The retina is a light-sensitive layer of tissue located in the back of the eye.  The retina receives images formed by the lens and transmits them through the optic nerve to the brain.

mouseover for arrows image from wikipedia

The macula  is an oval-shaped highly pigmented yellow spot near the center of the retina of the human eye. It has a diameter of around 5 mm and is often histologically defined as having two or more layers of ganglion cells.  The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive rods or cones to respond to a light stimulus at this point. This causes a break in the visual field called “the blind spot” or the “physiological blind spot”. The optic disc represents the beginning of the optic nerve (second cranial nerve) and is the point where the axons of retinal ganglion cells come together. The optic disc is also the entry point for the major blood vessels that supply the retina  (adapted from wikipedia)

To test for blindspot click 

Close your right eye and look directly at the number 3. Can you see the yellow spot in your peripheral vision? Now slowly move towards or away from the screen. At some point, the yellow spot will disappear.     Note how far you are from the screen when the yellow spot vanishes. Repeat the experiment looking at a larger and then again at a smaller number. Did you notice the difference in distance from the video screen when the spot disappeared?

This diagram was developed and published online by Peter K. Kaiser he has a great resource on eye topics here

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