INSTRUCTIONAL OBJECTIVES:

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INSTRUCTIONAL OBJECTIVES

• By the end of the class, you will be able to
• 1. Locate 14 parts of the human eyeball and
  state the function of each structure.
• Define accommodation and depth of field and
  explain how each is controlled in the human eye
  and in a camera.
• 3. Describe 4 types of visual problems that can
  occur in the optical apparatus of the eye and
  state a method for correcting each type of
  problem.
• 4. Explain why we are normally not aware of our
  retinal blood vessels, then describe a method for
  viewing them.

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Anatomy of the human eyeball
Parts of the eye for seeing

• optical apparatus
• cornea, lens, pupil
• neural apparatus
• retina

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Optical apparatus of the human eye

• light emitted, transmitted or reflected to eye is
  transmitted through cornea, aqueous humor, lens
  and vitreous humor
• focuses image on retina
• sharpness of image depends on ability of cornea
  (2/3) lens (1/3) to refract light
• photoreceptors in retina absorb light

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Optical apparatus of the human eye
accommodation the process by which the shape of
the lens in the eye is changed to bring objects
at different distances into focus on the retina
increased optical power
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Optical apparatus of the human eye

• pupil reflexes
• direct light reflex shining a light into one
  eye causes the pupil of that eye to contract
• consensual light reflex shining a light into one
  eye causes the pupil of the other eye to contract
  
• abnormal reflexes can indicate brain damage
• eg. no direct or consensual reflex in right eye,
  normal reflexes in left eye -- right oculomotor
  nerve damage
• eg. consensual but no direct reflex in right
  eye, direct but no consensual in left eye --
  right eye blind

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Optical apparatus of the human eye
pupil size ranges from 2 to 8 mm changes with
light level emotional responses
Mather (2006)
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Optical apparatus of the human eye
a small pupil provides a greater depth of field
range of distances over which objects are in focus
Blake Sekuler (2006)
large aperture (small f-stop)
small aperture (large f-stop)
small depth of field
large depth of field
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Optical problems
emmetropia eyeball right length for optical
elements
normal
focal length 16.8 mm optical power 59.52 D
hyperopia eyeball too short or optics too weak
images focused behind retina
myopia eyeball too long or optics too strong
distant objects focused in front of retina
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Optical problems
hyperopia (farsightedness)
easier to see distant objects accommodation
brings them into focus
cant focus on near objects
positive, convex lens brings both near distant
objects into focus
usually develops soon after birth
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Optical problems
myopia (nearsightedness)
cant relax lens enough to bring distant object
into focus
relaxed accommodation brings near objects into
focus
negative, concave lens brings distant objects
into focus
usually develops later in childhood, but may
develop in early adulthood
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Optical problems
emmetropia
mild myopia
severe myopia
Blake Sekuler(2006)
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Optical problems
presbyopia

• lose ability to accommodate
• due to loss of elasticity in lens which reduces
  ability to accommodate

• near point closest distance at which objects can
  be brought into focus

• corrected with positive, convex lens

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Optical problems
astigmatism visual distortion produced by
nonspherical cornea
astigmatism causes one line to look blacker
corrected by glasses with cylindrical lenses
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Optical problems
how the world looks to someone with uncorrected
astigmatism
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Neural apparatus of the human eye
fundus photograph
optic disc
blood vessels
fovea
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Neural apparatus of the human eye
retinal blood vessels in front of retina
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Neural apparatus of the human eye
Why do you need to jiggle the light to see your
retinal blood vessels?
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Neural apparatus of the human eye
images of objects outside the eye arent usually
stabilized because of involuntary eye movements
the afterimage of this pattern is burned into
place on your retina it jiggles because your
eyes are jiggling
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Neural apparatus of the human eye
finding your blindspot
look at the square with your left eye and move
the page closer until the top circle disappears
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Neural apparatus of the human eye
side view of retina
light capture transduction in photoreceptors
pigment epithelium keeps photopigment from
bleaching
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Individual Proposals - due Sept 29

• each student will prepare a written proposal for
  a specific experiment within their group topic
  (no need for group consultation)
• proposals should include a research question
  (e.g. what is the absolute threshold for
  detecting a sour taste?), a specific
  psychophysical method (constant stimuli, limits,
  adjustment, staircase or signal detection) and
  paradigm (yes-no or forced-choice), a description
  of the stimuli and procedure for presenting
  stimuli and the calculations/graphs required to
  determine threshold (in enough detail for the
  marker to conduct the experiment analysis)
• experiment does not have to be feasible with
  equipment you can bring to class, but your group
  planning will be easier if it is feasible
• include your name, student number and group
  number
• marks deducted for writing on wrong topic (i.e.
  not the one you signed up for)
• marked proposals will be returned for viewing
  during group experiment planning (Oct 8)