SENSES

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SENSES

• Three types of senses
• 1. SOMATIC SENSES Light touch (being touched
  by a feather), heat, cold, vibration, pressure,
  pain.
• These are routinely tested by doctors in a
  physical exam, especially for people with
  diabetes and lupus.

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SENSES

• 2. PROPRIOCEPTORS are found in the muscles,
  joints, and tendons. They measure the amount of
  movement, force, and position of the body.
• Proprioception is often tested by having the
  patient close their eyes and saying if their
  fingers are up or down.
• Proprioceptors send information to the
  cerebellum. Thats how you know your legs are
  crossed before you stand up.
• Somatic senses (including pain) and
  proprioception are NOT considered special senses.

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SENSES

• 3. SPECIAL SENSES Smell, taste, vision,
  hearing, equilibrium (balance).

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OLFACTORY SENSE (smell)

• Olfactory receptors are CHEMORECEPTORS a special
  type of neuron which senses particular chemicals
  and triggers an action potential.
• Chemoreceptors are at the roof of the nasal
  cavity. There are hundreds of thousands of
  types, and they can smell a wide variety of
  substances.
• They are extremely sensitive, and can detect
  parts per billion, as in the scent of natural
  gasjust a few molecules!
• The olfactory nerve goes through the cribiform
  plate to the OLFACTORY BULB (one of the shortest
  nerves in the body) and into the limbic system.

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OLFACTORY SENSE (smell)

• Scientists who are trying to find a way to make
  neurons divide to heal nerve injuries often study
  the bodys only mitotic neurons.
• These neurons are the olfactory receptors.
• People who experience imaginary odors have what
  are called unicate fits.

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Olfactory Receptors
Figure 16.3a, b
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Some towns are old factory towns.Some are ol
factory towns!
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GUSTATORY SENSE (taste)

• Sensed on taste buds, which are located mostly on
  the tongue surface, but are also on the palate,
  pharynx, and a few on the lips.
• Taste buds have specialized cells, which increase
  surface area and have chemoreceptors.
• They are surrounded by support cells (like glia).
  They synapse on sensory neurons, which go to the
  facial nerve.
• Someone with a damaged facial nerve can not
  easily taste sweet, sour, or salty substances.
  Taste buds are the only parts of the nervous
  system that can regenerate completely.
• The taste information is sent to the primary
  gustatory (taste) cortex, located in the parietal
  lobe of the brain.

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Taste Buds
Figure 16.1a, b
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Taste Bud
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GUSTATORY SENSE (taste)

• How many different tastes are there? Dozens.
  Salt, sweet, bitter, and sour are only a few.
• Where are they located on the tongue? All tastes
  are located all over the tongue.
• The picture in the book was drawn 120 years ago
  by an anatomist that knew his drawing was not
  right he just wanted to use it as a starting
  point for further experimentation.

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GUSTATORY SENSE (taste)

• Taste appreciation is also involved in texture (a
  mealy apple is not as good), temperature (cold
  pizza tastes different than warm), and smell
  (perfume or cigarette smoke clog the senses and
  decrease taste).
• There are dozens of taste receptors, hundreds of
  thousands of smell receptors, so the subtly of
  taste is from smell.
• Foods people like are in opposite proportion to
  the numbers of taste receptors for that. People
  that love sweets have FEWER taste receptors for
  sweets, so they crave more taste of sweet things.
  If you dislike something, its because you have
  lots of receptors for it. Also, as you get
  older, you become less tolerant of sweets and
  more tolerant of bitter tastes (like beer and
  coffee).

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Fun Facts

• The catfish has over 27,000 taste buds. (What
  could be so tasty on the bottom of a pond?)
• Flies taste with their feet.

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Tongue with bacteria
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• What did the right eye say to the left eye?
• Between you and me, something smells!

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THE EYE

• Structures Surrounding the Eye
• The eye is in the orbit of the skull for
  protection.
• Within the orbit are 6 extrinsic eye muscles,
  which move the eye.
• There are 4 cranial nerves Optic (II),
  Occulomotor (III), Trochlear (IV), and Abducens
  (VI).
• Eyelids are PALPEBRA, and eyelashes are CILIA.
• Fun fact there is a new medicine to make you
  grow longer eyelashes!
• People of Asian descent have an EPICANTHIC FOLD
  in the upper eyelid no functional difference.
• Around the eyeball are glands.

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Surface Anatomy of Eye
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Extrinsic Eye Muscles
Figure 16.6a, b
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FUN FACTS

• Do eyelashes grow back?
• Eyelashes take about four to eight weeks to grow
  back.
• What purpose do eyebrows serve?
• To keep the sweat and rain out of our eyes. The
  arch shape of the eyebrow diverts rain or sweat
  down our cheeks, keeping our eyes dry. Eyebrows
  also help us to communicate. Sometimes a raised
  eyebrow is more effective than words.

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Eyelashes
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GLANDS OF THE EYE

• 1. LACRIMAL GLANDS are the largest set. They
  are on the superior lateral eyelid and they
  produce tears, which drain into the nasal cavity
  via the LACRIMAL DUCT.
• The function is to moisten and lubricate the eye
  surface, and it has enzymes to kill bacteria
  (which thrive in warm, moist conditions).

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Figure 16.5b
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GLANDS OF THE EYE

• 2. LACRIMAL CARUNCLE (little meat) is the spot
  on the medial corner of the eye. It makes an
  oily secretion like a sebaceous gland.
• The function is to lubricate the eye a little bit
  for the eyelids. When the secretion dries, it is
  called sand in the eyes.

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GLANDS OF THE EYE

• 3. TARSAL GLANDS are sebaceous glands on the
  inside of the eyelid, and produce sebum, which is
  an oil to lubricate the eyeball.
• Therefore, the oil component found in tears is
  produced by the tarsal glands.
• The tarsal glands and the lacrimal caruncle make
  a waterproof surface so the eye wont dry out.
• When tarsal glands are clogged CHALAZION

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Chalazion
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GLANDS OF THE EYE

• 4. CILLIARY SEBACEOUS GLANDS go to only the
  cilia.
• When clogged STY.

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Dry Eye Syndrome
Sty
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FUN FACTS

• An ostrich's eye is bigger than it s brain!
• Is the human eye fully grown at birth?
• A typical newborn's eye is around 18 millimeters
  in diameter. A fully grown adult's eye measures
  24-25 millimeters. A fully developed eyeball is
  about two-thirds the size of a ping-pong ball.
• This means a human eye grows only about 28 over
  the course of its life. Fish supposedly have the
  ability to increase their eye size "steadily over
  the course of their entire lives," a talent lost
  on us.

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Ora serrata
Rods and cones
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The Eyeball

• 1. CONJUNCTIVA is like a Saran Wrap covering
  around the eye and under the eyelids. Its made
  of stratified columnar epithelium (the first time
  in the body weve seen this tissue).
• It also has lots of goblet cells to secrete
  moisture for those areas.
• Deep to the epithelium is loose connective tissue
  with lost of small blood vessels, which are not
  seen unless the conjunctiva becomes inflamed
• Blood-shot eyes just from being tired
• PINK EYE (laymans term), known as CONJUNCTIVITIS
  (from bacteria, very contagious).

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The Eyeball

• 2. FIBROUS TUNIC is the next layer, and has 2
  parts
• A. SCLERA is the white of the eye, made of dense
  irregular connective tissue. It is continuous
  with the dura mater of the brain. The eye is
  part of the brain. The sclera protects the eye.
• B. CORNEA is clear, and avascular (no blood
  supply) except around the periphery. Therefore,
  there is no tissue rejection when it is
  transplanted into another person there is also
  no need to find a donor match. It has lots of
  pain receptors, so a scratched cornea is very
  painful. Its function is to be the main focuser
  of light for the eye. If damaged, need a corneal
  transplant.

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Scleritis
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Conjunctivitis
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The Eyeball

• 3. VASCULAR TUNIC is deep to the fibrous tunic.
  It has several structures.
• A. CHOROID has lots of blood vessels and
  pigment. The function of the pigment is to make
  sure light does not enter from the sides. The
  blood vessels provide blood supply to the other
  layers.
• B. CILIARY MUSCLES surround the lens.
• C. SUSPENSORY LIGAMENTS (also known as the
  zonule) hold the lens in place.
• D. LENS functions to continue to focus the light
  after it passes through the cornea. It changes
  shape to allow you to distinguish close from far.
  The lens changes shape by the ciliary muscles
  pulling on the suspensory ligaments.

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The Vascular Tunic
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Vascular Tunic (Uvea)
Figure 16.8
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Rods and cones
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Figure 16.7a
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Figure 16.9a
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Ciliary Muscles

• When you are looking far away, the ciliary
  muscles are relaxed, the lens is stretched into a
  wide circle, and the suspensory ligaments are
  tight.
• When you look up close, the ciliary muscle
  contracts and gets smaller, to the ligaments
  relax. Constantly looking close puts strain on
  the ciliary muscles EYE STRAIN.

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Pupils

• Fun Fact -When you are looking at someone you
  love, your pupils dilate, and they do the same
  when you are looking at someone you hate.

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PROBLEMS WITH THE LENS

• With age, the lens loses flexibility, and is less
  likely to round up.
• It stays in the position for seeing far, so there
  is trouble focusing on things that are near
  PRESBYOPIA (old eyes).
• Occurs around age 45-50. The lens cannot
  accommodate.

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PROBLEMS WITH THE LENS

• Clouding of the lens leads to a clinical
  condition known as CATARACTS.
• Treatment is to remove the lens and replace it
  with a plastic one (which is not flexible
  either).
• If the lens yellows, you cant see the color
  blue. After surgery, can see blue again.

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Cataract
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Cataract Vision
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IRIS (the colored part of the eye)

• The function is to constrict or dilate the pupil
  (opening) to allow light in.
• Therefore, it regulates the amount of light
  passing to the visual receptors of the eye.
• If there is a lot of pigment, eye is brown a
  medium amount green, small amount blue, no
  pigment pink (albino).

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FUN FACTS

• Why are all babies born with blue eyes?
• Melanin is a brownish pigment that adds color to
  your hair, eyes, and skin. At the time babies are
  born, melanin hasn't yet been "deposited" in the
  eyes' iris. Hence, they appear blue.
• After about six months, eyes change color
  depending on the amount of melanin. If you have a
  lot of it, your eyes will turn brown or black. If
  you have little, they'll stay blue. And if you
  have no melanin, your eyes may appear pink.
  Interestingly, as the site notes, human beings
  aren't the only creatures with freaky
  color-morphing eyeballs. Kittens experience the
  same phenomenon.
• How can someone have two different colored eyes?
• Eye color is a polygenic trait. Many babies are
  born with blue eyes. Their eyes change color
  later as they begin to produce more melanin.

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RETINA

• The retina is on top of the choroid layer.
• The retina is made up of PHOTORECEPTORS, which
  are sensors for light.

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Rods and cones
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Figure 16.7a
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Fovea centralis
Optic Nerve
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Rods and Cones

• Two types of photoreceptors Rods and Cones.
• 1. CONES (red, green, and blue) they have less
  light sensitivity (poor at night) but see colors
  well. There is a region on the retina that has
  the highest concentration of cones it is called
  the FOVEA CENTRALIS. The fovea centralis is the
  very center point of a small circular region
  called the MACULA. When you want details, focus
  the light on the macula, because there are a lot
  of cones there. The other layers contain a
  mixture of both.

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Figure 16.7a
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Test for Colorblindness




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Rods and Cones

• 2. RODS (chartreuse yellowish green) have more
  light sensitivity (can see well at night) but
  does not see colors well.
• Above the photoreceptors are layers of neurons
  whose axons become the optic nerve.

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Fovea centralis
Optic Nerve
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Retina
Figure 16.10a
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Photoreceptors
Figure 16.11
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Blind Spot at the Optic Nerve

• The region where the optic nerve and blood
  vessels goes in and out of the eye has no
  photoreceptors BLIND SPOT.
• Hold your hands out at 45 and thats the
  location of the blind spot.
• You can still see your hands because the other
  eye sees it. Close your right eye and look for
  your right hand and youll find the blind spot.

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Figure 16.7a
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Find your blind spot!Stare at the center of X
and move head closer until one red spot disappears
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Blind Spot

• The light takes a path through the lens to the
  blood vessels, so this is the only place in the
  body where you can see blood vessels directly.
• The doctor can diagnose hypertension.
• On a clear, bright day, look at the blue sky and
  you can see the shadow of your own blood vessels
  on the photoreceptors as criss-cross lines in
  field of vision. The little moving dots are your
  blood cells.

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Normal Retina
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• The visual information travels from the retina
  deep into the brain through the optic chiasma
  (not visible with an opthalmascope).
• From here, it goes into the occipital lobe of the
  brain, where it is processed.

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Cranial Nerves II, III, IV, VI
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OPTHALMASCOPE

• An opthalmascope is the instrument used to look
  inside the eye.
• The doctor can see the optic disc, fovea
  centralis, macula, the lens, retina, blood
  vessels, but of course, not the optic chiasma,
  since that is on the brain surface, external to
  the eye.

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PROBLEMS WITH VISION

• FLOATERS are when a capillary breaks and cells
  break off. Floaters dont actually move, the eye
  just tries to track them.

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Floaters
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Floaters

• Floaters can best be seen when the person
  looks at a clear blue sky or white wall.

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RETINAL DETACHMENT

• The retina separates from the underlying choroid.
  
• Retinal detachment can be caused from a blow to
  the eye, or may occur spontaneously. Usually
  caused by an injury like a blow to the eye with a
  baseball, punch, or airbag to the eye.
• It may not cause blindness immediately. Although
  the detached portion contains capillaries, it is
  separated from the main blood supply, so if it is
  not lasered back into place immediately,
  permanent blindness can result.
• Cells in the retina die from lack of oxygen.
  Manifests as a shimmering light. This is
  considered a medical emergency and needs
  immediate treatment. Those who are most
  vulnerable to spontaneous detachment are those
  who are nearsighted.

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HYPEROPIA (far-sighted) eyes are too short
MYOPIA (nearsighted) eyes are too long
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The Eye as an Optical Device
Figure 16.14ac
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Hyperopia and Myopia

• Normal eyes are perfect spheres. When the eyeball
  is not a perfect sphere, the lens has to
  accommodate as much as possible, and corrective
  glasses are usually needed.
• Myopic eyes are elongated (overhead projector is
  in focus, but move it backward, gets fuzzy).
  Even badly nearsighted eyes are only 1mm from
  normal. Treatments are glasses or Lasix, which
  is laser surgery on cornea, when its shaved so
  it focuses light farther back to reach the retina.

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Lasik Surgery
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Hyperopia and Presbyopia

• Hyperopia and presbyopia have some features in
  common, but a key difference between these two
  conditions is that in hyperopia the lens can
  accommodate, but in presbyopia it cannot.

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ASTIGMATISM

• ASTIGMATISM is when the cornea has an irregular
  shape. Part of the field of view is out of
  focus.
• The eyeball changes shape until age 24.

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Astigmatism Test
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Astigmatism Vision
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MACULAR DEGENERATION

• The size of the macula is the size of the printed
  letter O in 14 pt font. When the macula
  degenerates, you lose a lot of sight. This is
  the most common cause of blindness in the US.
• Its due to bleeding in the eye, causing scar
  tissue. The retina does not get enough oxygen,
  and the cells die. Macular degeneration allows
  vision in the periphery, but they cant read or
  drive.

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Macular Degeneration
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DIABETIC RETINOPATHY

• This is when the high sugar levels destroy the
  photoreceptors in the retina.
• The blood vessels also swell and rupture and the
  clots block vision.
• Some of this damage can be repaired by using a
  laser to evaporate the blood clots, but any
  damage to the photoreceptors is permanent. It can
  lead to blindness.

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Diabetic Retinopathy
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Diabetic Retinopathy
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Diabetic Retinopathy vision
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INTERNAL STRUCTURES OF THE EYE

• There are two cavities
• Anterior Cavity
• Posterior Cavity

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Anterior Cavity

• 1. ANTERIOR CAVITY is anterior to the lens, and
  is filled with AQUEOUS HUMOR, similar to plasma,
  supplies nutrients to the cornea and lens.

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Figure 16.7a
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GLAUCOMA

• GLAUCOMA is increased pressure within the
  anterior chamber of the eye. It leads to
  blindness.
• This form of blindness is more common in
  third-world countries because we have tests to
  detect it and treat it.
• The test measures how much pressure there is here
  by seeing how easily the cornea is deformed,
  either with air or direct pressure. How many of
  you have had this test?

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Glaucoma
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• 2. POSTERIOR CAVITY is filled with VITREOUS
  HUMOR, which is jelly-like, and helps give shape
  to the eyeball. It leaks out from a cut, youll
  go blind because the body cant replace it.
• The four main things that cause blindness are
  macular degeneration, cataracts, glaucoma, and
  diabetic retinopathy.

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AMBLYOPIA

• AMBLYOPIA Lazy Eye. In a child, one eye will
  track and focus, the other wont.
• If untreated in children, eventual blindness in
  weak eye because the brain will shut down in the
  occipital lobe.
• Treatment is to patch the good eye to force the
  bad eye to make the connections, or a surgery to
  weaken the muscle to make the strong side just as
  weak.

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Other Eye Problems
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Cancer of the EyeChoroidal Melanoma
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Live worm in the eye
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NOTE

• If a child is blind until age 4-5, and then you
  restore the sight, he will still be blind because
  the brain doesnt form properly.
• With kids who have astigmatism or weak eye
  muscles, one eye stops seeing (or sees double).
• The thalamus in the brain will shut off all the
  signals from the bad eye.

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NOTE

• To protect your eyesight throughout your life,
  use the 20-20-20 rule
• Every 20 minutes look up for 20 seconds at
  something 20 feet away.
• The rest of this lecture is not on the exam!

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The red lines are straight!
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Look at the dot and move your head forward and
back
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Look at the dot and move your head forward and
back
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Stare at the for 30 seconds and the pink dots
will disappear!
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FUN FACTS ABOUT VISION

• Why do you cry when you cut onions?
• It releases an enzyme that reacts with the amino
  acids in the onion that create an acid that
  diffuses into the air and irritates your eyes.
  Scientists have tried to make a noncrying onion,
  but it turns out that enzyme is needed for the
  onion flavor. You can heat the onion before
  chopping or chop under running water. Or order
  take-out.
• Do cucumbers relieve puffy eyes?
• No, they are just cool and filled with water, so
  the cooling effect reduces the swelling.

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FUN FACTS ABOUT VISION

• Can carrots help improve your vision?
• This myth dates back to WWII when the British
  Royal Air Force was attempting to hide the fact
  that they developed a new radar system to shoot
  down German bombers. They bragged that the great
  accuracy of thie British fighter pilots at night
  was a result was a result of them being fed an
  enormous amount of carrots. It is true that
  carrots contain beta carotene which converts to
  vitamin A which is needed to prevent night
  blindness, but we only need a small amount, and
  having more than that will not improve vision. In
  fact, too many carrots can cause your skin to
  turn orange.

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FUN FACTS ABOUT VISION

• Can you lose a contact lens in the back of your
  head?
• No the underside of the eyelid is connected to
  the sclera (white part of the eye).
• Why do you get bags under your eyes when you are
  tired?
• The skin under the eyes is the thinnest in the
  body, and it allows the dark, venous blood to
  show through. Dark rings tend to be genetic and
  get worse as you age. Good rest and nutrition
  minimizes the rings.

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FUN FACTS ABOUT VISION

• Should you put a steak on a black eye?
• It doesnt do any more good than an ice pack
• Does hysterical blindness really exist?
• Yes. There is a device that can check for someone
  faking blindness they put a black and white
  spinning pinwheel in front of the eyes, and if
  you can see, your eyes will automatically move a
  little back and forth.

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FUN FACTS ABOUT VISION

• Why do you see stars when you are hit in the
  head?
• It happens to Wile E. Coyote every time he gets
  hit on the head with an anvil by the Road Runner.
  Yes, it can happen, and it indicates there is a
  concussion. The visual area of the brain has hit
  against the inside of the skull.
• Will staring at an eclipse make you go blind?
• The intense light burns some of the cells in the
  retina, but it doesnt cause complete blindness.

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FUN FACTS ABOUT VISION

• Why is it impossible to sneeze with your eyes
  open?
• Sneeze impulse affects a variety of body parts,
  including the abdomen, chest, neck, and face.
  During a sneeze, the impulses that travels
  through your face causes your eyelids to blink.
  This response is entirely automatic. There's
  nothing you can do about it. Sneezing puts a lot
  of pressure on your head and respiratory system,
  so blinking is probably a protective mechanism.
• The point is that all of these responses (the
  abdominal contraction, the sharp burst of air out
  of your lungs, the general lunging movement) are
  intertwined.

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FUN FACTS ABOUT VISION

• Can a person who is blind from birth "see images"
  in their dreams?
• People who are visually impaired from birth
  appear to lack visual imagery in their dreams but
  have a very high percentage of gustatory,
  olfactory, and tactual sensory references,"
  something very unusual for sighted dreamers to
  experience.

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FUN FACT OR FICTION?

• Extensive computer usage can cause dry eyes.
• Fact. Extensive computer use can lead to dry
  eyes. A person experiencing minor amount of
  dryness will feel much worse after prolonged
  computer use. Studies have shown that computer
  users tend to stare at the screen without
  blinking for a long time, which may cause dry
  eyes. Dry eyes are one of the factors leading to
  Computer Vision Syndrome. Thus frequent blinking
  is essential to lubricate the eyes and prevent
  them from drying.

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Eating carrots will improve your vision

• Fallacy. It is true that carrots are rich in
  Vitamin A, which is an essential vitamin for our
  eyes. However, we require only a small amount of
  this vitamin for good vision. A well- balanced
  diet, with or without carrots, provides all the
  Vitamin A necessary for good vision.

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FUN FACT OR FICTION?

• Sitting close to a television set, movie or
  computer screen can harm your eyes.
• Fallacy. Our eyes are not harmed by viewing these
  at a short distance. There is, however, a greater
  likelihood of experiencing eye fatigue or a
  headache.

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FUN FACT OR FICTION?

• Reading in dim light is harmful to your eyes.
• Fallacy. For centuries, all night time reading
  and sewing was done by candlelight or with gas or
  kerosene lamps. Reading in dim light does not
  damage the eyes. However, good lighting does make
  reading easier and prevents eye fatigue,
  especially for people who wear bifocals.

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Computers and eyestrain

• Computers can put stress on the eyes causing
  headaches, blurred vision and eye fatigue. The
  following steps can be taken to reduce eyestrain
• Computer screen is at least 18 to 26 inches away
  from your eyes.
• Arrange the monitor so that the top line of
  on-screen text is at eye level. Placing a monitor
  too high exposes more of the eye, causing it to
  dry out.
• Arrange lighting to minimize glare and
  reflections.
• Keep the computer screen clean and dust-free to
  minimize glare.
• Take frequent vision breaks to stretch your body
  and rest your eyes.
• Remember to blink often to keep your eyes moist.
• Place reference material alongside and as close
  to the computer screen as possible to avoid
  frequent head and eye movements and focusing
  changes.

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Television and your eyes

• Never watch TV in a completely darkened room. The
  best lightning conditions consist of a back light
  and dim general light in the room.
• Place the set to avoid glare and reflections from
  lamps, windows and other bright sources.
• View from a distance at least five times the
  width of the television screen.
• Have the set at approximately eye level.
• Wear lenses prescribed for vision correction.
• Avoid staring at the screen. Briefly look away
  from the picture, around the room.

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Avoid eye strain while reading

• Keep the reading material at the best distance
  place knuckles under your chin and book under the
  elbow. Try to avoid reading while lying on your
  back, stomach, or side. Make sure that there is
  good light on close work tasks and good room
  light as well. A light positioned behind and over
  one's shoulder works well for reading. Also,
  looking up from time to time from your reading
  can help keep your eyes relaxed.