Duplex Retina - Kenneth M. Steele PDF

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Kenneth M. Steele...

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Duplex Retina 

Dark adaption curve – adjust light intensity to be at threshold

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Longer you’re in the dark, the more sensitive you are (the lower the threshold) Notch at ~ 7 minutes  Switching from cones to rods Fovea only  Not as sensitive, reach absolute threshold very quickly (~ 6-7 minutes)

Purkinje Shift o Two colors: red and blue o Match for brightness in daylight. o At night time – colors will shift their brightness  Blue becomes brighter than the red o Color sensitivity

  Manipulating wave length (nanometers)  Low sensitivity – high threshold, high sensitivity = low threshold  Rods peak at about 500 nm  Cones peak at about 560 nm o Pigment bleaching – use light to break down the photo pigment  Starts out red, hit it with light until you bleach it out  Red  orange  yellow  clear  Pigment regeneration time – going from clear to yellow to orange to red  Fovea takes about 7 minutes  Outside fovea takes about 30 minutes Duplex theory – two separate visual systems o Photopic

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 Operates during day light  Cones  Fovea  Requires high illumination to activate  Color o Scotopic  Operates during night time  Rods  Outside fovea  Requires high illumination to activate  No color Night blindness – dysfunctional rod system o Rod system requires vitamin A  Vitamin A found in orange vegetables (e.g., carrots, sweet potatoes)

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Longer you go without vitamin A = level of sensitivity decreases until we have a cone only system  Have good vision during the day but blind at night  Not a permanent effect Achromatopsia – defective cone system o Genetic disorder o Can see during the night time but during the day time they’re blind  But they can see in low illumination  Fix by using sunglasses...