SENSE a physical system thatSENSE a physical system that
receives a particular kind of physicalreceives a particular kind of physical
stimulation and translate it into anstimulation and translate it into an
electrochemical message the brainelectrochemical message the brain
can understandcan understand
SENSATION message our brainsSENSATION message our brains
receives from a sensory receptorsreceives from a sensory receptors
that has stimulatedthat has stimulated
Light is the form of electromagnetic energy thatLight is the form of electromagnetic energy that
the receptors of our eyes are distinctivelythe receptors of our eyes are distinctively
designed to receivedesigned to receive..
Parts of the Eyes and its FunctionsParts of the Eyes and its Functions
CorneaCornea- is a clear membrane just in- is a clear membrane just in
front of the eye.front of the eye.
-is a curved exterior lens that-is a curved exterior lens that
gathers and focuses the enteringgathers and focuses the entering
PupilPupil- the hole in the center of the- the hole in the center of the
IrisIris- is the circular muscle that gives our- is the circular muscle that gives our
eyes its distinctive colors.eyes its distinctive colors.
*bright light- iris constrict*bright light- iris constrict
*dim light- iris is dilated*dim light- iris is dilated
lenslens- focusing images from multiple- focusing images from multiple
-causes light to bend as it passes through it.-causes light to bend as it passes through it.
-A transparent and somewhat flexible disk--A transparent and somewhat flexible disk-
like entity filled with a gelatinous materiallike entity filled with a gelatinous material
-Curved interior which causes bending of-Curved interior which causes bending of
light waves.light waves.
The RetinaThe Retina—a network of neurons—a network of neurons
that extends over most of the backthat extends over most of the back
surface of the interior of the eye.surface of the interior of the eye.
-retina is where electromagnetic light-retina is where electromagnetic light
energy is transduced into neuralenergy is transduced into neural
electrochemical impulses.electrochemical impulses.
*photoreceptors-transduce light*photoreceptors-transduce light
energy into electrochemical energy.energy into electrochemical energy.
Photoreceptors can be found in thePhotoreceptors can be found in the
third layer of the retina.third layer of the retina.
Types of PhotoreceptorsTypes of Photoreceptors
RodsRods—are long and thin receptors—are long and thin receptors
responsible for vision in dim light.responsible for vision in dim light.
-do not receive color.-do not receive color.
ConesCones-are short and thick-are short and thick
photoreceptors responsible for visionphotoreceptors responsible for vision
in bright light.in bright light.
- receive color.- receive color.
- there are 6 million cone cells in- there are 6 million cone cells in
human eyes.human eyes.
Blind SpotBlind Spot is the small area on theis the small area on the
retina where the optic nerve pushesretina where the optic nerve pushes
aside photoreceptors to exit theaside photoreceptors to exit the
Visual cortexVisual cortex—from the thalamus,—from the thalamus,
neurons carry information to theneurons carry information to the
primary visual cortex in the occipitalprimary visual cortex in the occipital
lobe of the brain.lobe of the brain.
Color Vision has two main theories:Color Vision has two main theories:
trichromatic theory and opponent theory.trichromatic theory and opponent theory.
Trichromatic theoryTrichromatic theory states that color perception isstates that color perception is
produced by three types of receptors (cone cells inproduced by three types of receptors (cone cells in
the retina)—green, red, and blue.the retina)—green, red, and blue.
Opponent-process theoryOpponent-process theory states that cells in thestates that cells in the
visual system respond to either red-green or blue-visual system respond to either red-green or blue-
yellow colors; a given cell might be excited by redyellow colors; a given cell might be excited by red
and inhibited by green, whereas another cell mightand inhibited by green, whereas another cell might
be excited by yellow and inhibited by blue.be excited by yellow and inhibited by blue.
Visual ImpairmentsVisual Impairments
What is a cataract?What is a cataract? A cataract is aA cataract is a
clouding of the clear lens in the eye and isclouding of the clear lens in the eye and is
one of the leading causes of visionone of the leading causes of vision
GlaucomaGlaucoma is a disease caused byis a disease caused by
increasedincreased intraocular pressureintraocular pressure (IOP)(IOP)
resulting either from a malformation orresulting either from a malformation or
malfunction of themalfunction of the
eye’s drainage structureseye’s drainage structures. Left untreated,. Left untreated,
an elevated IOP causes irreversiblean elevated IOP causes irreversible
damage thedamage the optic nerveoptic nerve and retinal fibersand retinal fibers
resulting in a progressive, permanent lossresulting in a progressive, permanent loss
of vision.of vision.
FarsightednessFarsightedness oror hyperopiahyperopia, occurs, occurs
when light entering the eye focuses behindwhen light entering the eye focuses behind
thethe retinaretina, instead of directly on it. This is, instead of directly on it. This is
caused by acaused by a corneacornea that is flatter, or an eyethat is flatter, or an eye
that is shorter, than a normal eye.that is shorter, than a normal eye.
Farsighted people usually have troubleFarsighted people usually have trouble
seeing up close, but may also have difficultyseeing up close, but may also have difficulty
seeing far away as well.seeing far away as well.
Nearsightedness or myopia, occurs when lightNearsightedness or myopia, occurs when light
entering the eye focuses in front of theentering the eye focuses in front of the retinaretina
instead of directly on it. This is caused by ainstead of directly on it. This is caused by a
corneacornea that is steeper, or an eye that is longer,that is steeper, or an eye that is longer,
than a normal eye. Nearsighted people typicallythan a normal eye. Nearsighted people typically
see well up close, but have difficulty seeing farsee well up close, but have difficulty seeing far
Astigmatism means that theAstigmatism means that the corneacornea is oval like ais oval like a
football instead of spherical like a basketball. Mostfootball instead of spherical like a basketball. Most
astigmatic corneas have two curves – a steeperastigmatic corneas have two curves – a steeper
curve and a flatter curve. This causes light to focuscurve and a flatter curve. This causes light to focus
on more than one point in the eye, resulting inon more than one point in the eye, resulting in
blurred vision at distance or near. Astigmatismblurred vision at distance or near. Astigmatism
often occurs along withoften occurs along with nearsightednessnearsightedness oror