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Chapter 2

Chapter 2 book notes

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Matthias Niemeier

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PSYB51:Chapter 2: The First stops in Vision
Chapter 2:
Light is a form of electromagnetic radiation: it is energy produced by vibrations of electrically charged
There are two ways to view light
oWave: an oscillation that travels through a medium by transferring energy from one
particle or point to another without causing any permanent displacement of the medium,
oPhoton: a quantum of visible light or other form of electromagnetic radiation
demonstrating both particle and wave properties
Visible light has wavelengths between 400-700 nanometres.
Once light reaches the atmosphere from the sun there are 5 things that can happen to it.
a. To take up light, noise, or energy and not transmit it at all.
a.To disperse light in an irregular fashion
a.To redirect something that strikes a surface especially light, sound, or heat usually back
towards its point of origin.
b.Light coloured objects tend to reflect off more light then dark coloured objects.
a.To convey something from one place to another. Its neither absorbed or reflected
5. Refracted:
a.To alter the course of a wave of energy that passes into something from another medium ,
as water does to light entering it from the air.
b.To measure the degree of refraction in a lens or eye.
Eyes that see light
Sensing light is important, it is even important for single cell organisms, because detection of
light can help their survival.

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How ever eyes on the other hand go beyond detection of light, they can form an image
A picture or likeness
Parts of the eye
oThis is the first layer of the eye.
oThis provides a window to the world because it is transparent.
oIt contains lots of transparent sensory nerve endings.
oIf you scratch your cornea, you tear up but it will regenerate within 24 hours.
Aqueous humour:
o The watery fluid in the anterior chamber of the eye.
o A fluid derived from blood fills the space immediately behind the cornea , supplying
oxygen and nutrients to and removing waste from the cornea and the crystalline lens
Crystalline lens:
The lens inside the eye that enables changing focus
It has no blood supply
The shape of the lens is controlled by ciliary muscles
oThe dark circular opening at the center of the iris in the eye where light enters the eye.
oThe coloured part of the eye, consisting of muscular diaphragms surrounding the pupil
and regulating the light entering the eye by expanding and contracting the pupil
Vitreous humor:
oThe transport fluid that fills vitreous chamber in the posterior part of the eye

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PSYB51:Chapter 2: The First stops in Vision
oA light sensitive membrane in the back of the eye that contains rods and cones which
receive an image from the lens and send it to the brain through the optic nerve.
Shinning starlight on to the retina:
Refraction of light ( the bending of light) is necessary to focus the light rays
The cornea and the aqueous and vitreous humors all refract light. However, the refractive power of
these parts is fixed so it cannot be changed.
What changes the refraction of light is the lens.
The process by which the eye changes its focus (in which the lens gets fatter as
gaze is directed toward nearer objects.
o The accommodation is accomplished through contraction of the ciliary muscles. these
muscles are attached through the lens by tiny fibres called Zonules of Zinn”
o When the muscle is relaxed the counsel are stretched and your most likely looking at
something in a distance .. and vice versa
o Literally old sight. The loss of near vision because of insufficient accommodation
oOpacity of the crystalline lens.
oIt can happen in many different ages and take different forms.
oCongenital cataract: present at birth
oBut usually ir happens around the age of 50 and basically the lens is replaced with a
plastic or silicone implant.
So to focus on the retina, the refractive power of the four optical components of the eye must be perfectly
matched to the length of the eyeball.
The condition in which there is no refractive error, because the refractive power of the eye is
perfectly matched to the length of the eyeball.
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