Vision part of the central nervous system which enables organisms to process visual detail, as well...
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VISION
Vision part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse
Vision part of the central nervous system which enables
organisms to process visual detail, as well as enabling several
non-image forming photoresponse functions. It interprets
information from visible light to build a representation of the
surrounding world
Slide 3
A. Stimulus : Light Waves Sun emits radiant energy or
electromagnetic waves. If this enters the eyes, it becomes a visual
stimulus. Light is electromagnetic radiation that travels in the
form of waves is emitted from the sun, stars, fire, and lightbulbs.
Most other objects just reflect light.
Slide 4
People experience light as having three features:
color,brightness, and saturation. The color or hue of light depends
on its wavelength, the distance between the peaks of its waves.
Brightness depends on light wave amplitude, the height of light
waves. Brightness is also somewhat influenced by wavelength. Yellow
light tends to look brighter than reds or blues.
Slide 5
Saturation or colorfulness depends on light complexity, the
range of wavelengths in light. Light of mixed wavelengths looks
duller or paler than pure light. Wavelength > Color Amplitude
> Brightness Complexity > Saturation
Slide 6
There are essentially four steps to vision. First we have to
gather light into our eye. The light has to be channeled to the
back of the eye. Transduction occurs. The information goes to our
brain where we interpret it.
Slide 7
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Slide 10
The Eyes the organ of vision detect light and convert it into
electro-chemical impulses in neurons complex optical system which
collects light from the surrounding environment, regulates its
intensity through a diaphragm, focuses it through an adjustable
assembly of lenses to form an image, converts this image into a set
of electrical signals, and transmits these signals to the brain
through complex neural pathways that connect the eye via the optic
nerve to the visual cortex and other areas of the brain
Slide 11
Slide 12
The cornea is the transparent, protective outer membrane of the
eye.
Slide 13
The iris, the colored part of the eye, is a ring of
muscle.
Slide 14
The iris surrounds an opening called the pupil, which can get
bigger or smaller to allow different amounts of light through the
lens to the back of the eye. In bright light, the pupil contracts
to restrict light intake; in dim light, the pupil expands to
increase light intake.
Slide 15
The lens, which lies behind the pupil and iris, can adjust its
shape to focus light from objects that are near or far away. This
process is called accommodation.
Slide 16
Light passing through the cornea, pupil, and lens falls onto
the retina at the back of the eye. The retina is a thin layer of
neural tissue. The image that falls on the retina is always upside
down.
Slide 17
Rods are responsible for vision at low light levels (scotopic
vision). They do not mediate color vision, and have a low spatial
acuity. Cones are active at higher light levels (photopic vision),
are capable of color vision and are responsible for high spatial
acuity.
Slide 18
The center of the retina, the fovea, is where vision is
sharpest. This explains why people look directly at an object they
want to inspect. This causes the image to fall onto the fovea,
where vision is clearest.
Slide 19
Light rays enter the eye through the cornea, the clear front
window of the eye. The corneas refractive power bends the light
rays in such a way that they pass freely through the pupil the
opening in the center of the iris through which light enters the
eye. The iris works like a shutter in a camera. It has the ability
to enlarge and shrink, depending on how much light is entering the
eye. After passing through the iris, the light rays pass thru the
eyes natural crystalline lens. This clear, flexible structure works
like the lens in a camera, shortening and lengthening its width in
order to focus light rays properly. Light rays pass through a
dense, transparent gel-like substance, called the vitreous that
fills the globe of the eyeball and helps the eye hold its spherical
shape.
Slide 20
In a normal eye, the light rays come to a sharp focusing point
on the retina. The retina functions much like the film in a camera.
It is responsible for capturing all of the light rays, processing
them into light impulses through millions of tiny nerve endings,
then sending these light impulses through over a million nerve
fibers to the optic nerve. Because the keratoconus cornea is
irregular and cone shaped, light rays enter the eye at different
angles, and do not focus on one point the retina, but on many
different points causing a blurred, distorted image. In summary,
the cornea is the clear, transparent front covering which admits
light and begins the refractive process. It also keeps foreign
particles from entering the eye. The pupil is an adjustable opening
that controls the intensity of light permitted to strike the lens.
The lens focuses light through the vitreous humor, a clear gel-like
substance that fills the back of the eye and supports the
retina.
Slide 21
The retina receives the image that the cornea focuses through
the eyes internal lens and transforms this image into electrical
impulses that are carried by the optic nerve to the brain. We can
tolerate very large scars on our bodies with no concern except for
our vanity. This is not so in the cornea. Even a minor scar or
irregularity in the shape can impair vision. No matter how well the
rest of the eye is functioning, if the cornea is scarred, clouded
or distorted, vision will be affected. In keratoconus, the
irregular shape of the cornea does not allow it to do its job
correctly, leading to distortion of the image it passed to the
retina and transmitted to the brain.
Slide 22
Visual Phenomena Inverted Retinal Image
Slide 23
Visual Acuity - this deals with the ability of the retina
distinguish differences in stimulation. - is influenced by three
factors: a. Size b. Illumination c. proximity
Slide 24
a. SIZE
Slide 25
b. Illumination
Slide 26
c. Proximity
Slide 27
Visual Accommodation - process of adjusting the lenses of the
eyes to varying distances within the visual field to obtain a clear
vision
Slide 28
Visual Adaptation - this due to the difference in the action
between the rods and the cones Photopia-adaption to light
Scotopia-adaption to dark
Slide 29
An afterimage or ghost image or image burn-in is an optical
illusion that refers to an image continuing to appear in one's
vision after the exposure to the original image has ceased. A
common form of afterimages is the bright glow that seems to float
before one's eyes after looking into a light source for a few
seconds.
Slide 30
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Eye Trouble Nearsightedness is the inability to clearly see
distant objects. (Myopia) Farsightedness is the inability to
clearly see close objects. (Hyperopia) A cataract is a lens that
has become opaque, resulting in impaired vision. Astigmatism due to
uneven curvature of the cornea or the lenses. Old-sightedness is a
condition where the lenses harden and lose the ability to
accomodate,. (Presbyopia)
Slide 32
There is a blindness to one side of the visual field due to
lesions on the optic tract. (Hemianopsia) Scotoma is a condition
where there are blind spots in the visual field. Visual paresthesia
I a condition where there are optic sensations without an object.
Color blindness. Certain colors are seen as black or green. Night
Blindness is a defect where there is inability to see well at night
due to the lack of vitamin A. -trichromat -dichromat
-monochromat
Slide 33
Test your eyes Eye test for myopia and hyperopia Cover one eye
with your hand, without pressing on the lid, and take the test.
Cover the other eye and begin the test again.
Slide 34
Your distance vision is deficient if you see the O sharper or
blacker, either in the red or the green color. Generally, if you
see the O blacker or sharper in the red part, you probably have
myopia or have a myopic tendency. Conversely, if you see the O
blacker or sharper in the green part, you are definitely hyperope
and have hyperopia. In any case, an eyesight check by an eye care
specialist would appear necessary.myopiahyperope
Slide 35
Test your eyes Eye test for Distance vision Cover one eye with
your hand, without pressing on the lid, and read the test below,
letter by letter. Cover the other eye and begin the test
again.
Slide 36
If you have read the test as successfully with the right eye as
with the left eye, you probably have good central acuity. If you do
not manage to read all the letters, either with one eye or with
two, an eyesight check by an eye care specialist would appear
necessary.
Slide 37
Test your eyes Eye test for Astigmatism Cover one eye with your
hand, without pressing on the lid, and take the test. Cover the
other eye and begin the test again. If some of the lines appear
grayer and some blacker, you probably have an astigmatism - consult
your eye care specialistastigmatism
Slide 38
Test your eyes The Ishihara test is commonly used to detect
Daltonism (color blindness of basic colors: red, blue and green). A
distinction is made between: protanopes, who do not see red;
deuteranopes, who do not see green; tritanopes, who do not see
either blue or yellow. Tritanopes cannot be identified using a
Ishihara test but instead requires a 100 Hue test, which needs to
be carried out by your eye care specialist.
Slide 39
Rarer are people with complete color blindness, who only
perceive levels of gray. They are said to suffer from
achromatopsia. What can you see inside each of these circles?
Slide 40
If you do not manage to read the figures 7, 16, 57 and 42, an
eyesight check by an eye care specialist would appear
necessary.
Slide 41
Color Vision - originated by the famous English Scientist Sir
Isaac Newton. The wave lenghts to which the human eye is sensitive
to range from 780-380 m.u. Color Quality Wavelenght(mu) Red760-647
Orange647-588 Yellow588-550 Green550-492 Blue 492-433
Violet433-390
Slide 42
SOME FUN FACTS YOU MAY NOT KNOW ABOUT EYES: The average blink
lasts for about 1/10th of a second. While it takes some time for
most parts of your body to warm up to their full potential, your
eyes are on their A game 24/7. Eyes heal quickly. With proper care,
it only takes about 48 hours for the eye to repair a corneal
scratch. Seeing is such a big part of everyday life that it
requires about half of the brain to get involved. Newborns dont
produce tears. They make crying sounds, but the tears dont start
flowing until they are about 4-13 weeks old. Around the world,
about 39 million people are blind and roughly 6 times that many
have some kind of vision impairment. Doctors have yet to find a way
to transplant an eyeball. The optic nerve that connects the eye to
the brain is too sensitive to reconstruct successfully.
Slide 43
The cells in your eye come in different shapes. Rod-shaped
cells allow you to see shapes, and cone-shaped cells allow you to
see color. You blink about 12 times every minute. Your eyes are
about 1 inch across and weigh about 0.25 ounce. Some people are
born with two differently colored eyes. This condition is
heterochromia. Even if no one in the past few generations of your
family had blue or green eyes, these recessive traits can still
appear in later generations. Each of your eyes has a small blind
spot in the back of the retina where the optic nerve attaches. You
dont notice the hole in your vision because your eyes work together
to fill in each others blind spot. Out of all the muscles in your
body, the muscles that control your eyes are the most active. 80%
of vision problems worldwide are avoidable or even curable.