One of the 5 Special Senses -The EYE!!

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One of the 5 Special Senses -The EYE!!
Chapter 17 pages 554-573
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Vision the Eye

• Vision is our dominant sense with 70 of our
  bodys sensory receptors found in the eye.
• Do blind people loose 70 of the sensory
  information that is available?
• Youtube video of how the eye works.
• Classic informational video about the eye

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Anatomy of the human eye
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Part Function
Iris Regulates the size of the pupil
Pupil Admits light
Retina Contains receptors for vision
Aqueous humor Transmits light rays and supports the eyeball
Vitreous humor Transmits light rays and supports the eyeball
Rods Allow black and white vision in dim light
Cones Allow color vision in bright light
Fovea An area of densely packed cone cells where vision is most acute
Lens Focuses the light rays
Sclera Protects and supports the eyeball
Cornea Focusing begins here
Choroid Absorbs stray light
Conjunctiva Covers the sclera cornea keeps eye moist
Optic nerve Transmits impulses to the brain
Eye lid Protects the eye
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Accessory Structures of the Eye

• Eyelids
• Superficial epithelium of eye
• Structures associated with production, secretion,
  and removal of tears

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Eyelids (Palpebrae)

• Continuation of skin
• Blinking keeps surface of eye lubricated, free of
  dust, and debris

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Eyelashes

• Robust hairs that prevent foreign matter from
  reaching surface of eye
• First defense to prevent foreign objects from
  entering the eye

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Tarsal Glands

• Secrete lipidrich product that helps keep
  eyelids from sticking together
• On inner margin of eyelid

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Lacrimal Caruncle

• Mass of soft tissue
• Contains glands producing thick secretions
• Contribute to gritty deposits that appear after
  good nights sleep
• Sty or cyst on eye is usually due to an infection
  of a tarsal or ciliary gland.

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Conjunctiva

• Epithelium covering inner surfaces of eyelids and
  outer surface of eye

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Conjunctivitis (Pinkeye)

• Results from damage to, and irritation of, the
  conjunctival surface
• Can be due to pathogenic infection or by
  physical, allergic, or chemical irritation to the
  surface of the eye.

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Lacrimal Apparatus

• Produces, distributes, and removes tears

• Tears reduce friction, remove debris, prevent
  bacterial infection, profice nutrients and
  oxygen to portions of the conjunctival epithelium

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Muscles of the Eye
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The Eye

• The eyes are extremely sophisticated visual
  instruments more versatile and adaptable than
  the most expensive cameras, yet compact and
  durable.
• Each eye is a slightly irregular spheroid with an
  average diameter of 24 mm (a little smaller than
  a Ping-Pong ball), and has a weight of about 8 g.
• Within the orbit, the eyeball shares space with
  extrinsic eye muscles, the lacrimal gland, and
  the cranial nerves and blood vessels that supply
  the eye and adjacent portions of the orbit and
  face. Orbital fat cushions and insulates the
  eye.
• The wall of the eye contains three distinct
  layers (tunics)

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The Three Tunics
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The (Outer) Fibrous Tunic

• The Fibrous Tunic is the outermost layer of the
  eye, it consists of the sclera (the white of the
  eye) and the cornea.
• Provides mechanical support and some degree of
  physical protection
• Serves as an attachment site
• for the extrinsic eye muscles
• Contains structures that assist
• in the focusing process.

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The (Intermediate) Vascular Tunic (Uvea)

• The middle layerContains numerous blood vessels,
  lymphatic vessels, and the intrinsic (smooth)
  muscles of the eye.
• The iris, the ciliary body, and the choroid
• Iris visible through the transparent corneal
  surface contains two layers of smooth muscle
  fibers called pupillary muscles.
• Ciliary body a thickened region that begins
  deep to the junction between the cornea and the
  sclera, it extends all the way to the neural
  tunic
• Choroid a vascular layer that separates the
  fibrous and neural tunics posterior to the ora
  serrata

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The Neural Tunic (Retina)

• The neural tunic, or retina is the innermost
  layer of the eye.
• It consists of a thin, outer layer called the
  pigmented part and a thick inner layer called the
  neural part
• The pigmented part of the retina absorbs light
  that passes through the neural part, preventing
  light from bouncing back through the neural part
  and causing visual echoes. The pigment cells
  have important biochemical reactions with the
  retinas light receptors, which are in the neural
  part of the retina.

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Optic Disc The Blind Spot

• Axons from an estimated 1 million ganglion cells
  converge on the optic disc, a circular region
  just medial to the fovea.
• This is the origin of the optic nerve
• Light striking this area goes
• unnoticed, the optic disc
• does not have any
• photoreceptors or other
• structures typical of the
• retina.

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Chambers of the Eye

• The ciliary body and lens divide the interior of
  the eye into a large posterior cavity, or
  vitreous chamber, and a smaller anterior cavity.
• The anterior cavity is subdivided into the
  anterior chamber, which extends from the cornea
  to the iris, and a posterior chamber, between the
  between the iris and the ciliary body and lens.
• BOTH chambers are filled with the fluid aqueous
  humor

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The Aqueous Humor

• Aqueous humor is the fluid that circulates within
  the anterior cavity, passing from the posterior
  to the anterior chamber through the pupil.

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The Vitreous Body

• The posterior chamber of the eye contains the
  vitreous body, a gelatinous mass.
• Its function is to stabilize the shape of the
  eye, which might otherwise distort as the
  extra-ocular muscles change its position within
  the orbit.
• Formed during the development of the eye and is
  not replaced.

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The Lens

• The lens lies posterior to the cornea, held in
  place by ligaments. The primary function of the
  lens is to focus the visual image on the
  photoreceptors. The lens changes shape to focus
  the visual image.

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Accommodation

• We focus images on the retina by changing the
  shape of the lens to keep the focal length
  constant, this process is called accommodation.
• During accommodation, the lens becomes rounder to
  focus the image of a nearby object on the retina
  the lens flattens when we focus on a distant
  object.

ADAM nearsighted and far sightedness
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Near sightedness (Myopia)

• Near sightedness tends to run in families.
• A near sighted person can see objects that are
  near them clearly but objects that are farther
  away appear blurry

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Farsightedness (Hyperopia)

• A farsighted person can see objects that are far
  from them clearly but objects that are close to
  them appear blurry
• Usually present at birth

Video with vision simulated
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Astigmatism

• In astigmatism, the degree of curvature in the
  cornea or lens is not refracted properly., the
  visual image will be distorted.

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Now we will move to the eye function how does
vision work?

• Bill nye http//www.youtube.com/watch?vcFVbLnX
  Wn6A
• Bausch and lomb
• http//www.youtube.com/watch?vgvozcv8pS3c
• Extensive part 1
• http//www.youtube.com/watch?vZ8asc2SfFHM

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Photoreceptor Cells - also known as rods and
cones
The discs in the outer segment of rods and cones
contain special organic compounds called visual
pigments rhodopsin consists of a protien, opsin,
bound to the pigment retinal or retinene, which
is synthesized from vitamin A . The visual
pigment is the same in cones, but the retinal is
attached to other forms of opsin.
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Rods and Cones are Found in the Retina

• Rods - The rods are more numerous, some 120
  million, and are more sensitive than the cones.
  However, they are not sensitive to color.
• Cones - The 6 to 7 million cones provide the
  eye's color sensitivity and they are much more
  concentrated in the central yellow spot known as
  the macula.

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The Retina (Neural Tunic) - photoreceptor cells
Do you want more information?
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The Retina

• The retina is the only part of the CNS which is
  directly observable!
• Light is coming through the eye from the right
• There are 3 layers of neurons shown,
  photoreceptors, bipolar ganglion cells (reflect
  the order of activity)
• The ganglion cells and bipolar cells are
  transparent dont significantly reduce the
  intensity of light passing to the photoreceptor

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Color Vision

• The color-responsive chemicals in the cones are
  called cone pigments and are very
• similar to the chemicals in the rods. The retinal
  portion of the chemical is the same,
• however the scotopsin is replaced with
  photopsins. Therefore, the color-responsive
• pigments are made of retinal and photopsins.
  There are three kinds of color-sensitive
• pigments
• Red-sensitive pigment
• Green-sensitive pigment
• Blue-sensitive pigment
• Each cone cell has one of these pigments so that
  it is sensitive to that specific color. The human
  eye can sense almost any gradation of color when
  red, green and blue are mixed.
• In the diagram above, the wavelengths of the
  three types of cones (red, green and blue) are
  shown. The peak absorbancy of blue-sensitive
  pigment is 445 nanometers, for green-sensitive
  pigment it is 535 nanometers, and for
  red-sensitive pigment it is 570 nanometers.

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Color Blindness

• Color blindness is the inability to differentiate
  between different colors. The most common type is
  red-green color blindness. This occurs in 8
  percent of males and 0.4 percent of females. It
  occurs when either the red or green cones are not
  present or not functioning properly. People with
  this problem are not completely unable to see red
  or green, but often confuse the two colors.
• This is an inherited disorder and affects men
  more commonly since the capacity for color vision
  is located on the X chromosome. (Women have two X
  chromosomes, so the probability of inheriting at
  least one X with normal color vision is high men
  have only one X chromosome to work with. Click
  here for more on chromosomes.). The inability to
  see any color, or seeing only in different shades
  of gray, is very rare.

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How The Eye Perceives Visual Stimuli

• Light passes through the pupil
• Light is focused by the cornea, lens the humors
• Image on retina is upside down and reversed
• Photoreceptors stimulated
• Optic nerve carries message to cerebral cortex of
  the brain
• Brain corrects the position of the image (right
  side up not reversed)
• Coordinates images coming from left right

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How Vision is measured

• 20/20 vision means that the level of detail seen
  at a distance of 20 feet by an individual with
  normal vision.
• 20/15 is better than normal vision
• 20/30 means that a person must be 20 feet away to
  see what the level of detail that a normal person
  could see at 30 feet away
• 20/200 is considered legally blind (half of the
  blind population is over 65 years old) Why?
• More than 400,000 blind people in the US
• Myopia, Hyperopia Astigmatism explained

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Glaucoma

• The leading cause of blindness
• Glaucoma is not just one eye disease, but a group
  of eye conditions resulting in optic nerve
  damage, which may cause loss of vision.
  Abnormally high pressure inside your eye
  (intraocular pressure) usually, but not always,
  causes this damage.
• The most common type of glaucoma, primary
  open-angle glaucoma, has no noticeable signs or
  symptoms except gradual vision loss.

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Cataracts

• A cataract is a clouding of the normally clear
  lens of your eye. For people who have cataracts,
  seeing through cloudy lenses is a bit like
  looking through a frosty or fogged-up window.
  Clouded vision caused by cataracts can make it
  more difficult to read, drive a car especially
  at night or see the expression on a friend's
  face.

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Macular Degeneration

• In some persons, the macula (which is
  responsible for fine detail in the center of
  vision) can deteriorate with age for unknown
  reasons. This causes loss of central vision. This
  can sometimes be helped with laser surgery.

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Vision Deteriorates With Age

• As we grow older, the lens becomes less elastic.
  It loses its ability to change shape. This is
  called presbyopia and is more noticeable when we
  try to see things that are close up, because the
  ciliary body must contract to make the lens
  thicker. The loss of elasticity prevents the lens
  from becoming thicker. As a result, we lose the
  ability to focus on close objects.
• At first, people begin holding things farther
  away in order to see them in focus. This usually
  becomes noticeable when we reach our mid-forties.
  Eventually, the lens is unable to move and
  becomes more or less permanently focused at a
  fixed distance (which is different for each
  person).
• To correct this, bifocals are required. Bifocals
  are a combination of a lower lens for close
  vision (reading) and an upper lens for distance
  vision.

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The Process of Perceiving Visual Stimulation
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Optical Illusions Why does the brain have
trouble interpreting these still visual images?
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