Fovea centralis in macula
<p>Mar 3, 2010 8:59 AM <b> thumbnail at arm's length = 2 degr = foveal vision</b>.
 
see diagram of visual acuity vs degrees.  fovea means PIT. 
 
fovea is 1 mm diameter with a high concentration. of cones; <b>foveola has ONLY cones and is .2 mm diam</b>.
1 to 1 with ganglion cells ... no loss of info.  Central fovea has very compact,
<b>thin more rod-like cones than elsewhere</b> .  Really packed in a hexagonal pattern and
local absence of blood vessels.   (rods and smallest cones are abt 2 microns in diameter (their outer segments)
 
The fovea comprises less than 1% of retinal size but takes up over 50% of the <a title="Visual cortex" href="/wiki/Visual_cortex">visual cortex</a> in the brain.Approximately 50% of the nerve fibers in the <a title="Optic nerve" href="/wiki/Optic_nerve">optic nerve</a> carry information from the fovea, while the other 50% carry information from the rest of the retina.
 
<b>The fovea sees only the central two degrees of the visual field, which is roughly equivalent to twice the width of your thumbnail at arm's length</b>...
 
Astronomers  use averted vision  (look to one side) to activate rods to see dim stars cuz
foveola has NO rods... NOT sensitive to dim light.
 
 
see the rod and cone density on the retina...
Note:  most cones right in the fovea... sharp spike.
  see diagrma below qv rod and cone density.
 
 
 
 
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