2 Mechanisms that take place in the eye 1) Pupil reflex (controls the amount of light that enters the eyes) 2) Accommodati...
1) Pupil reflex - controls the amount of light that enters the eyes
Image formation in eye
Controlling light entry into eye Pupil enlarges when? Pupil dims when?
Controlling entry of light into eye <ul><li>Through altering diameter of the pupil </li></ul><ul><li>Size of pupil control...
How pupil reflex works… High Low Becomes smaller Becomes bigger Contracts Relaxes Relaxes Contracts Radial muscle Circular...
Action of the iris
2) Accommodation (focusing)
Accommodation <ul><li>Definition: </li></ul><ul><li>The adjustment of the lens of the eye so that clear images of objects ...
Normal vision occurs when light is focused directly on the retina rather than in front or behind it
 
 
Near object Distant object Suspensory ligaments
Focusing for far vision (>7m) - parallel rays - circular muscle relaxes - flatter; less convex
Focusing for near vision - circular muscle contracts - more convex - diverging rays
How accommodation works… Distant Parallel Thinner; less convex Taut Relax Diverging Near Thicker; more convex Slacken Cont...
Near point <ul><li>Object so close to eye </li></ul><ul><li>Requires ciliary muscle to contract fully </li></ul><ul><li>Su...
Stereoscopic vision <ul><li>Visual field of our 2 eyes overlap </li></ul><ul><li>2 eyes may focus on same object but diffe...
 
 
Is seeing believing?
Stare at the pattern for 30 seconds or longer. Than immediately look at a blank sheet of white paper. Optical illusion1
 
What do you see? <ul><li>You should see the same pattern in reverse </li></ul><ul><li>Why?  </li></ul><ul><li>While you ar...
Optical illusion2 Is it really a square?
 
Optical illusion3 Are the centre circles equal sizes?
 
Optical illusion4 Are the red lines of different lengths?
 
Answers: <ul><li>It  is  a  square </li></ul><ul><li>The two center circles  are  exactly the  same size </li></ul><ul><li...
Resources <ul><li>Anatomy of the eye </li></ul><ul><li>http://www.discover-the-eye.com/dae060305en.swf   </li></ul><ul><li...
Upcoming SlideShare
Loading in …5
×

Chapter 14 The Human Eye Lesson 3 - The 2 Mechanisms of the Eye 1) Accommodation and 2) Pupil reflex

12,835 views

Published on

Published in: Education, Health & Medicine
0 Comments
16 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
12,835
On SlideShare
0
From Embeds
0
Number of Embeds
12
Actions
Shares
0
Downloads
0
Comments
0
Likes
16
Embeds 0
No embeds

No notes for slide

Chapter 14 The Human Eye Lesson 3 - The 2 Mechanisms of the Eye 1) Accommodation and 2) Pupil reflex

  1. 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. 2. 1) Pupil reflex - controls the amount of light that enters the eyes
  3. 3. Image formation in eye
  4. 4. Controlling light entry into eye Pupil enlarges when? Pupil dims when?
  5. 5. Controlling entry of light into eye <ul><li>Through altering diameter of the pupil </li></ul><ul><li>Size of pupil controlled by 2 sets of involuntary muscles (in iris) </li></ul><ul><li>One set arranged in a circle round the pupil </li></ul><ul><li>One set arranged radially </li></ul><ul><li>Antagonistic </li></ul><ul><li> circular contract; radial relax  pupil smaller </li></ul>
  6. 6. How pupil reflex works… High Low Becomes smaller Becomes bigger Contracts Relaxes Relaxes Contracts Radial muscle Circular muscle Pupil Light intensity
  7. 7. Action of the iris
  8. 8. 2) Accommodation (focusing)
  9. 9. Accommodation <ul><li>Definition: </li></ul><ul><li>The adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina </li></ul>
  10. 10. Normal vision occurs when light is focused directly on the retina rather than in front or behind it
  11. 13. Near object Distant object Suspensory ligaments
  12. 14. Focusing for far vision (>7m) - parallel rays - circular muscle relaxes - flatter; less convex
  13. 15. Focusing for near vision - circular muscle contracts - more convex - diverging rays
  14. 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
  15. 17. Near point <ul><li>Object so close to eye </li></ul><ul><li>Requires ciliary muscle to contract fully </li></ul><ul><li>Suspensory ligaments slacken </li></ul><ul><li>Lens becomes most convex </li></ul><ul><li>Beyond this point, image is blurred (lens cannot be adjusted anymore) </li></ul>
  16. 18. Stereoscopic vision <ul><li>Visual field of our 2 eyes overlap </li></ul><ul><li>2 eyes may focus on same object but different image received by each eye </li></ul><ul><li>Brain able to interpret images together to obtain a 3D view </li></ul><ul><li>Gives us a better perception of size, depth and distance of the object from us </li></ul>
  17. 21. Is seeing believing?
  18. 22. Stare at the pattern for 30 seconds or longer. Than immediately look at a blank sheet of white paper. Optical illusion1
  19. 24. What do you see? <ul><li>You should see the same pattern in reverse </li></ul><ul><li>Why? </li></ul><ul><li>While you are staring, the photoreceptors in your retina get tired—especially the cells viewing the white part of the pattern. When you switch your gaze, the least tired cells take over, producing the brightest part of the afterimage </li></ul>
  20. 25. Optical illusion2 Is it really a square?
  21. 27. Optical illusion3 Are the centre circles equal sizes?
  22. 29. Optical illusion4 Are the red lines of different lengths?
  23. 31. Answers: <ul><li>It is a square </li></ul><ul><li>The two center circles are exactly the same size </li></ul><ul><li>The two red lines are exactly the same length Go ahead. Use a ruler to make sure So what's going on? In each case your brain is comparing the item in question with the surrounding patterns—and misinterpreting the information. Perception is not always reality. </li></ul>
  24. 32. Resources <ul><li>Anatomy of the eye </li></ul><ul><li>http://www.discover-the-eye.com/dae060305en.swf </li></ul><ul><li>http://www.physpharm.fmd.uwo.ca/undergrad/medsweb/L1Eye/Eye.swf </li></ul>

×