The document discusses the structure and function of the human eye. It describes how light enters through the cornea and pupil, and is focused onto the retina by the lens. The retina contains light-sensitive rod and cone cells which convert light into electrical signals sent to the brain via the optic nerve. Common eye diseases like myopia, hyperopia, astigmatism, glaucoma and cataracts are also outlined, as well as modern vision correction methods like contact lenses and LASIK surgery.

1. The Human Eye

2. The Human Eye
• Refractive index of lens
different for each
wavelength (colour)
• Cool colours (blues)
appear closer; warm
colours (reds) further
away
• Agree?

3. Most people see the red,
Closer than the blue.
Others see the opposite.
How about you?

4. The Human Eye
• Your eyes are about to get a workout. Have
you stretched your eye muscles yet?
• No? Then do that now!

5. Are you seeing spots?

7. Look at the cross for 10 seconds. What do you see?

8. Are these lines
bent….?

9. …or straight?

21. Reading
What is wrong with
with this sentence?
Aoccdrnig to rscheearch at Cmabrigde
Uinervtisy, it deosn't mttaer in waht oredr the
ltteers in a wrod are, the olny iprmoetnt tihng is
taht the frist and lsat ltteer be at the rghit pclae.
The rset can be a toatl mses and you can sitll
raed it wouthit a porbelm. Tihs is bcuseae the
huamn mnid deos not raed ervey lteter by istlef,
but the wrod as a wlohe.

23. Do you see the rabbit or the duck?

24. Read This Out Loud

25. Are You Sure? Read it again

27. The Human Eye

28. Structure & Function
• IRIS
– colored part of eye
– controls light entering
• PUPIL
– black hole in iris
– where light enters

29. Structure & Function
• SCLERA
– whites of the eye
– supports eyeball
– provides attachment
for muscles
• LENS
– converging lens
– allows us to see
objects near and far

30. Structure & Function
• CORNEA
– transparent bulge over
pupil
– focuses light (refracts) onto
retina
• RETINA
– internal membrane
– contain light-receptive cells
(rods & cones)
– converts light to electrical
signal

31. Blind Spot
• On retina where optic
nerve leads back into the
brain
• No rod or cone cells
• Other eye compensates
for this area
• Try this test to prove you
have a blind spot…

32. Close left eye and approach screen while
staring at the letters…watch the dot!

33. Structure & Function
OPTIC NERVE
• Transmits electrical
impulses from retina to
the brain
• Creates blind spot
• Brain takes inverted
image and flips it so we
can see

34. Structure & Function
• RODS
– 120 million cells
– detect brightness
(black & white)
– for night vision
• CONES
– 6 million cells
– detect color (RGB)
– GANGLION CELLS
– Detect movement and
patterns

35. Normal Eye Focus
“Blind spot”

36. Video
• YouTube
“The Human Eye” and “How the Human Eye
Works”

37. Focusing Problems
HYPEROPIA
• Far-sightedness
• Problem seeing close
objects
• Distance between lens
and retina too small
• Light focused behind
retina
• Corrected with
converging lenses

38. Far-Sighted (Hyperopia)

39. Focusing Problems
PRESBYOPIA
• Form of far-sightedness
• Harder for people to read
as they age
• Lens loses elasticity
• Corrected by glasses with
converging lenses

40. Focusing Problems
MYOPIA
• Near-sightedness
• Problem seeing objects
far away
• Distance between lens
and retina too large
• Light focused in front of
retina
• Correct with diverging
lenses

41. Near-Sighted (Myopia)

42. Diseases of the Eye
ASTIGMATISM
• Eye cannot focus an
object’s image on a single
point on retina
• Cornea is oval instead of
spherical
• Causes blurred vision
• Some types can be
corrected with lenses

43. Diseases of the Eye
GLAUCOMA
• Group of diseases
• Affects optic nerve -
pressure
• Loss of ganglion cells
• Gradual loss of sight and
eventual blindness
• Check eyes regularly
• Can be treated

44. Diseases of the Eye
CATARACTS
• Clouding forms in lens
due to denaturing of lens
protein
• Obstructs passage of light
• Caused by age, chronic
exposure to UV, or due to
trauma
• Removed by surgery

45. Vision Correction
CONTACT LENSES
• Artificial lens placed over
cornea
• Same as glasses
• Corrects for both near
and far-sightedness
• Also used for cosmetic
purposes (eye colour,
Hollywood)

46. Vision Correction
LASIK
• “Laser Assisted In Situ
Keratomileusis”
• Refractive surgery
using laser
• Corrects near and far-
sightedness and
astigmatisms