Sec. 14.2 - 1
The Structure of the Eye
 One
of the primary ways humans gather
information about their environment is
through visual information supplied by the
sensory receptors in the eye.
 Video:
The Human Eye
http://www.youtube.com/watch?v=JunCyiGfreo
 Our
eye is made up of 3 layers:
1. Sclera
2. Choroid
3. Retina
Layer
 Sclera
- is the outer covering of the eye that
supports and protects the eye’s inner layers;
usually called the white of the eye.
 The
front of the sclera is called the cornea.
 Cornea
– transparent part of the sclera that
protects the eye and bends light toward the
pupil.
 The
cornea is a tissue and like all tissues it
requires oxygen and nutrients, but it cannot
have blood vessels running through it or our
vision would be clouded.
 Most
of the oxygen is absorbed from the
gases dissolved in tears.
 Nutrients
humour.
 Aqueous
are supplied by the aqueous
humour – water liquid that protects
the lens of the eye and supplies the cornea
with nutrients.
 The
choroid layer – is the middle layer of
tissue in the eye that contains blood vessels
that nourish the retina.
 The
 Iris
front of the choroid is called the iris.
– muscle tissue surrounding the pupil
(opening in iris) that regulates the amount of
light entering the eye.
 The
lens is found directly behind the iris.
 The
lens - focuses the image on the retina.
 Ciliary
muscles - alter the shape of the lens
so we can change our focus between close
and distant objects.
A
large chamber behind the lens is called the
vitreous humour.
 The
vitreous humour - contains a cloudy,
jelly-like material that maintains the shape
of the eyeball and allows light to flow to the
retina.
 The
retina – is the innermost layer of tissue
at the back of the eye containing
photoreceptors.
 There
are two types of photoreceptors:
1. Rods – allow us to see black and white
images and in dim light.
2. Cones – allow us to see colour.
 We
have about 18 times more rods than
cones.
 The
rods and cones receive the sensory
information and pass it to a bipolar cell.
 The
bipolar cell passes the information to a
clump of nerves called a ganglion.
 The
group of ganglions come together to
form the optic nerve.

The optic nerve then carries the impulse
through the temporal lobe to the occipital
lobe at the back of the brain.
 Rods
and cones are unevenly distributed
on the retina.
 In
the center of the retina is a tiny
depression called the fovea centralis.
 The
fovea centralis – is an area at the
center of the retina where cones are the
most dense and vision is the sharpest.
 Rods
surround the fovea centralis, which
explains why you may see an object from
your periphery in black and white.
 The
junction where the optic nerve comes
in contact with the retina does not
contain any rods or cones.
 We
cannot see out of this area and it is
therefore referred to as the blind spot.
Structure
Function
Sclera
- Supports and protects eye
Cornea
- Bends (refracts) light toward pupil
Aqueous humour - Supplies cornea with nutrients
Choroid layer
- Contains blood vessels that nourish the retina
Iris
- Regulates the amount of light entering the eye
Vitreous humour - Maintains shape of eyeball and allow light into
retina
Lens
- Focuses image on the retina
Pupil
- The opening in the iris that allow light in to eye
Retina
- Contains rods for b and w and cones for colour
Fovea centralis
- Cones are the most concentrated, clearest
vision
Blind spot
- Where the optic nerve attaches to retina