Observations

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How the Eye Works

• Observations

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Parts to the Puzzle

• Anatomy
• the study of the names of the structures in the
  human body
• When we learn the names of eye parts we are
  studying Anatomy.
• Physiology
• the study of the functions of body parts
• When we learn how the eye parts work we are
  studying Physiology.

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Humans

• Levels of Organization
• Highest-
• Organisms
• Organs (eye)
• Tissue (eg. lens, pupil, cornea, etc.)
• Cellular (eg. Rod and cone cells)
• Atoms - Lowest

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Eye Anatomy
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The Eye Diagram
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Frontal View of the Eye
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Vision Summary

• Light rays enters through the pupil after
  crossing through the cornea
• Light rays cross in the lens
• Retina receives reversed upside down image
• Rods cones are stimulated
• Optic nerve carries impulse to the brain

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ObservationIn your ScienceLog notes, copy and
carefully label the transverse waves. In your own
words, explain what you think wavelength and
frequency mean.
You have two minutes (2 minutes) to do this
activity. The clock is counting
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Electromagnetic Spectrum
Decreasing wavelength Increasing frequency

• Long wavelength Radio waves
• Visible Light range of wavelengths that humans
  can see
• Short wavelength Gamma rays

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(No Transcript)
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Law of Reflection
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Prism Refraction
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Overview of Image Processing
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Images and Light

• The image projected onto the retina is inverted
  or upside down. Visual processing in the brain
  reverses the image

• The pupils regulate the amount of light entering
  the eye.
• In bright light they constrict to 1.5 mm.
• In the dark they dilate to 8 mm.
• The increase in the depth of field seen under
  bright light results from a narrower beam of
  light focussing on the retina.

The diameter of the pupils is controlled by the
autonomic nervous system
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Fixation Point to Focus Point
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Focusing Abilities

• When an object is distant, the light rays are
  essentially parallel and brought to a focus on
  the retina.
• If the object moves closer, the focal point then
  moves behind the retina.
• To bring the image into focus on the retina, the
  lens refractive power must be increased. This is
  the process of accommodation.

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Optics the focal point
Focal point falls on beyond retina, image not in
focus
Lens accommodates to correct focal point, image
becomes in focus
Focal point falls on retina, image in focus
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Refraction How the light is bent

• Most of us (70) have a refractive error in
  which light rays come to a point focus either
  behind the retina (hyperopia) or in front of it
  (myopia).
• Hyperopia Myopia
• (farsighted)
  (nearsighted)

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Convex or Concave?
Convex
Concave
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Refractive errors
Long- or far-sighted
Corrective lenses
Short- or near-sighted
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Converting Light Stimulus to Electrical Impulse

• Requires great coordination of parts
• Also occurs with the other senses
• Ears sound waves
• Taste chemical stimulus
• Touch mechanical stimulation
• Scent chemical stimulus

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Cross-section of the eye
Eyelid
Choroid
Sclera
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Retina stimulation

• The photosensitive cells of the retina contain
  the rods and cone which convert the light
  stimulus to electrical stimulus.

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Rods and Cones
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Colour vision Rods and Cones

• Light sensitive visual pigments are bound to the
  cell membranes of the disk-like photoreceptors
  found within the rods cones.

• Rods have one visual pigment, rhodopsin which has
  an absorption max of 496nm

• Cones have one of 3 colour sensitive pigments
  related to rhodopsin.

• Cones are responsible for colour vision and a
  contain pigments that can be excited optimally
  for
• a) blue (absorption max 419nm)
• b) green (absorption max 530nm)
• c) red (absorption max 560nm)

• White light is seen when all three types of cone
  are equally stimulated.

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Rods and Cones
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Cones

• Cones allow for sharp color vision in bright
  light
• 3 types, each with a different pigment
• Cones are most concentrated towards the back of
  the eye

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Rods

• Rods provide for vision in dim light
• Most dense at the on the sides of the retina
• Contain the pigment rhodopsin

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Neuron Neervvve Cellllls
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Braineacts

• LGN
• a part of the thalamus that relays signals from
  the eye to the visual cortex.
• It also receives signals back from the cortex.

LGN
Visual Field
Retina
Primary Visual Cortex
Rods Cones
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Optic Nerve
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Cortical processing
or how do we fill in the gaps?
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RAINBOWS

• In a rainbow, raindrops in the air act like tiny
  prisms.

• Light enters the drop at A, is reflected at the
  back of the drop at B and leaves the drop at C.
  In the process the sunlight is broken into a
  spectrum just like it is in a triangular glass
  prism.
• The angle between the ray of sunlight coming in
  and the ray coming out of the drops is 42 degrees
  for red and 40 degrees for violet rays.
• This small difference in angles between the
  returning rays causes us to see the bow.

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Challenge Question

• Explain why the top of the rainbow appears red,
  while the bottom appears violet and not other way
  around?

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THANK YOU