move </li></ul>
    8. 8. Chapter 14 The Human Eye Structure and Function of the Eye (Concept Map) January 11, 2010
    9. 9. Vertical Section of The Human Eye January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
    10. 10. Vertical Section of The Human Eye Attaches lens to ciliary body January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. suspensory ligament
    11. 11. Vertical Section of The Human Eye Controls amount of light entering the eye January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. iris suspensory ligament
    12. 12. Vertical Section of The Human Eye Refracts light rays; keeps eyeball firm January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. aqueous humour iris suspensory ligament
    13. 13. Vertical Section of The Human Eye Allows light to enter the eye January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. pupil aqueous humour iris suspensory ligament
    14. 14. Vertical Section of The Human Eye Refracts light rays into pupil January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. cornea pupil aqueous humour iris suspensory ligament
    15. 15. Vertical Section of The Human Eye lens Focuses light rays onto retina January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. cornea pupil aqueous humour iris suspensory ligament
    16. 16. Vertical Section of The Human Eye ciliary body Contains ciliary muscles which control curvature or thickness of the lens January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. lens cornea pupil aqueous humour iris suspensory ligament
    17. 17. Vertical Section of The Human Eye viterous humour Refracts light rays; keeps eyeball firm January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. ciliary body lens cornea pupil aqueous humour iris suspensory ligament
    18. 18. Vertical Section of The Human Eye Controls movement of eyeball January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. viterous humour ciliary body lens cornea pupil aqueous humour iris suspensory ligament rectus muscles
    19. 19. Vertical Section of The Human Eye Protects against mechanical injury January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. viterous humour ciliary body lens cornea pupil aqueous humour iris suspensory ligament sclera rectus muscles
    20. 20. Vertical Section of The Human Eye Pigmented black to prevent internal reflection of light; blood vessels bring oxygen and nutrients to the eyeball January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. viterous humour ciliary body lens cornea pupil aqueous humour iris suspensory ligament choroid sclera rectus muscles
    21. 21. Vertical Section of The Human Eye Region where images are sharply focused January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. viterous humour ciliary body lens cornea pupil aqueous humour iris suspensory ligament fovea (yellow spot) choroid sclera rectus muscles
    22. 22. Vertical Section of The Human Eye Transmit nerve impulses from eye to brain optic nerve January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. fovea (yellow spot) choroid sclera rectus muscles viterous humour ciliary body lens cornea pupil aqueous humour iris suspensory ligament
    23. 23. Vertical Section of The Human Eye Region over optic nerve; no photoreceptors, so insensitive to light blind spot January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. viterous humour ciliary body lens cornea pupil aqueous humour iris suspensory ligament optic nerve fovea (yellow spot) choroid sclera rectus muscles
    24. 24. Vertical Section of The Human Eye Light-sensitive layer containing cones responsible for colour vision in bright light and rods responsible for vision in dim light retina January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. viterous humour ciliary body lens cornea pupil aqueous humour iris suspensory ligament blind spot optic nerve fovea (yellow spot) choroid sclera rectus muscles
    25. 25. Controlling the entry of light into the eye <ul><li>The pupil of the eye controls the amount of light that enters the eye </li></ul><ul><li>Size of the eye is controlled by 2 sets of involuntary muscles in the iris </li></ul><ul><ul><li>One set arranged radially </li></ul></ul><ul><ul><li>One set arranged in a circle around the pupil </li></ul></ul>
    26. 26. Chapter 14 The Human Eye Action of Iris in Bright Light January 11, 2010
    27. 27. Action of Iris in Bright Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Circular muscles of the iris contract 1
    28. 28. Action of Iris in Bright Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Radial muscles of the iris relax 2 Circular muscles of the iris contract 1
    29. 29. Action of Iris in Bright Light Pupil constricts and this reduces the amount of light entering the eye January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Radial muscles of the iris relax 2 Circular muscles of the iris contract 1 3
    30. 30. Chapter 14 The Human Eye Action of Iris in Dim Light January 11, 2010
    31. 31. Action of Iris in Dim Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Radial muscles of iris will contract Radial muscles of the iris contract 1
    32. 32. Action of Iris in Dim Light January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Radial muscles of the iris contract 1 Circular muscles of the iris relax 2
    33. 33. Action of Iris in Dim Light Pupil dilates and this increases the amount of light entering the eye January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Radial muscles of the iris contract 1 Circular muscles of the iris relax 2 3
    34. 34. <ul><li>High light intensity, Circular muscles contract, radial muscles relax </li></ul><ul><li>Pupil becomes smaller </li></ul><ul><li>Low light intensity , Circular muscles relax, radial muscles contract </li></ul><ul><li>Pupil becomes bigger </li></ul>
    35. 35. What is the pupil reflex? <ul><li>It is a reflex action (recall ‘Nervous System) </li></ul><ul><li>Pupil changes in size as a result of changes in light intensity </li></ul><ul><li>Pupil usually becomes larger when the surrounding light intensity is low, and smaller when the light intensity is high </li></ul>
    36. 36. <ul><li>Stimulus ( change in light intensity ) </li></ul><ul><li>Receptor ( retina ) </li></ul><ul><li>Sensory neurone in optic nerve </li></ul><ul><li>Brain </li></ul><ul><li>Motor neurone </li></ul><ul><li>Effector ( iris ) </li></ul>
    37. 37. 14.3 How do we see? <ul><li>Light falling on object is reflected. Reflected rays fall on the eye. </li></ul><ul><li>These rays are refracted through the cornea and the aqueous humour (watery fluid) onto the lens. </li></ul><ul><li>The lens causes further refraction and the rays converge to a focus on the retina </li></ul>
    38. 38. Continue…. <ul><li>The image on the retina stimulates either the rods or the cones depending on the intensity of the light. </li></ul><ul><li>Image formed can be: </li></ul><ul><ul><li>Upside down (inverted) </li></ul></ul><ul><ul><li>Back to front (reversed) </li></ul></ul><ul><ul><li>Smaller in size than the object being observed (diminished) </li></ul></ul>
    39. 39. Continue…. <ul><li>Impulses produced by light falling on the rods and cones are transmitted via the optic nerve to the rear of the cerebrum. </li></ul><ul><li>The brain interprets these impulses </li></ul>
    40. 40. Chapter 14 The Human Eye How Do We See? January 11, 2010
    41. 41. How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 1 Light rays are refracted through the cornea and the aqueous humour onto the lens object cornea lens aqueous humour
    42. 42. How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 1 2 The lens causes further refraction Light rays are refracted through the cornea and the aqueous humour onto the lens object cornea lens aqueous humour
    43. 43. How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 1 2 3 Rays converge to focus on retina The lens causes further refraction Light rays are refracted through the cornea and the aqueous humour onto the lens object cornea lens aqueous humour retina
    44. 44. How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 1 2 3 4 The image on the retina stimulates either the rods or the cones, depending on the intensity of the light Rays converge to focus on retina The lens causes further refraction Light rays are refracted through the cornea and the aqueous humour onto the lens object cornea lens aqueous humour retina image
    45. 45. How Do We See? January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 1 2 3 4 <ul><li>The image formed is </li></ul><ul><li>inverted </li></ul><ul><li>laterally inverted </li></ul><ul><li>diminished in size </li></ul>The image on the retina stimulates either the rods or the cones, depending on the intensity of the light Rays converge to focus on retina The lens causes further refraction Light rays are refracted through the cornea and the aqueous humour onto the lens object cornea lens aqueous humour retina image
    46. 46. Focusing (Accommodation) <ul><li>This is the adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina </li></ul>
    47. 47. Chapter 14 The Human Eye How Eyes Focus on Distant Objects January 11, 2010
    48. 48. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Parallel light rays from distant object enters eyes Vertical section of the eye 1
    49. 49. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Ciliary muscles relax Vertical section of the eye Enlarged portion of eye (front view) 1 2 2
    50. 50. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Suspensory ligaments become taut Vertical section of the eye Enlarged portion of eye (front view) 1 2 2 3 3
    51. 51. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Lens becomes thinner Vertical section of the eye Enlarged portion of eye (front view) 1 2 2 3 3 4 4
    52. 52. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Focal length increases Vertical section of the eye Enlarged portion of eye (front view) 1 2 2 3 3 4 5 4
    53. 53. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Light rays from distant object focused on retina 1 2 2 3 3 4 5 6 4
    54. 54. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Photoreceptors stimulated 7 1 2 2 3 3 4 5 6 4
    55. 55. How Eyes Focus on Distant Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Photoreceptors stimulated Nerve impulses produced by optic nerves 7 8 1 2 2 3 3 4 5 6 4
    56. 56. How Eyes Focus on Distant Objects Vertical section of the eye Enlarged portion of eye (front view) January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Photoreceptors stimulated Transmission of nerves to brain Nerve impulses produced by optic nerves 7 8 9 1 2 2 3 3 4 5 6 4
    57. 57. How Eyes Focus on Distant Objects Vertical section of the eye Enlarged portion of eye (front view) January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Photoreceptors stimulated Transmission of nerves to brain Brain interprets impulses Nerve impulses produced by optic nerves 7 8 9 10 1 2 2 3 3 4 5 6 4
    58. 58. How Eyes Focus on Distant Objects Photoreceptors stimulated Transmission of nerves to brain Vertical section of the eye Enlarged portion of eye (front view) Brain interprets impulses January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Person sees the distant object Nerve impulses produced by optic nerves 7 8 9 10 11 1 2 2 3 3 4 5 6 4
    59. 59. <ul><li>Far object, circular muscles of the ciliary body relax </li></ul><ul><li>Suspensory ligaments are pulled tight, causing the lens to become flatter and less convex </li></ul><ul><li>Image sharply focused onto retina </li></ul>
    60. 60. Chapter 14 The Human Eye How Eyes Focus on Near Objects January 11, 2010
    61. 61. How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Diverging light rays from near object enters eyes 1
    62. 62. How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Ciliary muscles contract 2 2 1
    63. 63. How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Suspensory ligaments become slacken 3 2 2 3 1
    64. 64. How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Lens becomes thicker January 11, 2010 3 2 2 3 4 1 4
    65. 65. How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Focal length decreases January 11, 2010 3 2 2 3 4 5 1 4
    66. 66. How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Light rays from near object focused on retina 3 2 2 3 4 5 6 1 4
    67. 67. How Eyes Focus on Near Objects January 11, 2010 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Photoreceptors stimulated 3 2 2 3 4 5 6 1 7 4
    68. 68. How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) January 11, 2010 Photoreceptors stimulated Nerve impulses produced by optic nerves 3 2 2 3 4 5 6 1 7 8 4
    69. 69. How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Photoreceptors stimulated Nerve impulses produced by optic nerves January 11, 2010 Transmission of nerves to brain 3 2 2 3 4 5 6 1 7 8 9 4
    70. 70. How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Photoreceptors stimulated January 11, 2010 Nerve impulses produced by optic nerves Transmission of nerves to brain Brain interprets impulses 3 2 2 3 4 5 6 1 7 8 9 10 4
    71. 71. How Eyes Focus on Near Objects Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Vertical section of the eye Enlarged portion of eye (front view) Photoreceptors stimulated January 11, 2010 Nerve impulses produced by optic nerves Transmission of nerves to brain Brain interprets impulses Person sees the near object 3 2 2 3 4 6 1 5 7 8 9 10 11 4
    72. 72. <ul><li>Near object, circular muscles of the ciliary body contracts </li></ul><ul><li>Suspensory ligaments releases the pull on the lens </li></ul><ul><li>Elastic nature of the lens causes it to become thicker and more convex </li></ul><ul><li>Image focused sharply on the retina </li></ul><ul><li>After a certain distant called near point, the lens cannot adjust anymore. The image formed will then be blur </li></ul>
    73. 73. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Pupil Reflex A reflex action in which the pupil changes size as a result of changes in light intensity.
    74. 74. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Pupil Reflex In bright light
    75. 75. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul>Pupil Reflex
    76. 76. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Pupil Reflex <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul>In dim light
    77. 77. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. <ul><li>In dim light </li></ul><ul><li>Radial muscles in iris contract . </li></ul><ul><li>Circular muscles in iris relax. </li></ul><ul><li>Pupil enlarges, hence more light enters the eye </li></ul>Pupil Reflex <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul>
    78. 78. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Pupil Reflex Focusing <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul>The adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina. <ul><li>In dim light </li></ul><ul><li>Radial muscles in iris contract . </li></ul><ul><li>Circular muscles in iris relax. </li></ul><ul><li>Pupil enlarges, hence more light enters the eye </li></ul>
    79. 79. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Pupil Reflex Focusing <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul>Distant object (7 metres or more) <ul><li>In dim light </li></ul><ul><li>Radial muscles in iris contract . </li></ul><ul><li>Circular muscles in iris relax. </li></ul><ul><li>Pupil enlarges, hence more light enters the eye </li></ul>
    80. 80. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Pupil Reflex Focusing <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul><ul><li>Distant object </li></ul><ul><li>(7 metres or more) </li></ul><ul><li>Ciliary muscles relax </li></ul><ul><li>Suspensory ligament become taut </li></ul><ul><li>Lens becomes thinner and less convex </li></ul><ul><li>In dim light </li></ul><ul><li>Radial muscles in iris contract . </li></ul><ul><li>Circular muscles in iris relax. </li></ul><ul><li>Pupil enlarges, hence more light enters the eye </li></ul>
    81. 81. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Pupil Reflex Focusing <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul><ul><li>Distant object </li></ul><ul><li>(7 metres or more) </li></ul><ul><li>Ciliary muscles relax </li></ul><ul><li>Suspensory ligament become taut </li></ul><ul><li>Lens becomes thinner and less convex </li></ul>Near object <ul><li>In dim light </li></ul><ul><li>Radial muscles in iris contract . </li></ul><ul><li>Circular muscles in iris relax. </li></ul><ul><li>Pupil enlarges, hence more light enters the eye </li></ul>
    82. 82. Vertical Section of The Human Eye Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. <ul><li>Distant object </li></ul><ul><li>(7 metres or more) </li></ul><ul><li>Ciliary muscles relax </li></ul><ul><li>Suspensory ligament become taut </li></ul><ul><li>Lens becomes thinner and less convex </li></ul><ul><li>Near object </li></ul><ul><li>Ciliary muscles contract </li></ul><ul><li>Suspensory ligaments slacken </li></ul><ul><li>Lens becomes thicker and more convex </li></ul>Pupil Reflex Focusing <ul><li>In bright light </li></ul><ul><li>Circular muscles in iris contract. </li></ul><ul><li>Radial muscles relax. </li></ul><ul><li>Pupil becomes smaller, hence less light enters the eye </li></ul><ul><li>In dim light </li></ul><ul><li>Radial muscles in iris contract . </li></ul><ul><li>Circular muscles in iris relax. </li></ul><ul><li>Pupil enlarges, hence more light enters the eye </li></ul>

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