EYE STRUCTURE and VISION

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EYE STRUCTURE and VISION
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GENERAL FACTS ABOUT THE EYE
Is a sphere about 1 inch in diameter (about 2.5
cm.) Is protected by the orbital socket of the
skull and by the eyebrows, eyelids, and
eyelashes. Continuously bathed in fluid secreted
by the lacrimal glands (tears empty into nasal
cavity.) Secretions have some antibiotic
properties. Thin membrane which lines the
eyelids and covers part of the eye is called the
conjunctiva. It secretes mucous to help
lubricate the eye.
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Sty (Hordeolum)

• Abcess at the base of an eyelash ( in sebaceous
  gland)
• Symptoms red, painful and swollen
• Rx warm, wet compresses, antibiotic ointments
  and occasionally incision and drainage

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Conjunctivitis

• Commonly known as pink eye
• Inflammation of conjunctival membranes in front
  of the eye
• Caused by a variety of pathogens including the
  bacterium Staphylococcus and Chlaymdia
• Symptoms are redness, pain, swelling, and
  discharge
• Highly contagious

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Wall of the eye is made up of 3 layers or coats.

• Sclera -
• Outer layer
• white of the eye
• tough, fibrous capsule which maintains the eyes
  shape
• Extrinsic Muscles - muscles that are attached to
  the sclera and responsible for moving the eye.

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Cornea - Window of the Eye

• Located in very front center of the sclera
• Transparent - no blood vessels
• Allows outside light to pass through the eye.
• Gets oxygen and nutrients through lymph fluid.
• Has pain and touch receptors
• Injury scarring and impaired vision.

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Choroid Coat - Middle Layer of the Eye

• Contains many blood vessels that provides
  nourishment to the eye.
• Pupil - dark circular opening in the center
• Iris - Colored muscular layer surrounding pupil
• Intrinsic Muscles in Iris- contraction of muscle
  dilates or constricts pupil. The larger the
  pupil - the more light that can enter the eye.

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Iris and Pupil

• Iris can be blue, green, gray,brown, or black.
• Eye color r/t number and size of melanin
  pigment.
• Blue eyes have the least amt. of pigment and
  brown eyes the most pigment.
• Iris is a sphincter muscle (can relax and
  contract)
• Low light or focused on a distant object-iris
  relaxes and pupil dilates. This allows more
  light in for a better image.

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PUPILS

• The word pupil comes from the Latin word pupa
  that means doll. The use of the word pupil for
  the center of the eye may have come from the
  observation that if you look into the eye of
  another person, a small version of yourself (a
  doll) is reflected back.

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LENS

• Transparent body behind the pupil and iris that
  bends light passing through the eye.
• Elastic, disc-shaped, biconvex
• Stituated between the anterior and posterior
  chambers
• As light enters the lens, it is refracted or
  bent. The light bends so much that the image
  appears upside down on the fovea (point where
  objects are clearly seen). When the image is
  sent to the brain, it is interpreted as being
  right side up.

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Cataracts

• Lens of eyes gradually becomes cloudy
• Frequently occurs in people over 70
• Causes a painful, gradual blurring and loss of
  vision
• Pupil turns from black to milky white
• Rx surgical removal of the lens

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Vision With Cataracts

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Chambers of Fluid Within the Eye(help to
maintain the eyeballs spherical shape

• Anterior Chamber
• Filled with a clear watery fluid called aqueous
  humor.
• Found in front of the lens.
• Constantly replenished by blood vessels behind
  the iris.

• Posterior Chamber
• Filled with a clear, jelly-like fluid called
  vitreous humor.
• Found in back of lens.

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Glaucoma Sneak Thief of Sight

• Excessive intraoccular pressure causing
  destruction of the retina and atrophy of the
  optic nerve
• 2nd most common cause of legal blindness in the
  US
• Caused by overproduction of aqueous humor, lack
  of drainage, or aging
• As fluid pressure against the retina increases,
  blood flow slows which causes degeneration of the
  retina and thus a lost of vision

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Glaucoma (continued)

• Damage appears first at the edge of the retina,
  causing a gradual lost of peripheral vision
  called tunnel vision.
• Symptoms develop gradually mild aching, loss of
  peripheral vision, halo around the light

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Tonometer

• A Tonometer is an instrument use to measure
  intraocular tension or pressure.
• An increase in pressure often indicates glaucoma
• Treatment for glaucoma include drugs or laser
  surgery

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Retina - Innermost Layer

• Located between the posterior chamber and the
  choroid coat.
• Light rays focus an image on the retina
• It is upon this light-sensitive layer that light
  rays from an object form an image.
• The image travels by electrical impulses via the
  optic nerve to the visual part of the cerebral
  cortex (occipital lobe) where it is interpreted.
• If light rays do not focus correctly on the
  retina, can correct condition with glasses or
  contact lenses which will bend the light rays as
  required.
• Contains rods and cones.

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Detached Retina

• May occur with aging. Eye tumors, or trauma to
  the head can cause it at a younger age
• Retina detaches from choroid
• Warning signs sudden appearance of floating
  spots that may decrease over a period of weeks
  and flashes of light when eye moves
• If retina detaches completely total blindess in
  afftected eye
• Rx laser or freezing technique

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CONES RODS

• Contains 2 type of light sensing receptors
  (photoreceptors neurons)
• Rods - receptors for night vision shape and
  movement.
• Have about 120 million.
• Detect black and white images and work well
  in dim light.
• Cones - receptors for day vision color vision
• Have about 6 - 7 million.
• Function in bright light and provide us with
  color vision.
• 3 types - each contains a pigment that responds
  to a different light wavelength (green, red, or
  blue.)

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Color-Blindess

• Deficiency in the ability to perceive colors of
  the spectrum distinctly is commonly termed color
  blindness.
• This is due to changes that happen in the
  pigments of the cones in the retina of the eyes
  as they react to colored lights of red, green,
  and blue.

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Tyeps of Color Blindness

• Daltonism
• Most common.
• Person cannot tell the difference between red and
  green.
• It is an hereditary disorder.

• Achromatic Vision
• Total color blindness and very rare.
• Person cannot recognize any color at all. (
  These people see everything in white, gray, or
  black.)
• Cause is the cones in the retina are defective or
  there may be none at all.

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Colorblindness

• Ishihara color plates are used to test for color
  blindness.
• Patients are asked to trace the pattern of color
  with their fingers as you observe them. There
  are letters and numbers that are one color within
  another.
• Make sure the room is well lit with natural
  daylight if possible so the patient will not have
  to squint.
• Make sure you have normal vision before you give
  the test.

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OPTIC DISC AND FOVEA

• If you look at the retina with an ophthalmoscope
  you will see a yellow disc (macula lutea.)
• Within this disc is the fovea (contains cones for
  color vision.)
• Slightly to the side of the fovea is a pale disc
  called the optic disc or blind spot. (Contain no
  rods or cones and is insensitive to light.)
• Never fibers gather here to form the optic disc
• Each eye compensates for the blind spot of the
  other eye.

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Macular Degeneration

• Eye disorder that occurs with aging
• The macula (part of the retina responsible for
  sharp color vision) degenerates
• Vision is reduced but usually doesnt cause total
  blindness

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Vision with Macular Degeneration

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Pathway of Vision
Cornea
Pupil
Lens (Where light rays are refracted)
Retina
Optic Nerve
Rods and Cones (pick up stimulus)
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Myopia

• Nearsighted
• Eyeball too long
• Light focuses in front of the retina (in normal
  eye light focuses on the retina)
• Concave lenses help
• Surgical Tx Photo Refractive Keratectomy
  laser therapy used to reshape the anterior cornea
  of the eye.

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Myopia
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Hyperopia

• Farsighted
• Light focuses behind the retina because the
  eyeball is too short
• Objects must be moved farther away from the eye
  to be seen clearer
• Convex lenses help

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Hyperopia

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Presbyopia

• Oldsightedness
• Lens loses elasticity, cant focus on close or
  distant objects
• Usually occurs after age 40
• Rx - Bifocals

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Astigmatism

• Irregular curvature of the cornea or lens,
  causing blurred vision and eye strain
• Rx corrective lenses

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Stabismus

• Strabismus (cross-eye)
• Eye muscles do not coordinate their actions
• If not corrected early, visual centers in the
  brain will learn to ignore information from one
  eye causing permanent blindness in affected eye
• Usually in children
• Rx eye exercises or surgery

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Additional Visual Disorders

• Amblyopia reduction or dimness of vision
• Diplopia double vision

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Lights out folks!