Human eye 2014

Sec 4 Human Eye

1. My boyfriend has 20/20
vision after lasik surgery
but he is not pleased!
WHY???
He thought I
was prettier
before…
That
makes
sense.
Prepared By, Ms Wong Fui Yen 2012 Prepared By, Ms Wong Fui Yen 2012

2. The EyeThe Eye

3. Lesson ObjectivesLesson Objectives

Describe the gross structure of the eye as seen Describe the gross structure of the eye as seen
in:in:
- front view; and- front view; and
- horizontal section.- horizontal section.

State the principal functions of the component State the principal functions of the component
parts of the eye in producing a focused image parts of the eye in producing a focused image
of:of:
- near objects; and- near objects; and
- distant objects on the retina. - distant objects on the retina.

Describe the pupil reflex in response to:Describe the pupil reflex in response to:
- bright light; and- bright light; and
- dim light.- dim light.

4. ““EyeEye”is a ”is a sensesense organorgan responsible to detect responsible to detect
lightlight and transmit the and transmit the
image formed to the brain image formed to the brain in the form of in the form of
nerve signals in the body.nerve signals in the body.
..
NerveNerve
impulsesimpulses
2

5. 
The internal structure of the eye is made The internal structure of the eye is made
up of 3 main layers:up of 3 main layers:

ScleraSclera (white outer covering) (white outer covering)

Choroid Choroid (Middle layer)(Middle layer)

RetinaRetina (innermost layer) (innermost layer)

7. Class ActivityClass Activity : :
Look at your friend eyeball to eyeball. Look at your friend eyeball to eyeball.
Which part of the eye you could see?Which part of the eye you could see?
9
Conjunctiva
(covers
sclera)
Lower eyelid

8. retina
vitreous humour
iris
optic nerve
lens
cornea
pupil

9. Frontal viewFrontal view
CorneaCornea refracts light rays into the eye.refracts light rays into the eye.
Most of the refraction Most of the refraction occurs hereoccurs here
Sclera Sclera
(white outer
covering):
Outermost layer; protects & gives eye Outermost layer; protects & gives eye
shapeshape
Choroid Choroid
((middle
layer)
Pigmented blackPigmented black to prevent internal to prevent internal
reflection of light & contains reflection of light & contains blood blood
vesselsvessels that bring oxygen and nutrients
to the eyeball and remove metabolic
waste products.

10. Ciliary BodyCiliary BodyContains ciliary muscles which control Contains ciliary muscles which control
thicknessthickness of the lens. of the lens.
Suspensory Suspensory
LigamentsLigaments
AttachesAttaches the edge of the lens to the the edge of the lens to the
ciliary bodyciliary body
LensLens Refracts/focuses light Refracts/focuses light onto retina by onto retina by
changing its shape or thicknesschanging its shape or thickness
IrisIris Controls the Controls the amount of lightamount of light entering the entering the
eye using its 2 sets of muscles (circular eye using its 2 sets of muscles (circular
and radial muscles)and radial muscles)
PupilPupil A hole in the centre of the iris that A hole in the centre of the iris that
allows light to enter the eyeallows light to enter the eye

11. Aqueous Chamber Aqueous Chamber
containing containing aqueous aqueous
humourhumour
Keeps eyeball firm. Keeps eyeball firm.
Refracts light onto the lensRefracts light onto the lens
Vitreous Chamber Vitreous Chamber
containing containing vitreous vitreous
humourhumour
Refracts light onto retinaRefracts light onto retina
RetinaRetina - light sensitive layer light sensitive layer
- high concentration of high concentration of
photoreceptorsphotoreceptors (rods and (rods and
cones);cones); - allows image to be - allows image to be
formed and color to be seenformed and color to be seen

12. Optic nerveOptic nerveTransmits Transmits nerve impulses nerve impulses to the to the
brain. brain.
Blind spotBlind spotPlace where optic nerve leaves the Place where optic nerve leaves the
eye, cannot see when images are eye, cannot see when images are
projected here (does not contain projected here (does not contain
any photoreceptors) thus it is any photoreceptors) thus it is
insensitiveinsensitive to light to light
FoveaFovea
(yellow spot)(yellow spot)
Images are focused hereImages are focused here
Greatest concentration of cones Greatest concentration of cones
but no rods(have colour vision in but no rods(have colour vision in
bright light)bright light)

13. How The Eye WorksHow The Eye Works

Light rays are reflected from an object.Light rays are reflected from an object.

Light rays are Light rays are refractedrefracted as they pass through as they pass through
cornea and lens. cornea and lens.

The lens are involved in The lens are involved in focusingfocusing ( or ( or
accommodation) so that clear images of objects accommodation) so that clear images of objects
at at different distancesdifferent distances can be formed on retina. can be formed on retina.

Focusing for vision involves the Focusing for vision involves the ciliary musclesciliary muscles
and and suspensory ligamentssuspensory ligaments to help adjust the to help adjust the
lens.lens.

14. I. Accommodation/ FocusingI. Accommodation/ Focusing

Accommodation is the Accommodation is the
process by which the process by which the
lens adjust its thicknesslens adjust its thickness
according to the according to the different different
distancesdistances so as to get a so as to get a
focused image on the focused image on the retinaretina

Involves lens, Involves lens, ciliary ciliary
musclesmuscles & & suspensory suspensory
ligaments.ligaments.

15. Focusing on Near ObjectFocusing on Near Object
1.
2.
3.
4.

16. Focusing on Distant ObjectFocusing on Distant Object
1.
2.
3.
4.

17. Ciliary
muscle
Suspensory
ligament
Lens
Yellow spot

18. Ciliary
muscle
Suspensory
ligament
Lens
Yellow spot

19. Distance:Distance: Near Near FarFar
Ciliary muscleCiliary muscle ContractContract RelaxRelax
Suspensory Suspensory
LigamentsLigaments
BecomeBecome
slackenedslackened
Are pulled Are pulled
tight tight
(become taut)(become taut)
LensLens ThickerThicker
and and
more convexmore convex
ThinnerThinner
and and
less convexless convex
Focusing by lens involves:Focusing by lens involves:
As a result, the light rays from object is focused on the retina where
photoreceptors are stimulated.

20. Focusing on near objectFocusing on near object
1.1.Ciliary muscleCiliary muscle contractcontract..
2.2.Suspensory ligamentsSuspensory ligaments slackenslacken, relaxing , relaxing
their pull on the lens.their pull on the lens.
3.3.Lens Lens becomes thickerbecomes thicker and more convex, and more convex,
decreasing its focal length.decreasing its focal length.
4.4.Light rays from near object are sharply Light rays from near object are sharply
focused on the retinafocused on the retina. Photoreceptors on . Photoreceptors on
retina are stimulated.retina are stimulated.
5.5.Nerve impulses produced are transmitted by Nerve impulses produced are transmitted by
optic nerveoptic nerve to the brain. The brain to the brain. The brain
interprets the impulses and sees the object.interprets the impulses and sees the object.

21. Bob
What kind of help does Bob need?
I am seated right at the
back of the class and I
can’t see well.
Mr Ng always scold me
for not copying down
notes.

23. Common eye problemsCommon eye problems
Short-sightedness
results when light rays
focus in front of the retina.
Long-sightedness
results when light rays
focus at the back of the
retina.

24. Short-sightedness
Correction using lens

25. Implanted tooth helps blind
woman recovers sight
http://sg.news.yahoo.com/afp/20090917/tts-health-research-us-eye-972e412.html

27. The size of the pupil is controlled by two sets of The size of the pupil is controlled by two sets of
muscles in the iris.muscles in the iris.
1.1.Circular Circular musclesmuscles
2.2.Radial Radial musclesmuscles
II. Controlling amount of lightII. Controlling amount of light

28. • Pupil changes size as a result of changes in light intensity.
• Pupil becomes larger when the surrounding light intensity is
low, and smaller when the light intensity is high.
Stimulus (change in
light intensity)
Receptor (retina)
Sensory neurone in
optic nerve
BrainMotor neuroneEffector (iris)
The Reflex Arc involved in the pupil reflex: The Reflex Arc involved in the pupil reflex:

29. PUPIL REFLEXPUPIL REFLEX

30. radial muscles
circular muscles
pupil
In bright light:
Less light to enter eye 
pupil becomes smaller
(constricts)
• Circular muscles contract;
• Radial muscles relax
 Pupil constricts
In dim light:
More light to enter eye 
pupil becomes bigger
(dilates)
• Circular muscles relax;
• Radial muscles contract
 Pupil dilates

31. Controlling amount of light entering Controlling amount of light entering
the eyethe eye
Light
intensity
Circular
muscles
Radial
muscles
Pupil size eventual amt
of light
entering
high light
intensity
Contract Relax Becomes
smaller
Decreases
low light
intensity
relax Contract Becomes
bigger
Increases

33. What happen to the pupil when you
leave the dark halls of the cinema?
The circular muscles will
contract while the radial
muscles of iris will relax.
Hence, it reduces the size of
the pupil, thus decreasing the
amount of light entering the
eye in the light.

34. Why we cannot see colour at night?
•The cones, which allow
detection of colour do not
function under low light
intensities.
•Since only the rods
function, no colour is
seen.

35. Why vision becomes blur when our
eyes are filled with tears?
•Light entering the
eye will be refracted
by the tears as
well as by the
corneal surface.
•This results in a
blurred image.

36. Photoreceptors…
(a) Cones: See colours in bright light.
-3 types of cones: Red, blue, green and
contain different pigment which absorbs
light of different wavelengths. All work tgt
to enable us see a variety of colours.
-Do not work well in dim lights.

37. (b)Rod : More sensitive to light than cones.
Enable us to see things in black and white in
dim light because they are sensitive to low
intensity light. (Reason: Contain Visual
purple pigment)
Nerve impulses cannot be send to brain from
rods hence person cannot see anything.
Visual purple must be formed again before
the person can see in the dark.

38. Colour blindness
People that are effected by colour blindness,
have less numbers of particular cones
than normal, so they get colours confused.
They may be able to see a bright green
coloured object out side, but when viewed in
artificial light, the same object may appear
brown in colour.
Or if the object was a dull green, it could even
appear red.

39. People with normal
colour vision should see
the number 8.
Those with red-green
colour vision deficiencies
should see the number 3.
Total colour blindness
should not be able to
read any numeral.

42. Concentrate on the 4 dots for 30 secs.
Then, shift your eyes to the wall and blink.
Who do you see???

43. Which part of the
eye is responsible
for the
“red eye effect” ?

44. How cataracts affect vision?
http://www.allaboutvision.com/conditions/cataracts.htm

45. Online Online
ResourcesResources
http://www.1800contacts.com/vision101/frames.htmlhttp://www.1800contacts.com/vision101/frames.html
http://www.horton.ednet.ns.ca/staff/selig/Activities/nervous/eye1.htmhttp://www.horton.ednet.ns.ca/staff/selig/Activities/nervous/eye1.htm
http://www.med.uwo.ca/physpharm/courses/sensesweb/L1Eye/l1eye.swfhttp://www.med.uwo.ca/physpharm/courses/sensesweb/L1Eye/l1eye.swf
http://www.richmondeye.com/simulation.htmhttp://www.richmondeye.com/simulation.htm