Rose, Natalie, Sarah, Nick

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• Rose, Natalie, Sarah, Nick

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The Big QuestionWhats happening when you
apply pressure to the medial surface of your eye?
Describe the physiology of this entoptic
phenomenon
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What do you see?

• You should be seeing a
• circle or semicircle on
• the opposite corner of your eye as the spot
  where pressure is applied.
• This mechanically stimulated vision is called a
  phosphene.
• We have all encountered the perception of light
  when rubbing our closed eyes.

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Visual Pathway at the Retina
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Visual Fields and Binocular Vision

• Light from one side of visual field will
  stimulate photoreceptors on opposite side of eye.
• We perceive the light as coming from that lateral
  visual field.
• In binocular vision, this pathway will also
  stimulates the visual cortex on the opposite side
  of brain
• In our example, we are only stimulating one side
  of the cortex.

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Optic Chiasma
http//www.ouhscphysio.org/humanphys/images/CNN5.j
pg
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The Bottom Line

• Phosphenes are generated through the same process
  as normal sight, just different stimulation.
• The phosphene appears as a circle simply because
  that is the shape of the pressure applied (round
  finger).

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Sleeping Seeing

• You can fall asleep by
• Being tired
• Passing out (Drunk)
• Taking sleeping pills
• Boredom
• Physical exhaustion

• You can stimulate the retina by
• Light
• Pressure
• Magnets
• Electrodes
• Radiation

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References

• Silverthorn, 2007. Human Physiology.
• Tortora, 2005. Principles of Human Anatomy.
• http//www.oubliette.zetnet.co.uk/Three.html
• Tehovnik, T. J., Slocum, W. M., Carvey, C. E.,
  Schiller, P. H. (2004). Phospene induction and
  the generation of saccadic eye movements by
  striate cortex. Journal of Neurophysiology, 93,
  1-19.