Post on 19-Jan-2016
9.5 Light and VisionPages 441-444
The HypothesesDemocritus• Matter composed of atoms
which are carried to the soul to be viewed
Empedocles • Matter composed of 4
elements• Earth, Air, Wind and Fire
and vision must be related to fire
• Light radiated from eyeGalen• Optic nerve conducted
visual spirits
Today we accept the following theories:
Sir Isaac Newton and Christian Huygens
•Particles of light (photons) travel in waves of various lengths
•Light enters the eye as it is reflected or transmitted from objects
Afterimages
Two types of afterimages:Positive Afterimage•Occurs after you look into a bright light
and then close your eyes•The image of the light can still be seen
even with eyes closedNegative Afterimage•Eye is exposed to bright coloured light for
an extended period of time
Focusing the ImageRefraction: slowing of light by dense
material (cornea)
•Light is first bent by the cornea toward the pupil
•It is further bent by the lens to a focal point behind the lens
•Image is projected on the retina
Focusing the Image
Light bent by cornea toward pupil
Light bent by cornea toward pupil
Bent by lens to focal point
Bent by lens to focal point
Image projected on
retina
Image projected on
retina
Accommodation
•The adjustment of the lens to objects far and near
•Objects up close pupil constricts in attempt to bring the image into focus
•Objects far away pupil dilates to in an attempt to capture light
Vision Defects
Glaucoma•Build-up of
aqueous humour•Ducts are blocked • Increases fluid
pressure•Lack of oxygen
and neurons can result in blindness
Cataract•Lens becomes
opaque•Prevents light
from passing through
•Solution: remove lens and use strong eyeglasses or replace with plastic lens
Myopia (nearsightedness)•Eye ball is too long•Distant image is brought into focus in
front of the retina
Hyperopia (farsightedness)•Eye ball is too short•Distant image is brought into focus
behind retina