3. • Cornea refracts light through the pupil & lens
• Lens may change shape for objects at distance
• Image is projected INVERTED on the retina
• Each eye has a blind spot where the optic nerve
& blood vessels enter the eye.
4. Retina • A thin layer on the back
of the eye where light is
converted to an
electrical signal and
passed through the optic
nerve to the eye.
5. • Photoreceptors
called RODS &
CONES sense light
• RODS: great at
low light
sensing, poor
resolution &
colour
• CONES: functions
only in bright light
& provides
information about
colour & detail
6. CONES are responsible for our colour vision is
known as TRI-CHROMATIC vision
We see as a combination of 3 colours:
RED (630 nm) BLUE (420 nm) GREEN (560 nm)
Rods absorb light best at 540 nm
Each cone cell contains pigment molecules
designed to absorb different wavelengths of light
7. Visual Pigments • Each pigment is composed
of two molecules:
– OPSIN
• Proteins that react to specific
wavelengths of light
• All rods contain a specific type
– CHROMOPHORE
• RETINAL – a modified form of
Vitamin A which changes
shape in response to light
8. Different firing rates of
photoreceptor cells
are sent to the brain
where the rates are
compared.
The optic nerves cross
at the OPTIC CHIASM
and each eye’s signal is
sent to the occipital
lobe of the brain
where the image is
‘assembled’.
