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Vision
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Light Enters the Eye Photoreceptors in the eye are sensitive to wavelengths of light energy called the visible spectrum Visible spectrum ranges from red to violet
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Light Enters the Eye Human eyes can only perceive a tiny fraction of the light that makes up the electromagnetic spectrum
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Why Can’t We See All Light Waves?
Human eyes have evolved to be able to see only the visible spectrum Birds’ eyes evolved differently Can see ultraviolet light just like any other color Human Vision UV Vision ONLY Bird Vision
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Structures of the Eye Sclera Mostly “white part” of the eye
Provides protection and structure
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Structures of the Eye Cornea
Specialized, transparent portion that surround the eyeball Light enters
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Structures of the Eye Iris Pupil Pigmented muscle
Gives the eye its color Regulates the size of the pupil Controls the amount of light entering the eye Pupil Opening in the iris
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Lights Off.
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Why Did Pirates Wear Eyepatches?
WRONG. Had nothing to do with a missing eye! Had everything to do with being able to see—specifically, above decks and below them. Eyes adapt quickly when going from darkness to light HOWEVER, ~25 minutes vice versa
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Structures of the Eye Lens
Transparent, shape-changing structure that focuses images onto the retina Must change shape in order to focus in on specific objects Naturally curves more for objects close by Naturally curves less for objects far away
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Glasses & Contacts Needed if your lenses won’t focus naturally
Glasses & contacts act as an artificial “lens,” which focuses light instead
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Structures of the Eye Retina Inner layer
Contains two types of photoreceptors Rods Cones Converts light energy into electrochemical energy
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(Another View)
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The Retina Rods (120-125 million) Cones (7-8 million)
Located primarily in the retina’s periphery Receive light energy Not involved with color perception Cones (7-8 million) Concentrated in the middle of the retina Involved with color perception in bright light
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The Retina Both rods and cones are connected by synapses to bipolar neurons Bipolar neurons are connected by synapses to neurons called ganglion cells Ganglion cells converge to form the optic nerve
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Your Blind Spot Yes, you ALL have one!
Point at which the optic nerve connects to the eye and contains neither rods nor cones Here.
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The Occipital Lobe Located in the back of the brain Both hemispheres
Responsible for vision EYES SENSE; OCCIPITAL LOBE PERCEIVES
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Coding Information in the Retina
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